Chemistry 溫習題目 12
1. Chlorofluorocarbons (CFCs) are compounds that contain carbon, fluorine and chlorine only. 1-chloro-1,1,2,2,2-pentafluoroethane and dichlorodifluoromethane are two examples of CFCs. CFCs are usually used as refrigerants.
a) (i) Write the structural formulae of 1-chloro-1,1,2,2,2-pentafluoroethane and dichlorodifluoromethane.
(ii) Do they belong to the same homologous series? Explain your answer.
b) CFCs are greenhouse gases which cause global warming.
(i) What is global warming?
(ii) Suggest one harmful effect of global warming.
c) Hydrocarbons can also be used as refrigerant.
(i) What is the meaning of the term 'hydrocarbon'?
(ii) Suggest one advantage of using hydrocarbons as a refrigerant over CFCs.
2. When hexane and bromine (dissolved in an organic solvent) are mixed in the dark, no reaction occurs. However, a reaction occurs when they are mixed in sunlight.
a) State what would be observed in the reaction.
b) Explain why light is needed for the reaction to proceed.
c) Methane also reacts with bromine in sunlight. When bromine (dissolved in an organi solvent) reacts with excess methane, bromomethane forms as the major product.
(i) Use chemical equations to illustrate the production of bromomethane from the reaction between bromine and methane. Name the steps involved.
(ii) Is the above reaction an appropriate method to prepare bromomethane? Explain.
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(ii) No, as they cannot be represented by the same general formula.
b) [This is Chemistry?]
(i) rise in average tempature of the Earth's surface.
(ii) more extreme weather events.
(i) A compound which consists of carbon and hydrogen only.
(ii) CFCs deplete ozone (which causes the ozone layer of the Earth get thinner) while hydrocarbons do not.
a) The brownish-red bromine solution is decolorized.
b) Light provides energy to break the Br–Br bonds, forming bromine radicals and start the chain reaction.