Lab: Is Dilution the Solution?
Name ___________________
The saying goes “A dilute solution is a safe solution”
Practice with Dilutions: Solve for the new concentration after the prescribed dilution has taken place.
_____ 1) Equal volumes of 2.0 M NaCl solution mixed with water
_____ 2) Three parts water is added to one part 1.0 M Sugar solution
_____ 3) Nine parts water is added to one part 1.0 M NaCl solution
_____ 4) A solution of concentration 0.010 ppm has an equal volume of water added to it
Visual Dilution
Procedure: Measure out approximately 1.0 grams of a food dye. Add this to an approximate volume of
250 mL of water. Record the concentration of the food dye in ppm and how visible the pollutant is.
Poor out 250 mL of the solution (down the sink), then add another fresh 250 mL of water. Repeat until
1500 mL is reached or the pollutant is no longer visible. If at 1500 mL it is still not reached, continue
diluting and record the final volume/concentration at which the pollutant ceased to be visible.
Volume of
250 mL
water
Ppm (food
dye)
Visual
Observations
500 mL
750 mL
1000
mL
1250
mL
1500
mL
Final Volume
Taste Dilution
Note: This is an exception to normal lab procedure. You will be allowed to drink the solution made. We
will not be using our lab equipment (flasks and such), just normal every day cups).
Procedure: Record the mass of the kool-aid packet. Empty the packet into the kool-aid container and fill
it to the recommended volume. Mass the empty packet to determine the mass of mix added. Record
the mass of kool-aid and initial volume of container. Poor everyone a small amount of kool-aid (you will
be repeating this step). Record whether you can taste it (and how strongly). Empty the kool-aid
container so that it is now half-full and add water to the original volume (diluting by half). Drink, record,
and repeat until you no longer taste the koolaid. Make sure to keep track of how many times you
diluted the solution!
Data table found on back.
Mass
Packet
Mass
Empty
packet
Mass
Koolaid
Initial
Volume
Koolaid
Initial
Total
Concentration Dilutions
(ppm)
(Tally)
Final Concentration
(ppm) where
undected
Follow up questions
1) What do you think: Are your eyes more sensitive to the pollution present in water or is your tongue?
Does it matter what type of pollutant it is?
2) Discuss how likely it is for each of the following solutions to become polluted beyond safe levels:
a) Standing ditchwater in an agricultural area
b) The ocean
c) The groundwater in an aquifer
2) The Mississippi river is a very large river, with an average volume flow of 16,500 m3/s.
a) How many grams of nitrate can this river absorb and still be considered safe to drink from (10
ppm legal limit) on an annual basis?
b) According to http://pubs.usgs.gov/fs/fs155-99/fs155-99.html the USA applies approximately
11.5 million metric tons of Nitrogen based fertilizers annually, with the bulk of the use occurring in the
Midwest. What do you think; can the Mississippi river manage the job of diluting down the nitrogen to
safe levels?
3) The ocean is extremely large; it has a volume of 1.3 billion km3 and a mass of 1.4 x 1021 kg. Is the
ocean safe from pollution because of dilution? Do the math to find out
a) Consider cadmium, which is found in an abundance of about 0.1 ppm of the Earth’s crust.
The Earth’s crust has a mass of 4 x 1022 kg. If we were to harvest all of the cadmium out of the Earth’s
crust, and then subsequently just threw it in the ocean, what would the concentration of cadmium be in
the ocean?
b) Consider how rare cadmium is compared to other toxic heavy metals such as lead and
mercury. Do you feel that the ocean is capable of absorbing our pollution without having negative
effects on the aquatic life there?
c) Mercury, as well as many pollutants, will bioaccumulate. While these pollutants will dilute in
an aquatic environment, they actually become more concentrated in living organisms higher up the food
chain. Explain how the process of bioaccumulation leads to dangerous concentrations in living
organisms even though the pollutant may be becoming more dilute in the river.