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Transition elements

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Question 3

Tutton's salts are 'double salts' with the formula X2Y(ZO4)2⋅6H2O\text{X}_2\text{Y}(\text{ZO}_4)_2 \cdot 6\text{H}_2\text{O}X2​Y(ZO4​)2​⋅6H2​O.

A Tutton's salt contains two cations: X+\text{X}^+X+ and Y2+\text{Y}^{2+}Y2+.

  • X+\text{X}^+X+ can be an ion of the Group 1 elements K\text{K}K, Rb\text{Rb}Rb, Cs\text{Cs}Cs or Fr\text{Fr}Fr, or an ammonium ion (NH4+\text{NH}_4^+NH4+​).
  • Y2+\text{Y}^{2+}Y2+ can be a 2+2+2+ ion of magnesium or an ion of most of the transition elements in Period 4.
  • Z\text{Z}Z can be S\text{S}S or Cr\text{Cr}Cr.

(NH4)2Cu(SO4)2⋅6H2O(\text{NH}_4)_2\text{Cu}(\text{SO}_4)_2 \cdot 6\text{H}_2\text{O}(NH4​)2​Cu(SO4​)2​⋅6H2​O is an example of a Tutton's salt.

a.

Predict the formula of a Tutton's salt containing different ions from (NH4)2Cu(SO4)2⋅6H2O(\text{NH}_4)_2\text{Cu}(\text{SO}_4)_2 \cdot 6\text{H}_2\text{O}(NH4​)2​Cu(SO4​)2​⋅6H2​O.

[1]
b.

A student prepares a sample of the Tutton's salt, (NH4)2Cu(SO4)2⋅6H2O(\text{NH}_4)_2\text{Cu}(\text{SO}_4)_2 \cdot 6\text{H}_2\text{O}(NH4​)2​Cu(SO4​)2​⋅6H2​O using the method shown below.

  • Step 1: Dissolve 0.035 mol0.035\text{ mol}0.035 mol of ammonium sulfate and 0.035 mol0.035\text{ mol}0.035 mol of hydrated copper(II) sulfate, CuSO4⋅5H2O\text{CuSO}_4 \cdot 5\text{H}_2\text{O}CuSO4​⋅5H2​O, in water and make up to 100 cm3100\text{ cm}^3100 cm3.
  • Step 2: Heat the resulting mixture for 2 minutes and allow to cool.
  • Step 3: Allow the solvent to evaporate slowly. Light-blue crystals of the Tutton's salt form.

What masses are needed of ammonium sulfate and CuSO4⋅5H2O\text{CuSO}_4 \cdot 5\text{H}_2\text{O}CuSO4​⋅5H2​O?

  • mass of ammonium sulfate
  • mass of CuSO4⋅5H2O\text{CuSO}_4 \cdot 5\text{H}_2\text{O}CuSO4​⋅5H2​O
[2]
c.

In Step 3, why does the student allow the solvent to evaporate and not boil off all the solvent in Step 2?

[1]
d.

The student dissolves their Tutton's salt in water. A pale-blue solution forms.

The student carries out two tests on this aqueous solution.

The student adds an excess of aqueous ammonia to their aqueous solution of Tutton's salt. A deep-blue solution forms.

The complex ion responsible for the deep-blue solution has a molar mass of 167.5 g mol−1167.5\text{ g mol}^{-1}167.5 g mol−1.

Suggest the formula of this complex ion.

[1]
e.

The student adds NaOH(aq)\text{NaOH(aq)}NaOH(aq) to the aqueous solution of Tutton's salt and warms the mixture.

A precipitate and a gas are formed.

Write the formulae of the precipitate and gas and suggest a test that could confirm the identity of the gas.

  • Formula of precipitate
  • Formula of gas
  • Test to confirm the identity of the gas
[3]
f.

How could the student carry out a test-tube test to confirm the anion in the Tutton's salt?

[1]

Transition elements Questions

  1. A Level
  2. /Chemistry
  3. /Transition elements