6.3 Reactions of Acids and Bases

Agenda Hand in Urban Gold-mining Assignment Discuss homework Lesson 6.3 Reactions of Acids and Bases Science at Work Read pages Vocabulary Learning Check p.238 #1,3 p. 243 #5, 6, Review questions p. 246 #2, 5

Learning Goals Students will define the following terms: neutralization, liming. Students will examine the neutralization reaction between acids and bases Students will list the causes of acid precipitation and the measures that can be taken to prevent it or reduce its effects Students will identify the detrimental effects of acid precipitation Students will describe how liming can be used to renew acidified lakes Students will determine how the properties of acids that make them useful for extracting metals from ore can be used to remove toxic metals from soil

Environmental Consequences Emissions and acid rain produced by smelters around Sudbury have had a devastating impact on the local environment. The Canadian and U.S. governments agreed to decrease the emissions form local smelters. Smelters- industrial facilities in which metals are separated from ores. Reductions in the levels of these pollutants have given the area a chance to recover.

Acid and Base Neutralization What do you do when you have some strong acid and don’t want it anymore? Pour it down the drain? Bad idea. Equally bad idea would be pouring a strong base down the drain. Both acids and bases can really do damage to materials. But if you add an acid and a base together, look what happens - HCl + NaOH ----> NaCl + H 2 O Now instead of two substances that could harm your drains, HCl (hydrochloric acid) and NaOH,( sodium hydroxide), you’ve combined them and they form harmless NaCl, ( a salt), and water. This is an example of a double displacement reaction. The ions of the reactants switch places to form new compounds.

Neutralization Neutralization is the reaction of an acid and a base to form a salt and water. The water forms as the hydrogen ions of the acid and the hydroxide ions of the base combine. The removal of both hydrogen ions and hydroxide ions causes the ph of the mixture to approach 7. You will not completely neutralize an acid and a base unless you have just the right amounts and just the right strengths.

Salt Note: NaCl is what we call salt in everyday life. But in chemistry: A SALT IS A COMPOUND FORMED WHEN YOU COMBINE AN ACID AND A BASE. It is soluble in water and will not form a precipitate.

Antacids: An Application of Neutralization The lining of the stomach secretes HCl, hydrochloric acid to help break down food during digestion. Some people produce excess amounts of acid. This excess acid leads to a burning sensation called heartburn. Antacids contain baes such as magnesium hydroxide o aluminum hydroxide to neutralize the acid.

Neutralizing Acid Spills Spills occur when tanker cars or trucks containing acids derail or turn over. When an acid spill occurs it is important to act quickly to minimize the size of the spill by containing the acid and stopping any leaks. The acid must be neutralized and people evacuated. In March 2007 at train derailed and spilled 150, 000 L of sulfuric acid into the Blanche River near Englehart Ontario. It was neutralized by adding calcium hydroxide. H 2 SO 4 (aq) + Ca(OH) 2 (aq) CaSO 4 (aq) + H 2 O (l)

Acid Precipitation Rainwater is naturally acidic and has a pH of 5.6. This is the result of carbon dioxide in the air dissolving and reacting with water to form carbonic acid. CO 2 (g) + H 2 O(l) H 2 CO 3 (aq) Similar synthesis reactions of other non-metal oxides form additional acids, which lower pH of rainwater even more

Causes of Acid Precipitation High temperatures in a car’s engine causes nitrogen and oxygen to react and form several different nitrogen oxides These oxides can react with water to form acids NO 2 (g) + H 2 O(l) HNO 3 (aq) Catalytic converters help decrease the amount of nitrogen oxides that enter the atmosphere, but they don’t eliminate the nitrogen oxides completely

Another major contributor to acid precipitation is sulfur oxides, which come from industrial processes. Ores smelted in Sudbury region contain sulfur, which forms sulfur dioxide during the smelting process. It is also produced during the combustion of fossil fuels that contain sulfur (coal and natural gas). SO 3 (g) + H 2 O(l) H 2 SO 4 (aq)

Effects of Acid Precipitation Eastern Canada and Ontario contain mostly granite rock which is not basic. Granite rock cannot help neutralize the effects of acid precipitation in the soil. In Western Canada the rocks have more limestone which is basic This helps to reduce the effects of acid precipitation.

Abrupt and Gradual Changes in Water pH The rushing waters of snowmelt can release deadly does of acid into stream and lakes resulting in massive deaths of fish. As a lake or stream becomes more acidic many types of tiny organisms start to disappear. This decreases the food source for fish, waterfowl, and other mammal that rely on the fish. As the pH decreases fish also have trouble reproducing.

Case Study Turn to page 240 of the text. Read the Case Study: Update on Acid Precipitation.

Reducing Emission that Cause Acid Precipitation Sulfur oxides are a major contributor to acid precipitation. Scrubbers on smokestacks of industrial plants that burn coal in their furnaces help to decrease these emissions. When the coal burns the sulphur contaminant also burns. Sulfur dioxide is removed form the exhaust gases through a reaction with calcium oxide that forms calcium sulphite.

Renewing Acidified Lakes Attempts are being made to reverse the effects of acid precipitation on lakes. One strategy for reversing the effects of acid precipitation is to add basic materials to neutralize the acid in lakes. A process called liming applies basic material usually lime- based to these lakes.

The Effects of Liming on Lakes Liming is an expensive procedure to do on all lakes. If acid precipitation continues however, liming will only be temporary. Liming can also increase the calcium content of a lake which in turn affects certain water vegetation and insects.

Acid Leaching and Metals Smelters create acids as a by-product of the process. Acids are important in refining metals. i.e. Gold is leached from ore using sodium cyanide. Other metals such as copper and nickel also use acids in their processing. This results in environmental problems.

Toxic Metal Contamination and Clean-up Tailings are solid and liquid materials that are left after the desired metal is removed form ore. The piles are often stored in above-ground facilities where they are exposed to air and water. This can form acids which run-off into the local environment.

Acid Leaching Acid leaching can be used to clean up soils that have been contaminated by toxic metals that were by- products of mining operations. It is an expensive process so preventing contamination in the first place is the best option.

1. The first step involves removing any solid metal pieces from the contaminated soil. 2. Next the soil is treated with acid in order to leach out metal ions and small pieces of metal. 3. Once the metal has been dissolved in the acid, it is recovered through precipitation. 4. The metal ions form solids with chemicals added to the liquid. The solids are removed. 5. The liquid is recycled and used the leaching process again.

Summary A neutralization reaction occurs when an acid and a base react to form water and a salt. Acid precipitations forms from non-metal oxides such as the oxides of sulphur and nitrogen. These oxides react with water in the atmosphere to form acids. Scrubbers are used to remove sulphur dioxide from exhaust gases. Acid precipitation has detrimental effects on rivers and lakes. Renewing a lake involves adding limestone to the water to help neutralize the acid The properties of acids make them useful for extracting metal from ores but the process results in contamination. Acids can be used to leach toxic metals from contaminated soils.

Success Criteria I am able to define the following terms: neutralization, liming. I am able to examine the neutralization reaction between acids and bases I am able to list the causes of acid precipitation and the measures that can be taken to prevent it or reduce its effects I am able to identify the detrimental effects of acid precipitation I am able to describe how liming can be used to renew acidified lakes I am able to determine how the properties of acids that make them useful for extracting metals from ore can be used to remove toxic metals from soil