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The elements of the third period of the Periodic Table, sodium to sulfur, all form chlorides by direct combination.
(a) (i) Sulfur forms a number of chlorides which are liquid at room temperature. Which other element of the third period forms a chloride which is liquid at room temperature?
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(ii) Name one element of the third period which burns in chlorine with a coloured flame.
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(iii) Aluminium chloride may be produced by passing a stream of chlorine over heated aluminium powder in a long hard-glass tube. State two observations you could make during this reaction.
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(iv) Write a balanced equation, with state symbols, for this reaction of aluminium with chlorine.
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(v) No chloride of argon has ever been produced. Suggest a reason for this.
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(b) When chlorides of the elements of the third period are added to water, some simply dissolve while others can be seen to react with the water.
(i) Complete the table below, stating how the chlorides of Na, Al, and Si behave when mixed with water. In the first column use only the terms 'dissolve' or 'react'.
[Table_1]
(ii) What type of reaction takes place between a chloride and water?
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(c) Sulfur forms the compound $S_4N_4$ with nitrogen. The structure of $S_4N_4$ is shown below. Assume all bonds shown are single bonds.
(i) Determine the number of lone pairs of electrons around a nitrogen atom and a sulfur atom in $S_4N_4$.
nitrogen atom ..............................
sulfur atom ..............................
(ii) Which bond angle, a or b, in the $S_4N_4$ molecule will be smaller? Explain your answer.
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579
579
571
Alcohols such as methanol, CH₃OH, are considered to be possible replacements for fossil fuels because they can be used in car engines.
(a) Define, with the aid of an equation which includes state symbols, the standard enthalpy change of combustion, $\Delta H_c^\circ$, for methanol at 298 K.
equation .................................................................................................................................
definition ...............................................................................................................................
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Methanol may be synthesised from carbon monoxide and hydrogen. Relevant $\Delta H_c^\circ$ values for this reaction are given in the table below.
[Table_1]
compounds | $\Delta H_c^\circ/\text{kJ mol}^{-1}$
CO(g) | -283
H₂(g) | -286
CH₃OH(g) | -726
(b) Use these values to calculate $\Delta H_{\text{reaction}}^\circ$ for the synthesis of methanol, using the following equation. Include a sign in your answer.
CO(g) + 2H₂(g) → CH₃OH(g)
$\Delta H_{\text{reaction}}^\circ = ......... \text{kJ mol}^{-1}$ [3]
(c) The operating conditions for this reaction are as follows.
pressure: 200 atmospheres (2 × 10⁷ Pa)
temperature: 600 K
catalyst: oxides of Cr, Cu, and Zn
In the spaces below, explain how each of these conditions affects the rate of formation of methanol.
pressure ................................................................................................................................
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temperature ............................................................................................................................
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catalyst .................................................................................................................................
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521
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514
Food additives are substances added to food to preserve the flavour or to improve its taste and appearance.
European Union legislation requires most additives used in foods to be labelled clearly in the list of ingredients, either by name or by an ‘E number’. E296 is malic acid which occurs in unripe fruit.
Malic acid has the structural formula HO$_2$CCH$_2$CH(OH)CO$_2$H.
(a) Some reactions of malic acid are shown below.
In the boxes below, give the structural formulae of organic compounds A to F.
(b) What type of reaction is each of the following conversions?
malic acid into C ..................................................
C into D ..................................................
C into E ..................................................
(c) Suggest one major commercial use of compounds such as A or B.
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(d) (i) Malic acid is chiral.
Draw fully displayed formulae of the two optical isomers of malic acid. Indicate with an asterisk (*) the chiral carbon atom.
(ii) Compound C also shows stereoisomerism.
Draw the skeletal formulae of each of the stereoisomers of C. Label each isomer.
(e) The food additive E330 is another organic compound which occurs naturally in fruit.
E330 has the following composition by mass: C, 37.5%; H, 4.17%; O, 58.3%.
Calculate the empirical formula of E330.
575
501
560
(a) On treating compounds containing each of these functional groups with the reagents below, only five reactions occur. Complete the table by placing a tick (✔) in each box where you believe a reaction will occur. You should place no more than five ticks in the table.
[Table]
Reagent | Alcohol $R_2CHOH$ | Aldehyde $RCHO$ | Carboxylic acid $RCO_2H$ | Ester $RCO_2R'$ | Ketone $RCOR'$
NaHCO$_3$ | | | | |
Na | | | | |
$Cr_2O_7^{2-}/H^+$ | | | | |
[5]
Compound G has the empirical formula CH$_2$O and $M_r$ of 90.
An aqueous solution of G is neutral. There is no reaction when G is treated with NaHCO$_3$.
When 0.30 g of pure G is reacted with an excess of Na, 80 cm$^3$ of H$_2$, measured at room temperature and pressure, is produced.
(b) (i) What functional group do these two reactions show to be present in G?
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(ii) Use the data to calculate the amount, in moles, of hydrogen atoms produced from 0.30 g of G.
(iii) Hence, show that each molecule of G contains two of the functional groups you have given in (i).
[4]
(c) Treatment of G with 2,4-dinitrophenylhydrazine reagent produces an orange solid. When G is warmed with Fehling’s reagent, no reaction occurs.
(i) What functional group do these reactions show to be present in G? Draw the displayed formula of this functional group.
(ii) Use your answers to (b)(i) and (c)(i) to deduce the structural formula of G.
[2]
(d) Compound G can be both oxidised and reduced.
(i) When G is heated under reflux with acidified $K_2Cr_2O_7$, compound H is formed. Give the structural formula of compound H.
(ii) When G is reacted with NaBH$_4$ under suitable conditions, compound J is formed. Give the structural formula of compound J.
[2]
547
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515
