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(a) Draw a diagram to show the shape of the molecule of each of the oxides, SO$_3$ and Cl$_2$O. Name each shape. In SO$_3$ each oxygen atom forms a double bond with the sulfur atom. [Image_1 - SO$_3$] [Image_2 - Cl$_2$O]
(b) (i) Explain why the melting point of MgO is higher than that of Na$_2$O. .............................................................................................................................................................. .............................................................................................................................................................. .............................................................................................................................................................. .............................................................................................................................................................. [2]
(ii) Explain why the melting point of SiO$_2$ is much higher than that of SO$_3$. .............................................................................................................................................................. .............................................................................................................................................................. .............................................................................................................................................................. .............................................................................................................................................................. .............................................................................................................................................................. .............................................................................................................................................................. [2]
(c) SO$_3$ is produced by the reaction between SO$_2$ and O$_2$ in the Contact process. A dynamic equilibrium is established. $$2\text{SO}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{SO}_3(g) \qquad \Delta H = -196\, \text{kJ mol}^{-1}$$ (i) Explain why increasing the total pressure, at constant temperature, increases the rate of production of SO$_3$ and increases the yield of SO$_3$. rate .............................................................................................................................................................. .............................................................................................................................................................. .............................................................................................................................................................. yield .............................................................................................................................................................. .............................................................................................................................................................. .............................................................................................................................................................. [4]
The graph shows how the concentrations of all three species in the system change with time for a typical reaction mixture. The gradients of all three lines decrease with time and then level off in this dynamic equilibrium. [Image_3 - Graph] (ii) Explain why the gradients of the SO$_2$ and O$_2$ lines decrease with time. .............................................................................................................................................................. .............................................................................................................................................................. [2]
(iii) Explain why all three lines become horizontal. .............................................................................................................................................................. .............................................................................................................................................................. [1]
(iv) Suggest a reason why the initial gradient of the SO$_2$ line is steeper than that of the O$_2$ line. .............................................................................................................................................................. .............................................................................................................................................................. [1]
(d) 2.00 moles of SO$_2$(g) and 2.00 moles of O$_2$(g) are sealed in a container with a suitable catalyst, at constant temperature and pressure. The resulting equilibrium mixture contains 1.98 moles of SO$_3$(g). The total volume of the equilibrium mixture is 40.0 dm$^3$. $$2\text{SO}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{SO}_3(g)$$ (i) Write the expression for the equilibrium constant, $K_c$, for the reaction between SO$_2$(g) and O$_2$(g) to produce SO$_3$(g). $$K_c = ext{...........................}$$ [1]
(ii) Calculate the amount, in moles, of SO$_2$(g) and O$_2$(g) in the equilibrium mixture. $$\text{SO}_2(g) = \text{........................... mol}$$ $$\text{O}_2(g) = \text{........................... mol}$$ [2]
(iii) Use your answers to (d)(i) and (d)(ii) to calculate the value of $K_c$ for this equilibrium mixture. Give the units of $K_c$. $$K_c = \text{...........................}$$ $$\text{units} = \text{...........................}$$ [3]
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One reason for the wide variety of organic compounds is isomerism, either structural isomerism or stereoisomerism.
(a) (i) Explain the meaning of the term structural isomerism.
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(ii) Explain the meaning of the term stereoisomerism.
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(b) Pent-1-ene, $CH_2=CH(CH_2)_2CH_3$, does not show stereoisomerism.
(i) Give two reasons why pent-1-ene does not show stereoisomerism.
reason 1 ..........................................................................................................................
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reason 2 ..........................................................................................................................
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(ii) A structural isomer of pent-1-ene is used as the monomer to form a polymer. The repeat unit of this polymer is shown.
Draw the displayed formula of the monomer used to make this polymer.
Give the name of the monomer.
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(iii) A different structural isomer of pent-1-ene shows geometrical isomerism.
Draw the structure of one of the two geometrical isomers with the formula $C_5H_{10}$.
Give the full name of this isomer.
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(a) At room temperature fluorine and chlorine are gases, bromine is a liquid and iodine is a solid.
(i) State the trend in the volatility of the Group 17 elements down the group.
(ii) Explain this trend.
(b) Iodine, $I_2$, can be displaced from NaI(aq), by chlorine, $Cl_2$.
Write an equation for this reaction.
(c) Silver nitrate solution, $AgNO_3$(aq), is added to separate solutions of NaI and NaCl.
Precipitates form. An excess of aqueous ammonia is then added to both precipitates.
(i) Complete the table to give the colour and name of the precipitate formed in each reaction and the effect of the addition of an excess of aqueous ammonia to each of the precipitates formed.
(ii) Write an ionic equation, including state symbols, to show the reaction occurring when $AgNO_3$(aq) is added to NaI(aq).
(d) Solid NaI reacts with concentrated sulfuric acid to form purple fumes of $I_2$(g) and hydrogen sulfide gas, $H_2S$(g).
However, when solid NaCl reacts with concentrated sulfuric acid the only gas produced is HCl(g).
Explain the difference in the reactions of concentrated sulfuric acid with NaI and with NaCl. Your answer should refer to the role of the sulfuric acid in each reaction.
(e) Chlorine is commonly used in water purification. When chlorine is added to water it reacts to produce a mixture of acids, one of which is chloric(I) acid, HClO, a powerful oxidising agent.
(i) Explain the meaning of the term oxidising agent, in terms of electron transfer.
(ii) Suggest an equation for this reaction of chlorine with water.
(iii) Write an equation for the reaction of chlorine with hot aqueous sodium hydroxide.
Use oxidation numbers to explain why this is a redox reaction.
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A is $\text{CH}_3\text{CHBrCH}_2\text{CH}_3$.
(a) Some reactions of A are shown.
$$\text{CH}_3\text{CHBrCH}_2\text{CH}_3 \xrightarrow{\text{reaction 1}} \text{CH}_3\text{CH(OH)CH}_2\text{CH}_3 \xrightarrow{\text{H}^+/\text{Cr}_2\text{O}_7^{2-}} \text{C}_4\text{H}_8\text{O}$$
$$\text{A} \xrightarrow{\text{reaction 2 NaOH}} \text{C}_4\text{H}_8$$
(i) Name A.
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(ii) Name the class of compound to which B belongs.
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(b) There are three structural isomers of A.
Draw the structures of these three isomers of A.
[2]
(c) Reaction 1 occurs by two different mechanisms at the same time.
These mechanisms are referred to as $S_N1$ and $S_N2$.
(i) State what the letters ‘S’ and ‘N’ represent in the abbreviation $S_N1$.
S ..............................................................................................................................................
N .............................................................................................................................................. [1]
(ii) Complete the $S_N1$ mechanism for reaction 1.
Include the structure of the intermediate and all necessary charges, dipoles, lone pairs and curly arrows.
[3]
(d) The $S_N1$ mechanism for reaction 1 is repeated using $\text{CH}_3\text{CHClCH}_2\text{CH}_3$ or $\text{CH}_3\text{CHICH}_2\text{CH}_3$ in place of the $\text{CH}_3\text{CHBrCH}_2\text{CH}_3$.
State and explain how the rates of these two reactions will compare with the rate of the original reaction using $\text{CH}_3\text{CHBrCH}_2\text{CH}_3$.
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(e) Reaction 2 uses the same reagent as reaction 1, but under different conditions.
State two differences in the conditions needed to ensure that reaction 2 is more likely to take place than reaction 1 when this reagent is added.
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