(a)i. State two characteristics of a homologous series.
(ii) Explain briefly why there are differences in the reaction of ethane and ethene.
(b) When crystals of sodium chloride were warmed with concentrated tetraoxosulphate( VI) acid, a gas was evolved.
(i) Name the gas.
(ii) State two physical properties of the gas.
(iii) Write a balanced chemical equation for the reaction.
(d) Draw and label a diagram of a set-up that could be used to electroplate a copper ornament with silver
(a)
(i) Homologous series have members that have similar chemical properties and successive members differ by a -CH2- unit.
(ii) Ethane is a saturated hydrocarbon and cannot undergo addition reactions, whereas ethene is an unsaturated hydrocarbon and can undergo addition reactions due to the presence of a double bond.
(b)
(i) The gas evolved is hydrogen chloride (HCl).
(ii) Hydrogen chloride is a colorless gas with a pungent odor and is highly soluble in water.
(iii) NaCl(s) + H2SO4(l) → NaHSO4(s) + HCl(g)
(c)
(i) Hydrocarbons are organic compounds made up of hydrogen and carbon atoms.
(ii) Two natural sources of hydrocarbons are crude oil and natural gas.
(iii) Let's assume we have 100g of the hydrocarbon. Therefore, the mass of carbon present in the hydrocarbon is:
83g = (83/12) mol of carbon
The mass of hydrogen present in the hydrocarbon is:
(100 - 83)g = 17g = (17/1) mol of hydrogen
The empirical formula is the simplest ratio of the atoms in the compound, and it can be calculated by dividing the number of moles of each element by the smallest number of moles. In this case, the smallest number of moles is 1. Therefore, the empirical formula of the hydrocarbon is:
C(83/12)/1 : H(17/1)/1
which simplifies to:
C7H2
(d)
To electroplate a copper ornament with silver, we need a set-up that includes a silver anode, a copper cathode, and a solution of a silver salt such as silver nitrate in water. The ornament is connected to the negative terminal of a power supply, which is also connected to the copper cathode. The silver anode is connected to the positive terminal of the power supply.
When an electric current flows through the set-up, silver ions from the silver anode move towards the copper cathode and gain electrons to form silver atoms, which deposit on the surface of the copper ornament. This process is known as electroplating, and it allows us to coat a less expensive metal with a more expensive metal, such as copper with silver.
