IB.8 Laboratory Activity
Water Testing (Micro)

Good afternoon, Mr. Phelps. A sample of water has been intercepted from KGB agents and is thought to contain the following ions: Fe³⁺, Ca²⁺, Cl^1-, and SO₄^2-. There are specific tests which will help you determine if a given ion is present in solution. (See Confidential Background Information. ) Your task, should you decide to accept it, is to

1. indicate the specific test required to prove that each of these ions is present,
2. indicate what a positive test for the ion would look like, and
3. supply answers to the questions at the end of this paper.

When you return tomorrow, you will test these water samples. Remember, Mr. Phelps, the fate of Dolton rests on your shoulders.

1. What is meant by the reference solution ?
   
   
2. What is meant by the control ?
   
   
3. What is an anion ?
   
   
4. What is a cation?

CONFIDENTIAL BACKGROUND INFORMATION

PROCEDURE:

1. Rinse spot plate with distilled water and shake dry.
   
2. Set up the spot plate in this manner:
   
   
3. Make a large data table in your lab notebook, leaving room for observations. The data table can be set up just like the spot plate.
   
   
4. Iron (III) Ion Test [Fe³⁺]
   a. Add one drop of potassium thiocyanate reagent [KSCN] from the dropper bottle in your kit to each well in the first column .
   b. Mix the cell contents thoroughly with a clean toothpick. Be sure you use a clean toothpick each time. A color change, however slight, indicates the presence of the ion.
   c. Record the results in your data table.
   
   
5. Calcium Ion Test [Ca²⁺]
   a. Add one drop of dilute acetic acid [HC₂H₃O₂] and one drop of sodium oxalate [Na₂C₂O₄] from the dropper bottles in your kit to each well in the second column .
   b. Mix the cell contents thoroughly with a clean toothpick. Be sure you use a clean toothpick each time. A color change, however slight, indicates the presence of the ion.
   c. Record the results in your data table.
   
   
6. Chloride Ion Test [Cl^1-]
   a. Add one drop of silver nitrate solution [AgNO₃] from the dropper bottle in your kit to each well in the third column .
   b. Mix the cell contents thoroughly with a clean toothpick. Be sure you use a clean toothpick each time. A color change, however slight, indicates the presence of the ion.
   c. Record the results in your data table.
   
   
7. Sulfate Ion Test [SO₄^2-]
   a. Add one drop of barium chloride solution from the dropper bottle in your kit to each well in the fourth column .
   b. Mix the cell contents thoroughly with a clean toothpick. Be sure you use a clean toothpick each time. A color change, however slight, indicates the presence of the ion.
   c. Record the results in your data table.
   
   
8. Clean-up. Discard solutions into the sink, rinse twice with distilled water and shake dry.

QUESTIONS. Copy and answer these questions in your lab notebook.

1. Why was a control used in each test?
   
2. Why was distilled water used as the control?
   
3. The tests you performed cannot absolutely confirm the absence of an ion. Why?
   
4. How might your observations have changed if you hadn't used a clean toothpick each time?