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

The solution with the lowest pH among the given options is the 1.0 mol/dm³ hydrogen chloride solution. Strong acids, such as hydrogen chloride, completely ionize, leading to a lower pH compared to the other solutions listed.

1. Swirling the solution during titration ensures thorough mixing of the reactants, leading to a more accurate endpoint.

2. Using a white tile beneath the flask will improve visibility and make it easier to detect the endpoint changes when the indicator shifts color.

To find the mass of ethanoic acid needed, we can use the formula:

$ext{Mass} = ext{Concentration} imes ext{Volume} imes ext{Molar mass}$

Substituting the known values:

ext{Mass} = 0.0480 ext{ mol/dm}^3 imes rac{250 ext{ cm}^3}{1000} imes 90 ext{ g/mol} = 4.32 ext{ g}

Using the balanced equation, the moles of ethanoic acid used can be calculated as:

ext{Moles of H₂C₂O₄} = 0.0480 rac{ ext{mol}}{ ext{dm}^3} imes rac{15.00 ext{ cm}^3}{1000} = 0.00072 ext{ mol}

From the stoichiometry of the reaction, the moles of NaOH would be:

$ext{Moles of NaOH} = 2 imes 0.00072 = 0.00144 ext{ mol}$

Calculating the concentration:

ext{Concentration} = rac{0.00144 ext{ mol}}{0.0250 ext{ dm}^3} = 0.0576 ext{ mol/dm}^3