Chemical formulae, equations and calculations

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Question 80

A student wants to find the value of $x$ in hydrated copper(II) sulfate, $CuSO4⋅xH2O\text{CuSO}_4 \cdot x\text{H}_2\text{O}$ .

She uses this method:

weigh an empty crucible to find its mass
place a sample of hydrated copper(II) sulfate crystals into the crucible and reweigh
heat the crucible gently
allow the crucible to cool and reweigh
repeat the process until the mass no longer changes (heating to constant mass)

The crystals decompose according to this equation:

\text{CuSO}_4 \cdot x\text{H}_2\text{O} \rightarrow \text{CuSO}_4 + x\text{H}_2\text{O}

These are the student's results:

Mass of empty crucible: $g14.65\text{ g}$
Mass of crucible and $CuSO4⋅xH2O\text{CuSO}_4 \cdot x\text{H}_2\text{O}$ : $g19.65\text{ g}$
Mass of crucible and contents after heating to constant mass: $g17.85\text{ g}$

State why it is necessary to heat the crystals to constant mass.

[1]

Calculate the mass of $CuSO4\text{CuSO}_4$ formed after heating to constant mass.

[1]

Calculate the mass of water lost from the crystals.

[1]

Calculate the value for $x$ in the formula $CuSO4⋅xH2O\text{CuSO}_4 \cdot x\text{H}_2\text{O}$ . Give your answer to the nearest whole number.

[M_r\text{ of }\text{CuSO}_4 = 160; M_r\text{ of }\text{H}_2\text{O} = 18]

[3]

When water is added back to the anhydrous copper(II) sulfate, the student observes that the mixture gets warm and changes colour from white to blue. Explain these observations.

[2]

Chemical formulae, equations and calculations

Question 80

A student wants to find the value of $x$ in hydrated copper(II) sulfate, $CuSO4⋅xH2O\text{CuSO}_4 \cdot x\text{H}_2\text{O}$ .

She uses this method:

weigh an empty crucible to find its mass
place a sample of hydrated copper(II) sulfate crystals into the crucible and reweigh
heat the crucible gently
allow the crucible to cool and reweigh
repeat the process until the mass no longer changes (heating to constant mass)

The crystals decompose according to this equation:

\text{CuSO}_4 \cdot x\text{H}_2\text{O} \rightarrow \text{CuSO}_4 + x\text{H}_2\text{O}

These are the student's results:

Mass of empty crucible: $g14.65\text{ g}$
Mass of crucible and $CuSO4⋅xH2O\text{CuSO}_4 \cdot x\text{H}_2\text{O}$ : $g19.65\text{ g}$
Mass of crucible and contents after heating to constant mass: $g17.85\text{ g}$

State why it is necessary to heat the crystals to constant mass.

[1]

Calculate the mass of $CuSO4\text{CuSO}_4$ formed after heating to constant mass.

[1]

Calculate the mass of water lost from the crystals.

[1]

Calculate the value for $x$ in the formula $CuSO4⋅xH2O\text{CuSO}_4 \cdot x\text{H}_2\text{O}$ . Give your answer to the nearest whole number.

[M_r\text{ of }\text{CuSO}_4 = 160; M_r\text{ of }\text{H}_2\text{O} = 18]

[3]

When water is added back to the anhydrous copper(II) sulfate, the student observes that the mixture gets warm and changes colour from white to blue. Explain these observations.

[2]

Chemical formulae, equations and calculations

Question 80

Chemical formulae, equations and calculations Questions

Chemical formulae, equations and calculations

Question 80

Chemical formulae, equations and calculations Questions