Edexcel IGCSE Chemistry 1.31 Experimental Formulae Questions

Practise using measured salt and water masses to find hydration numbers, checking for constant mass and explaining how incomplete heating affects the result.

Exam points

Use measured salt and water masses to calculate their mole ratio and the hydration number x
Repeat heating, cooling and weighing to constant mass to check that no more water is released
Subtract the tube mass to find the metal mass and use mass loss to find the oxygen removed
Explain how incomplete heating leaves water behind and makes the calculated hydration number too low

[Maximum number: 4]

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

This is the equation for the reaction.

\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 $25.0 \mathrm{~cm}^{3}$ 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 Edexcel IGCSE Chemistry 1.31 Experimental Formulae Questions question 1 — Edexcel IGCSE Chemistry

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

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

Table for Question Edexcel IGCSE Chemistry 1.31 Experimental Formulae Questions question 1 — Edexcel IGCSE Chemistry

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

value of x=

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Edexcel IGCSE Chemistry 1.31 Experimental Formulae Questions question 1