MCl2
+ H2), they do not all react in exactly the same way. Building materials, like
limestone and marble (CaCO3), also react with acids. CHEM L110 - Chemistry and Society Laboratory
INTRODUCTION
When the air pollutants, NOx and SO2, react with moisture in the atmosphere, "acid rain" is produced. Organic and inorganic acids make up an important group of chemical compounds. They are used in industrial applications as well as being found in certain foods and beverages, our bodies, and frequently in rain or snow. While some reactions involving acids are important and necessary, others can be very undesireable. Acid rain has an adverse effect on some building materials, monuments, and statues as well as our environment as a whole.
Aqueous solutions of acids contain excess H+ ions. Although most metals
react with acids to produce hydrogen (H2) gas (e.g., M + 2 HCl MCl2
+ H2), they do not all react in exactly the same way. Building materials, like
limestone and marble (CaCO3), also react with acids.
In this experiment, you will investigate the reactions of three common inorganic acids, HCl (hydrochloric acid), H2SO4 (sulfuric acid), and HNO3 (nitric acid) with chalk (CaCO3), zinc (Zn), copper (Cu), paper clips, aluminum (Al), and magnesium (Mg). Aqueous solutions with acid concentrations that are much higher than those found in acid rain will be used here. Even so, the same reactions occur with acid rain, but at a much slower rate.
EXPERIMENTAL PROCEDURE
You will be using a white ceramic wellplate for all the reactions in this experiment.
Make sure it
is clean and dry before you start.
I. Wellplate Setup
1. Using a plastic pipet, add enough 6 M HCl to each of the six wells in row A so that each well is about half-filled.
2. Using a plastic pipet, add enough 6 M H2SO4 to each of the six wells in row B so that each well is about half-filled.
3. Using a plastic pipet, add enough 1 M H2SO4 (this concentration is 1/6 of that used in row B) to each of the six wells in row C so that each well is about half-filled.
4. Using a plastic pipet, add enough 6 M HNO3 to each of the six wells in row D so that each well is about half-filled.
II. Reactions
Warning: All reactions of metals with HNO3
(nitric acid) must
be done in the hood because a poisonous gas, NO2, is produced.
1. Put a small piece of chalk, at the same time, in each of the four wells in column 1. Observe what happens. On your report sheet, rank the acids 1- 4 according to speed of reaction. (1 = fastest and 4 = slowest). Also record your observations.
2. Put a piece of zinc (Zn), at the same time, in each of the first three wells in column 2 (but not in the fourth well that contains nitric acid). Observe what happens. On your report sheet, rank the acids 1- 4 according to speed of reaction. (1 = fastest and 4 = slowest). Remember to include the nitric acid results (to be done later) in your rankings. Also record your observations.
3. Put a piece of copper (Cu), at the same time, in each of the first three wells in column 3 (but not in the fourth well that contains nitric acid). Observe what happens. On your report sheet, rank the acids 1- 4 according to speed of reaction. (1 = fastest and 4 = slowest). Remember to include the nitric acid results (to be done later) in your rankings. Also record your observations.
4. Put a small piece of paper clip, at the same time, in each of the first three wells in column 4 (but not in the fourth well that contains nitric acid). Observe what happens. On your report sheet, rank the acids 1- 4 according to speed of reaction. (1 = fastest and 4 = slowest). Remember to include the nitric acid results (to be done later) in your rankings. Also record your observations.
5. Put a piece of aluminum (Al), at the same time, in each of the first three wells in column 5 (but not in the fourth well that contains nitric acid). Observe what happens. On your report sheet, rank the acids 1- 4 according to speed of reaction. (1 = fastest and 4 = slowest). Remember to include the nitric acid results (to be done later) in your rankings. Also record your observations.
6. Put a piece of magnesium (Mg), at the same time, in each of the first three wells in column 6 (but not in the fourth well that contains nitric acid). Observe what happens. On your report sheet, rank the acids 1- 4 according to speed of reaction. (1 = fastest and 4 = slowest). Remember to include the nitric acid results (to be done later) in your rankings. Also record your observations.
7. Carefully take your wellplate along with samples of the five metals to the fume hood where you will perform the remainder of the experiment. Put a piece of Zn in well #D-2. Make your observations. Record them on your report sheet. Include the nitric acid results in your ranking for speed of reaction with Zn metal.
Continue with the other metals in a similar fashion: Cu in well #D-3; paper clip in well #D-4; etc. Make your observations. Record them on your report sheet.
8. After results have been discussed with the class, empty the contents of your wellplate into the designated waste container. Using your squeeze bottle, rinse the wellplate into the waste container. Back at your bench, rinse the wellplate thoroughly with tap water. Make sure your wellplate is clean and dry before you put it away.
