Structured Question Worked Solutions1. Ethyl ethanoate is made by esterification.
ethanoic acid + ethanol <--> ethyl ethanoate + water
The table below gives the relative molecular masses for the reactants and products in the reaction.
| substance||relative molecular mass Mr |
| ethanoic acid|| 60|
| ethanol|| 46|
| ethyl ethanoate|| 88|
| eater|| 18|
a. In an experiment, 3.0g of ethanoic acid and 4.6g of ethanol were heated together with a catalyst.
i. how many moles of ethanoic acid were used?
ii. how many moles of ethanol were used?
iii. which reactant (ethanol or ethanoic acid) was in excess?
iv. what mass of ethyl ethanoate would be made if there was 100% conversion?
v. in an experiment, only 2.20g of ethyl ethanoate were obtained. What was the percentage yield of ethyl ethanoate?
b. Propanoic acid has the following structural formula.
Draw the structural formula of the ester formed when propanoic acid reacts with ethanol.Solution
1ai. amount of acid used = 3.0/60 = 0.05 mole
1aii. amount of ethanol used = 4.6/46 = 0.1 mole
1aiv. amount of ester produced = 0.05 mole
mass of ester produced = 0.05 x 88 = 44 g
1av. % yield = 2.20/4.4 x 100% = 50%
1b. 2. Ethanol, C2H5OH is used in Brazil as a liquid fuel instead of gasoline (petrol). The ethanol is manufactured by a fermentation process from sugar cane.
ai. describe how cane sugar can be converted into ethanol by the process of fermentation.
aii. what is the name of the gas produced during this fermentation? How would you test for this gas?
b. When ethanol is completely burnt in air, it forms carbon dioxide and water. One mole of ethanol will release 1370 kJ of heat energy during this reaction.
i. Construct the balanced equation for the burning of ethanol.
ii. The mass of 1 litre of ethanol is 780 g. How much heat energy will be released when 1 litre (1dm3) of ethanol is completely burnt?
c. When completely burnt, 1 litre of gasoline releases 38000 kJ of heat energy. Comparing ethanol and gasoline as liquid fuels, suggest
i. one advantage of using ethanol rather than gasoline
ii. one advantage of using gasoline rather than ethanol
2ai. A mixture of sugar cane (which contains glucose) with some yeast is allowed to ferment in a closed container in the absence of air for some time.
OH + 2CO2
2aii. carbon dioxide. This gas can be tested by passing it through limewater and the solution turns milky (white precipitate formed)
OH (l) + 3O2
(g) --> 2CO2
(g) + 3H2
2bii. Mr of ethanol = 2 x 12 + 6 x 1 + 16 = 46
amount of ethanol used = 780/46 moles
amount of energy released = 780/46 x 1370 = 23230 kJ
2ci. Burning ethanol produces less carbon dioxide, which is one of the components responsible for the Greenhouse effect.
2cii. Burning gasoline produces more energy.
3. The following questions refer to compounds with the structures drawn below.
Using the letters A to F as appropriate, answer the following.
a. Which compound is an unsaturated hydrocarbon?
b. Which compounds are members of the same homologous series?
c. Which compound reacts with sodium carbonate?
d. Which compounds are isomers of each other?
3b. B, F
3d. A, D4. Olive oil contains oleic acid which is unsaturated.
ai. By naming the reagent and giving the observation, describe a simple test to confirm that olive oil contains an acid.
aii. Explain what is meant by unsaturated
aiii. By naming the reagent and giving the observation, describe a simple test to confirm that oleic acid is unsaturated.
b. The molecular formula of oleic acid is C17H31CO2H. How many double bonds between carbon atoms are present in one molecule of oleic acid? Explain your answer.
4ai. reagent: sodium carbonate
observation: effervescence. Gas turns limewater milky.
4aii. An unsaturated compound is one that contains multiple bonds eg double bonds
4aiii. reagent: bromine
observation: the brown color of bromine is discharged
4b. number: 2
Explain: If oleic acid does not contain C=C double bond, its formula should be
H). Since its formula has 4 hydrogen less than 33, it should therefore contain 2 double bonds.5. The structure of fluorochloroethane is shown below
a. Suggest a name for, and sketch the structure of, the macromolecule formed when fluorochloroethene polymerizes.
b. When 20 tonnes of fluorochloroethene polymerised, 18 tonnes of the polymer were obtained. Calculate the percentage yield.
c. Name and give a use for a commercially available polymer containing a halogen.Solution
5b. Theoretically, 20 tonnes of products should be obtained. Therefore % yield = 18/20 x 100% = 90%
5c. polyvinylchloride (PVC). It is used as plastics.
6. Ethyne, C2H2, burns in oxygen to give a very hot flame. The temperature is so high that the flame can be used to cut metal.
ai. Name the two products of the complete combustion of ethyne.
aii. Describe a chemical test for one of these products
b. Calcium carbide, CaC2, is a greyish-white solid. Ethyne can be made by the reaction of calcium carbide with water. Calcium hydroxide, Ca(OH)2 is the other product of the reaction.
i. Construct an equation, including state symbols, for the reaction between carlcium carbide and water.
ii. The mixture obtained after this reaction was tested using Universal Indicator. What was the final color of the Universal Indicator? Explain your answer.
6ai. carbon dioxide and water
6aii. Bubble the gas through limewater. A white precipitate would be observed
(s) + 2H2
O (l) --> Ca(OH)2
(aq) + C2
6bii. Blue. Ca(OH)2
is alkaline.7a. The following terms are used in the description of organic compounds.
From this list, choose two terms which can be applied to each of the compounds below.
b. One of the general characteristics of homologous series is that all the members can be represented by a general formula.
i. What is the general formula of the alkene series?
ii. Give one other general characteristics of homologous series.
7ai. alkane, hydrocarbon
7aii. alkene, hydrocarbon
7aiii. alkane, polymer
7aiv. amide, polymer
7bii. The members show similar chemical reactions.
8a. Heptane is an alkane with seven carbon atoms per molecule. It is a colorless liquid with a boiling point of 100ºC.
i. deduce the molecular formula of heptane
ii. suggest two tests you could use to decide whether a colorless liquid was heptane or water.
Predict the results of the tests for both heptane and water.
b. Fructose is a carbohydrate. One form of fructose has the following structure.
i. deduce the molecular formula of fructose
ii. suggest why the term 'carbohydrate' is used for this type of compound
iii. name another carbohydrate
8aii. test 1: add anhydrous copper(II) sulphate
heptane: solid copper(II) sulphate remains white and insoluble
water: solid turns blue and then dissolves to give a blue solution
test 2: ignite with a flame
heptane: burns with a luminous flame
water: the flame dies off
8bii. The molecular formula seems to suggest 6 units of carbon, and hydrogen and oxygen in the ratio 2:1 just like water C6
ie. hydrate of carbon.
8biii. glucose9a. Hydrogen can be manufactured by the reaction between methane and steam.
i. Name a source of the methane required for this reaction.
ii. Give the equation for this reaction between methane and steam.
iii. Calculate the maximum volume of hydrogen, measured at r.t.p. which can be obtained from 16g of methane.
b. Margarine is manufactured using the addition reaction between hydrogen and a vegetable oil.
i. state the conditions used for this reaction
ii. what type of bond must be present in the vegetable oil for this reaction to take place?
c. The diagram represents the structure of a common plastic.
i. Name this plastic and draw the structure of the monomer from which it is made.
ii. This plastic is non-biodegradable. Explain the meaning of this term and describe the problems which this property creates.
d. If this plastic is burned, a thick, black smoke and a very acidic gas are produced.
i. suggest the identity of the black particles in the smoke
ii. suggest the identity of the very acidic gas.Solution
9ai. natural gas
(g) + H2
O (g) --> CO (g) + 3H2
9aiii. Mr of CH4
amount of CH4
= 16/16 = 1 mol
amount of H2
formed = 3 mol
volume of 1 mole of gas at r.t.p. = 24dm3
volume of H2
formed = 3 x 24 = 72 dm3
9bi. Nickel catalyst, high pressure
9bii. double bonds
9ci. polyvinylchloride (PVC)
9cii. Non-biodegradable means cannot be broken down by biochemical reactions by bacteria.
9dii. hydrogen chloride10. Ethene is an unsaturated hydrocarbon.
ai. what is meant by 'unsaturated'?
b. Ethene is made by the cracking of long chain hydrocarbon molecules such as C16H34.
Construct an equation to illustrate the cracking of C16H34 to make ethene and another hydrocarbon as the only products.
c. Ethene is bubbled through aqueous bromine to form 1,2-dibromoethane. What would you observe during the reaction?
d. Give the name of the product and the conditions needed for the reaction of ethene with water.
e. Calculate the volume of carbon dioxide, measured at r.t.p., produced by the complete combustion of 1.40g of ethene.
f. Ethene can be made into poly(ethene). Draw the structure of poly(ethene).
10a. An unsaturated compound is one that contains multiple bonds eg C=C
10c. Decolorization of brown bromine
(g) + 3O2
(g) --> 2CO2
(g) + 2H2
Mr of C2
25g of C2
give 48 dm3
--> 1.40g of C2
give 1.40 x 48/28 = 2.4dm3
10f. 11. The following is a list of formulae of organic compounds.
Which of the above formula fit the following descriptions?
a. a compound which dissolves in water to form an acidic solution
b. a compound which is not a hydrocarbon
c. two compounds which are from the same homologous series
d. two compounds which react to form an ester
e. a compound which undergoes an addition reaction with steam
f. a compound which is oxidised by acidified potassium dichromate(VI) to give ethanoic acidSolution
COOH or C2
COOH and C2
OH12. Ethanol, CH3CH2OH is a liquid fuel. Ethanol can be manufactured either from glucose C6H12O6 or from ethene.
a. Briefly describe the manufacture of ethanol from glucose. Include the balanced equation in your answer.
bi. Draw the displayed formula for ethene
bii. Name the substance that reacts with ethene to make ethanol
biii. Give the conditions needed for this reaction.
12a. Yeast cells are added to a solution of glucose. The mixture is kept at 18-20ºC under anaerobic conditions. Glucose will be broken down by zymase enzyme in yeast cells to form ethanol and carbon dioxide. Ethanol is obtained by fractional distillation of the mixture.
OH + CO2
12biii. 300ºC, 70 atmospheric pressure and phosphoric acid catalyst13. Styrene-butadiene rubber is a synthetic rubber. It is made by polymerising a mixture of the monomers butadiene and styrene.a. What type of polymerization will take place when the monomers polymerise? Explain.
One possible structure for the polymer is shown below.
b. Give the full structural formula for the repeating unit in this polymer structure.
c. When the mixture of styrene and butadiene polymerises, the polymer is unlikely to contain only this regular, repeating pattern. Explain why.
Butadiene can be made by cracking butane in a cracking tower.
di. Butane cracks to form butadiene and one other product. Write an equation to show this reaction.
dii. Give a use of the other product of this reaction.
e. 2.90kg of butane entered the cracking tower. After the reaction, 2.16kg of butadiene had been made. Calculate the percentage yield of butadiene.
13a. Addition polymerization. Addition polymerization is the joining together of two or more simple molecules, called monomers, to form a long chain compound without any loss of small molecules. The addition polymerization process can only occur when the monomer molecule is unsaturated (contain double bonds or triple bonds)
13c. Since two different monomers are mixed together before being polymerized the chain will have the different monomers distributed randomly along its length. Let styrene monomer be A and butadiene monomer be B. One possible random distribution is
Sometimes the same type of monomers may be polymerised to form short chains and then these chains mixed and further addition polymerization occurs. For eg.
13di. hydrogen gas
13dii. used in the manufacture of ammonia in the Haber process
13e. Mr of butane = 58
Mr of butadiene = 54
no. of moles of butane = 2900/58 = 50
From the eq, 1 mol of butane undergoes cracking to form 1 mol of butadiene.
no. of mole of butadiene formed = 50
mass of butadiene = 50 x 54 = 2700g --> 2.7kg
experimental yield of butadiene = 2.16kg
% yield of butadiene = 2.16/2.7 x 100 = 80%14. This is the structure of an ester made in a reversible reaction between a carboxylic acid and an alcohol.
ai. State the conditions for this reaction
aii. Draw the structure of the carboxylic acid used in the reaction.
aiii. Write an equation for this reaction.
b. A student carried out some experiments to compare the relative strengths of dilute ethanoic acid with dilute hydrochloric acid.
i. Describe a test that can be used to distinguish between dilute ethanoic acid and dilute hydrochloric acid.
ii. Explain, using ideas about ions, why the two acids behave differently.
iii. Name a solid substance that will react with both acids. Describe what you will see during the reaction.Solution
14ai. Heat the carboxylic acid with alcohol ethanol using a few drops of concentrated sulphuric acid as catalyst.
OH --> CH3
14bi. Place about 2cm3
of each acid in separate test tubes. Add a few drops of silver nitrate solution to each test tube. A white precipitate will be observed in the test tube containing hydrochloric acid.
14bii. Dilute hydrochloric acid is a strong acid and ethanoic acid is a weak acid. Dilute HCl dissociates fully in water whereas a weak acid dissociates partially in water to form hydrogen ions, H+
HCl (aq) --> H+
(aq) + Cl-
Ethanoic acid dissociates partially in water to form a solution containing H+
ions. There are more acid molecules in a solution of weak acid than H+
COOH <--> CH3
14biii. solid calcium carbonate.
observations: Effervescence occurs. Colorless, odourless gas formed white precipitate with limewater.