A student investigated the temperature change in the reaction between dilute sulfuric acid and potassium hydroxide solution - AQA - GCSE Chemistry - Question 9 - 2019 - Paper 1

Plot the temperature changes against the volume of dilute sulfuric acid added from Table 6 on a graph. Draw a line of best fit through the plotted points, ensuring all six points from Table 6 are plotted accurately. Extend both lines of best fit until they intersect, providing a clear point indicating the volume for complete reaction.

From the graph in Figure 11, the volume of dilute sulfuric acid needed to completely react with 25.0 cm³ of potassium hydroxide solution is found to be approximately 11 cm³.

To find the overall temperature change, subtract the initial temperature (18.9 °C) from the final temperature (27.1 °C) observed when the reaction is complete. The overall temperature change is 27.1 °C - 18.9 °C = 8.2 °C.

First, calculate the moles of $moles \ H_2SO_4 = 0.500 \ mol/dm^3 \times \frac{15.5 \ cm^3}{1000} = 0.00775 \ moles$.

Since 2 moles of KOH react with 1 mole of H₂SO₄, the moles of KOH are: $moles \ KOH = 2 \times 0.00775 = 0.0155 \ moles$.

To find the concentration of KOH: $conc \ KOH = \frac{moles \ KOH \times 1000}{25.0 \ cm^3} = \frac{0.0155 \ times 1000}{25.0} = 0.62 \ mol/dm^3$.

Then, to find the mass concentration in g/dm³, use the molar mass of KOH (56 g/mol): $conc = 56 \times 0.62 = 34.72 \ g/dm^3$.