Chemistry 5070/31 — October/November 2019

Experiment 1

• Pipette $25.0\text{ cm}^3$ of $\mathbf{P}$ into a plastic cup supported in a beaker. Measure the temperature of $\mathbf{P}$ to the nearest $0.5\,^\circ\text{C}$ and record the value in column E of the table.
• Put $\mathbf{Q}$ into a burette. Measure $5.0\text{ cm}^3$ of $\mathbf{Q}$ from the burette into a $25\text{ cm}^3$ measuring cylinder. To the $\mathbf{Q}$ in the measuring cylinder, add water until the total volume of liquid in the cylinder is $25\text{ cm}^3$.
• Pour this mixture into the plastic cup containing $\mathbf{P}$. Stir, using the thermometer, and measure the highest temperature reached. Record the value in column F of the table.
• Empty the plastic cup and rinse it with water.

Experiments 2–7

• Repeat Experiment 1 using the different volumes of $\mathbf{Q}$ and water given in columns C and D of the table. Refill the burette as necessary.
• Calculate the temperature rise for each of experiments 1–7 and record in column G of the table.

Plot a graph of temperature rise (column G) against volume of $\mathbf{Q}$ (column C) on the grid. Use these points to draw two intersecting straight lines.

From the graph, read the volume of $\mathbf{Q}$ where the two lines cross.

volume of $\mathbf{Q}$ = ______ $\text{cm}^3$

Your answer to (c) is the volume of $\mathbf{Q}$ that exactly neutralises $25.0\text{ cm}^3$ of $\mathbf{P}$.

Calculate the concentration, in $\text{mol / dm}^3$, of potassium hydroxide in $\mathbf{P}$. Give your answer to 2 significant figures.

$$2\text{KOH} + \text{H}_2\text{SO}_4 \rightarrow \text{K}_2\text{SO}_4 + 2\text{H}_2\text{O}$$

concentration of potassium hydroxide in $\mathbf{P}$ = ______ $\text{mol / dm}^3$

How has heat loss been reduced in the experiments?

______

Suggest two ways in which the accuracy of the temperature rises in the experiments can be improved.

1. ______
2. ______