10 Nov A Level | IP Chemistry Tuition

Question And Answer

Question 1

Hydrogen reacts with chlorine to make hydrogen chloride. The reaction is exothermic.
The reaction can be represented by the equation below.

H-H + Cl-Cl  H-Cl + H-Cl ∆H = – 184 kJ/mol

1. A mixture of 2.5g of hydrogen and 142g of chlorine is allowed to react.
   1. Which gas, hydrogen or chlorine, is in excess? Explain your answer.
   2. Calculate the energy released when 2.5g of hydrogen reacts completely with chlorine gas.
2. Explain why the reaction is exothermic, in terms of the energy changes that take place during bond breaking and bond making.

Question 2

A sample of powdered magnesium carbonate was divided into two equal portions. One portion was added to an excess of 2 mol/dm3 hydrochloric acid. The second portion was added to an excess of 2 mol/dm3 sulphuric acid. The same volume of gas was evolved in each case but the gas was produced more rapidly from the reaction with sulphuric acid.

1. Explain why the same volume of gas was evolved in each case…….[1]
2. Explain why the reaction was faster with the sulphuric acid……[1]
3. Describe the method you would use to obtain a pure sample of salt when magnesium carbonate reacts with sulphuric acid…….[2]

Question 3

Explain each of the following.

1. A copper (II) sulphate fungicide solution should not be restored in a can made of galvanised iron……[1]
2. Fruits and vegetables that are being transported from one port to another on ships are stored in an atmosphere of nitrogen……[1]
3. Although lime, calcium oxide is not a fertiliser, it is still added to the soil by farmers to help some crops grow better……[1]
4. Although aluminium is more reactive than iron, aluminium cans do not corrode as much as iron cans in damp air……[1]

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Did you answer the Chemistry Tuition Question correctly?

Question 1

1. 1. Chlorine is in excess;
      According to the equation, 1.25 moles of H2 requires only 1.25 moles of chlorine
   2. No. of moles of H2 = 1.25.
      -184 x 1.25moles = -230 kJ;
      230 kJ released
2. Energy released in bond formation of 2 moles of H-Cl is greater; than the energy required to break 1 mole of H-H; and 1 mole of Cl-Cl bonds.

Question 2

1. Same amount of magnesium carbonate is used. It is the limiting reagent.
2. There are twice as much of hydrogen ions in sulphuric acid as compared to hydrochloric acid. Thus, reaction is faster.
3. 1. pour the magnesium sulphate solution into an evaporating dish.
   2. Heat to evaporate most of the water to obtain a saturated solution.
   3. Cool saturated solution to obtain magnesium sulphate crystals

Question 3

1. The zinc coating on iron can displace copper from copper (II) sulphate solution.
2. 1. To prevent the fruits and vegetables to be oxidized by air.
   2. To prevent the fruits and vegetables to be oxidized by air.
3. Lime is added to neutralize the acid in the soil.
4. Aluminium is protected by a layer of aluminium oxide which adheres strongly on the surface, Iron corrodes in damp air.

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