Titration Calculations Flashcards

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What is the formula linking moles, concentration and volume of a solution?

e.g. $25.0\ \mathrm{cm^3}$ of $0.100\ \mathrm{mol\ dm^{-3}}$ hydrochloric acid

moles = concentration $\times$ volume in $\mathrm{dm^3}$ = $\dfrac{\text{conc} \times \text{vol in cm}^3}{1000}$
$= \dfrac{0.100 \times 25.0}{1000} = 0.00250$ mol

What are the steps to calculate an unknown concentration from titration results?

e.g. $25.0\ \mathrm{cm^3}$ of NaOH needs $20.0\ \mathrm{cm^3}$ of $0.100\ \mathrm{mol\ dm^{-3}}$ HCl (NaOH + HCl $\rightarrow$ NaCl + H$_2$O)

1. Moles of acid = $\dfrac{0.100 \times 20.0}{1000} = 0.00200$ mol
2. Use the ratio in the equation: 1 : 1, so moles of NaOH = $0.00200$ mol
3. Concentration = $\dfrac{0.00200 \times 1000}{25.0} = 0.0800\ \mathrm{mol\ dm^{-3}}$

What are the steps to calculate the volume of a solution needed for complete reaction?

e.g. what volume of $0.200\ \mathrm{mol\ dm^{-3}}$ HCl reacts with $25.0\ \mathrm{cm^3}$ of $0.100\ \mathrm{mol\ dm^{-3}}$ NaOH

1. Moles of NaOH = $\dfrac{0.100 \times 25.0}{1000} = 0.00250$ mol
2. Use the ratio in the equation: 1 : 1, so moles of HCl = $0.00250$ mol
3. Volume = $\dfrac{0.00250 \times 1000}{0.200} = 12.5\ \mathrm{cm^3}$

True or false? In the titration $\mathrm{H_2SO_4 + 2KOH \rightarrow K_2SO_4 + 2H_2O}$, the moles of KOH equal the moles of $\mathrm{H_2SO_4}$.

False. The ratio is 2 : 1, so moles of KOH = $2 \times$ moles of $\mathrm{H_2SO_4}$.