You're viewing 1 free preview question for Chemistry SL — subscribe to unlock 103 more, plus the Full Question Bank, Mock Papers & Worksheets.Upgrade

Counting Particles by Mass: The Mole · Paper 2 — Free Chemistry SL Practice Questions

1ChallengeSAQ-LMolar mass and its calculation20 marksPaper 2~30 min

A student investigates the composition of hydrated magnesium sulfate,

\text{MgSO}_4 \cdot n\text{H}_2\text{O}

. The student places a clean, dry crucible on a balance and records a mass of

18.24\,\text{g}

. A sample of the hydrated salt is added and the new mass recorded as

28.76\,\text{g}

. The crucible and contents are heated strongly for several minutes to drive off all water of crystallisation, then cooled in a desiccator. The final mass of the crucible and anhydrous salt is

23.54\,\text{g}

M(\text{MgSO}_4) = 120.4\,\text{g\,mol}^{-1} \qquad M(\text{H}_2\text{O}) = 18.02\,\text{g\,mol}^{-1}

(a)

Calculate the number of moles of water of crystallisation lost and the number of moles of anhydrous

\text{MgSO}_4

remaining. Hence determine the value of

n

\text{MgSO}_4 \cdot n\text{H}_2\text{O}

. [5 marks]

(b)

Explain why the student cooled the crucible in a desiccator rather than on the laboratory bench. [2 marks]

(c)

The student's calculated value of

n

6.6

. Evaluate whether this result supports the accepted formula

\text{MgSO}_4 \cdot 7\text{H}_2\text{O}

, and identify one source of systematic error that could account for the discrepancy. [2 marks]

(d)

State one specific modification to the procedure that would improve the reliability of the value of

n

obtained, and explain how it achieves this. [2] Total: [11 marks]

Solutions

Questions 2-104

Unlock these questions with Premium

That's every free question here — 1 of 104.

+103 more questions, plus Mock Papers & Worksheets, are waiting in Premium.

Upgrade