IB Docs (2) Team MC test: Alkanes, alkenes & addition polymers
Multiple choice test on 10.2(1) Alkanes, alkenes & addition polymers
Use the following 'quiz' to test your knowledge and understanding of this sub-topic. You will need access to a periodic table (Section 6 of the IB data booklet).
If you get an answer wrong, read through the explanation carefully to learn from your mistakes.
Using integers, what is the smallest sum of all the coefficients when the equation for the complete combustion of octane, C8H18 in oxygen is correctly balanced?
2 C8H18(l) + 25 O2(g) → 16 CO2(g) + 18 H2O(l)
A possible equation for the incomplete combustion of one mole of butane in air is:
C4H10(g) + 5O2(g) → xCO2(g) + yCO(g) + 5H2O(l)
Which are the correct values for x and y?
x + y must equal 4 as a molecule of butane contains 4 carbon atoms. 2x + y must equal 10 − 5. so y = 5 − 2x.
Substituting for y: x + (5 − 2x) = 4 so x = 1 and y = 3.
Which factors contribute to the explanation as to why alkanes are not very reactive?
I. Unlike the other elements in group 14, carbon cannot expand its octet.
II. C−H and C−C bonds are relatively strong compared to other covalent single bonds.
III. Alkanes either are non-polar or have very low polarity.
All three are important. Because alkanes are non-polar, electrophiles and nucleophiles are not attracted to them. It requires considerable energy to overcome their bond strengths and molecules such as water cannot use their lone pair to form coordinate bonds with carbon atoms in alkanes as they have no empty available orbitals. This last point explains why CCl4 is immiscible and does not react with water whereas SiCl4 reacts violently with water to form fumes of HCl.
Methane reacts with chlorine in the presence of ultraviolet light to form chloromethane and hydrogen chloride. What is the function of the ultraviolet light?
The Cl−Cl bond has a bond enthalpy of 242 kJ mol−1 which, unlike the C−H bond (414 kJ mol−1), can be dissociated homolytically by ultraviolet light to form free radicals.
Which is a propagation step in the substitution reaction between ethane and bromine in the presence of ultraviolet light?
A propagation step must produce more radicals.
What will be the product of the reaction between pent-2-ene and bromine in the dark?
Bromine adds across the double bond in the 2- and 3- positions.
What product will be formed when water is reacted with ethene in the presence of a catalytic amount of concentrated sulfuric acid?
Water adds across the double bond. This reaction is carried out in industry by reacting ethene with steam using phosphoric acid as the catalyst.
Under high pressure alkenes can be polymerized to give addition polymers.
Polystyrene is an addition polymer.
Which monomer is used to make polystyrene?
Many alkenes with the formula H2C=CHX polymerise to give addition polymers with the repeating unit −(−CH2−CHX−)−.
Which product will be formed when but-2-ene reacts with hydrogen bromide?
HBr adds across the double bond: .png)
What simple test can be used to distinguish a liquid alkene from a liquid alkane?
Bromine water is yellow-brown. Bromine adds to an alkene to give a colourless product so the alkene will decolourize a small amount of bromine water rapidly. There will be no rapid change to the bromine colour with an alkane although if sunlight or ultraviolet light falls on the mixture it will slowly decolourise the bromine solution as substitution takes place.
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