Sulphur and its Compounds Questions and Answers - Chemistry Form 3 Topical Revision

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  1. Sulphur is extracted from underground deposits by a process in which three concentric pipes are sunk down to the deposits as shown below
    extraction of sulphur
    1. Name the process represented above
    2. What is passed down through pipe J?
    3. Name the two allotropes of sulphur
  2. Commercial sulphuric acid has a density of 1.8gcm3.
    1. Calculate the molarity of this acid
    2. Determine the volume of commercial acid in (a) above that can be used to prepare 500cm3 of 0.2M H2SO4 solution
  3. Oleum (H2S2O7) is an intermediate product in the industrial manufacture of sulphuric acid
    1. How is oleum converted into sulphuric (IV) acid?
    2. Give one use of sulphuric acid
  4. Differentiate between the bleaching action of chloride and sulphur (IV) oxide gas.
    1. Is concentrated sulphuric acid a weak acid or a strong acid?
    2. Explain your answer in (i) above.
  5. In the manufacture of sulphuric acid, sulphur (IV) oxide is oxidized to sulphur (VI) oxide.
    1. Name the catalyst used
    2. Write the equation representing the conversion of sulphur (IV) oxide to sulphur(VI)oxide
    3. Explain using equations how dilute sulphuric acid is finally obtained from sulphur (VI) oxide
  6. When a mixture of concentrated sulphuric acid and copper turnings is strongly heated, a colourless gas and solid mixture of white and black solids are formed. When this solid mixture is treated with distilled water, and filtered, a blue solution and black solid residue are collected. Explain the observations on the solid mixture formed in the above experiment
  7. The set-up below is used to prepare dry sulphur (IV) Oxide in the laboratory. Answer questions that follow:
    preparation of SO2
    1. Identify the mistake in the set-up
    2. Write an equation for the reaction in the set-up
    3. State how the polluting effects of the gas on the environment can be controlled
    1. State the observation made at the end of the experiment when a mixture of iron powder and sulphur are heated in a test-tube
    2. Write an equation for the reaction between the product in (a) above and dilute hydrochloric acid
    3. When a mixture of iron powder and sulphur is heated it glows more brightly than that of iron fillings and sulphur. Explain this observation
    1. Name one reagent that can be reacted with dilute hydrochloric acid to produce Sulphur (IV) oxide
    2. What would be observed if moist blue litmus paper is dropped into a gas jar of sulphur (IV) oxide? Explain your answer with an equation
    1. State two properties that vulcanized rubber posses as a result of vulcanization
    2. During Frasch process molten sulphur flows out through the middle pipe but not through the outer pipe. Give a reason
    1. Give two reasons why during the manufacture of sulphuric (VI) acid, sulphur (VI) Oxide, is dissolved in concentrated Sulphuric (VI) acid instead of dissolving in water
    2. State one use of sulphuric (VI) acid
  8. The diagram below may be used to react hydrogen sulphide and sulphur (IV) oxide.
    Study it and answer the questions that follow:-
    reaction between H2S and SO2
    1. What is observed in the jars
    2. Write an equation for the reaction
    3. What is the role of sulphur (IV) oxide in the reaction
  9. The diagram below shows the extraction of sulphur by Frasch process.
    frasch process
    1. State the uses of pipes A, B and C.
    2. Give two crystalliric allotropes of sulphur.
    3. Write an equation for the combustion of sulphur.
    4. Name the product formed when a mixture of sulphur and Iron is heated.
    5. Give two uses of sulphur.
    6. 6.0 dm3 of sulphur (IV) oxide were oxidized by oxygen to sulphur (VI) oxide.
      1. Write an equation for the reaction.
      2. Calculate the number of moles of sulphur (IV) oxide and oxygen used at R.T.P.
      3. Determine the volume of oxygen used. (Molar volume of a gas at R.T.P. is 24.0 dm3)
  10. The diagrams below represent two allotropes of Sulphur. Study them and answer the questions which follow:-
    allotropes of sulphur
    1. Name the two allotropes labelled X and Y
      1. Explain why a piece of burning magnesium continues to burn in a gas jar of Sulphur (IV) Oxide
      2. Explain how one of the products formed in (I) above can be obtained from the mixture
      1. Name the two crystalline forms of sulphur
      2. Briefly explain how plastic sulphur is formed
    1. The scheme below represents the steps followed in the contact process. Study it and answer the questions that follow:-
      scheme contact proces
      1. Name two possible identities of solid A
      2. Name one impurities removed by the purifier
      3. Why is it necessary to remove impurities?
      4. Write down the equation of the reaction taking place in the converter
        1. Name the two catalysts that can be used in the converter
        2. What is the function of heat exchanger?
      5. Sulphuric (VI) Oxide is not dissolved directly into water? Explain
        1. Name the main pollutant in the contact process.
        2. How can the pollution in vii (I) above be controlled?
      6. Give one use of sulphuric (VI) acid
  11. The set-up below was used to prepare dry sample of hydrogen sulphide gas
    preparation of hydrogen sulphide
      1. Complete the diagram to show how the gas was collected
      2. Identify the following:-
        1. Solid H ………………………………………………………………………………
        2. Solid I ……………………………………………………………………………..
      3. Write an equation for the reaction that occurred in the flask between solid H and dilute hydrochloric acid
    1. When hydrogen sulphide gas was passed through a solution of Iron (III) chloride, the following observations were made:-
      1. the colour of the solution changed from reddish-brown to green and
      2. a yellow solid was deposited. Explain the observation
    2. In the manufacture of Sulphuric (VI) acid by contact process sulphur (IV) oxide is made to react with air to form sulphur (VI) oxide as shown:-
      2SO2(g) + O2(g) ⇌ 2SO3(g) ΔH = -196KJ
      1. Name the catalyst in this reaction
      2. State and explain the effect of the following changes on the yield of sulphur (VI) oxide
        1. Increasing the pressure
        2. Using a catalyst
      3. Explain why sulphur (VI) oxide gas is absorbed in concentrated sulphur (VI) acid before dilution
  12. The flow chart below shows a sequence of chemical reactions starting with sulphur.
    Study it and answer the questions that follow:-
    reactions of sulphur
    1. State one observation made when the reaction in step 1 was in progress
    2. Explain why dilute hydrochloric acid cannot be used in step 1
    3. Write the equation for the reaction that took place in step 1
    4. Name the reactions that took place in step 4
    5. Name solution A ……………………………………………………………….
    6. State and explain the harmful effects on the environment of the gas C produced in step 1
    1. Sulphur occurs naturally in two different forms called allotropes;
      1. What are allotropes
      2. the two allotropes of sulphur are stable at different temperatures, as shown in the equations below.
                                      above 95.5o
        Rhombic sulphur           ⇌          monoclinic sulphur
                                     below 95.5º
        Give the name to the temperature 95.5ºC
    2. Below is a flow diagram for the contact process for manufacture of sulphuric acid(VI)
      flowchart manufacture of sulphuric acid
      1. Give the name of the chambers labelled (1½mks)
      2. State the three conditions in the converter (1½mks)
      3. Explain why the gases are passed though:
        1. The dust precipitator and drying power
        2. The chamber labeled Y
      4. Write the balanced equations for the reactions in :
        1. Step 2
        2. Step 3
        3. Step 4
  13. Study the figure below:
    State and explain the observations made in:
    Test tube L ………………………………………………………………..
    Test tube K ………………………………………………………………………..
  14. The set-up below was used to prepare and collect hydrogen sulphide gas. Study it and answer the questions that follow:-
    hydrogen sulphide collection and preparation
    1. Name solid V
    2. Give a reason why warm water is used in the set-up
  15. Sulphur (IV) oxide and nitrogen (II) oxide are some of the gases released from internal combustion engines. State how these gases affect the environment
  16. When hydrogen sulphide gas was bubbled into an aqueous solution of Iron (III) chloride, a yellow precipitate was formed.
    1. State another observation that was made.
    2. Write an equation for the reaction that took place.
    3. What type of reaction was undergone by hydrogen sulphide in this reaction?
  17. In an attempt to prepare Sulphur (IV) Oxide gas, dilute Sulphuric acid was reacted with barium carbonate. The yield of Sulphur dioxide was found to be negligible. Explain


    1. Frasch process
    2. Hot compressed air
    3. Monoclinic / prismatic sulphur /beta sulphur
      Rhombic/octahedral sulphur /alpha sulphur
    1. RFM of H2SO3 = 98 (no units)
      Number of moles of H2SO4 = 1.8/98
      = 0.01837moles
      Molarity of H2SO4 = 0.01837 x 1000
      = 18.37M
    2. Apply formular; M conc. × Vol conc. = Mdil. x Vdil.
      18.37 x V conc: = 0.2 x 500 Vconc. = 0.2 x 500
      = 5.44cm3 of conc. H2SO4
    1. By dissolving in water
    2. - Manufacture of fertilizers
      - Manufacture of detergents
      - Cleaning of metal surfaces
      - As an electrolyte in car batteries
      - In refining of petroleum
      - Manufacture of synthetic fibre (e.g. rayon)
      - Manufactures of paints, dyes and explosives (award 1mk any one)
  4. Chlorine bleaches permanently by oxidation ✓1 while sulphur (IV) oxide bleaches temporary by eduction. ✓1
    1. Weak acid ✓1
    2. Has few free H+ (Hydrogen) ions
    1. Vanadium (V) oxide V2O5½
    2. 2SO2 (g) + O2 (g) → 2SO3 (g)½
    3. SO3 (g) + H2SO4 (l) → H2S2O7 (l)
      H2S2O7(l) + H2O (l) → H2SO4(l)
      Student must explain Explanation 1 mark
  7. – Concentrated sulphuric acid oxidizes copper turnings to copper(II) oxide black solid,SO2 gas and water. ½ mk
    - Then copper (II) oxide reacts with excess conc. sulphuric acid to produce copper (II) sulphate mk
    - Which is dehydrated by conc. Sulphuric acid to an hydrous copper (II) sulphate white solid 1½
    Which dissolves in water to produce blue solution
    1. Method of collection is wrong. ½ Should be collected by downward delivery/upward displacement of air ½ since the gas is denser than air.
    2. Na2SO3(s) + H2SO4(aq) → Na2SO4(aq) + SO2(g) + H2O(l) 1
    3. By passing it through calcium hydroxide in which the gas dissolves. 1
    1. Dirty grey solids are formed. 1
    2. FeS(s) + 2HCl(aq) → FeCl2(aq) 1 + H2S(g)
    3. Iron powder has high surface area hence the reaction is none vigorous than iron fillings with low surface area.
    1. a sulphate e.g. sodium sulphate1
    2. moist blue litmus paper turns to red½ then after some minutes to white½ .it is bleached by ✓½ sulphur(iv)oxide
      SO2(g) + H2O(l) + Dye → H2SO4(aq) + (Dye-O)1
                              (litmus)                     (white)
    1. - Flexible /elastic
      - Strong and tough
      - Non-sticky (any two)
    2. Molten sulphur would have lost heat to the surrounding hence solidify/ in the middle pipe sulphur cannot solidify since hot air in the inner pipe and hot water in the outer pipe mountains high temperature.
    1. It dissolves in water releasing √1 a lot of heat which boils the acid which can easily be spilt to the body. √1 (2 mks)
    2. - It is used in manufacture √1 of batteries/acid accumulators. 
      - Manufacture of soap, plastics, detergents. any one
    1. Deposits of a yellow solid; and droplets of colourless liquid;
    2. 2H2S(aq) + SO(g) → 2H2O(l) + 3S(s)
    3. Oxidizing agent
    1. A – takes in hot compressed air to force out molten sulphur to the surface.
      B - takes out molten sulphur.
      C – takes in super heated water to melt the sulphur.
    2.  Rhombic, Monoclinic
    3. S(s) + O2(g) → SO2(g)
    4.  Iron (II) sulphide.
    5. – Vulcanization of rubber.
      - Making chemicals
      - Manufacture of matches and fire works.
      1. 2SO2(g) + O2(g) ⇌ 2SO3(g)
      2. 24 dm3 of SO2 = 1 mole
        6.0 dm3 = ?
        1 mol x 6 dm3 ✓ ½ = 0.25 mole ✓ ½
                24 dm3
        From the equation :-
        Moles of O2 used = 0.25/2 ✓½ = 0.125 moles ✓½
      3. 1 mole of O2 = 0.125
        0.25 mole = 24 dm3 x 0.125 mol ✓1
                                    1 mol
        = 3.dm3 ✓1
    1. X – Rhombic √½
      Y – Monoclinic √½
      1. Mg has a higher √1 √1 affinity for combined oxygen than S.
      2. Add √1 dilute nitric acid to the mixture. It reacts with MgO√1 to form Mg(NO3)2
        Filter √1 to obtain S as residue.
      1. – Rhombic sulphur (½ mk)
      2. Sulphur is heated until it boils. The boiling liquid sulphur is then poured into a beaker containing water to form plastic sulphur ( ½ mk)
      1. – sulphur (½ mk)
        - Iron (II) Sulphide (Iron pyrites)
        - Zinc sulphide (Zinc blend)
      2. - Dust or Arsenic compounds (½ mk)
    3. – Avoid poisoning of the catalyst (Avoid destruction of catalytic properties by impurities)
    4. 2SO2(g) + O2(g) → 2SO3(g)
      1. – Vanadinim (V) Oxide (½ mk)
      2. - Heat incoming air (SO2 & Air)
        - Cools the SO3
    6. - The reaction between SO2 and water is highly exothermic which makes the solution boil to form a mist of dilute sulphuric (VI) acid which pollutes the environment
      1. – SO2
      2. - Un reacted SO2 is recycled
        - Absorbed by Ca(OH)2 in tall chimneys
        - Passed over hot carbon (IV) Oxide and sulphur which is recycled and Carbon (IV) Oxide released to the environment
    8. Manufacture of fertilizers
        1. ion II sulphide or copper II Sulphur
        2. anhydrous Calcium Chloride (zero of Calcium chloride)
        3. FeS(l) + HCl(aq) → FeCl2(aq) + H2S(g)
    2. Fe3+ is reduced or Fe2+ or Fe2+(aq) ions and formed
      H2S is oxidized to sulphur on sulphur is formed.
      1. Vanadium V oxide or platinised asbestos
        1. The yield of SO3 increase because increase in pressure favour the forward reaction since less number of SO3
        2. The yield of SO3 is the same because catalyst only speeds the rate at which equibrium.
      3. Exothermic reaction occurs. When dissolved in water produce acid spray (fumes) cause pollution.
      1. Red-brown fumes
      2. It is not an oxidizing agent
      3. S(s) + 6HNO3(l) → 2H2O(l) + 6NO2(g) + H2SO4(l)
      4.  Neutralization
      5. Sulphuric acid
      6. Forms acid rain / plant + yellowing corrodes metallic and stone works
      1. They are different physical/ structural forms of an element
      2. Transition temperature
      1. X - Diluter
        Y- Heat exchanger
        Z- Roaster/ Burner
      2. Catalyst- Vanadium (V) Oxide, V2O5
        Temperature – 450oC
        Pressure – 1 atmosphere
        1. - They are purified not to poison the catalyst
        2. - The reaction in the convertor/ production of sulphur (VI) Oxide is exothermic/heat is produced. Chamber Y is used to ensure temperature does not rise above 450oC
      4. Step 2: 2S02(g) +O2(g) → 2S03(g) ✓ 1 mark
        Step 3: S03(g) + H2SO4(l) → H2S2O7(l) ✓ 1 mark
        Step 4: H2S2O7(l) + H2O(l) → 2H2SO4(l) ✓ 1 mark
  20. - Test tube L- Acidified KMnO4 changed from purple to colourless (it is decolourized) – SO2 is a reducing agent.
    - Test tube K H+/KMnO4 was not decoloured – SO2 was absorbed by ash solution hence did not reach the H+/KMnO4.
    1. Metal sulphide
    2. Hydrogen sulphide is less soluble in warm water compared to cold water
  22. SO2 form acidic when it dissolves in atmospheric moisture. The acidic rain lowers soil PH/ corrodes stone building
    No – disrupts the Ozone cycle hence causing depletion of Ozone layer which react with oxygen in the atmosphere to form NO2 gas
    1. The solution changed from brown/yellow ✓½ to light/pale green ✓½
    2. 2FeCl(aq) + H2S(g) → 2FeCl2(aq) + 2HCl(aq) + S(s) ✓1 mk
    3. Oxidation. ✓1 mk
  24. Barium carbonate reacts with dilute sulphuric (VI) acid to form the insoluble Barium sulphate (BaSO4) which covers the reactant. Barium Carbonate preventing any contact between the acid and the Carbonate salt.
    Hence, the reaction is slow and stops after a very short time.
    BaCO3(s) + H2SO4(aq) → BaSO4(s) + CO2(g) + H2O(l)
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