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Edexcel IGCSE Chemistry 1.31 Experimental formulae

Practise deriving formulae from heating data, mass changes and mole ratios for oxides and hydrated salts with water of crystallisation.

Syllabus
First assessment 2019
Course
Chemistry 4CH1

Exam points

  • use mass loss on heating to calculate moles of water and find x in a hydrated salt
  • recognise constant mass as evidence that all water of crystallisation has been removed
  • use weighing data to separate masses of metal and oxygen before forming a mole ratio

1.31 Experimental formulae question 1

[Maximum number: 4]

Sodium sulfate can be prepared by the reaction between sodium hydroxide solution and sodium hydrogensulfate ( NaHSO4\mathrm{NaHSO}_{4} ) solution.

This is the equation for the reaction.

NaOH(aq)+NaHSO4(aq)→Na2SO4(aq)+H2O(l)\mathrm{NaOH}(\mathrm{aq})+\mathrm{NaHSO}_{4}(\mathrm{aq}) \rightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})

Sodium hydrogensulfate solution is acidic.
A student adds 25.0 cm325.0 \mathrm{~cm}^{3} of sodium hydroxide solution to a conical flask and adds two drops of indicator.

The student does a titration.

Crystals of hydrated sodium sulfate decompose when heated.

This is the equation for the decomposition.

Figure for Question 1.31 Experimental formulae question 1 — Edexcel IGCSE Chemistry

A student uses this apparatus to find the value of x .
hydrated sodium sulfate

Figure for Question 1.31 Experimental formulae question 1 — Edexcel IGCSE Chemistry

The student heats the crystals until the decomposition is complete.
The table shows the student's results.

Table for Question 1.31 Experimental formulae question 1 — Edexcel IGCSE Chemistry

Use the results to calculate the value of x .
[for Na2SO4,Mr=142\mathrm{Na}_{2} \mathrm{SO}_{4}, M_{\mathrm{r}}=142 for H2O,Mr=18\mathrm{H}_{2} \mathrm{O}, M_{\mathrm{r}}=18 ]


value of x=

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