Quick questions on Mole calculations and reacting masses: N(A)-Level Chemistry

6short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What is the standard reacting-mass method?

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Almost every reacting-mass question follows the same four steps:

What is concentration of a solution?

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The concentration tells you how much solute is dissolved in a given volume. It is measured in moles per cubic decimetre. The relationship is:

What is percentage yield?

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In real experiments you rarely collect all of the product, so the percentage yield compares what you got to what you should have got:

What is q1?

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Calculate the number of moles in

250\ \text{cm}^3

of a solution of concentration

0.2\ \text{mol per dm}^3

. [2 marks]

What is q2?

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Magnesium reacts with oxygen:

2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}

. Calculate the mass of magnesium oxide formed from

0.2\ \text{mol}

of magnesium (

M_r

of MgO = 40). [2 marks]

What is q3?

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A reaction should give

50\ \text{g}

of product but only

45\ \text{g}

is collected. Calculate the percentage yield. [1 mark]

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