Question
This question is about compounds of sulfur.
(a) Sulfuric acid, H2SO4, is manufactured using the Contact process. This manufacture involves four stages.
stage 1 Molten sulfur burns in air to produce sulfur dioxide.
stage 2 Sulfur dioxide reacts with oxygen to form sulfur trioxide.
stage 3 Sulfur trioxide combines with concentrated sulfuric acid to form oleum, H2S2O7.
stage 4 Oleum reacts to form concentrated sulfuric acid.
(i) Write a chemical equation for the reaction occurring in stage 1.[1]
(ii) State the essential conditions that are necessary for stage 2. Write an equation for the chemical reaction that occurs.[4]
(iii) Write a chemical equation for the reaction occurring in stage 3.[1]
(iv) Name the substance that reacts with oleum in stage 4.[1]
(b) Hydrogen sulfide has the formula H2S.
(i) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of hydrogen sulfide. Show outer shell electrons only.[2]
(ii) Balance the chemical equation for the reaction of hydrogen sulfide with sulfur dioxide shown.
H2S + SO2 → S + H2O [1] [Total: 10]
Answer/Explanation
Ans:
4(a)(i) S + O2 → SO2
4(a)(ii) (temperature) 450 °C (1)
(pressure) 1–2 atmosphere(s) (1)
vanadium(V) oxide catalyst (1)
2SO2 + O2 ⇌ 2SO3 (1)
4(a)(iii) SO3 + H2SO4 → H2S2O7
4(a)(iv) water
4(b)(i) 2 bonding pairs as one dot and cross each (1)
2 lone pairs on S (and no additional electrons on Hs) to complete the outer shell on S and both Hs (1)
4(b)(ii) 2H2S + SO2 →3S +2H2O
Question
Zinc is extracted from an ore containing zinc sulfide.
(a) State the name of this zinc ore…………………………………………………………………………………………………………………………….. [1]
(b) This ore is converted to zinc oxide, ZnO.
Zinc oxide is then reacted with carbon.
(i) Write a chemical equation for the reaction of zinc oxide with carbon………………………………………………………………………………………………………………………. [1]
(ii) State what type of chemical change happens to the zinc in zinc oxide in this reaction.
Explain your answer.
chemical change …………………………………………………………………………………………………..
explanation ……………………………………………………………………………………………………………………………………………………………………………………………………………………………………….[2]
(iii) Explain why aluminium is not extracted from aluminium oxide by heating with carbon………………………………………………………………………………………………………………………. [1]
(iv) Suggest an alternative method for the extraction of zinc from zinc oxide……………………………………………………………………………………………………………………… [1]
(c) Brass is an alloy of zinc.
Explain, in terms of particles, why brass is harder than pure zinc…………………………………………………………………………………………………………………………….. [3]
▶️Answer/Explanation
Ans:
2(a) zinc blende
2(b)(i) $\begin{aligned} & \mathrm{ZnO}+\mathrm{C} \rightarrow \mathrm{Zn}+\mathrm{CO} \\ & \text { or } \\ & 2 \mathrm{ZnO}+\mathrm{C} \rightarrow 2 \mathrm{Zn}+\mathrm{CO}_2\end{aligned}$
2(b)(ii) chemical change: reduction (1)
explanation: oxygen is lost (1)
2(b)(iii) aluminium is more reactive than carbon
2(b)(iv) electrolysis
2(c) exists as layers (1)
(alloy) contains different sized (copper) atoms (1)
makes it more difficult for layers (of atoms) to slide over each slip/shift other (1)
Question
Iron is a typical transition element.
Iron:
● acts as a catalyst
● forms coloured compounds
● has more than one oxidation state.
(a) Name one major industrial process that uses iron as a catalyst and name the product made in
this process.
process ……………………………………………………………………………………………………………………..
product made ……………………………………………………………………………………………………………..
(b) When aqueous sodium hydroxide is added to aqueous iron(II) sulfate, a precipitate forms.
(i) What colour is this precipitate?
(ii) Write the ionic equation for this reaction. Include state symbols.
(c) Iron(II) sulfate can be converted to iron(III) sulfate by potassium manganate(VII) at room
temperature.
(i) What is the role of potassium manganate(VII) in this reaction?
(ii) What condition must be used for this reaction to occur?
(iii) In terms of electron transfer, what happens to the iron(II) ions in this reaction?
(iv) State the colour change seen during this reaction.
from purple to …………………………………………………………………………………………………
(d) Deduce the charge on the iron ion in each of these compounds.
\(FeF_3\) ………………………………………………………………………………………………………………………….
\(Fe(NO_3)_3\) ……………………………………………………………………………………………………………………
Answer/Explanation
Answer:
(a) Haber (process) (1)
ammonia (1)
(b) (i) green
(ii) \(Fe^{2+}(aq) + 2OH^–(aq) \rightarrow Fe(OH)_2(s)\)
\(Fe(OH)_2\) (as only product) (1)
\(Fe^{2+}\) and \(2OH^–\) (as reactants) (1)
state symbols (1)
(c) (i) oxidising agent
(ii) presence of an acid
(iii) lose an electron
(iv) colourless
(d) 3+
3+