IB Chemistry SL Reactivity 2.1.3 Limiting Reactants

Practise determining which reactant is consumed first when more than one starting amount is specified. Compare moles divided by stoichiometric coefficients, use the limiting…

Exam points

calculate the available moles of every reactant from the different data supplied
compare amount-to-coefficient ratios to identify the limiting rather than smallest reagent
use only the limiting reactant to calculate the maximum product mass or amount

[Maximum number: 3]

Chlorine undergoes many reactions.

(a)

2.67 g of manganese(IV) oxide was added to $200.0 \mathrm{~cm}^{3}$ of $2.00 \mathrm{moldm} \mathrm{m}^{-3} \mathrm{HCl}$ .

\mathrm{MnO}_{2}(\mathrm{~s})+4 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{Cl}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{MnCl}_{2}(\mathrm{aq})

[ 3 ]

(i)

Determine the limiting reactant, showing your calculations.

[ 2 ]

《 $n_{\mathrm{HCl}}=2.00 \mathrm{~mol} \mathrm{dm}^{-3} \times 0.2000 \mathrm{dm}^{3}$ 》 $=0.400 \mathrm{~mol}$

« $\frac{0.400}{4}=$ » 0.100 mol AND $\mathrm{MnO}_{2}$ is the limiting reactant

Marking guidance:

Accept other valid methods of determining the limiting reactant in M2.

(ii)

Determine the excess amount, in mol , of the other reactant.

[ 1 ]

« $0.0307 \mathrm{~mol} \times 4=0.123 \mathrm{~mol}$ »

« $0.400 \mathrm{~mol}-0.123 \mathrm{~mol}=$ » 0.277 «mol»

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2.1.3—Limiting reactant question 1

Question (a)

Question (i)

Question (ii)