Water Testing Lab Report

Abstract:

In this lab, the class was assigned to test water for different ions through confirming tests, tests confirming the presence or absence of the ion in question. Our group, the "Metals", conducted multiple tests in hopes of achieving a solution change in color, or by the appearance of a precipitate, an insoluble material. We worked with 5 different water samples: a reference solution, that we labeled as #1 in our dish, a control sample, #2, a tap water sample, #3, a distilled water sample, #4, and an ocean water sample, #5. The reference solution is a solution with a strong presence of the ion being tested; therefore, it was different each time we refilled our dish depending on the ion being tested for, and it acted as an example of what the precipitate should look like when the ion is present in the water sample. However, it is important to note that the precipitate of the other samples did not mimic the precipitate of the reference solution, for the other samples did not contain the same high quantities of the ions being tested for. In order to test for the calcium ion, (Ca^2+), our reference solution was calcium chloride, or (CaCl^2), and we added about three drops of sodium carbonate (Na2CO3) to each of the five liquid-holding wells. To test for the iron(III) ion, (Fe^3+), our reference solution was ferric nitrate, (Fe3^+), and we added three drops of potassium thiocyanate (KSCN) to each well. To test for the chloride ion, (Cl^-), our reference solution was, again, calcium chloride, or (CaCl^2), and we added three drops of (toxic) silver nitrate (AgNO3) to each well. Finally, in our last test for the sulfate ion, (SO4^2-), our reference solution was ferrous sulfate, (SO4^2-) and we added three drops of barium chloride (BaCl2) to each well. We analyzed how the substances in the wells reacted with the test reagents and what (if any) precipitates were formed. The qualitative and quantitative tests determined what substance and how much of the particular substance was in our samples, and therefore, reflected the tests necessary to conduct for the "Snake River fish kill" case in Riverwood in order to reach a conclusion as to what contaminated the water and killed the fish.

Procedure:

Although this procedure was repetitive, it was very important to remain focused and fully alert as to what was going on, and what was being done to prepare and execute each test properly. First, my group prepared for the procedure by making a list numbered 1-5, corresponding to the numbers 1-5 labeled on the wellplate. We decided that well #1 would always be the reference solution would be held, well #2 would always be the control solution would be held, well #3 would be where tap water would be held, well #4 would be where distilled water would be held, and well #5 would be where ocean water would be held (we would fill each well only 3/4 full each time we filled them). By doing this, we remained organized throughout the entire process. In our first test, for the calcium ion (Ca^2+), we filled our reference solution well with calcium chloride (CaCl2). As I said before, reference solutions are meant to be rich in the ion being tested for, and calcium chloride (CaCl2) has plenty calcium ions, (Ca^2+). Our test reagent was sodium carbonate (Na2CO3); we added 3 drops of this to each well (from the opening at the top of its bottle) to see what precipitates and color changes (if any) each solution produced. The reference solution (calcium chloride) formed cloud-like precipitates that were spaced out from each other and floating in the solution, the control solution became urine yellow and formed a round, watery and milky precipitate at the bottom of the well, the tap water and distilled water solutions did not change, and the ocean water became slightly milkier in color. With this data we concluded that the Ca^2+ cations were present in the reference solution, control solution, and ocean water, but not in the tap water or distilled water.

Calcium ion test wellplate before sodium carbonate:

Calcium ion test wellplate after sodium carbonate:

Before we proceeded to the next test, we thoroughly rinsed and dried our wellplate.

In our second test, for the iron(III) ion (Fe^3+), we filled our reference solution well with ferris nitrate (Fe^3+). Our test reagent was potassium thiocyanate (KSCN); we added three drops of this to each well (from the opening at the top of its bottle) to see what precipitates and color changes each solution produced. Our originally yellow reference solution (ferris nitrate) became dense black in color without any visible precipitate and our control solution became blood red with a yellowish-brown rim. Nothing happened to the tap water, distilled water, or the ocean water. With these results, we concluded that the Fe^3+ cations were present in the reference solution and in the control solution, but not the tap, distilled, or ocean waters.

Iron(III) ion test wellplate before potassium thiocyanate:

Iron(III) ion test wellplate after potassium thiocyanate:

Before we proceeded to the next test, we thoroughly rinsed and dried our wellplate.

In our third test, the test for the chloride ion (Cl-), we filled our reference solution well with calcium chloride (CaCl2), the same reference solution we used for the calcium ion test. Our test reagent was [toxic] silver nitrate (AgNO3), that we added three drops of to each well (from the opening at the top of its bottle) in order to see what precipitates were produced and what color changes occurred. Our originally clear reference solution (calcium chloride) became a milky and foggy color with some watery cracks. It almost looked like thin frozen ice over a lake in the winter. The control solution formed a thick milk-colored rounded precipitate that sat at the bottom of the well with some control solution surrounding it. The tap water became cloudy in color, nothing happened to the distilled water, and the ocean water became even foggier and whiter than the reference solution. With these results, we concluded that the Cl- anions were present in the reference solution, the control solution, the tap water, and the ocean water, but not the distilled water.

Chloride ion test wellplate before silver nitrate:

Chloride ion test wellplate after silver nitrate:

Before we proceeded to the next test, we thoroughly rinsed and dried our wellplate.

In our fourth and final test, the test for the sulfate ion (SO4^2-), we filled our reference solution well with ferrous sulfate (SO4^2-). Our test reagent was barium chloride (BaCl2), and we added three drops of it to each well (from the opening at the top of its bottle) in order to analyze what color changes occurred and what precipitates were produced. Our originally muddy-red reference solution (ferrous sulfate) formed a milky precipitate that colored much of the solution, but left the muddy-red color visible underneath. The control solution became slightly cloudier and the ocean water developed a fairly heavy white fog, yet the tap water and distilled water remained the same. With these results, we concluded that the SO4^2- anions were present in the reference solution, the control solution, and the ocean water, but not the tap or distilled water.

Sulfate ion test wellplate before ferrous sulfate:

Sulfate ion test wellplate after ferrous sulfate:

Overview: Final Results:

Analyzing my data:
-Calcium Ion (Ca^2+) Test: Ca^2+ cations were present in the reference solution, control solution, and ocean water, but not in the tap water or distilled water.
-Iron(III) Ion (Fe^3+) Test: Fe^3+ cations were present in the reference solution and in the control solution, but not the tap, distilled, or ocean waters.
-Chloride Ion (Cl-) Test: Cl- anions were present in the reference solution, the control solution, the tap water, and the ocean water, but not the distilled water.
-Sulfate Ion (SO4^2-) Test: SO4^2- anions were present in the reference solution, the control solution, and the ocean water, but not the tap or distilled water.

Questions on page 45:
1) Why were a reference solution and a blank used in each test?

A reference solution was used in order to see what reaction happens between a test reagent and a solution with a high value of the ions being tested. A blank was used to show that there is no reaction when the ion being tested for is not present in the solution.

2) What are some possible problems associated with the use of qualitative tests?

A qualitative test is a test that can be done when, for example, a tap is turned on. One immediately sees the color of the water and can smell the water, and determine that it is clear and odorless. Even if it is clear and odorless, the water can be contaminated. Also, qualitative tests only test for the presence or absence of a substance, not the amount of the substance.

3) These tests cannot absolutely confirm the absence of an ion. Why?

Sometimes these tests cannot absolutely confirm the absence of an ion because sometimes, the ion is present in such small amounts, it is not detected through the tests.

4) How might your observations have changed if you had not cleaned your wells or stirring rods thoroughly after each test?

If we had not cleaned our wells or stirring rods, our samples would have been contaminated by the previous substances. This could lead to unwanted reactions, inaccurate reactions, or no reactions at all; therefore, we would not be collecting correct data.