Air Pollution and Acid Rain - Doplay – Eginaz Ikasi ... Notes 1 Air Pollution and Acid Rain...

Teacher Notes

1

Air Pollution and Acid Rain

Objectives

Students will investigate chemical reactions that are important in the formation of acid rain to

better understand the relationship between certain types of man-made (anthropogenic)

emissions and problems arising from acid rain.

Observe the effect of three different anthropogenic gases on the pH of water.

Consider the effect of such changes in the pH of water on the environment.

Time Requirement

Preparation time 15 minutes

Pre-lab discussion and activity 30 minutes

Lab activity 50 minutes

Materials and Equipment

For each student or group:

SPARK Science Learning System Graduated pipette and pipetting bulb

pH sensor (1) Graduated cylinder, 10- or 100-mL

Erlenmeyer flask, 50-mL (1) Sodium bicarbonate (NaHCO3), 5 g

1-hole rubber stopper for flask (1) Sodium bisulfite (NaHSO3), 5 g

Glass tubing for rubber stopper (1) Sodium nitrite (NaNO2), 1.5 g

Flexible Teflon tubing to fit glass tubing, 20 cm (1) 1 M HCl (15-mL)

Beaker 40-mL (1) Water or deionized water, 1 L

Balance or mass scale (1/class) Wash bottle containing distilled or deionized water (1)

Goggles; aprons or lab coats, gloves

Concepts Students Should Already Know

Students should be familiar with the following concepts:

Most cells function best within a narrow range of acidity.

pH is a logarithmic measurement of the concentration of hydrogen ions in water.

(pH = -log10[H+]). pH measurements can range from 0 through 14, and the lower the value,

the higher the concentration of hydrogen ions. pH can be a measure of acidity, with values

below 7 becoming increasingly acidic as the value approaches 0. Therefore, the lower the

pH the higher the concentration of hydrogen ions and the higher the acidity. A pH of 7 is


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neutral—neither acidic nor basic. pH values greater than 7 are considered basic. Practically

speaking, a pH of 6 to 8 is considered to be in the neutral zone.

Lab Preparation

These are the materials and equipment to set up prior to the lab.

1. Prepare the 1.0 M hydrochloric acid solution by adding 16.6 mL of concentrated HCl per

100.0 mL of solution. Pour the concentrated HCl into about 80 mL of water, and then bring

the solution up to 100 mL with water. Do not pour water into the concentrated acid. Pour 15

mL into a beaker for each group.

Teacher Tips:

Use tap water unless the water in your area has a high level of dissolved solids (as is the case

for some well water, for instance), which can produce a significant buffering action. The pH of

distilled and deionized water is highly susceptible to large changes as a result of minute

contaminants.

Because the pH measurements in this activity are relative only to measurements within this

lab, it is not necessary to calibrate the pH sensor to obtain useful and meaningful data.

If your classroom does not have a vented hood, students can perform the generation of CO2

part of the activity at their lab benches, and the parts for SO2 and NO2 can be performed by

one group or the teacher in the chemistry lab, with results being presented to the class for

analysis.

If students will be working on ordinary bench tops to do the work with sodium bicarbonate

only and you do not have access to 1 M HCl, you can substitute household white vinegar for 1

M HCL.

Safety

Add these important safety precautions to your normal laboratory procedures:

Consult the manufacturer's MSDS for hydrochloric acid, sodium bisulfite, and sodium

nitrite for instruction on handling, storage, and disposing of these chemicals. (These can be

found on the Web.) Keep these available in case of accidents.

Students creating sulfur dioxide and nitrogen dioxide should work under a vented hood.

Emphasize the need to keep water away from any sensitive electronic equipment.

Use goggles and aprons or lab coats

Students should not touch HCl and should handle the pipettete with HCl with extreme care

Caution students to not remove the rubber stopper from the Erlenmeyer flask once the

reaction has started.

Solutions can be disposed down the drain with excess water.

At completion of the lab students should wash up properly.

Teacher Notes

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Answer Key

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Air Pollution and Acid Rain - Doplay – Eginaz Ikasi ... Notes 1 Air Pollution and Acid Rain...

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