Name:______________________________________________________________________________
(Unit 5.1)
INTRODUCTION
How can chemists detect and identify certain ions in water solutions? In this activity, you will perform
confirming tests for dissolved ions in water. That is, a positive test confirms that the ion in question is present. In each confirming test, you will look for a change in solution color or for the appearance of an insoluble material called a
precipitate. A negative test (no color or precipitate) does not necessarily mean that the ion in question is absent. The ion may simply be present in such a small amount that the test result may not be observed.
These tests are qualitative tests, one that identify the presence or absence of a particular substance in a sample.
In contrast, quantitative tests determine the amount of a specific substance present. You will test for the presence of
Iron (III) (Fe 3+ ) and calcium (Ca 2+ ) cations, as well as chloride (Cl ) and sulfate (SO
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2) anions. You will perform each test on several different water samples. The first solution will be a reference solution- one that contains the ion of interest. The second will be a control- a sample known not to contain the ion. The control in this activity is distilled water. The other solutions will be tap water and three mineral water samples. To determine whether these solutions contain the ion, you will need to compare you results with your reference and control samples.
PRE-LAB QUESTIONS
1) What is qualitative data? Give an example.
2) What is quantitative data? Give an example.
3) What is the difference between a reference solution and a test solution?
4) How many drops of each test solution are put in each of the wells of the 24-well plate?
5) If the ion you are testing for is present in solution, what will you observe?
6) What kind of change, physical or chemical, takes place in the well between the test solution and the reference solution so that you can determine if the ion is present?
PROCEDURE
1) Water Samples: Fill each well with 20 drops of water sample, as indicated in the diagram on the next page. Each reference solution contains the ion in question. For example, the Ca reference solution contains Ca 2+ ion. Distilled water is the control.

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II
I
Name:______________________________________________________________________________
Reference Control Sample A Sample B Sample C Sample D
Ca
Ref.
Dis.
H
2
O
Sam.
A
Sam.
B
Sam.
C
Sam.
D
Fe
Ref.
Cl
Ref.
Dis.
H
H
2
2
O
Dis.
O
Sam.
A
Sam.
A
Sam.
B
Sam.
B
Sam.
C
Sam.
C
Sam.
D
Sam.
D
IV SO
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Ref.
Dis.
H
2
O
Sam.
A
Sam.
B
Sam.
C
Sam.
D
2) Test Solutions: Next, add the following number of drops of each of the test solutions: 3 drops of Ca 2+ test solution to all the wells in row I, 1 drop Fe 3+ test solution to all the wells in row II, 3 drops of Cl test solution to all the wells in row
III, and 2 drops of SO
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2 test solution to all the wells in row IV. Wait 2 minutes; then mix each reaction mixture with a clean toothpick.
3) Observe what a positive test looks like (Column 1 produces positive tests). If the ion of interest is present, a chemical reaction will take place, producing either a colored solution or a precipitate. Using the template on the next page, record the appearance of the reference cell. Record any solution color change, precipitate color and amount of precipitate.
4) For the remaining columns, record the level of positive result: use +++ for very positive, ++ for less positive, + for barely positive, 0 for a negative result.
5) In a confirming test, so few ions may be present that it is difficult to determine if the reaction actually took place.
Here are 3 useful ways to decide whether the expected color or precipitate is actually present: a) Compare the control (distilled water) test with that of each sample sample. Distilled water does not contain any of the ions tested, so even a faint color or cloudiness in the solution confirms that the ion is present. b) Place a sheet of white paper under the well plate to make any color more visible. c) Place the well plate on a black surface to make a white precipitate more visible.

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Name:______________________________________________________________________________
Reference Control Sample A Sample B Sample C Sample D
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CONCLUSIONS- Use complete sentences!
1) In this lab, what type of data is gathered, qualitative or quantitative? Is this type of data sufficient to make a strong scientific argument? Explain your opinion.
2) Why were a reference and a control used in each test? Why was distilled water chosen as the control?

Name:______________________________________________________________________________
3) These tests cannot absolutely confirm the absence of an ion. Why?
4) How might your observations have changed if you had not cleaned your wells or stirring sticks thoroughly between each test?
5) What is a real-life example in which a confirming test is used to draw a conclusion?