5.3 Reactions and Environmental Issues

Agenda Take up the homework Lesson 5.3 Reactions and Environmental Issues Read pages Vocabulary Learning Check page page 204 5, 7

Learning Goals Students will discuss the use of catalytic converters to help combat exhaust pollutants. Students will learn about the chemical reactions involved in gold extraction. Students will review the hazards involved in the use and handling of household chemicals. Students will discuss safe practices for the handling and use of chemicals and review the WHMIS and HPPS symbols and warnings

Reactions and Environmental Issues Although chemical reactions can cause environmental issues, they can also be used to help solve environmental challenges.

Treating Car Exhaust Our society has come to rely on the burning of fossil fuels for heating, energy production and transportation. In a car`s engine gasoline burns and reacts with oxygen. The complete combustion of gasoline in a car’s engine is represented by the following chemical equation. 2C 8 H 18 (l) + 25O 2 (g) 16CO 2 (g) + 18H 2 O(g) Incomplete combustion occurs when there is not enough oxygen. It can result in carbon (C) (soot), poisonous carbon monoxide (CO), and unburned gasoline vapours to enter the exhaust.

Forming Nitrogen Oxides at High Temperatures The exhaust also includes a variety of nitrogen oxides, such as NO 2 and NO. These compounds contribute to smog and the formation of ground level ozone.

Recovering Gold using Cyanide and Zinc Gold mining is an important part of the economy in Canada. The mining and recovery of gold depends on several small reactions to separate the gold from the rock or ore that it is found in. One method involves reactions with cyanide ions (CN - ) and zinc metal. The problem is that cyanide compounds are very toxic and lethal and can escape into the environment. Zinc (Zn) can then be used in a single displacement reaction to displace the gold from the solution.

The rock that makes up the gold ore is crushed into a fine powder to expose as much of the gold as possible. The powder is placed in piles. Then the heaps are sprayed with a sodium cyanide solution. The gold forms a soluble compound. The soluble compound is then drained away from the ore. This is referred to as leaching. Leaching, a technique that removes gold from ore by dissolving it in an aqueous solution.

Getting Gold Out of the Solution

Cleaning and Disinfecting Pools To keep pools safe, chemicals need to be used to prevent the growth of bacteria and other organisms that can cause illness. A variety of compounds containing chlorine (Cl) are used to prevent the growth of bacteria and other organisms in the water in swimming pools and hot tubs. Some of these chemicals are corrosive or some when mixed together can be explosive Care must be taken when using these chemicals to ensure that they are effective in disinfecting the water but remain safe for the users.

Hazards in the Home Precautions must be taken when using household chemicals. When mixed, reactions could occur that might be harmful to the user’s health. Important to pay attention to warning labels and the handling precautions in order to safely handle the materials.

Bleach and Ammonia – A Toxic Combination The mixing of bleach (NaClO) (a compound containing chlorine), and ammonia (NH 3 ) can have dire consequences. 2NH 3 (aq) + 2NaClO(aq) 2NaONH 3 (aq) + Cl 2 (g) Toxic chlorine gas (Cl 2 ) is produced in this reaction. Two other ammonia and bleach reactions produce toxic compounds called chloramines (NCl 3 (g) and NH 2 Cl(g)). NH 3 (aq) + 3NaClO(aq) 3NaOH(aq) + NCl 3 (g) NH 3 (aq) + NaClO(aq) NaOH(aq) + NH 2 Cl(g)

Remember Your Chemical Safety Be familiar with the WHMIS and HHPS symbols that identify the hazards associated with the handling and use of chemicals at home and in the workplace. Workplace Hazardous Materials Information System (WHMIS) Hazardous Household Product Symbols (HHPS)

Success Criteria I am able to discuss the use of catalytic converters to help combat exhaust pollutants. I have learned the chemical reactions involved in gold extraction. I have reviewed the hazards involved in the use and handling of household chemicals. I have discussed safe practices for the handling and use of chemicals and reviewed the WHMIS and HPPS symbols and warnings