Form 4 Term 1 2017 Chemistry Paper 2 Exam Set 5 [PDF] with Marking Scheme

Question 1

Use the grid below to answer the questions that follow. Letters do not represent the actual symbol of the elements.

What family name is given to elements G and H?
State and explain the difference in reactivity between.
1. I and J
2. N and P
How does atomic radius of K compare to that of L? Explain.
Explain the trend in melting points down the group of elements to which I and J belong.
Write down an equation for the reaction between K and P.
Give one use of element Q.
Write down the electronic arrangement of a stable ion of H.

Answer

Alkali metals
State and explain the difference in reactivity between.
1. J is more reactive than I because J loses valence electrons more easily since it has more occupied energy levels
2. P is more reactive than N because P gains an electron more easily it has a smaller atomic radius than N
K has a larger atomic radius because it has a weaker nuclear charge attraction than L
Melting point decreases down the group because metallic bonding weakens as atomic size increases down the group
2K_(s) + 3P_2(g) → 2KP_3(s) OR
2Al_(s) + 3Cl_2(g) → 2AlCl_3(s)
In light bulbs to prevent oxidation of the filament As an insulator in arch-welding
2.8.8

Question 2

The set-up below was used during the electrolysis of aqueous magnesium sulphate using inert electrodes.

1. Name a suitable pair of electrodes for this experiment.
2. Identify the anions and cations in the solution
3. On the diagram label the cathode.
4. Write an equation for the reaction that took place at the cathode.
5. Explain the change that occurred to the concentration of magnesium sulphate solution during the experiment
6. During the electrolysis, a current of 2 amperes was passed through the solution for 4 hours. Calculate the volume of the gas produced at the cathode. (1 Faraday= 96500 coulombs , molar volume of a gas at room temperature = 24000cm3)
7. One of the uses of electrolysis is electroplating.
8. Give two reasons why electroplating is necessary.
1. On the diagram, show with a (+) sign the positive terminal
2. Write the equation for the reaction in which electrons are produced
3. Give one disadvantage of dry cells.

Answer

Question 3

The scheme below shows the industrial manufacture of sulphuric (VI) acid. Study it and answer the questions that follow.

1. State two functions of the chamber A.
2. Explain why concentrated Sulphuric (VI) acid is used in the absorption chamber and not water
3. Write the equation for the reaction that takes place at the absorption chamber
4. Name two catalysts that can be used in the catalytic chamber
Sulphuric (VI) acid is used in making fertilizers. What volume of ammonia gas will be required to make 25kg of ammonium sulphate?( N = 14, H = 1.0, S = 32, O = 16.0 Molar gas volume at r.t.p=24.0dm3)
The equation below shows the oxidation of Sulphur (IV) oxide to Sulphur (VI) oxide in the contact process.
2SO₂_(g) + O_2(g) → 2SO₃_(g) ∆H = -196kJ/mol-
1. State and explain the effect on the yield of Sulphur (IV) oxide when.
  1. the temperature increased.
  2. the amount of oxygen is increase

Answer

1. Preheating of gases / cooling of gases
2. Reaction with water is exothermic, heat generated boils the acid forming tiny misty droplets in air
3. SO₃_(g)+H₂SO_4(l)→ H₂S₂O₇_(l)
4. Platinum and Vanadium (V) oxide
1. 1. Yield decreases 1 forward reaction is exothermic
  2. Yield increases 1 Oxygen reacts with Sulphur (IV) oxide forming more Sulphur (VI) oxide

Question 4

Study the following table and then use it to answer the questions that follow.

These organic compounds belong to the same homologous series
1. What is meant by the term homologous series?
2. Select one hydrocarbon that would be a liquid at room temperature
3. Compare the boiling point of CH₄ and C₆H₁₄ ? Explain your answer
4. Give one chemical test to distinguish between C₂H₆ and C₂H₄
Study the scheme below and answer the questions that follow
1. Name the reagents used in Step I Step II
2. Write an equation for the complete combustion of CH≡CH
3. Explain one disadvantage of the continued use of items made from the compound formed in Step III

Answer

1. Group of compounds with similar chemical properties, chemical formulae and they exhibit a steady gradual change in physical properties
2. Alkanes
3. C₆H₁₄
4. C₆H₁₄ has a higher boiling point than CH₄ it has more carbon atoms thus increased strength of the Van der Waals forces
5. Bubble both substances separately into acidified pottasium manganate(VII) or potassium chromate(VI) solution solution turns from purple to colourless in C₂H₄ and remains purple in C₂H₆ /turns from orange to green in C₂H₄ and remains green in C₂H₄
1. Step I hydrogen gas
  Step II hydrogen chloride
2. C₂H_2(g) + O_2(g) → CO_2(g) + H₂O_(l)
3. they cause environmental pollution because they are non biodegradable.

Question 5

Study the flow diagram below and answer the questions that follow:-

1. Describe how nitrogen is obtained from air
2. Name the element M
3. Write an equation for the reaction in step 7
4. State two uses of ammonia gas
State and explain the observations made if a sample of sulphur is heated in concentrated Nitric(V) Acid

Answer

1. - First pass the air through concentrated potassium hydroxide or sodium hydroxide which absorbs carbon (iv)oxide
  - The remaining part of air is then passed over heated copper turnings to remove oxygen
  - The residual gas is then collected
2. Hydrogen gas
3. To ensure all the ammonia gas is oxidized to NO₂
4. - as a fertilizer
Red brown fumes are seen…this is because the nitric(v)acid is reduced to nitrogen(iv) oxide

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Form 4 Term 1 2017 Chemistry Paper 2 Exam Set 5 [PDF]