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(a) Chlorine can be prepared using the following reaction.
$MnO_2(s) + 4HCl(aq) \rightarrow MnCl_2(aq) + 2H_2O(l) + Cl_2(g)$
(i) Explain why $MnO_2(s)$ is described as an oxidising agent in this reaction.
Refer to oxidation numbers in your answer.
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(ii) State what you would observe during this reaction.
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(b) The halogens chlorine, bromine and iodine are all volatile elements.
State and explain the trend in volatility down Group 17.
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(c) Chlorine undergoes disproportionation during many chemical reactions.
(i) Write an equation for the reaction of chlorine with cold aqueous sodium hydroxide, NaOH.
Explain why it is a disproportionation reaction.
equation ................................................................................................................................
explanation ..................................................................................................................................
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(ii) One of the products of the reaction of chlorine with hot aqueous sodium hydroxide differs
from those in (c)(i).
Identify the compound that is formed in this reaction that is different from that formed in the reaction in (c)(i).
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(d) State and explain the use of chlorine in water purification.
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(e) Under certain conditions, chlorine undergoes a free-radical substitution reaction with ethane.
(i) State the conditions required to initiate this reaction.
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(ii) Write the overall equation for this free-radical substitution reaction.
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(a) Complete the table to give details of the type of bonding and structure shown by some of the oxides of Period 3 elements.
[Table_1]
Na_{2}O: 1275 °C, basic
MgO: 3670 °C, basic
Al_{2}O_{3}: 2977 °C, amphoteric
SiO_{2}: 2950 °C, acidic
SO_{3}: 45 °C, acidic
(b) (i) Explain why the boiling point of SiO_{2} is much higher than the boiling point of SO_{3}.
[3]
(ii) Al_{2}O_{3} is an amphoteric oxide.
Explain what is meant by the term amphoteric. Use chemical equations to illustrate your answer.
[3]
(iii) State what you would observe when a small sample of Na_{2}O is placed in water.
[1]
(c) Selenium is a Group 16 element which shows similar chemical reactions to sulfur.
(i) Selenium reacts with fluorine to form SeF_{6} molecules.
Predict the shape of a molecule of SeF_{6}.
[1]
(ii) The most stable oxide of selenium is SeO_{2}.
Gaseous SeO_{2} reacts to form a solid polymer, as shown. In the reaction one Se=O is replaced by two Se—O to form a polymer.
The bond enthalpy of Se=O is 514 kJ mol^{-1}.
Use these data to calculate the bond enthalpy, in kJ mol^{-1}, of Se—O.
[2]
(iii) SeO_{2} shows similar chemical reactions to SO_{2}.
Suggest an equation to show the reaction of SeO_{2} with aqueous sodium hydroxide, NaOH.
[1]
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Crude oil is a natural source of hydrocarbons that are used as fuels.
(a) Hydrocarbons with low relative molecular mass, $M_r$, are used as fuels in industry, in the home and for transport. There is a high demand for the hydrocarbons with low $M_r$.
(i) Name the process by which long-chain hydrocarbons are broken down into shorter-chain hydrocarbons. [1]
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(ii) Give one reason why hydrocarbons with low $M_r$ are suitable for use as fuels. [1]
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(iii) Incomplete combustion of hydrocarbons can release carbon monoxide, CO, into the atmosphere. Write an equation for the formation of CO from the incomplete combustion of butene, C$_4$H$_8$. [1]
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(iv) Identify an analytical technique that can be used to monitor the levels of CO in the atmosphere. Outline how this analytical technique may be used to monitor the levels of CO. [2]
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(b) Thiophene, C$_4$H$_4$S(l), is an organic compound that is found as a contaminant in crude oil.
(i) Construct the equation for the complete combustion of thiophene, C$_4$H$_4$S(l). Include state symbols in your answer. [2]
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(ii) A student carries out an experiment to determine the enthalpy change of combustion of C$_4$H$_4$S(l). Explain the meaning of the term enthalpy change of combustion. [2]
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(iii) The student uses the following apparatus in the experiment.
Calculate the heat energy released, in J, by the reaction. Assume that 4.18 J of heat energy changes the temperature of 1.0 cm$^3$ of water by 1.0°C. Assume no heat is lost to the surroundings. heat energy released = .............................. J [2]
(iv) The student used 0.63 g of C$_4$H$_4$S(l) in the experiment. Calculate the enthalpy change of combustion of thiophene, $\Delta H_c$(C$_4$H$_4$S(l)). Include a sign in your answer. $\Delta H_c$(C$_4$H$_4$S(l)) = ............................. kJ mol$^{-1}$ [2]
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(CH₃)₃CCHO is used in the synthesis of some antibiotics.
(a) (i) Give the name of (CH₃)₃CCHO. [1]
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(ii) State the hybridisation of the carbon atom labelled with an asterisk, *. [1]
$$\text{}$$
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(b) Two reaction sequences are shown.
$$\text{}$$
(i) Reaction 1 is an oxidation reaction.
Identify the reagent(s) and conditions for reaction 1. [1]
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(ii) A, (CH₃)₃CCO₂H, is a solid at room temperature.
B, CH₃CO₂(CH₂)₂CH₃, is an isomer of A. B is a liquid at room temperature.
Explain the difference in the physical states of A and B, with reference to any intermolecular forces that may exist. [3]
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(iii) Give the balanced equation for the reaction of (CH₃)₃CCHO with NaBH₄ to form S. [1]
Use [H] to represent an atom of hydrogen provided by NaBH₄.
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(iv) Draw the structure of the organic molecule T that reacts with A, (CH₃)₃CCO₂H, in reaction 2, to form U.
Suggest a catalyst for reaction 2. [2]
$$\text{}$$
catalyst .........................................................................................................
(c) X, Y and Z are all isomers of (CH₃)₃CCHO.
A summary of some of the reactions and properties of X, Y and Z is shown in the table.
$$\text{[Table_1]}$$
(i) X and Y each contains a carbonyl group.
Complete the table with the expected observations for the reactions of X and Y with 2,4-DNPH. [1]
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(ii) Identify the functional group present in Y that causes the recorded observation with Fehling’s solution. [1]
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(iii) Y has a chiral centre and exists as a pair of optical isomers.
State what is meant by the term chiral centre. [1]
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(iv) Draw the optical isomers of Y using the conventional three-dimensional representation. [2]
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(v) Complete the table with the bond responsible for each of the principal absorptions seen in the infra-red spectrum of Z. [1]
$$\text{[Table_2]}$$
(vi) Draw the skeletal formula of Z. [3]
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(vii) X contains a carbonyl group. X reacts with HCN, in the presence of a small amount of NaCN, to form (C₂H₅)₂C(OH)CN as shown.
X + HCN → (C₂H₅)₂C(OH)CN
Draw the mechanism of the reaction of X with HCN. [3]
● Draw the structure of X and the intermediate.
● Include all charges, partial charges, lone pairs and curly arrows.
$$\text{}$$
(viii) State the role of NaCN in the reaction in (c)(vii). [1]
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