Biology 9700/33 — October/November 2019

Think about the hazards of using the materials in Table 1.1.

Decide whether the risk of using E, S and C is low, medium or high.

Complete Table 1.1, using the words low, medium or high, to state the risk of using E, S and C. You may use each word once, more than once or not at all.

You will need to make a serial dilution of 2.0% copper sulfate solution, C, which reduces the concentration by a factor of ten between each successive dilution.

Fig. 1.1 shows you the first two beakers you will use to make your serial dilution.

Decide which other concentrations of copper sulfate solution you will use to make your serial dilution.

Complete Fig. 1.1 by drawing as many extra beakers as you need for your serial dilution.

For each beaker:

• state, under the beaker, the volume and concentration of copper sulfate solution available for use in the investigation
• use one arrow with a label, above the beaker, to show the volume and concentration of copper sulfate solution added to prepare the concentration
• use another arrow with a label, above the beaker, to show the volume of W added to prepare the concentration.

Carry out step 1 to step 19.

1. Prepare the concentrations of copper sulfate solution as decided in (a)(ii) and shown in Fig. 1.1.

Use a glass rod to mix the copper sulfate solutions and water.

1. Label the test-tubes with the concentrations of copper sulfate solution prepared in step 1.

2. Label another test-tube W.

3. Wipe the white tile clean with a damp paper towel and then dry the white tile.

4. Label the white tile, as shown in Fig. 1.2. The numbers indicate the sampling times in seconds.

1. Put one drop of iodine on the white tile at each sampling time, as shown in Fig. 1.2.

2. Put $1\ \text{cm}^3$ of W into the test-tube labelled W.

3. Put $3\ \text{cm}^3$ of S into the same test-tube. Mix well.

4. Put $0.5\ \text{cm}^3$ of E into the same test-tube. Use a glass rod to mix.

5. Start timing.

6. After 15 seconds, use the glass rod to transfer a drop of the mixture from the test-tube onto the iodine that is labelled 15, on the white tile.

7. Clean the glass rod with a paper towel.

8. Repeat step 11 to step 12 at intervals of 15 seconds until the iodine does not change colour.

9. Record the time taken for the starch to disappear in an appropriate table in (a)(iii). If the starch has not disappeared at 180 seconds, record 'more than 180'.

10. Repeat step 4 to step 14 replacing the $1\ \text{cm}^3$ of W with $1\ \text{cm}^3$ of the lowest concentration of copper sulfate solution.

11. Repeat step 15 with the other concentrations of copper sulfate solution.

Record your results in an appropriate table.

1. Label a test-tube with the letter U.

2. Repeat step 4 to step 13 with U instead of W.

3. Record in (a)(iv) your result for U.

State the result for U.

result for U = ______

Using your results in (a)(iii) and (a)(iv), estimate the concentration of copper sulfate in U.

State one significant source of error in this investigation.

Explain why this is a source of error.

source of error = ______

explanation = ______

Suggest how you could make one improvement to the independent variable so that a more accurate estimate of the concentration of copper sulfate in U can be obtained.

Suggest how you could make two improvements to the measuring of the dependent variable so that a more accurate estimate of the concentration of copper sulfate in U can be obtained.

Plot a graph of the data in Table 1.2 on the grid in Fig. 1.3.

Use a sharp pencil for drawing graphs.

Use your graph in Fig. 1.3 to determine the rate of reaction when the temperature is $37.5^\circ\text{C}$.

rate of reaction = ______ arbitrary units

Explain the shape of the graph:

between $5.5^\circ\text{C}$ and $36.0^\circ\text{C}$

between $36.0^\circ\text{C}$ and $49.5^\circ\text{C}$