This question is about acids - AQA - GCSE Chemistry - Question 9 - 2021 - Paper 1

The solution with the lowest pH is the 1.0 mol/dm³ hydrogen chloride solution. Strong acids like hydrogen chloride fully ionise, leading to lower pH values compared to that of weak acids.

1. Use a more precise measuring instrument, such as a digital burette, to reduce human error in reading the volume of the ethanoic acid solution used.
2. Perform the titration multiple times and calculate an average volume to minimize random errors in measurement.

To find the mass of ethanoic acid needed:

1. Calculate the number of moles required:

   $\text{moles} = 0.0480 \text{ mol/dm}^3 \times \frac{250}{1000} \text{ dm}^3 = 0.012 \text{ mol}$

2. Then, use the molar mass to find the mass:

   $\text{Mass} = 0.012 \text{ mol} \times 90 \text{ g/mol} = 1.08 \text{ g}$

Using the relation between moles and volume:

1. Calculate the moles of ethanoic acid:

   $\text{moles H₂C₂O₄} = 0.0480 \text{ mol/dm}^3 \times \frac{15.00}{1000} \text{ dm}^3 = 0.00072 \text{ mol}$

2. From the balanced equation, the moles of sodium hydroxide are:

   $\text{moles NaOH} = 0.00072 \text{ mol} \times 2 = 0.00144 \text{ mol}$

3. Finally, calculate the concentration:

   $\text{Concentration} = \frac{0.00144 \text{ mol}}{0.0250 \text{ dm}^3} = 0.0576 \text{ mol/dm}^3$