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
- A mixture of 2.5g of hydrogen and 142g of chlorine is allowed to react.
- Which gas, hydrogen or chlorine, is in excess? Explain your answer.
- Calculate the energy released when 2.5g of hydrogen reacts completely with chlorine gas.
- 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.
- Explain why the same volume of gas was evolved in each case…….[1]
- Explain why the reaction was faster with the sulphuric acid……[1]
- 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.
- A copper (II) sulphate fungicide solution should not be restored in a can made of galvanised iron……[1]
- Fruits and vegetables that are being transported from one port to another on ships are stored in an atmosphere of nitrogen……[1]
- Although lime, calcium oxide is not a fertiliser, it is still added to the soil by farmers to help some crops grow better……[1]
- 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
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- Chlorine is in excess;
According to the equation, 1.25 moles of H2 requires only 1.25 moles of chlorine - No. of moles of H2 = 1.25.
-184 x 1.25moles = -230 kJ;
230 kJ released
- Chlorine is in excess;
- 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
- Same amount of magnesium carbonate is used. It is the limiting reagent.
- There are twice as much of hydrogen ions in sulphuric acid as compared to hydrochloric acid. Thus, reaction is faster.
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- pour the magnesium sulphate solution into an evaporating dish.
- Heat to evaporate most of the water to obtain a saturated solution.
- Cool saturated solution to obtain magnesium sulphate crystals
Question 3
- The zinc coating on iron can displace copper from copper (II) sulphate solution.
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- To prevent the fruits and vegetables to be oxidized by air.
- To prevent the fruits and vegetables to be oxidized by air.
- Lime is added to neutralize the acid in the soil.
- Aluminium is protected by a layer of aluminium oxide which adheres strongly on the surface, Iron corrodes in damp air.
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