Acid Rain Lab Name______Per._____
In this lab, you will study the effects of acid deposition on various materials. An acid indicator, bromcresol green (BCG) will indicate whether acid is present. BCG turns yellow when it is exposed to acid.
Background
Acidic deposition: the transfer of acidic snow, rain, gases, or aerosols from the atmosphere to the lithosphere and hydrosphere.
Acid rain: precipitation having a pH lower than 5.6 (the pH of water saturated with atmospheric CO2).
Sulfur oxide pollution: The major natural sources of sulfur oxide pollution are volcanic emissions, sea spray, and biogenic releases (mostly as H2S and dimethyl sulfide). The major anthropogenic sources of SOx in the US is stationary fuel combustion (coal and oil). The sulfur content in coal ranges from 1-8%. In the US, coal must contain no more than 2%, but sometimes coal with a higher sulfur content is used. The burning of coal in plants converts the sulfur to SO2, and some of this may react with the oxygen in the air to form SO3. The SO3 dissolves in rain to produce sulfuric acid.
These are the reactions: 2SO2 + O2 à 2SO3 2SO3 + H2O à 2H2SO4
Petroleum refining and smelting of ores are also sources of SOx: 2ZnS + 3O2 à 2ZnO + 2SO2
Part 1: Deposition of sulfuric acid directly onto samples
Materials: Marble (CaCO3) Gypsum (CaSO4)
Magnesium wire (Mg) Iron filings (Fe)
Eggshell (contains CaCO3) Basalt (silicate minerals with Si, Na, Ca, K, Fe, Mg)
Cement (contains clay & CaCO3) BCG acid indicator
2 M Sulfuric Acid (H2SO4)
Procedure:
1. Collect a small piece of each sample and arrange in a circle within the petri dish. Place 2 drops of BCG indicator onto petri dish (separately, not on top of other samples).
2. Place 2 drops of 2 M H2SO4 directly onto each sample and closely observe the effects.
SAMPLE DATA
Material / Effects of H2SO4Marble / Fizzles
Mg wire / Fizzles violently
Eggshell / A few bubbles
Cement / Fizzles
Gypsum / No change
Fe filings / No change
Basalt / No change
BCG / Turned yellow
Part 2: Indirect acid deposition through the creation of atmospheric sulfuric acid
In this part of the lab, you will be creating atmospheric sulfuric acid by reacting sodium sulfite with sulfuric acid. Here are the reactions that will take place within your petri dishes:
H2SO4(aq) + Na2SO3(aq) à SO2(g) + H2O(l) + Na2SO4(aq)
2SO2(g) + O2(g) à 2SO3(g) 2SO3(g) + H2O(g) à 2H2SO4(g)
Acid deposition in the form of sulfuric acid vapor will occur on the samples in your petri dish.
Materials: Marble (CaCO3) Gypsum (CaSO4)
Magnesium wire (Mg) Iron filings (Fe)
Eggshell (contains CaCO3) Basalt (silicate minerals with Si, Na, Ca, K, Fe, Mg)
Cement (contains clay & CaCO3) BCG acid indicator
2 M Sufuric Acid (H2SO4) 0.5 M Sodium Sulfite (Na2SO3)
Procedure:
1. Throw solids from Part 1 into the waste container and thoroughly clean and dry your petri dish.
2. Arrange seven new material samples in a circle in the petri dish, including 2 drops of BCG in one area.
3. Place 2 drops of BCG on top of each sample. Observe and record the color.
4. Place 2 drops of 0.5 M Na2SO3 in the center of the petri dish (do not let it touch the other samples)
5. Place 2 drops of 2 M H2SO4 on top of Na2SO3. Cover the petri dish immediately and observe effects. Let the reaction run for a few minutes before you record your final observations.
6. Throw solids into the waste container and thoroughly clean and dry your petri dish.
Material / Color BCG before SO2 Production / Color BCG after SO2 production / Comments (include observations about BCG in contact with samples vs. not in contact)Marble / GREEN / GREEN and YELLOW / Yellow on edges
Mg wire / GREEN / GREEN and YELLOW / Yellow on edges
Eggshell / GREEN / GREEN and YELLOW / Yellow on edges
Cement / GREEN / GREEN and YELLOW / Yellow on the edges
Gypsum / GREEN / YELLOW
Fe Filings / GREEN / YELLOW
Basalt / GREEN / YELLOW
BCG
/ GREEN / YELLOW
Analysis Questions:
1. Which samples had the greatest reaction with direct H2SO4 deposition (Part 1)?
2. BCG turns yellow when it is exposed to acid. In part 2, with which samples did BCG turn yellow where it was in direct contact with the sample materials?
3. In part 2, with which samples did BCG not turn yellow where it was in direct contact with the samples?
4. What is the relationship between the samples that reacted the most with acid in part 1, and whether or not the BCG in contact with those samples turned colors in part 2?
5. The reaction of calcium carbonate with sulfuric acid is:
CaCO3(s) + H2SO4(aq) à CO2(g) + CaSO4(s) + H2O(l)
The reaction of metals such as magnesium with sulfuric acid is:
Mg(s) + H2SO4(aq) à MgSO4(s) + H2(g)
There is an acid atmosphere inside the petri dish in part 2. BCG will turn yellow when it comes in contact with acid. So, why would BCG not turn yellow when in contact with some of the samples? Why might the above reactions keep the BCG from turning yellow? Explain.
6. Which materials resisted the effects of acid rain the best (no reactions seen in part 1)? Why?
7. What effect will particle size have on the reaction with acid rain?
8. Explain how buffers work in neutralizing acids.
9. Acids dissolve calcium carbonate. Many organic materials, such as bones, shells (of both birds and marine organisms including plankton), and corals contain calcium carbonate. Explain how acid rain might affect animals, birds, and marine organisms.
10. Many building materials are made from calcium carbonate. Limestone and marble are pure calcium carbonate, and cement usually has calcium carbonate in it. Explain some of the consequences of acid rain on buildings in urban areas.
11. Acids dissolve metals. Many metals are essential plant nutrients. However, high concentrations of metals in lakes and rivers can be harmful to aquatic life. Explain how acid rain might lead to a depletion of nutrients in soils, a loss of productivity in forests, and an increase in toxic levels of metals in lakes and streams. (See p. 481-482 in text).