Safe Drinking Water
Notebook Lab
Introduction:
Just because water is clear doesn’t mean that it is safe!!! Ions can be dissolved in water and consumed from
drinking tap water. Many ions can bind to biological molecules (eg. Proteins) and alter their function. To
determine if lead (or other) ions are found in solution, it is often useful to run a precipitation reaction. This is
what is happening in many commercial water testing kits. By mixing tap water (which is actually an aqueous
solution that has dissolved ions!) with other aqueous compounds and looking for precipitates you can
systematically determine if tap water contains a large amount of a certain type of ion.
Define:
Soluble
Insoluble
Aqueous
Precipitate
Dissociation
Cation
Anion
The purpose of this activity, is to use the solubility rules to analyze precipitation reactions and determine if
there are lead ions in a water sample.
Hypothesis:
If… (what will we be looking for!)
Then…(what will this tell us!!
Why? (what is the chemistry!!!)
Procedure:
You are sampling tap water, and based on the location that it comes from, these are the possible contaminants:
Cation
Possible Anion that would allow for
this ion to be soluble!
Soluble Compound
Pb2+
Ag+1
NH4 +1
Na+1
In order to complete the reactions:
1.
2.
3.
4.
5.
6.
Neatly smooth a piece of wax paper over the blank data sheet provided.
Put a drop of each water sample in each data box.
Then put a drop of the aqueous solutions provided on top of the water drop.
Observe whether there is NR (no reaction) or the formation of a precipitate (indicate the color).
Use the information to complete the analysis.
Write the molecular equation and net ionic equation for one reaction that forms a precipitate for each
positive water sample. For the contaminant, you can choose any anion that would allow the
contaminant to dissociate in solution.
7. For your data, take and print a picture of your analysis.
Data: Indicate if a precipitate forms; and what observation you make!
Water Sample # Cu2SO4 or
K3PO4
NaNO3 or KNO3
Fe2(SO4)3
1
2
3
4
NaOH
KI or KBr or
KCl or MgCl2
Analysis:
Water
Sample
1
Ion
Contaminant
Molecular Equation that allowed you to
determine the contaminant.
Net Ionic
2
3
4
Conclusion:

Respond to your hypothesis by explaining how you determined the contaminant present in each water
sample.

Using your solubility table, discuss sources of error. Did the tests determine with absolute certainty
which ion was contaminating the solution?

Are these tests quantitative or qualitative? Explain. Read the following website from the EPA
http://water.epa.gov/drink/info/lead/lead1.cfm Would it be useful to have a quantitative test? Explain
why or why not?

Sources of error: Are certain precipitation reactions better able to indicate a reaction than others?
Explain your reasoning. Which of the reactions was least conclusive? Did it depend on which of the
compounds you chose to use to react with your water sample?

From the website above describe:
1) Three sources of lead contamination in drinking water.
2) Two ways to reduce the risk.

Find information about another ion that contaminates drinking water. Explain what a common source
of this ion is and what can be done to reduce the risk.

How does the theme stability and change relate?
o
Think about how they affect biological molecules!!!
Water Sample #
Cu2SO4 or
Fe2(SO4)3
K3PO4
NaNO3 or KNO3
NaOH
KI or KBr or
KCl or MgCl2
Cu2SO4 or
Fe2(SO4)3
K3PO4
NaNO3 or KNO3
NaOH
KI or KBr or
KCl or MgCl2
1
2
3
4
Water Sample #
1
2
3
4