A Beginner's Guide to
Water Management 
Symbols, Abbreviations & Conversion Factors
Information Circular 105
Florida LAKEWATCH
Department of Fisheries and Aquatic Sciences
Institute of Food and Agricultural Sciences
University of Florida
Gainesville, Florida
October 2001
:. UNIVERSITY OF ,
FLORIDA
Institute of Food and A ricultural Scien es
Acknowledgment
Many thanks to Dr. Roger Bachmann and Dr. Chuck Cichra
at the University of Florida, for their editorial assistance.
This publication was produced by:
Florida LAKEWATCH
University of Florida / Institute of Food and Agricultural Sciences
Department of Fisheries and Aquatic Sciences
7922 NW 71st Street
Gainesville, FL 326533071
Email: lakewat@ufl.edu
Web Address: http://lakewatch.ifas.ufl.edu
Copies of this document are available for download from the Florida LAKEWATCH website:
http://lakewatch.ifas.ufl.edu/LWcirc.html
As always, we welcome your questions or comments.
A Beginner's Guide to
Water Management 
Symbols, Abbreviations & Conversion Factors
Information Circular 105
Florida LAKEWATCH
Department of Fisheries and Aquatic Sciences
Institute of Food and Agricultural Sciences
University of Florida
Gainesville, Florida
October 2001
UNIVERSITY OF :tty JA
'FLORIDA _
Institute f Food ad Agricultural Sciences AKCH
Before reading this circular, we encourage you to
read the four circulars that precede it:
A Beginner's Guide to Water Management The ABCs (Circular #101)
A Beginner's Guide to Water Management Nutrients (Circular #102)
A Beginner's Guide to Water Management Water Clarity (Circular #103)
A Beginner's Guide to Water Management Lake Morphometry (Circular #104)
Copies of any of these publications can be obtained by
contacting the Florida LAKEWATCH office at
1 800LAKEWATCH
(18005253928)
They can also be downloaded
for free from the Florida LAKEWATCH web site:
http://lakewatch.ifas.ufl.edu/LWcirc.html
or from the
UF/IFAS Electronic Document Information System (EDIS):
http://edis.ifas.ufl.edu
communication is the basis for most human greatest communications challenge: communicating with
interactions. It could even be said that societies nonscientists. For the lay public, language used by
cease to function when they lose the ability to scientists remains shrouded in mystery. Unfamiliar words
communicate. Because of this need to express ideas and often convey unintended meanings, or in many instances,
exchange information, people around the world have gone no meaning at all. Even the most intelligent or welleducated
to great lengths to develop languages for use within a listeners have difficulty understanding scientific jargon,
common geographic region or culture. Given the diversity especially when the language is not part of their everyday
of the human race, some of these languages are vastly experience.
different. Even within a single language there are dialects Communication is further complicated by the fact
or slang expressions that can hinder communication, that there are a multitude of distinct disciplines within the
Many cultures have tried to solve this dilemma by scientific community itself: some scientists study the
developing dictionaries, standard abbreviations and universe, some study the human body, while others
symbols an attempt to share their language r may study the natural world. Even in closely
with those who are willing to learn. The .a L related subjects such as limnology or oceanogra
scientific community is no different as it has phy, researchers tend to gravitate toward highly
attempted to resolve communication difficulties specialized topics such as the biological,
by developing glossaries for its numerous disci chemical or physical aspects of freshwater and/
plines (e.g., biology, chemistry, physics, zoology or marine environments. As a result, scientists
etc.). Such glossaries can usually be found within essentially end up developing their own customized
any textbook or journal relating to a specific V language that only their immediate peers under
discipline and they provide a good starting point sand. This is unfortunate because in the long run,
Scientists have also taken things one step furthc i much of the research being done these days can
by developing an International System (SI) foi potentially have an impact on our daily lives.
standardizing scientific and mathematical symbols 'So what can we do to bridge this gap?
abbreviations, and units of measure to be used I ,,,I For starters, it's imperative that the public not be
around the world. While this system has certainly intimidated by science and to remember that
helped reduce communication problems within hie science is, after all, a human endeavor. Although
general scientific community, problems still occur. scientists may be highly trained individuals,
For example, even though the U.S. scientific they make mistakes too and contrary to popular belief, they
community adopted the metric system (the basis of the don't always have the answers. Those of us with
SI system) many years ago, some people still need LAKEWATCH are of the opinion that the best scientists
conversion tables to insure their measurements are are those who know how to say "I don't know, but I'll
properly translated into the metric system. Failure to do do my best to find out."
this can cause problems. A case in point is the U.S. Mars Secondly, continue asking questions! This can be a
Climate Orbiter that missed its target in September of difficult assignment as many people are afraid to ask
2000 and burned up deep in Mars' atmosphere due to a questions for fear that it will show their ignorance. All of
mistake in measurement units within the engineering us need to be reminded that (1) there is no such thing as
process. Contractors building the spacecraft specified the a dumb question, and (2) this problem is not just limited
engine's thrust in English units (i.e., pounds), while to the lay public; scientists are afraid to ask questions too.
navigators planning the orbiter's flight path assumed the Such fears prevent us all from learning something new.
units were in metric units of newtons. The oversight As our LAKEWATCH team continues to help
resulted in the loss of the $125 million orbiter. As they translate the scientific concepts and ideas related to
say, "old habits die slowly" and many of the individuals water management, we hope that you'll be patient if any
that grew up with the English system are obviously still information should happen to get lost in the translation.
adjusting to the metric system. Even the best translators make mistakes in interpretation
However, aside from the English vs. metric quandary, evidence of just how imperfect language can be and
scientists will probably always continue to face their how important it is for us all to keep trying.
ii
.V.
Fishery scientists often measure the h!.i ji and weight of individual fish to assess the "health"
of a fish population.
lorida LAKEWATCH is committed to Much of this information is typically only
helping nonscientists become familiar available by searching numerous publications,
with the language used by scientists, but we have assembled it here under one cover
particularly the terminology related to freshwater for quick reference. Emphasis is placed on the
and marine sciences. This circular and the four others International System (SI) so that readers can
that precede it are evidence of that commitment. become familiar with the metric system and perhaps
The first in the series, A Beginner's Guide even begin to use it in their everyday activities. It
to Water Management TheABCs (Circular should be noted that, while we tried to make this
101), was designed to help readers become booklet as comprehensive as possible, the informa
acquainted with terminology and management tion provided is not totally inclusive. Therefore, if
concepts used by limnologists and water manage you encounter something you don't understand or
ment professionals. if you need more information about any of the
The circular you have in hand, the fifth in material, feel free to contact Florida LAKEWATCH
our series, is a sequel of sorts to Circular 101 for assistance.
as it provides the tools for interpreting and/or It is hoped that continued use of and exposure
translating units of measure, conversion factors, to the SI system will ultimately reduce problems
symbols, and abbreviations used by scientists in related to metric conversions and enhance the
the U.S. and on an international basis. communication of scientific ideas and concepts.
Included in this circular:
Part I Common SI Prefixes
Part II Commonly Used Abbreviations and Symbols
Part III Commonly Used Metric and English Conversion Factors
Listed in units of Area, Concentration, Length, Mass, Power, Pressure, Temperature, and Volume.
Part IV A Glossary of Commonly Used Metric and English Conversion Factors
Part V Elements and Atomic Weights
Part VI Interpreting Water Chemistry Formulas and Calculating Molecular Weights
Part VII Different Ways of Expressing a Chemical Compound
Part VIII Using Atomic Weights to Compare Different Measures of Concentration
iv
UF students Eric Porak and Amber Paxton collect and weigh aquatic plants to determine the aquatic plant
biomass (kilogrami wet weight/m2) of emergent plants at Lake Wauberg in Gainesville. Florida LAKEWATCH staff,
students, and volunteers work ;i dl i. reach summer to collect this information on a number of lakes ;li, I~i ili ,,
the state.
V
W while reading scientific literature, you may have noticed that many of the words
used to indicate the size or quantity of things (i.e, units of measure) are often compound
words. Deciphering the meaning of these words is easy if you remember that the first part of the
word, the prefix, often denotes a numerical value and the second part indicates the actual unit of
measure. For example, the term milligram can be translated by defining the two parts of the word
separately: if the prefix milli means onethousandth, then a milligram is onethousandth of a gram.
Listed below are some of the common prefixes and their corresponding symbols used by
scientists. Notice that the multiplying factor' for each prefix is also provided along with the
appropriate scientific notation. It's important to be familiar with these factors as they are often
used in scientific literature and/or mathematical text. For example, if you should see the number
"10" depicted with an exponent2 while reading a scientific journal, graph or chart, you'll be able to
translate that number into its numerical equivalent by using the information provided below.
Prefix Symbol Multiplying Factor
giga G 1,000,000,000 = 109
mega M 1,000,000 = 106
kilo k 1,000 = 103
hecto h 100 = 102
deca da 10 = 101
(no prefix for the number 1) 1 = 100
deci d 0.1 = 10'
centi c 0.01 = 102
milli m 0.001 = 103
micro p 0.000,001 = 106
nano n 0.000,000,001 = 109
pico p 0.000,000,000,001 = 1012
1 The iirhl ii.. factor for the prefix Megaa" is 1,000,000. Therefore, the scientific notation equivalent for
1,000, 000 is expressed as 106.
2 Exponent the small number or symbol placed above and to the right of the base number (e.g., 10').
1
mg/L
a.i. .
avdp
iil
The use of abbreviations and symbols in scientific writing reduces the number of
letters and words needed thus making manuscripts less cumbersome for both the writer
and the reader. It can also shorten the actual length of an article, saving paper.
With this in mind, we've provided the following list of commonly used symbols and abbrevia
tions within both the metric and English systems of measurement. While it's not necessary to learn
all of these, familiarity with some of them can certainly help, particularly those related to
water management. Consider this a cheat sheet to assist you in your efforts to become better
acquainted with the wild and wonderful world of chemistry and water management.
2
Commonly Used Abbreviations and Symbols
Abbreviation Definition Abbreviation Definition
a annum (year) m2 square meter
acreft acre foot m3 cubic meter
a.i. active ingredient mb millibar
atm atmosphere mg milligram
avdp avoirdupois mi mile (statute)
C Celsius mi2 square mile
cal calorie min minute
cc cubic centimeter mm millimeter
cm centimeter PLg microgram
cm2 square centimeter Lg/L microgram per liter
cm3 cubic centimeter pLg L1 microgram per liter
d day pmhoscm1 micromho per centimeter
diam diameter Pm micrometer
doz dozen aM micromole
F Farenheit jM L1 micromole per liter
fm fathom amol/L micromole per liter
ft foot LScm' microsiemen per centimeter
ft2 square foot mg/m3 milligram per cubic meter
ft3 cubic foot mg m3 milligram per cubic meter
g gram mgd million gallons per day
gal gallon (US) mg/L milligram per liter
gcal gram calorie mg L' milligram per liter
gpm gallons per minute ml milliliter
grains/gal grains per U.S. gallon mol/L mole per liter
h hour mol L mole per liter
ha hectare ng nanogram
hp horsepower oz ounce
in inch ppb part per billion
in2 square inch ppm part per million
in3 cubic inch ppt part per thousand
j joule psi pound per square inch
kcal kilocalorie pt pint
kg kilogram qt quart
km kilometer s second
km2 square kilometer t tonne (metric)
kw kilowatt ton ton (English)
L liter W watt
lb pound yr year
log logarithm (common) yd yard
In logarithm (natural) yd2 square yard
loge logarithm (natural) yd3 cubic yard
m meter
3
As you probably know by now, there are a multitude of ways to measure things and
not everyone uses the same unit of measure. That's one reason why the scientific
community developed an International System (SI) for standardizing scientific and math
ematical symbols, abbreviations and units of measure. While this system has helped reduce confusion
within the scientific community and even some portions of the general public, problems still occur
as not everyone has universally adopted the SI system. As a result, conversions often need to be done
so that measurements are properly translated and interpreted an important step toward insuring
that within the communication process, everyone is "on the same page."
For this reason, conversion factors are provided in the following section so the reader
may convert from metric to English or vice versa. We've organized the information under
units of measure that are commonly applied within the water management arena (i.e., Area,
Concentration, Length, Mass, Power, Pressure, Temperature and Volume). For a more compre
hensive listing, see Part IVA Glossary of Common Metric and English Conversion Factors.
.
Florida LAKEWATCH volunteer Susan Wright carefully measures water volume in a graduated cylinder
before pouring it into the filtration system to the right of the cylinder This water volume measurement must
be accurately measured and recorded.
4
To convert...
square centimeters (cm2) to multiply by
square centimeters square feet 0.001076
square centimeters square inches 0.155
square centimeters square meters 0.0001
square meters (m2) to multiply by
square meters acres 0.0002471
square meters square centimeters 10,000
square meters square feet 10.76
square meters square miles 0.0000003861
square meters square yards 1.196
square kilometers (km') to multiply by
square kilometers acres 247.1
square kilometers square feet 10,760,000
square kilometers square miles 0.3861
hectares (ha) to multiply by
hectares acres 2.471
hectares square feet 107,639
hectares square meters 10,000
5
To convert...
square inches (in2) to multiply by
square inches square centimeters 6.452
square inches square meters 0.0006452
square inches square feet 0.00694
square feet (ft') to multiply by
square feet acres 0.00002296
square feet square centimeters 929
square feet square meters 0.0929
square yards (yd2) to multiply by
square yards square meters 0.8361
square yards hectares 0.00008361
square yards acres 0.000207
square miles (mi') to multiply by
square miles acres 640
square miles square kilometers 2.59
square miles hectares 259
square miles square meters 2,590,000
acres (acre) to multiply by
acres hectares 0.40470
acres square meters 4,047
acres square feet 43,560
acres square yards 4,840
6
To convert...
milligrams / liter (mg/L or mg L') to multiply by
milligrams/liter parts/million 1
milligrams/liter grains/U.S. gallon 0.0584
milligrams/liter micrograms/liter 1,000
milligrams/liter milligrams/cubic meter 1,000
milligrams I cubic meter imglm: oi mg m : to multiply by
milligrams/cubic meter micrograms/liter 1
milligrams/cubic meter milligrams/liter 0.001
micrograms I liter (pg/L or pg L') to multiply by
micrograms/liter parts/billion 1
micrograms/liter milligrams/cubic meter 1
micrograms/liter milligrams/liter 0.001
micrograms/liter ppm 0.001
f l c: l miLay ni ,,,:t ill :ui tables ilr el thait a : :inc :entiat:ll :f milligrams per liter
:aln tre iattr e l.latea d either as mg/L 1:1i as mg L' B,:,tn arrtte'.'; ti.l:ls aie
c::insid leed1 t: be eur.'lelnt tei: :a iuse I :f the i ilgetriall : pI:ipe ty L' = 1lL
ii lll i $ ii abb .\ Cllh iiilll l\ lll 1K \ccond abbll. i.io ll\
s, ImboI l m g/L iiic.iii Otil C. J111,.1 c .x aic w %Cll ,_ h A '" 1 .,i.1h
ci ll lllliiL lll 'l c lll of I llhi.lsJIiCC II m I lj lII m g lI K. c 11 1
i Mg I 1_ '11 LIIIK 10 11 I sli sinch L I of I silbsLin mg I 11111IS o1ll
i mg i L\ illi \ olinilc i \ % u h i iL i L id d \ ik \ olnim in %\ Inich
dllis.olcd Ion lh.ll 01 Li s is dlssol\ l i.onIK hI 01 Li
V\,I l //,i ,,' 1 iir ',,,i, ,,i niilligrtinim per Lu/hiL
iiii'ier n'i i/L \/% i aitJ i iili & / L' gli llf { 'l L' llmg L
W hil 1e 1ie ding S: ientifi: pLl riil:l:tll:ns y:o Ill m:11 likely See 5 negt11 L .: el Ip nent s l ll ed ia3ihe
than the slashes as thi s 1 :fiiflently the a3:,:erpte menth:d :i f ni:ittil:n This is dj:cne tl:l ,,,:,.,
:011:nllfsiiS:ll IIn :31a : ilatll:ns h' h el ie 31 illultiple .11 S,:ii 1S 1 3 I:I:llllmr1110 ed illln I :i 11c3SIUi e llt
F:,i e;iaJ mple let s say th3it 'e 3ie keeping tial:k :f lhe eight fi: fish hrai.ested fli:ll 3 ;1ke
'e se .,e 31 yeais 1'f 'e 'ni ed : ,: :I:imp3 e 1:t1 I fish 'eight I313t Ilth the 'eights :Af fish
h3ai.ested fi: i :nl theiri a1kes O:f different SIzes 'e ':illj need ti:, ,::31 alLl te i11 [he h3ai esl t a133
In tells r:,f kilograms of fish per hectare per year This :':tuli3 re il:ited as kg/ha/yr
H,:, e.e the piefeie ll '3 ti:, a l~ri te'. h3e lihe tll 'c:llAd re kg ha yr
7
%* 0 '41 t
To convert...
parts per billion (ppb) to multiply by
parts/billion micrograms/liter 1
parts/billion milligrams/liter 0.001
parts/billion parts/million 0.001
parts per million (ppm) to multiply by
parts/million grains/U. S. gallon 0.0584
parts/million parts/thousand 0.001
parts/million micrograms/liter 1,000
parts/million parts/billion 1,000
parts/million milligrams/liter 1
parts per thousand (ppt) to multiply by
parts/thousand parts/billion 1,000,000
parts/thousand parts/million 1,000
parts/thousand milligrams/liter 1,000
parts/thousand micrograms/liter 1,000,000
moles per liter ImollL o mol L' or MIL to multiply by
moles/liter parts/million (molecular weight) x 1,000
moles/liter milligrams/liter (molecular weight) x 1,000
micromoles per liter (umoliL or umol L'or LMIL) to multiply by
micromoles/liter parts/million (molecular weight) x 0.001
micromoles/liter milligrams/liter (molecular weight) x 0.001
micromoles/liter micrograms/liter (molecular weight) x 1
8
millimeters (mm) to multiply by
millimeters feet 0.003281
millimeters inches 0.03937
millimeters microns 1,000
millimeters centimeters 0.1
millimeters meters 0.001
centimeters (cm) to multiply by
centimeters feet 0.03281
centimeters inches 0.3937
centimeters meters 0.01
meters (m) to multiply by
meters feet 3.281
meters inches 39.37
meters miles (statute)* 0.0006214
meters yards 1.094
meters millimeters 1,000
meters centimeters 100
meters kilometers 0.001
kilometers (km) to multiply by
kilometers feet 3,281
kilometers miles (statute) 0.6214
kilometers centimeters 100,000
kilometers meters 1,000
SStatute mile a unit of distance used on land in the English speaking countries equal to 5,280feet or 1,760 yards
9
inches (in) to multiply by
inches centimeters 2.54
inches meters 0.0254
inches fathoms 0.01389
inches yards 0.0278
feet (ft) to multiply by
feet centimeters 30.48
feet meters 0.3048
feet kilometers 0.0003048
feet inches 12
feet fathoms 0.1667
feet miles (statute)* 0.0001893
yards (yd) to multiply by
yards centimeters 91.44
yards meters 0.9144
yards kilometers 0.0009144
yards feet 3
yards fathoms 0.5
fathoms (fm) to multiply by
fathoms inches 72
fathoms feet 6
fathoms yards 2
miles (mi) to multiply by
miles (statute)* kilometers 1.609
miles (statute) meters 1,609
miles (statute) miles (nautical)** 0.8684
miles (statute) feet 5,280
miles (statute) yards 1,760
Statute mile a unit of distance used on land in the English speaking countries equal to 5,280feet or 1,760yards.
Nautical mile ulftitilli fixed in the United States at 6,080.20 feet and in Great Britain at 6,080feet.
10
To convert...
kilograms (kg) to multiply by
kilograms ounces (troy)* 32.15
kilograms pounds (avoirdupois)** 2.205
kilograms tons (short)*** 0.0011
kilograms tons (long)""* 0.000984
kilograms grams 1,000
grams (g) to multiply by
grams grains 15.43
grams ounces (avoirdupois) 0.03527
grams ounces (troy) 0.03215
grams pounds (avoirdupois) 0.002205
grams milligrams 1,000
grams micrograms 1,000,000
grams kilograms 0.001
milligrams (mg) to multiply by
milligrams grains 0.01543
milligrams ounces (avoirdupois) 0.00003527
milligrams ounces (troy) 0.00003215
milligrams pounds 0.000002205
milligrams grams 0.001
milligrams micrograms 1,000
micrograms (pg) to multiply by
micrograms pounds 0.000000002205
micrograms milligrams 0.001
micrograms grams 0.000001
tonnes (t) ,i,,,iii to multiply by
tonnes (metric)"*** pounds (avoirdupois) 2,205
tonnes (metric) tons (long) 0.984
tonnes (metric) tons (short) 1.102
tonnes (metric) kilograms 1,000
*Troy weight a system of weights (i.e., 12 ounces to a pound) used for precious metals, gems, and formerly also
for bread, etc.
*Avoirdupois weight a system of weights used in Great Britain and the U.S. for goods other than gems, precious
metals, and drugs.
** Short ton refers to avoirdupois weight used for the ton in the U.S. (i.e., 2,000 pounds).
*" Long ton refers to the avoirdupois weight used for the ton in Great Britain (i.e., 2,240 pounds).
****Metric ton refers to a unit of 1, 000 kilograms, equivalent to 2,205 avoirdupois pounds.
11
To convert...
ounces (oz) to multiply by
ounces (troy)* pounds (troy) 0.0833
ounces (troy) grams 31.103
ounces (troy) milligrams 31,103
ounces (avoirdupois)** pounds (avoirdupois) 0.0625
ounces (avoirdupois) grams 28.35
ounces (avoirdupois) milligrams 28,350
pounds (Ib) to multiply by
pounds (avoirdupois) grains 7,000
pounds (avoirdupois) ounces (avoirdupois) 16
pounds (avoirdupois) grams 453.5924
pounds (avoirdupois) kilograms 0.4536
tons (ton) to multiply by
tons (short)*** pounds (avoirdupois) 2,000
tons (long)**** pounds (avoirdupois) 2,240
tons (short) tonnes (metric)***** 0.907
tons (long) tonnes (metric) 1.016
*Troy weight refers to a system of weights (i.e., 12 ounces to a pound) used for precious metals, gems, and
formerly also for bread, etc.
** Avoirdupois weight refers to a system of weights used in Great Britain and the U.S. for goods other than
gems, precious metals, and drugs.
** Short ton refers to avoirdupois weight used for the ton in the U.S. (i.e., 2,000 pounds).
*** Long ton refers to the avoirdupois weight used for the ton in Great Britain (i.e., 2,240 pounds).
**** Metric ton refers to a unit of 1000 kilograms which is equivalent to 2,205 avoirdupois pounds.
12
To convert...
watts (w) to multiply by
watts kilowatts 0.001
watts kilocalories/minute 0.01434
watts joules/sec 1
watts horsepower (electric) 0.00134
watts ergs/second 10,000,000
watthours (whr) to multiply by
watthours ergs 36,000,000,000
watthours gram calories 859.18
kilowatts (kw) to multiply by
kilowatts watts (Int.) 1,000
kilowatts joules/sec 1,000
kilowatts horsepower (electric) 1.34
To convert...
horsepower (hp) to multiply by
horsepower (electric) watts 746
horsepower (electric) kilowatts 0.746
horsepower (electric) joules/sec 746
Florida LAKEWATCH
regional coordinators can often be found
in the field working with citizens on
freshwater lakes or coastal waters. Regional
coordinator Dan Willis, pictured here, is
involved in various activities such as
monitoring fish populations and
aquatic plant communities.
13
To convert...
millibars (mb) to multiply by
millibars atmospheres 0.000987
millibars bars 0.001
millibars pounds/square inch 0.0145
To convert...
pounds per square inch (psi) to multiply by
psi atmospheres 0.068
psi bars 0.0689
psi grams/square cm 70.3
psi millibars 68.9
14
To convert...
degrees Celsius (oC) to multiply by
Celsius Fahrenheit (oC x 9/5) + 32
To convert...
degrees Fahrenheit (OF) to multiply by
Fahrenheit Celsius (OF 32) x 5/9
Florida LAKEWATCH volunteer
Dave Byrd takes a temperature reading
from waters adjacent to Sqi.,, ,IfKey
in the lower Florida Keys.
15
To convert...
cubic centimeters (cm") to multiply by
cubic centimeters cubic feet 0.00003531
cubic centimeters cubic inches 0.06102
cubic centimeters gallons 0.0002642
cubic centimeters milliliters 1
cubic centimeters liters 0.001
cubic centimeters cubic meters 0.000001
milliliters (ml or mL ) to multiply by
milliliters cubic inches 0.0610
milliliters ounces 0.0338
milliliters pints 0.00211
milliliters liters 0.001
milliliters cubic centimeters 1
liters (L) to multiply by
liters cubic feet 0.03531
liters gallons 0.2642
liters quarts 1.0567
liters milliliters 1,000
liters cubic centimeters 1,000
liters cubic meters 0.001
cubic meters (ma) to multiply by
cubic meters acrefeet 0.00081
cubic meters cubic feet 35.31
cubic meters cubic yards 1.308
cubic meters gallons 264.2
cubic meters liters 1,000
S Florida LAKEWATCH volunteers may use a variety of graduated cylinders for
measuring water samples for the filtering process. The smaller graduated cylinder
allows one to measure and filter smaller amounts of water This is particularly helpful
to volunteers monitoring waterbodies with an abundance of algae in the water as they
won't need to filter as much water to obtain a chlorophyll sample.
16
To convert...
cubic inches (in') to multiply by
cubic inches cubic centimeters 16.39
cubic inches cubic meters 0.00001639
cubic inches liters 0.0164
cubic inches gallons 0.00433
cubic inches quarts 0.0173
cubic inches pints 0.0346
cubic feet (ft:) to multiply by
cubic feet cubic meters 0.02832
cubic feet liters 28.32
cubic feet acrefeet 0.0000230
cubic feet gallons 7.48052
cubic feet quarts 29.9
cubic feet/second (ft'/sec) to multiply by
cubic feet/second gallons (U.S.)/minute 448.83117
cubic feet/second liters/minute 1698.963
cubic feet/second liters/second 28.31605
gallons (gal) to multiply by
gallons cubic centimeters 3,785
gallons cubic feet 0.1337
gallons cubic meters 0.003785
gallons liters 3.785
gallons of water pounds of water 8.3452
gallons quarts 4
gallons pints 8
quarts (qt) to multiply by
quarts cubic centimeters 946.4
quarts cubic feet 0.03342
quarts cubic meters 0.0009465
quarts liters 0.9463
quarts gallons 0.25
quarts pints 2
quarts ounces 32
17
To convert...
pints (pt) to multiply by
pints cubic centimeters 473.2
pints cubic feet 0.0167
pints cubic meters 0.000473
pints liters 0.473
pints gallons 0.125
pints ounces 16
ounces (oz) to multiply by
ounces cubic centimeters 29.57
ounces liters 0.02957
ounces pints 0.0625
ounces quarts 0.03125
ounces gallons 0.00781
acre feet (acreft) to multiply by
acrefeet cubic feet 43,560
acrefeet gallons 325,851
acrefeet cubic yards 1,613.3
acrefeet cubic meters 1,233.5
cubic yards (yd') to multiply by
cubic yards cubic feet 27
cubic yards gallons 201.97
cubic yards liters 764.5
Florida LAKEWATCH volunteers collect
water samples in two different sized bottles.
The larger bottle shown here on the left holds
up to 500 milliliters (ml) of water and is used
for coastal monitoring. The smaller 250ml
bottle on the right is used for freshwater
sampling.
18
Florida LAKEWATCH regional coordinators Jeanette Lamb and David Watson collect aquatic plant data in Crystal River.
The technique involves throwing a quartermeter square into the water and letting it sink to the bottom. Plants are then collected
from within the quartermeter square frame, ide'rtiifed. and then weighed to obtain an average plant biomass data.
To convert... to... multiply by...
acres hectares 0.4047
acres square meters 4,047
acres square feet 43,560
acres square yards 4,840
acrefeet cubic feet 43,560
acrefeet gallons 325,851
acrefeet cubic yards 1,613.3
acrefeet cubic meters 1,233.5
Celcius Fahrenheit (oC x 9/5) + 32
centimeters feet 0.03281
centimeters inches 0.39370
centimeters meters 0.01
cubic centimeters cubic feet 0.00003531
cubic centimeters cubic inches 0.06102
cubic centimeters gallons 0.0002642
19
To convert... to... multiply by...
cubic centimeters milliliters 1
cubic centimeters liters 0.001
cubic centimeters cubic meters 0.000001
cubic feet cubic meters 0.02832
cubic feet liters 28.32
cubic feet acrefeet 0.0000230
cubic feet gallons 7.48052
cubic feet quarts 29.92
cubic feet/second gallons/minute (US.) 448.83117
cubic feet/second liters/minute 1698.963
cubic feet/second liters/second 28.31605
cubic inches cubic centimeters 16.39
cubic inches cubic meters 0.00001639
cubic inches liters 0.0164
cubic inches gallons 0.00433
cubic inches quarts 0.0173
cubic inches pints 0.0346
cubic meters acrefeet 0.00081
cubic meters cubic feet 35.31
cubic meters cubic yards 1.308
cubic meters gallons 264.2
cubic meters liters 1000
cubic yards cubic feet 27
cubic yards gallons 201.97
cubic yards liters 764.5
ergs gram calories 0.00000002389
ergs kilocalories 0.00000000002389
ergs/second kilocalories/minute 0.000000001433
Fahrenheit Celcius (OF 32) x 5/9
fathoms meters 1.8288
fathoms feet 6
feet centimeters 30.48
feet meters 0.3048
feet kilometers 0.0003048
feet inches 12
feet fathoms 0.1667
feet miles (statute)* 0.001893
Statute mile a unit ofdistance used on land in the English speaking countries equal to 5,280feet or 1,760 yards.
20
To convert... to... multiply by...
footcandles lumens/square meter 10.764
gallons cubic centimeters 3,785
gallons cubic feet 0.1337
gallons cubic meters 0.003785
gallons liters 3.785
gallons quart 4
gallons pints 8
gallons (U.S) of water (40C) pounds of water 8.3452
gallons (U.S.)/minute cubic feet/second 0.002228
gallons (US.)/minute liters/second 0.06308
grains/gallon (U.S.) parts/million 17.119
grams milligrams 1,000
grams micrograms 1,000,000
grams kilograms 0.001
grams grains 15.43
grams ounces (avoirdupois)* 0.03527
grams ounces (troy)** 0.03215
grams pounds (avoirdupois) 0.002205
grams/centimeter pounds/inch 0.0056
grams/liter parts/million 1,000
grams/square centimeter pounds/square foot 2.0481
gram calories ergs 0.00000041868
hectares acres 2.471
hectares square feet 107,639
hectares square meters 10,000
horsepower (electric) watts 746
horsepower (electric) kilowatts 0.746
horsepower (electric) joules/sec 746
inches centimeters 2.54
inches meters 0.0254
inches fathoms 0.01389
inches yards 0.0278
joules ergs 10,000,000
joules kilocalories 0.0002389
*Avoirdupois weight a system ofweights used in Great Britain and the U.S. for goods other than gems, precious metals, and drugs.
* Troy weight a system of weights usedfor precious metals and gems i .. .. also for bread, etc.)
21
To convert... to... multiply by...
kilograms ounces (troy)* 32.15
kilograms pounds (avoirdupois)** 2.205
kilograms tons (short)*** 0.0011
kilograms tons (long)""* 0.000984
kilograms grams 1,000
kilograms/cubic meter pounds/cubic foot 0.06243
kilograms/meter pounds/foot 0.6720
kilograms/square meter pounds/square foot 0.2048
kilometers feet (U.S.) 3,281
kilometers miles (statute)**** 0.6214
kilometers centimeters 100,000
kilometers meters 1,000
kilometers/hour feet/second 0.9113
knots statute miles/hour 1.151
liters cubic feet 0.03531
liters gallons 0.2642
liters quarts 1.057
liters milliliters 1,000
liters cubic meters 0.001
liters/minute cubic feet/second 0.0005886
lumens/square foot footcandles 1
lux footcandles 0.0929
meters feet 3.281
meters inches 39.37
meters miles (statute) 0.0006214
meters yards 1.094
meters millimeters 1,000
meters centimeters 100
meters kilometers 0.001
meters/minute feet/second 0.05468
micrometers meters 0.000001
*Troy weight refers to a system of weights used for precious metals and gems rii. n1 also for bread, etc.).
*Avoirdupois weight is a system of weights used in Great Britain and the U.S. for goods other than gems, precious metals, and drugs.
***Short ton refers to avoirdupois weight used for the ton in the U.S. (i.e., 2,000 pounds).
****Long ton refers to the avoirdupois weight used for the ton in Great Britain (i.e., 2,240 pounds).
Statute mile is a unit of distance used on land in the English speaking countries equal to 5,280feet or 1, 760 yards.
22
To convert... to... multiply by...
micrograms pounds (avoirdupois)* 0.000000002205
micrograms milligrams 0.001
micrograms grams 0.000001
micrograms/liter milligrams/cubic meter 1
micrograms/liter milligrams/liter 0.001
micrograms/liter ppm 0.001
micromoles/liter parts/million (molecular weight) x 0.001
micromoles/liter milligrams/liter (molecular weight) x 0.001
miles (statute) kilometers 1.609
miles (statute) meters 1,609
miles (statute) miles (nautical)" 0.8684
miles (statute) feet 5,280
miles (statute) yards 1,760
millibars atmospheres 0.000987
millibars bars 0.001
millibars pounds/square inch 0.0145
milligrams grains 0.01543
milligrams ounces (avoirdupois) 0.00003527
milligrams ounces (troy)*** 0.00003215
milligrams pounds 0.000002205
milligrams micrograms 1,000
milligrams grams 0.001
Conversion Factors Used in Water Management
To Convert... to... multiply by...
mg/L ig/L 1,000
g/L mg/L 0.001
p M/L mg/L (molecular weight) x 0.001
mg/m3 mg/L 0.001
mg/m3 p.g/L 1
ppm mg/L 1
ppm ppb 1,000
ppb ppm 0.001
pounds/acre kg/ha 1.12
*Avoirdupois weight is a system ofweights used (i.e., Great Britain, US.) for goods other than gems, precious metals, and drugs.
*Nautical mile otiti illv fixed in the United States at 6,080.20feet and in Great Britain at 6,080feet.
irny weight refers to a system of weights usedfor precious metals and gems (formerly also for bread, etc.)
23
To convert... to... multiply by...
milligrams/cubic meter micrograms/liter 1
milligrams/cubic meter milligrams/liter 0.001
milligrams/liter parts/billion 1,000
milligrams/liter parts/million 1
milligrams/liter grains/U.S. gallon 0.0584
milligrams/liter micrograms/liter 1,000
milligrams/liter milligrams/cubic meter 1,000
milliliters cubic inches 0.061
milliliters ounces 0.0338
milliliters pints 0.00211
milliliters liters 0.001
milliliters cubic centimeters 1
millimeters feet 0.003281
millimeters inches 0.03937
millimeters microns 1,000
millimeters centimeters 0.1
millimeters meters 0.001
millimicrons meters 0.000000001
moles/liter parts/million (molecular weight) x 1,000
moles/liter milligrams/liter (molecular weight) x 1,000
million gallons/day cubic feet/second 1.54723
ounces (troy)* pounds (troy) 0.0833
ounces (troy) grams 31.104
ounces (troy) milligrams 31,104
ounces (avoirdupois)** pounds (avoirdupois) 0.0625
ounces (avoirdupois) grams 28.35
ounces (avoirdupois) milligrams 28,350
parts/billion micrograms/liter 1
parts/billion milligrams/liter 0.001
parts/million grains/U. S. gallon 0.0584
parts/million parts/billion 1,000
parts/million parts/thousand 0.001
parts/million micrograms/liter 1,000
parts/million milligrams/liter 1
parts/thousand parts/billion 1,000,000
parts/thousand parts/million 1,000
parts/thousand milligrams/liter 1,000
STroy weight refers to a system of weights usedforprecious metals and gems r... ..., also for bread, etc.)
**Avoirdupois weight is a system ofweights used in Great Britain and the U.S. for goods other than gems, precious metals, and drugs.
24
To convert... to... multiply by...
parts/thousand micrograms/liter 1,000,000
pints cubic centimeters 473.2
pints cubic feet 0.0167
pints cubic meters 0.000473
pints liters 0.473
pints gallons 0.125
pints ounces 16
pounds (avoirdupois)* grains 7,000
pounds (avoirdupois) grams 453.5924
pounds (avoirdupois) kilograms 0.4536
pounds (avoirdupois) ounces (avoirdupois) 16
pounds of water/minute cubic feet/minute 0.01602
pounds of water/minute cubic inches/minute 27.68
pounds of water/minute gallons (U.S.)/minute 0.1198
pounds/foot kilograms/meter 1.488
pounds/inch grams/centimeter 178.6
pounds/square foot inches of mercury 0.01414
psi atmospheres 0.068
psi bars 0.0689
psi grams/square cm 70.3
quarts cubic centimeters 946.4
quarts cubic feet 0.03342
quarts cubic meters 0.0009464
quarts liters 0.9463
quarts gallons 0.25
quarts pints 2
quarts ounces 32
square centimeters square feet 0.001076
square centimeters square inches 0.155
square centimeters square meters 0.0001
square feet acres 0.00002296
square feet square centimeters 929
square feet square meters 0.0929
square inches square centimeters 6.452
square inches square meters 0.0006452
square inches square feet 0.00694
Avoirdupois weight is a system of weights used in Great Britain and the U.S. for goods other than gems, precious metals, and drugs.
25
To convert... to... multiply by...
square kilometers acres 247.1
square kilometers square feet 10,763,910
square kilometers square miles 0.3861
square meters acres 0.0002471
square meters square centimeters 10,000
square meters square feet 10.76
square meters square miles 0.0000003861
square meters square yards 1.196
square miles acres 640
square miles square kilometers 2.59
square miles hectares 259
square miles square meters 2,589,988.1
square yards square meters 0.8361
square yards hectares 0.00008361
square yards acres 0.000207
tons (short)* pounds (t,"ii,, I/, I 2,000
tons (long)* pounds (avoirdupois) 2,240
tons (short) tonnes (metric) 0.907
tons (long) tonnes (metric) 1.016
tonnes pounds 2,205
tonnes tons (long) 0.984
tonnes tons (short) 1.102
tonnes kilograms 1,000
watts kilowatts 0.001
watts kilocalories/minute 0.01433
watts joules/sec 1
watts horsepower (electric) 0.00134
watts ergs/second 10,000,000
watthours ergs 36,000,000,000
watthours gram calories 859.85
yards centimeters 91.44
yards kilometers 0.0009144
yards meters 0.9144
yards feet 3
yards fathoms 0.5
*A short ton refers to avoirdupois weight usedfor the ton in the U.S. (i.e., 2,000 pounds).
*A long ton refers to the avoirdupois weight used for the ton in Great Britain (i.e., 2,240 pounds).
*Avoirdupois weight is a system of weights used in Great Britain and the U.S. for goods other than gems, precious metals, and drugs.
26
Element ~ One dictionary defines it as a substance with "a chemical
composition that is in a class unto itself here on earth and even in this
universe." Another defines it as a substance containing "atoms of only
one kind that singly or in combination constitute all matter."
To put it simply, elements are the basic building blocks of the chemical and physical world,
as we know it.
While many of us remember this basic concept from high school chemistry class, details such as the
name, abbreviation, and atomic weight2 of each element are probably a bit fuzzy. This is understandable as
there are more than 100 elements recognized by the international scientific community. Fortunately, a list of
elements and their international atomic weights can be found in most chemistry books, in some dictionaries,
and at a number of online web sites.3 (A good reference source for anyone working in the aquatic sciences
is STANDARD METHODS for the Examination of Water and Wastewater.) For your convenience however,
we've provided a table of international relative atomic weights in this section along with a brief explanation of
how relative atomic weights are determined (page 29) and how they are used to calculate the molecular weight
of the various chemical compounds found on earth (page 30).
Why do we need to know about elements and their atomic weights?
For starters, many elements, including calcium, magnesium, nitrogen, phosphorus and silicon, are
considered to be important nutrients found in aquatic environments. Familiarity with their names and abbre
viations is useful from a communications perspective as scientists commonly use abbreviated terminology in
their journal articles, graphs, charts, and lectures. For example, when a scientist discusses the effects of "N"
or "P" in a lake system, an educated reader/listener will know that the scientist is referring to the elements
nitrogen or phosphorus, respectively.
Secondly, knowledge of an element's atomic weight is required for accuracy when converting from one
unit of measure to another. A marine scientist, for instance, might record nutrient concentrations in units of
micromoles per liter (jM/L) while a freshwater scientist may use milligrams per liter (mg/L) or micrograms
per liter (lg/L). If either scientist wants to combine databases for comparison, conversions would need to be
made to standardize the units of measure. To make the conversions, the atomic weight of each element, such as
nitrogen or phosphorus, would have to be known. An explanation of how to do these conversions is provided
in Section VII on page 35. And remember, if you should encounter any difficulties converting from one unit of
measure to another, don't feel bad as this can be a difficult task even for professionals!
2 An element's atomic weight is approximately equal to the number ofprotons and neutrons found in an atom.
3 Atomic Weights of the Elements. 1999. World Wide Web version prepared by G.R Moss, originallyfrom afile
provided by D.R. Lide.
27
Element Symbol Atomic Weight Element Symbol Atomic Weight
Actinium Ac 227* Lawrencium Lr 262
Aluminum Al 26.981538 Lead Pb 207.2
Americium Am 243 Lithium Li 6.941
Antimony Sb 121.760 Lutetium Lu 174.967
Argon Ar 39.948 Magnesium M 24.3050
Arsenic As 74.92160 Manganese Mn 54.938049
Astatine At 210 Meitnerium Mt 268
Barium Ba 137.327 Mendelevium Md 258
Berkelium Bk 247 Mercury Hg 200.59
Beryllium Be 9.012182 Molybdenum Mo 95.94
Bismuth Bi 208.98038 Neodymium Nd 144.24
Bohrium Bh 264 Neon Ne 20.1797
Boron B 10.811 Neptunium Np 237
Bromine Br 79.904 Nickel Ni 58.6934
Cadmium Cd 112.411 Niobium Nb 92.90638
Calcium Ca 40.078 Nitrogen N 14.0067
Californium Cf 251 Nobelium No 259
Carbon C 12.0107 Osmium Os 190.23
Cerium Cc 140.116 Oxygen Os 15.9994
Cesium CS 132.9054 Palladium Pd 106.42
Chlorine Cl 35.453 Phosphorus P 30.973761
Chromium Cr 51.9961 Platinum Pt 195.078
Cobalt Co 58.933200 Plutonium Pu 244
Copper Cu 63.546 Polonium Po 209
Curium Cm 247 Potassium K 39.0983
Dubnium Db 262 Praseodymium Pr 140.90765
Dyprosium Dy 162.50 Promethium Pm 145
Einsteinium Es 252 Protactinium Pa 231.03588
Erbium Er 167.259 Radium Ra 226
Europium Eu 151.964 Radon Rn 222
Fermium Fm 257 Rhenium Re 186.207
Fluorine F 18.9984032 Rhodium Rh 102.90550
Francium Fr 223 Rubidium Rb 85.4678
Gadolinium Gd 157.25 Ruthenium Ru 101.07
Gallium Ga 69.723 Rutherfordium Rf 267
Germanium Ge 72.64 Samarium Sm 150.36
Gold An 196.96655 Scandium Sc 44.955910
Hafnium Hf 178.49 Selenium Se 78.96
Hassium Hs 277 Seaborgium Sg 266
Helium He 4.002602 Silicon Si 28.0855
Holmium Ho 164.93032 Silver Ag 107.8682
Hydrogen H 1.00794 Sodium Na 22.989770
Indium In 114.818 Strontium Sr 87.62
Iodine I 126.90447 Sulfur S 32.065
Iridium Ir 192.217 Tantalum Ta 180.9479
Iron Fc 55.845 Technetium Tc 98
Krypton Kr 83.80 Tellurium Te 127.60
Lanthanum La 138.9055 Terbium Tb 158.92534
28
Element Symbol Atomic Weight Element Symbol Atomic Weight
Thallium TI 204.3833 Yttrium Y 88.90585
Thorium Th 232.0381 Zinc Zn 65.39
Thulium Tm 168.93421 Zirconium Zr 91.224
Tin Sn 118.710
Titanium Ti 47.867 Based on the assigned relative atomic mass of12 C=12.
Tungsten W 183.84 Relative weights shown here as whole numbers indicate the
Ununilium Uun 281 mass number of the longestlived isotope of that element.
Ununquadium Uuq 289 Note: The atomic weights you may see here and in other
Uranium U 238.02891 publications may vary ,;, lid. This is due to each publisher
Vanadium V 50.9415 rounding ot/ trl numbers dlitreirtih It' also important to note
Xenon Xe 131.293 that atomic weight values are periodically redetermined; this
Ytterbium Yh 173.04 may also contribute to minor/, I..'.... in weights shown.
Before the age of nuclear technology, scientists Take hydrogen, for example. The relative atomic
were limited to studying chemical reactions that weight of hydrogen is expressed as 1.008. This
involved large numbers of atoms at once, as there means that the mass of a hydrogen atom is slightly
were no methods for isolating a single atom to greater than onetwelfth the mass of a carbon12
atom.** See illustration below.
determine its weight. However, scientists were able
We can use the element copper (Cu) as a second
to devise a system for assigning weights to the example. Copper has a relative atomic weight of
elements by comparing how heavy a given atom 63.546. This means that the mass of a copper atom is
was in relation to other atoms. This is known as nearly 64 times that of one carbon12 atomic unit
the system of relative atomic weights. The (i.e., 1/12t).
following is a brief explanation of how it works. To further visualize this, imagine 12 individual spheres
S. clustered together as seen in the figure below.
The current practice is to express the weight of clustered together as seen in thefigu below.
a given element as it relates to the weight of some ** The expressed weight ofl1.008 is the average weight of
known standard. In recent years, the accepted naturally occurring hydrogen; the reason it is not exactly 1.000
standard is a carbon isotope known as carbon12 is that a smallfraction ofnaturally occurring hydrogen atoms
have a weight of2, rather than 1.
with an assigned weight of 12 atomic mass units.
Using only one of these twelve
units (i.e., 1/12h), we can A hydrogen atom is assigned an atomic weight of 1
assign atomic weights for all (rounded from 1.008) because the mass of a hydrogen
the other elements. atom is roughly equal to 1/12th the mass of a 12c
In other words, when carbon12 atom (depicted on the right).
expressing the atomic weight
of an element, we simply This cluster of 12 protons and neutrons
need to express the mass of represents the total mass of a
that element relative to the carbon12 atom. The sphere that is circled
mass of onetwelfth of a represents one atomic unit (i.e., 1/12th)
of that atom. This unit is the basis for
carbon12 atom. These units determining the relative atomic weight
of weight are referred to as for all other elements.
"atomic mass units."
29
Now that we've got a better understanding of relative atomic weights (see page 29),
we can begin to consider chemical compounds and learn how to interpret them.
It's important to be able to interpret such formulas because elements are rarely found alone in nature.
More often than not, they combine with other elements to form chemical substances or compounds. For
example, let us consider one of the most commonly known compounds water. The abbreviation alone tells us
that a water molecule (H20) is comprised of two atoms of hydrogen (H2) and one atom of oxygen (0). When
combined with one more atom of oxygen, we end up with a compound known as hydrogen peroxide (H202).
We can find the molecular weight of a chemical compound by totaling up the weight,
in atomic mass units, of all the atoms in that given formula.
We use molecular weights to describe how many grams are in one mole* of a substance. When dealing
with concentrations of chemicals, it's often helpful to know the molecular weight of a specific compound so
that we can evaluate how it is interacting with other substances. While you may not have the opportunity to
do this in a laboratory, it is still helpful to be able to interpret the language used by the chemists. Learning to
calculate the molecular weight of a substance is the first step toward a better understanding of water chemistry.
To help you in this endeavor, we've provided several practice exercises below.
*A mole is the standard unit of measure used by chemists for c. ,mI, .,t,,' 1i quantities ofa chemical compound; a mole is
also referred to as a gram molecule. The term "mole" is abbreviated as "mol" or "M. "
Step 1
Before we can calculate the molecular weight of a chemical compound,
we need to know how many atoms are present for each element.
For the purposes of this exercise, we've chosen three chemical compounds that are
commonly associated with water chemistry.
For NaCI (sodium chloride) there will be: For Fe (OH)3 (hydratedferric hydroxide)
one atom of sodium (Na) there will be:
one atom of chlorine (Cl) one atom of iron (Fe),
three atoms of oxygen (0)
For CaCO, (calcium carbonate) there will be: three atoms of hydrogen (H)
one atom of calcium (Ca), Note: Ifa i,,,/... ; ... an atom abbreviation with no
one atom of carbon (C) parenthesis, that number tells us how many atoms are present for
Sa f o () that element. Ifparentheses are involved, you must multiply each
three atoms of oxygen () individual subscript on the inside or.il, parentheses by the
subscript number on the outside.
30
Step 2
To calculate the molecular weight of a substance or compound,
you must first know the atomic weight of each element within the compound.
International Relative Atomic weights can be found in the table on pages 2829.
For your convenience, we've provided atomic weights for the compounds used in this exercise.
SNa = 22.989770
NaCI c = 35.453 Fe = 55.845
Fe(OH) { O = 15.9994
H = 1.00794
Ca = 40.078
CaCO, { c = 12.0107
0 = 15.9994
Step 3
Once you have a relative atomic weight for each element in a compound, multiply the
weight of each atom by the number of atoms that are present in the formula,
then add the answers.
One atom of sodium (Na) = 1 x 22.989770 = 22.989770
One atom of chlorine (Cl) = 1 x 35.453 = 35.453
Add these values for the molecular weight:
22.989770 + 35.453 = 58.44277 atomic mass units (amu)
The answer 58.44277 represents the molecular weight for one mole
of NaCI in atomic mass units (amu).
One atom of calcium (Ca) = 1 x 40.078 = 40.078
One atom of carbon (C) = 1 x 12.0107 = 12.0107
Three atoms of oxygen (0) = 3 x 15.9994 = 47.982
Add these values for the molecular weight:
40.078 + 12.0107 + 47.982 = 100.0707 atomic mass units (amu)
The answer 100.0707 represents the molecular weight for one mole of CaCO3.
One atom of iron (Fe) = 1 x 55.845 = 55.845
Three atoms of oxygen (0) = 3 x 15.9994 = 47.982
Three atoms of hydrogen (H) = 3 x 1.00794 = 3.02382
Add these values for the molecular weight:
55.845 + 47.982 + 3.02382 = 106.85082 atomic mass units (amu)
The answer 106.85082 represents the molecular weight for one mole of Fe(OH)M.
31
Many elements that are important to most communities in the United States, the
lakes are found in more than one maximum amount of nitrates allowed in drinking
chemical form. Nitrogen (N) is a good water is considered to be 45 mg/L NO,. (While
example. It can combine with two oxygen atoms occurrences have been rare, it's been found that
to form nitrites (expressed by the compound in small babies, higher nitrate levels can interfere
formula NO21) or it can combine with three with the ability of the blood to carry oxygen,
oxygen atoms to form nitrates resulting in a phenomenon
(NO31). Ammonium ions (NH4+1) known as the blue baby
are formed when one nitrogen syndrome.)
atom is combined with four If we made a separate
hydrogen atoms. Nitrogen can measurement of just the
also be found in various organic nitrogen contained in the
molecules produced by living nitrate formula mentioned
organisms in lakes.5 above, we would express the
The sum of these various concentration as 10.2 mg/L
nitrogen compounds is known as NO3N. This is known as a
total nitrogen. We often rely on nitratenitrogen formula. An
total measurements because interpretation of this particular
some elements, nitrogen included, formula tells us that there are
tend to continually transfer from 10.2 mg of nitrogen contained
one form to another through the within the nitrates in a liter of
metabolism of aquatic organisms, Because nitrogen compounds are water. The "N" symbol
Because nitrogen compounds are
making it difficult to track constantly changing within an aquatic found in the latter portion of the
individual chemical compounds. environment, some water monitoring formula tells us that the number
This is true for phosphorus as programs, includingFloridaLAKEWATCH, value (10.2 mg/L) is describing
well. Florida LAKEWATCH prefer to measure total nitrogen the weight of nitrogen only
concentrations. Such information helps
measures total phosphorus scientists estimate the potentialfor contained in that compound.
concentrations for the same biologicalproductivity in a waterbody. A similar approach would
reason. These compounds are be used if we were to make a
commonly measured in concentrations of milligrams
per liter (mg/L) or micrograms per liter (Lg/L). 5 Organic molecules are formed by the actions of
There are times however, when we may living ;li,, i and/or have a carbon backbone.
want to isolate and measure a specific chemical Methane (CH) is an example, ,l i,,r gh it's
compound. A case in point is the standard that important to note that not all methane is formed by
has been set for nitrates in drinking water: In living organisms.
32
separate measurement of the nitrogen contained To convert units of nitrates to units of
in an ammonium compound. The formula would nitratenitrogen we need to multiply by a conversion
be expressed as mg/L NH4 N and is known as an factor consisting of the atomic weight of nitrogen
ammoniumnitrogen formula. And if we wanted divided by the combined atomic weights of one
to measure the weight of nitrogen only as it combines nitrogen and three oxygen atoms. An example of
with organic molecules, we would use an organic this conversion process is provided below.
nitrogen formula expressed as mg/L organicN.
As you can see from the examples above, Note: The same approach can be used for other
a nitrate formula is expressed differently than a chemical compounds found in water For instance,
nitratenitrogen formula, even though they both there may be times when one would want to isolate
the weight ofphosphorus contained in phosphates
represent measurements of nitrates found in one i r i
r o or the weight ofsulfur contained in sulfates, etc.
liter of water.
45mg/L NO = 45 x (14* + (14 +48**)) = ?
(original nitrate formula)
45 mg/L NO3 = 45 x 0.226 = 10.2 mg/L NO3 N
(nitratenitrogen formula)
14 is the relative atomic weight for nitrogen (rounded from 14.00674).
** The number 48 was attained by ,,lij!' ,ii. the relative atomic weight of a single oxygen
atom (16) by 3, as there are three oxygen atoms in a nitrate molecule.
The nitrate formula (top left) tells us that there is a total concentration
of 45 mg of nitrates in a liter of water. After doing the conversion, the
nitrate nitrogen formula (bottom right) tells us that out of the 45 mg/L
of nitrates, there are 10.2 mg of actual nitrogen within that same liter of
water. It should be noted that the nitrate nitrogen formula is currently
being used by most water chemistry labs as the preferred way to
express this relationship.
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Kelly Schulz (left) processes total phosphorus samples for the Florida LAKEWATCH program at a UF/IFAS water
chemistry laboratory. The freshwater total phosphorus concentrations she records into the LAKEWATCH database
are expressed as micrograms per liter p,.. i). Erin Bledsoe, ,hi.n prepares a Van Dorn sampler before lowering it
into marine
often expressed as micromoles per liter p.l I ). If the two were to be compared, conversions would be needed.
A though most aquatic scientists have adopted the International System (SI) for standardizing
scientific units of measure, it doesn't necessarily mean they will use the same units of
measure for the same things. For example, scientists who study saltwater systems (i.e.,
oceanographers, etc.) and those that study freshwater systems (i.e., limnologists) often express
their work differently. Oceanographers tend to use the micromole per liter (LM/L) as a unit of
measure in their analyses while limnologists tend to use the milligram per liter (mg/L) or micro
gram per liter (pLg/L) units of measure for their studies.
This isn't a problem unless one scientist decides to compare his or her data with those of
another, in which case conversions must be made so that one can compare "apples with
apples." See the examples on the next page for an explanation on how atomic weights are
used to convert from one unit of measure to another.
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Converting micromoles per liter (gM/L) to micrograms per liter (gg/L)
To convert a concentration of an element given as micromoles per liter (I1M/L) to units of micrograms
per liter (glg/L), you would simply multiply the concentration in micromoles times the relative atomic weight
of the element. For example, to convert a phosphorus concentration of 10 [iM P/L to units of pg P/L, you
would multiply 10 times the relative atomic weight for phosphorus (31)* to get 310 glg/L of phosphorus.
Notice how the abbreviation for phosphorus (P) is expressed in the equation below.
10 pM P/L = 10 (micromoles) X 31 (relative atomic weight for phosphorus) = 310 p1g P/L
Using the table on page 28 we can see that the relative atomic weightfor phosphorus is 31 (roundedfrom 30.973761).
Converting micrograms per liter (gg/L) to micromoles per liter (gM/L)
To convert a concentration of an element given as micrograms per liter (lg/L) to units of
micromoles per liter (pM/L), you would divide the concentration in micrograms by the relative
atomic weight of the element. For example, to convert a nitrogen concentration of 100 Lgg/L to units of
jMM/L you would divide 100 by nitrogen's relative atomic weight of 14 to get 7.142 dlM/L of nitrogen.
Notice how the abbreviation for nitrogen (N) is expressed in the equation below.
100 gg N/L = 100 (micrograms) + 14 (relative atomic weight for nitrogen) = 7.142 LM N/L
Using the table on page 28 we can see that the relative atomic weight for nitrogen is 14 (roundedfrom 14.0067).
Speaking in MolecularTerms
The following are terms that you are likely to hear within the water chemistry arena:
Atomic weight is approximately equal to the number of protons and neutrons found in an atom.
Gram atomic weight refers to the weight of an element in units of grams. Along those same
lines, if one were to express the weight of an element in units of milligrams, you would then refer
to it as the milligram atomic weight.
Micromolar solution refers to the molecular weight of a substance expressed as "micrograms
contained in one liter of water" (i.e., onemillionth of a gram molecular weight). For example a
micromolar solution of phosphorus contains 31 micrograms (pgg) of phosphorus in one liter of water.
Molar solution is one mole dissolved in enough water to make one liter.
Mole is the molecular weight of a substance expressed in grams; also known as a gram molecule.
Chemists tend to use moles to describe chemical compounds.
Molecular weight refers to the combined (the sum) atomic weight of all the atoms in a
molecule.
Relative atomic weight refers to the relative weight of each element, based on the assigned
relative atomic mass of 12C = 12.
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Selected Scientific References
APHA. 1992. STANDARD METHODS for the examination of Water and Wastewater. American
Public Health Association, American Water Works Association, Water Environment Federation.
Washington, DC.
Florida LAKEWATCH. 1999. A Beginner's Guide to Water Management The ABCs (Circular 101).
Descriptions of Commonly Used Terms. Florida LAKEWATCH, Department of Fisheries and
Aquatic Sciences, Institute of Food and Agricultural Sciences (IFAS), University of Florida,
Gainesville, Florida.
Florida LAKEWATCH. 2000. A Beginner's Guide to Water Management Nutrients (Circular 102).
Florida LAKEWATCH, Department of Fisheries and Aquatic Sciences, Institute of Food and
Agricultural Sciences (IFAS), University of Florida, Gainesville, Florida.
Florida LAKEWATCH. 2000. ABeginner's Guide to Water Management Water Clarity (Circular 103).
Florida LAKEWATCH, Department of Fisheries and Aquatic Sciences, Institute of Food and
Agricultural Sciences (IFAS), University of Florida, Gainesville, Florida.
Florida LAKEWATCH. 2001. A Beginner's Guide to Water Management Lake Morphometry
(Circular 104). Florida LAKEWATCH, Department of Fisheries and Aquatic Sciences,
Institute of Food and Agricultural Sciences (IFAS), University of Florida, Gainesville, Florida.
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