Chemistry Answer1-17

1.(a) (i) A monomer is a compound whose molecules join together repeatedly during polymerization.(ii) Addition polymerization is a reaction in which the monomer molecules join to form polymer molecules. No elimination of small molecules occurs.
(c) Plastic X: Polyvinyl chloride (PVC)Plastic Y: Polystyrene(d)

2.(a) (i) A polymer is a compound consisting of very large molecules formed by many small molecules being joined together repeatedly.(ii) Compound II(iii) (iv) The polymer is a thermoplastic. Both polythene and polypropene are thermoplastics. Cross-links are unlikely to form in these polymers.
(b) Compounds IV and V
(c) Test the compounds with bromine in 1,1,1-trichloroethane. Compound II can decolorize the bromine while compound I cannot.
(d) (i) Alkanol and salt of alkanoic acid(ii)

3.(a) Polymerization is the process of repeatedly joining together many small molecules to form very large molecules.

4.(a) It is because thermoplastics cannot resist high temperatures.
(b) (i) Condensation polymerization
(c) (i) Nylon(ii) Condensation polymerization
(d) (i) Perspex(ii)

5.(a) •Lighter •Not easily broken
(b) •Corrosion resistant •Low weight •No chrome plating required
(c) •Corrosion resistant •No sharp edges •Can be coloured easily •Water resistant •Will not dent easily
(d) •Non-toxic •Not easily broken •Can be coloured easily [paint clips off lead toys]

6.(a) 1 Add a spoonful of ‘living’ yeast to a dilute solution of glucose in a conical flask.2 Set up the apparatus as shown below.3 Leave it for a few days.
(b) C6H12O6(aq) à 2C2H5OH(aq) + 2CO2(g)
(c) Starch such as rice
(d) (i) Fractional distillation(ii)

7.(a) Yeast
(b) Carbon dioxide
(c) 10-15%
(d) (i) Fractional distillation(ii) Brandy
(e) Ethanol in the drinks is oxidized to ethanoic acid by oxygen in the air.
(f) Health hazard: damage to the liver Social problem: many traffic accidents are caused by drunken drivers

8.(a) Propanoic acid
(b) This prevents any loss of the reaction mixture and favours the oxidation of propan-l-ol to propanoic acid.
(c) CH3CH2CH2OH à CH3CH2COOH
(e) (i) Mix propanoic acid, ethanol and a few drops of concentrated sulphuric acid in a test tube. Warm the mixture with a warm water bath for a few minutes. Pour the contents of the test tube into water in a beaker. The product forms an insoluble layer on the water.(ii) Ethyl propanoate(iii) (iv) Esterification

9.(a) (i) Ethene(ii) Pass ethene with steam over a catalyst of phosphoric acid at a temperature of 300 °C and a pressure of 65 atmospheres.
(b) The sodium metal dissolves in ethanol and a colourless gas is given off.
(d) (i) Ethyl ethanoate(ii) Warm a mixture of ethanol, ethanoic acid and concentrated sulphuric acid.(iii) Pour the reaction mixture into cold water, a pleasant smell will be detected if the product is present. (iv) Esterification
(e) Pass the breath of the driver into an acidified potassium dichromate solution (or gel). There will be a colour change from orange to green in the test if ethanol is present in the breath of the driver.

10.(b) This prevents any loss of the reaction mixture and favours the oxidation of ethanol to ethanoic acid rather than to ethanal.
(c) (i) It acts as a catalyst.(ii) Alkanol A is flammable.(iii) Two layers of liquids resulted. A pleasant smell can be detected.
(d) (i) Hydrolysis(ii) The products can be separated by fractional distillation. The alkanol is obtained as distillate. The salt of alkanoic acid remains in the solution as it is less volatile. Free alkanoic acid can be obtained by adding excess mineral acid to the solution.

11.(a) (i) CH3(CH2)3CH＝CH2(ii) Addition reaction CH3(CH2)3CH＝CH2 à CH3(CH2)3CHBrCH2Br + Br2 (in 1,1,1-trichloroethane) (in 1,1,1-trichloroethane)
(b) (i) CH3CH2OH(ii) Oxidation(iii) The orange dichromate ion changes to green chromium(III) ion in the reaction.
(c) Mix each reagent with ethanol and warm with concentrated sulphuric acid. The reagent that gives a product with a pleasant smell is CH3CH2COOH.

12.(a) Part Y is hydrophilic. It is ionic and attracts the water molecules.
(b) Part X is hydrophobic. It is covalent and does not attract the water molecules.
(c) A soap can be prepared using vegetable oil and concentrated sodium hydroxide solution. First gently heat, while stirring, a mixture of castor oil and concentrated sodium hydroxide solution for about 20 minutes. Most of the soap formed dissolves in the reaction mixture. Then add concentrated sodium chloride solution to the mixture. This lowers the solubility of soap in water. The soap separates from the solution and floats to the surface.
(d) (e) Soap does not form lather in hard water, scum is formed instead. Soap cannot be used in strongly acidic solutions.

13.(a) When a solution of detergent I is added, the ‘tails’ of the detergent particles dissolve in the grease mark. The ‘heads’ of the detergent particles are insoluble in the grease and they remain outside. The ‘heads’ are attracted by the surrounding water molecules and the grease mark is lifted off the surface. By stirring, the grease particle breaks up into smaller grease particles suspended in the water. The smaller grease particles cannot come together again due to the repulsion between ‘heads’ of detergent particles on their surfaces. An emulsion is formed. Rinsing washes away the greasy suspension, and leaves the surface clean.
(b) Chemical derived from petroleum

14.(a) Detergent III is probably a soapy detergent. Soapy detergents are biodegradable, alkaline and form scum with hard water.
(b) Detergent IV would irritate the skin. The pH value of the skin is about 6. Detergents with a pH value greater than 9 would irritate the skin.
(c) Detergent III cannot be used in strongly acidic solutions. At pH values much lower than 7, the detergent is converted to an alkanoic acid. The alkanoic acid has a high relative molecular mass and is insoluble in water. The cleaning property of the detergent is thus lost.
(d) Biodegradable detergents are detergents that can be decomposed by bacteria.
(e) Non-biodegradable detergents are not decomposed by bacteria in sewage treatment plants. The lather produced form thick foams. These foams would kill water lives in rivers and seas.
(f) Bacteria use up oxygen in the water during the decomposition of biodegradable detergents. This makes the water qualities worse.
(g) The detergent can emulsify the petroleum. The petroleum can then be carried away by water current.

15.The structures of thermoplastics and thermosetting plastics are different. In a thermoplastic, the giant molecules are in the form of separate long chains. Each chain is formed from monomer molecules that join repeatedly. The chains are not joined to one another. Only weak intermolecular forces hold the chains together. Upon heating, these weak forces are overcome and the chains move over one another. The plastic then goes soft and melts. A thermosetting plastic also consists of separate long chains during its first stage of formation. Hence, it goes soft upon heating and can be moulded into the desired shape. As heating continues, strong links begin to form between the chains to give three-dimensional networks of bonds. These links are called cross-links. As a result, thermosetting plastics do not soften or melt on heating.

16.Recycling of plastic waste is carried out in two main ways: direct recycling and pyrolysis. In direct recycling, the plastic objects in the waste are separated, cleaned, ground to powder and remoulded into new plastic items. The success of this method depends on the collection of clean and uncontaminated plastic objects, which is the most difficult step. This method applies only to thermoplastics. In pyrolysis, plastics are heated in the absence of air to about 700 °C. The molecules break down to form smaller molecules. This process does not require the separation of the various types of plastics. Common plastics, such as polythene, polypropene and polystyrene, give hydrocarbons (such as methane, ethene, propene and benzene) in the pyrolysis process. The hydrocarbons can be separated out by fractional distillation. They are used as starting materials for making other chemicals, including plastics.

17.Many places in the world produce ethanol by fermentation and use the ethanol as a fuel for cars. Using ethanol as a fuel for cars has several advantages. Ethanol can burn directly as a fuel and does not require other additives to improve its efficiency. Ethanol burns to form mainly carbon dioxide and water, so it is a cleaner fuel compared with fossil fuels. Cars can be easily converted to run on pure ethanol. Besides that, ethanol can be produced from many different types of food crops, which is renewable. Moreover, ethanol can be easily transported to various places. Lastly, distilleries are built for ethanol production and this creates jobs for people. However, there are several disadvantages associated with the use of ethanol as a fuel for cars. It requires a large area of land to produce enough food crops to meet the demand. It may also lead to diversion of investment from food production, resulting in increased food prices. The toxic effluent from distilleries cause water pollution. Fuels are required to produce ethanol in distilleries. Moreover, combustion of 1 kg of ethanol can give only 60% of the energy that can be released from 1 kg of petrol. Ethanal is also produced during combustion. Without adequate pollution control, ethanal can harm vegetation, irritate the skin and eyes, and damage the lung at high concentrations. Lastly, it may not be possible to obtain cheap ethanol in every part of the world.