Organic Chemistry Questions and Answers (Page 1)
The hydrocarbon methane is the first member of the alkanes homologous series.
a) Draw diagrams to show the first 3 members of the alkanes homologous series.
b) What substances will be formed when methane burns in plentiful air supply? How would you test for each product formed?
c) Why is it dangerous to burn methane in a limited oxygen supply?
d) Write a word equation to show the burning of methane in plentiful oxygen supply.
b) Carbon dioxide and Water.
Test for carbon dioxide – bubble the gas through limewater (calcium hydroxide) and the limewater turns milky.
Test for water – dip cobalt chloride paper in the collected liquid and the cobalt chloride paper turns pink.
c) In limited supply of oxygen, methane burns to produce carbon monoxide which is poisonous and soot which causes respiratory problems.
d) Methane + oxygen → carbon dioxide + water
A hydrocarbon Y (Mr = 42) quickly decolourises bromine water.
a) What is its structural formula likely to be?
b) Name the compound.
a) Give 2 advantages of using solar energy as a source of energy over wood or coal in Zimbabwe.
b)(i) Name the chemical reaction that depends upon solar energy and is vital to all living organisms.
(ii) Into what form is the solar energy converted by this reaction?
(iii) How is this energy used by people?
a)(i) Solar energy is a renewable energy resource.
(ii) Solar energy is cheap to use because there is plenty of sunshine in Zimbabwe.
(ii) Chemical energy
(iii) Chemical energy is taken in as food and converted by our bodies into kinetic energy when we walk, sound energy when we talk and heat energy when we are cold. The chemical energy produced by photosynthesis is also found in fuels such as wood and people use those fuels for activities such as cooking.
Reactions that release energy in humans and in engines can be written respectively as follows:
sugar + oxygen → carbon dioxide + water + energy
petrol + oxygen → carbon monoxide + carbon dioxide + water + energy
a) How do these equations suggest that a human being is a more efficient machine than an engine?
b) How would you attempt to show that whether or not sugar contains more energy than petrol?
c) Which two elements are available in all organic liquid fuels?
a) In a petrol engine there is incomplete combustion and petrol is not fully oxidised as shown by the release of carbon monoxide. This means that some of the energy is lost as partial oxidised carbon monoxide. In a human being all the sugar is completely oxidised and no energy is lost by incomplete combustion.
b) Take two small tin lids, fill one which a measured mass of sugar and another with the same amount of petrol. Ignite the sugar, use it to heat a beaker of water and record the temperature rise. Ignite the petrol and heat the same amount of water. The fuel that contains more energy will produce a greater rise in temperature.
c) Hydrogen and Carbon
To make home made beer, sugar is dissolved in hot water and yeast is added after the mixture has cooled. The solution is left in a warm place for 48 hours and is then filtered and bottled.
a) Write a word equation for the action of the yeast on the sugar.
b) Why do bottles of home-made beer explode if kept closed for some time?
c) Why is the mixture cooled before adding the yeast?
d) How is the ethanol separated from the mixture?
a) glucose → carbon dioxide + alcohol
b) They explode due to the build up of the pressure caused by the carbon dioxide produced as the reaction proceeds.
c) High temperatures kill the enzyme in yeast.
d) By fractional distillation.