Question
This question is about alkanes and alkenes.
(a) Short-chain alkanes and alkenes can be formed from long-chain alkanes in a chemical reaction.
(i) Name the type of chemical reaction which forms short‑chain alkanes and alkenes from long‑chain alkanes.[1]
(ii) Decane has 10 carbon atoms. It forms ethane and ethene as the only products in this type of chemical reaction.
Write the chemical equation for this reaction.[3]
(b) Ethane reacts with chlorine at room temperature to form chloroethane, C2H5Cl, and one other product.
(i) Name the other product formed.[1]
(ii) State the condition needed for this reaction to take place.[1]
(c) Ethene reacts with chlorine at room temperature to form dichloroethane, C2H4Cl2.
C2H4 + Cl2 → C2H4Cl2
(i) State why this is an addition reaction.[1]
(ii) The chemical equation for this reaction can be represented as shown.
The energy change for the reaction is –180kJ/mol.
Use the bond energies in the table to calculate the bond energy of a C–Cl bond, in kJ/mol.
Use the following steps.
step 1 Calculate the energy needed to break bonds.
energy needed to break bonds = kJ
step 2 Use your answer in step 1 and the energy change for the reaction to determine the energy released when bonds are formed.
energy released when bonds form = kJ
step 3 Use your answer in step 2 and bond energy values to determine the energy of a C–Cl bond.
bond energy of a C–Cl bond = kJ/mol
[4][Total: 11]
Answer/Explanation
Ans:
5(a)(i) cracking
5(a)(ii) C10H22 → 4C2H4 + C2H6
C10H22 as only reactant
formulae of ethene and ethane as only products
correct equation
5(b)(i) hydrogen chloride
5(b)(ii) ultraviolet light
5(c)(i) (only) one product is formed
5(c)(ii) M1 Bond energy in breaking bonds
= [(4 × 410) + 610 + 240] = 2490 (kJ / mol)
M2 Use of total E change to find bond energy of C2H4Cl2
= M1 + 180 = 2490 + 180 = 2670 (kJ / mol)
M3 Determination of total C–Cl bond energy
= M2 – [(4 × 410) + 350] = 2670 – 1990 = 680 (kJ / mol)
M4 Determination of each C–Cl bond energy
= M3 / 2 = 680 / 2 = 340 (kJ / mol)
Question
Biogas is made by fermenting animal and vegetable waste.
(a) The table shows the percentage composition of the gases present in a sample of biogas.
Deduce the percentage of nitrogen present in this sample of biogas.[1]
(b) (i) Balance the chemical equation for the complete combustion of methane.
CH4 + __ O2 → CO2 + __ H2O [2]
(ii) Which one of these compounds belongs to the same homologous series as methane?
Draw a circle around the correct answer.
methanolic acid methanol propane propanol propene [1]
(iii) Methane is present in the refinery gas fraction produced by the fractional distillation of petroleum.
Match the fractions on the left with their uses on the right.
The first one has been done for you.
(c) (i) Draw a dot-and-cross diagram to show the electron arrangement in a molecule of hydrogen. [1]
(ii) State one use of hydrogen.[1]
(d) The biogas contains a small amount of compound C.
The structure of compound C is shown.
(i) On the structure shown, draw a circle around the carboxylic acid functional group. [1]
(ii) How many different types of atoms are present in compound C?[1]
(e) Describe the manufacture of ethanol by fermentation.
In your answer include:
- the names of the substances needed for fermentation
- the conditions needed for fermentation. [4] [Total: 14]
Answer/Explanation
Ans:
(a) 6.0 / 6 (%)
(b)(i) 2 (O2) (1)
2 (H2O) (1)
(b)(ii) propane
(b)(iii) 3 correct (2)
1 or 2 correct (1)
fuel oil → fuel for ships
bitumen → making roads
naphtha → making chemicals
(c)(i) two (hydrogen) atoms with pair of electrons between and no other electrons
(c)(ii) fuel
(d)(i) circle around the COOH group only
(d)(ii) 5
(e) glucose / sugar (1)
yeast (1)
AND
1 mark each for any two of:
-
- oxygen absent / anaerobic
- room temperature / stated temperature between 5 °C and 40 °C (inclusive)
- pH near neutral
- presence of water / aqueous solution
- purify by distillation
Question
The table shows the structures of four hydrocarbons.
(a) Why are compounds P, Q, R and S known as hydrocarbons?[2]
(b) Compound P is saturated.
What is meant by the term saturated?[1]
(c) Compound P undergoes a substitution reaction with chlorine.
(i) What is meant by the term substitution reaction?[1]
(ii) State a condition required for this reaction to occur.[1]
(iii) Write a chemical equation for this reaction.[2]
(d) Compound R undergoes an addition reaction with bromine.
(i) Why is this reaction an addition reaction?[1]
(ii) A compound containing bromine is formed in this reaction.
Draw the structure of this compound. Show all of the atoms and all of the bonds. [1]
(e) Draw the structure of an unbranched isomer of compound S. Show all of the atoms and all of the bonds. Name this unbranched isomer of compound S.[2]
structure
name
(f) Compound Q undergoes polymerization.
(i) Name the polymer formed.[1]
(ii) Complete the chemical equation to show the polymerization of compound Q.[2]
n CH2=CH2 →
(g) Amino acids undergo polymerization to form proteins. Part of a protein molecule with the linkages missing is shown.
Draw the linkages on the diagram. Show all of the atoms and all of the bonds.[2]
(h) The structure shows an ester.
Write the word equation for a reaction which could be used to make this ester.[3] [Total: 19]
Answer/Explanation
Ans:
6(a) (they contain) carbon and hydrogen (atoms)
only
6(b) (all) the (C–C) bonds are single
6(c)(i) (one) atom or group is replaced by another (atom or group)
6(c)(ii) ultra-violet light OR sunlight
6(c)(iii) C2H6 + Cl2 → C2H5Cl + HCl
1 mark for C2H5Cl
1 mark for the rest of the equation
6(d)(i) only one product (compound) forms
6(d)(ii) fully displayed formula of 1,2-dibromopropane
6(e) fully displayed formula of but-2-ene
but-2-ene
6(f)(i) poly(ethene)
6(f)(ii) single bond between two C atoms
fully correct answer
6(g) any one correct amide link showing all bonds
both amide links shown in the correct orientation for three amino acids
6(h) ethanol + butanoic acid → ethyl butanoate + water
1 mark for the names of the reactants
1 mark for the name of the ester
1 mark for water as a product