C3 Chemicals in Our Lives – Risks & Benefits Lesson 8: Making Alkalis

Objectives MUST interpret data showing that the chlorination of drinking water improved public health SHOULD describe the possible health risks of chlorine in water COULD understand how people perceive risk and how governments assess risk

Key Words You need to be able to define the following: ◦ Disinfectant

Textbook Answers 1)Overcrowded living conditions; drinking water contaminated by sewage. 2)Chlorine is a disinfectant; it kills microorganisms. 3)a) 26–28; b) 10–12 years 4)The probability of death fell; from about 26 in (about 1 in 4000) to 4 in (about 1 in ); a fall of over 80%. 5)0.05 ÷ 0.2 × 100 = 25% 6)People are probably more scared of things they do not understand or are unfamiliar with, such as DBPs in water; so they overestimate the risk compared with risks they are familiar with. 7)Chlorine is a corrosive, toxic gas and can cause a great deal of harm; it can react with substances in water to make harmful compounds; but it is present in such a small concentration in water that it is a very low risk; the risk from diseases is greater than the risk from DBPs.

Worksheet Answers Activity 1 (Low demand) 1)Should mention the dangers of untreated water, the correct dose and the hazard of using the disinfectant. 2)Should note the reduction cases of waterborne diseases. Activity 2 (Standard demand) 1)a) 4000; b) ; c) 7–8 per ; d) –12 500; e) death rate fell by over 70%. 2)a) Accurate bar chart; b) 1 in 1250; c) reduced the risk of catching cholera to 1 in d) Chlorine solution is a hazard; particularly if drunk undiluted (it has happened). 3)Work of UNICEF, Médecins sans Frontières etc. Activity 3 (High demand) 1)Risk of bladder cancer in USA is 1 in 6000; risk of cholera in Haiti 1 in 170 (and possibly higher); cancers have other causes; suggests that risk without chlorination is much greater than the risk of cancers with chlorine. 2)a) E.g. fear of flying; the MMR vaccine debacle; smokers who do not give up. b) People tend to over-estimate the risk of unfamiliar things and under-estimate familiar risks. c) Education; rules on advertising

Practical Answers

Part D 1)sodium carbonate + hydrochloric acid  sodium chloride + carbon dioxide + water 2)hydroxide + acid  salt + water; carbonate + acid  salt + carbon dioxide + water 3)a) potassium hydroxide + nitric acid  potassium nitrate + water b) sodium hydroxide + sulfuric acid  sodium sulfate + water c) sodium carbonate + sulfuric acid  sodium sulfate + carbon dioxide + water d) potassium carbonate + nitric acid  potassium nitrate + carbon dioxide + water e) calcium hydroxide + hydrochloric acid  calcium chloride + water