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2 marksThe Mole Concept

CAPE Chemistry Unit 1 · 2021 · Paper 2 · Question 1(e)(ii)

Ammonium sulfate reacts with aqueous sodium hydroxide according to (NH4)2SO4 + 2NaOH -> 2NH3 + Na2SO4 + 2H2O. A sample of ammonium sulfate was heated with 100 cm³ of 0.500 mol dm⁻³ NaOH(aq) to ensure excess. Heating continued until all NH3 boiled off. The remaining unreacted NaOH required 27.3 cm³ of 0.600 mol dm⁻³ HCl for neutralization.

Calculate the number of moles of HCl in 27.3 cm³ of 0.600 mol dm⁻³ hydrochloric acid.

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  1. 1(a)(i)Define the term 'radioactive isotope'.[1 mark]
  2. 1(a)(ii)Give the names and symbols for TWO other forms of radioactive emissions.[2 marks]
  3. 1(a)(iii)List THREE uses of radioactive isotopes.[3 marks]
  4. 1(a)(iv)Determine the value of A and Z in the equation: ^{241}_{95}\text{Am} \rightarrow \text{ }^{A}_{Z}\text{Np} + \text{ }^{4}_{2}\text{He} + \text{energy}[2 marks]
  5. 1(b)The element rhenium consists of two isotopes ^{185}\text{Re} and ^{187}\text{Re}, in the atomic ratio of 2:3. Calculate the relative atomic mass of rhenium to…[2 marks]
  6. 1(c)(i)List TWO chemicals and ONE piece of apparatus that the student may use to carry out the investigation.[3 marks]
  7. 1(c)(ii)Describe ONE physical change that the student may observe while carrying out the investigation.[1 mark]
  8. 1(c)(iii)Identify the oxidizing agent that the student may use while conducting the investigation.[1 mark]
  9. 1(c)(iv)Write relevant half equations to illustrate the chemical changes that occur with EACH element used to carry out the investigation.[2 marks]
  10. 1(d)(i)Define the term 'Molar mass'.[1 mark]
  11. 1(d)(ii)Define the term 'Mole'.[1 mark]
  12. 1(e)(i)Calculate the original number of moles of NaOH in 100 cm³ of 0.500 mol dm⁻³ aqueous sodium hydroxide.[2 marks]
  13. 1(e)(iii)Deduce the number of moles of unreacted NaOH neutralized by the hydrochloric acid.[1 mark]
  14. 1(e)(iv)Calculate the number of moles of NaOH which reacted with the ammonium sulfate.[2 marks]
  15. 1(e)(v)Use your answer in (e)(iv) to calculate the number of moles and the mass of ammonium sulfate in the sample.[3 marks]
  16. 1(e)(vi)Write the ionic equation, including physical states, for the reaction between ammonium sulfate and aqueous sodium hydroxide.[1 mark]

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