Chemistry:

Water Testing Lab Background Information: Chemists can detect and identify ions in water solution in several different ways. In this lab you will use some chemical tests to check for the presence of certain ions in aqueous solution. Positively charged ions are called cations; negatively charged ions are called anions. The tests you will perform are confirming tests. If the test is positive, it confirms that the ion in question is present. In each confirming test you will look for a change in solution color, or the appearance of an insoluble material called a precipitate. A negative test (no color change or precipitate) doesn’t necessarily mean the ion in question is not present. The ion may simply be present in such a small amount that the color or precipitate cannot be seen. Purpose:

§ To use chemical tests to determine the presence of ions in three different water samples. Objectives:

§ To test for the presence of cations iron (III) Fe3+, calcium Ca2+, copper Cu+, as well as the anions chloride Cl-, phosphate PO43-, and sulfate SO42-.

§ To perform each of the following confirming tests on three different samples: 1. A reference solution (known to contain the ion of interest) 2. Tap water (which may or may not contain the ion) 3. A control (distilled water, known not to contain the ion)

§ Test for water hardness using ion-testing strips. § Complete a confirmative ion-testing using a complete ion-testing strip.

Materials:

§ 10 test tubes § Test tube rack § 10 mL graduated cylinder § Test reagent solutions in dropper bottles

o Potassium thiocyanate (KSCN) o Potassium oxalate (K2C2O4) o Acetic acid (HC2H3O2)

o Silver nitrate (AgNO3) o Barium Chloride (BaCl2)

§ Reference ion solutions o Iron (III) Nitrate - Fe(NO3)3 o Calcium Chloride – CaCl2 o Iron (II) Sulfate – FeSO4

Procedures: PART ONE

1. Safety goggles should be worn at ALL times during this lab exercise. If you spill any of the reagents on your hands, wash them immediately.

2. Clean five test tubes with water and dry all glassware before starting the experiment. 3. In this lab, you are testing water samples for the presence of four different ions: Ca2+, Fe3+, Cl-,

and SO42-. For EACH of the test procedures you will test a reference solution (known to contain the ion), a control (distilled water-known not to contain the ion), and your water samples brought from home. Follow the diagram below and be sure to keep track of your water samples:

4. Measure 1 pipette full (about 2 mL) of reference solution, control, and the three water samples into five clean test tubes. Label the three test tubes Reference (R), Control (C), and Water Sample #1, 2, & 3.

5. Follow the table below to test for each ion: 6. As you perform each test, record your observations in the data table below. 7. When you have completed an ion test, wash your test tubes with water and dry them

thoroughly before moving on to the next ion test.

Procedures: PART TWO 1. Complete Copper (Cu+) Ion testing using the directions located at the Copper station. 2. Complete Phosphate (PO43-) Ion testing using the directions located at the Phosphate station. 3. Complete Water Hardness testing using the directions located at the Water testing station.

Procedures: PART THREE

1. Obtain a comprehensive testing strip by showing me your completed ion data tables. 2. Complete a comprehensive ion confirmative test using the total ion-testing strip.

Clean and return all lab materials before leaving the lab area.

Observations & Data: Copy all data tables and observations into your lab notebook and fill in as you complete each testing station. Use the table below as a guide.

________________Ion Testing

Solution Observations (color, precipitate, etc.)

Ion present in solution? (Y/N)

Reference Control Sample Sample #1 Sample #2 Sample #3

Analysis & Conclusions: 1. List the ions present in each of the water samples:

Sample #1: ____________________________

Sample #2: ____________________________

Sample #3: ____________________________

2. In the lab you tested for the presence of different ions by dropping reagent solutions into your water samples. If the ion was present a color change was visible or a precipitate (solid material) was formed when the ions from the reagents combined with the ions you were testing for to form an ionic compound. Write the name of the ionic compounds or give the formula of the ionic compounds that were formed in this lab. Use the list of cations and anions listed below.

7. Why was a control used in each test? 8. Why was distilled water chosen as the control? 9. Describe some difficulties associated with the use of qualitative tests (experiments based on

observations with no measurements or numbers produced)? 10. If one of these tests came up negative, does that prove that the ion is not present? Why or

why not? 11. How might your observations have changed if you hadn’t cleaned your test tubes thoroughly

between each test? 12. List some possible sources of contamination that could possibly have caused your results to be

incorrect? What could be other possible sources of contamination or error?