Concentration (\(c\)) connects the world of liquids (volume) to the world of moles.
n = moles (mol)
c = conc (\( \text{mol dm}^{-3} \))
V = Volume (\( \text{dm}^{3} \))
Lab apparatus (beakers, pipettes) measure in cm³ (mL).
The formula requires dm³ (Liters).
Standard Solutions
A solution of precisely known concentration. Prepared using a volumetric flask.
- Weigh pure solid.
- Dissolve in distilled water.
- Transfer to flask and top up to the mark.
Dilutions
Adding water changes volume (V) and concentration (c), but moles (n) stay constant.
\( c_1 V_1 = c_2 V_2 \)
Titration Calculation
Paper 2 Style1. Calculate Moles of Known (HCl):
Don't forget to convert volume!
\( n(HCl) = c \times V = 0.100 \times \frac{25}{1000} = 0.0025 \text{ mol} \)
2. Stoichiometry Ratio:
Ratio is 1:1. Therefore, \( n(NaOH) = 0.0025 \text{ mol} \)
3. Calculate Concentration of Unknown:
\( c = \frac{n}{V} = \frac{0.0025}{0.020} = 0.125 \text{ mol dm}^{-3} \)