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(a) Dust particles in the air move around in a random way.
(i) What term describes the random movement of the dust particles?
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(ii) Identify the particles in the air which cause the random movement of the dust particles.
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(iii) Explain why the dust particles move in this way.
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(b) When chlorine gas, $Cl_2$, is put into a gas jar, it spreads out to fill the gas jar.
When bromine gas, $Br_2$, is put into a gas jar, it also spreads out to fill the gas jar.
The process takes longer for bromine gas than for chlorine gas.
(i) What term describes the way that the gas particles spread out?
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(ii) Use data from the Periodic Table to explain why bromine gas takes longer to fill a gas jar than chlorine gas.
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(iii) Explain why increasing the temperature increases the rate at which the gas particles spread out.
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(a) Complete the table to show the electronic structure of the atoms and ions.
[Table_1]
F: 2,7
Si:
Ca^{2+}:
N^{3-}:
[3]
(b) Predict the formula of the compound formed between Ca^{2+} and N^{3-}.
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(c) Draw a dot-and-cross diagram to show the electron arrangements in the two ions present in lithium chloride, LiCl.
Show outer shell electrons only. Include the charges on the ions. [3]
(d) Sulfur dichloride, SCl_{2}, is a covalent compound. It has the structure Cl–S–Cl.
Draw a dot-and-cross diagram to show the electron arrangement in a molecule of sulfur dichloride.
Show outer shell electrons only. [3]
(e) In terms of attractive forces, explain why LiCl has a higher melting point than SCl_{2}.
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(f) Suggest the identity of a covalent compound with a higher melting point than LiCl.
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The chemical equation for the complete combustion of ethanol, C₂H₅OH, is shown.
C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
The energy released when one mole of ethanol undergoes complete combustion is 1280 kJ.
Part of the energy level diagram for this reaction is shown.
(a) Complete the energy level diagram to show
• the products of the reaction,
• the overall energy change of the reaction. [3]
(b) What does X represent? [1]
(c) The chemical equation for the complete combustion of methanol, CH₃OH, is shown.
2CH₃OH + 3O₂ → 2CO₂ + 4H₂O
The equation can be represented as shown.
Use the bond energies in the table to determine the energy change, ΔH, for the complete combustion of one mole of methanol.
[Table_1]
• energy needed to break bonds ..................... kJ
• energy released when bonds are formed ..................... kJ
• energy change, ΔH, for the complete combustion of one mole of methanol ..................... kJ/mol [4]
(d) Dodecane is an alkane containing 12 carbon atoms. Ethanol can be manufactured from dodecane in a two-stage process.
In stage 1, each molecule of dodecane is converted into three molecules of ethene and one molecule of another hydrocarbon.
(i) Name the process which occurs in stage 1. [1]
(ii) Write a chemical equation for the reaction which occurs in stage 1. [2]
In stage 2, ethene reacts with steam to produce ethanol.
(iii) State two conditions needed for stage 2.
1 ...............................................................
2 ............................................................... [2]
(iv) Name the type of reaction which occurs in stage 2. [1]
(v) Suggest how to test the purity of the ethanol produced. [2]
(e) Ethanol can also be manufactured by the fermentation of glucose, C₆H₁₂O₆.
(i) State two conditions needed for the fermentation of glucose.
1 ...............................................................
2 ............................................................... [2]
(ii) Complete the chemical equation for the fermentation of glucose.
C₆H₁₂O₆ → ......C₂H₅OH + ............................ [2]
(iii) One disadvantage of fermentation is that the maximum concentration of ethanol produced is about 15%.
Suggest why the concentration of ethanol produced by fermentation does not exceed 15%. [1]
(iv) Give one other disadvantage of manufacturing ethanol by fermentation. [1]
(v) Give one advantage, other than cost, of manufacturing ethanol by fermentation. [1]
(vi) Suggest the name of a process to obtain ethanol from a mixture of ethanol and water. [1]
(f) Ethane-1,2-diol has the following structure.
(i) Write the empirical formula of ethane-1,2-diol. [1]
(ii) Ethane-1,2-diol can undergo condensation polymerisation but cannot undergo addition polymerisation.
Explain why ethane-1,2-diol cannot undergo addition polymerisation. [1]
(iii) Ethane-1,2-diol undergoes condensation polymerisation with molecule Y.
The diagrams represent the structures of ethane-1,2-diol and molecule Y.
Draw the condensation polymer formed between ethane-1,2-diol and molecule Y. Show one repeat unit. Show all of the atoms and all of the bonds in the linkage. [3]
(iv) Name the type of condensation polymer formed between ethane-1,2-diol and molecule Y. [1]
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A student sets up the following electrolysis experiment.
(a) Define the term electrolysis.
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(b) The student observes bubbles of colourless gas forming at each electrode.
(i) Name the main gas produced at the positive electrode (anode).
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(ii) Describe a test for the gas produced in (b)(i).
test ................................................................................................................................................
result .............................................................................................................................................. [2]
(iii) Write the ionic half-equation for the reaction taking place at the negative electrode (cathode).
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(c) Charge is transferred during electrolysis.
Name the type of particle responsible for the transfer of charge in
the wires, .......................................................................................................................................
the electrolyte. ............................................................................................................................... [2]
(d) The student replaces the dilute aqueous sodium chloride with concentrated aqueous sodium chloride.
Suggest two differences that the student observes.
1 ....................................................................................................................................................
2 .................................................................................................................................................... [2]
(e) The student has a small piece of impure copper. The main impurities in the copper are small quantities of silver and zinc.
The student uses electrolysis to extract pure copper from the small piece of impure copper.
(i) Complete the labels on the diagram of the student’s electrolysis experiment.
(ii) Use your knowledge of the reactivity series to suggest what happens to the silver and zinc impurities. Explain your answers.
silver impurities ..............................................................................................................................
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zinc impurities ................................................................................................................................
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(a) Aqueous potassium chromate(VI), $K_2CrO_4$, is a yellow solution.
Aqueous potassium dichromate(VI), $K_2Cr_2O_7$, is an orange solution.
The two compounds interconvert when the pH of the solution changes.
$2K_2CrO_4 + H_2SO_4 \rightleftharpoons K_2Cr_2O_7 + K_2SO_4 + H_2O$
yellow
Solution Y is a mixture of aqueous potassium chromate(VI) and aqueous potassium dichromate(VI) at equilibrium.
● Explain, in terms of the position of the equilibrium, what you would see if sulfuric acid were added to solution Y.
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● Explain, in terms of the position of the equilibrium, what you would see if sodium hydroxide were added to solution Y.
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(b) Hydrogen can be manufactured using a reversible reaction between methane and steam.
$CH_4(g) + H_2O(g) \rightleftharpoons CO(g) + 3H_2(g)$
At 900°C, in the presence of a nickel catalyst, the yield of hydrogen is 70%.
(i) What volume of hydrogen is produced from 100 cm3 of methane under these conditions?.............................. cm3 [2]
Under different conditions, different yields of hydrogen are obtained.
(ii) If the pressure is increased, the yield of hydrogen becomes less than 70%.
Explain why, in terms of the position of the equilibrium.
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(iii) If the temperature is decreased, the yield of hydrogen decreases.
What does this information indicate about the reaction between methane and steam?
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(iv) Why is a catalyst used in this reaction?
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