IB Chemistry HL R2.1 How much? The amount of chemical change questions

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Question 1

Paper 2Medium7 marks

A student prepares magnesium hydroxide by mixing aqueous magnesium chloride with aqueous sodium hydroxide. The reaction is

\ceMgCl2(aq)+2NaOH(aq)−>Mg(OH)2(s)+2NaCl(aq)\ce{MgCl2(aq) + 2NaOH(aq) -> Mg(OH)2(s) + 2NaCl(aq)}

Figure 1 shows the quantities used and the mass of solid collected after filtration and drying.

MgCl₂(aq) aliquotn(MgCl₂) = 7.50 × 10⁻³ molNaOH(aq)V = 30.0 cm³c = 0.400 mol dm⁻³mixfilter, thendrycollected solidmeasured mass =0.325 g

Use relative atomic masses from the data booklet where required.

(a)

Calculate the amount, in mol, of NaOH used. Give your answer to three significant figures.

[1]
(b)

Using your answer to (a) and Figure 1, determine the limiting reactant and calculate the theoretical mass, in g, of \ceMg(OH)2\ce{Mg(OH)2} Show your working.

[3]
(c)

Calculate the percentage yield of \ceMg(OH)2\ce{Mg(OH)2} to three significant figures.

[1]
(d)

Explain one reason why an experimental yield could be lower than the theoretical yield, and one reason why its apparent value could be higher.

[2]

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