6 marksGrapes are soft fruits that contain sugars. Some students investigated the concentration of reducing sugars in grapes.
| Step 1 |
The students determined the volume of the grapes by placing 50 cm3 of distilled water into a measuring cylinder. |
| Step 2 | Four grapes were placed into the measuring cylinder and the total volume of the distilled water and grapes was measured. |
Fig. 1 shows the total volume of the distilled water and grapes in the measuring cylinder.
Fig. 1
Table 1
| Total volume of distilled water and grapes in the measuring cylinder / cm3 | Total volume of the grapes / cm3 |
Calculate the total volume of the four grapes using the information in Step 1 and Fig. 1
Write your answers in Table 1
[1]
Calculate the average volume of one grape using your answer to a) i).
[1]
| Step 3 | Three test-tubes were labelled, S1, S2 and S3. |
| Step 4 | 5.0 cm3 of a sugar solution (S) was added to test-tube S1. |
| Step 5 | 1.0 cm3 of solution S and 4.0 cm3 of distilled water were added to test-tube S2. The contents of S2 were mixed. |
| Step 6 | 0.2 cm3 of solution S and 4.8 cm3 of distilled water were added to test-tube S3. The contents of S3 were mixed. |
| Step 7 | Grape juice was extracted from ten grapes. |
| Step 8 | 5.0 cm3 of the extracted grape juice was placed into a test-tube labelled G. |
| Step 9 | 5.0 cm3 of Benedict’s solution was added to each of test-tubes S1, S2, S3 and G. |
| Step 10 | Test-tubes S1, S2, S3 and G were placed into an 80 °C water-bath. |
| Step 11 | The time at which a colour change first appeared in each test-tube was recorded. |
| Step 12 | Steps 3 to 11 were repeated to obtain a second set of results. |
Fig. 2 shows the students’ results in minutes and seconds.
Fig. 2
Prepare a table to record the results, shown in Fig. 2
Your table should include:
- The solutions tested.
- The time, in seconds, of the first appearance of a colour change in each solution.
3 marksi)
The concentration of reducing sugar in solution S1 is 200 g per dm3.
The concentration of reducing sugar in solution S3 is 8 g per dm3.
Calculate the concentration of reducing sugar in solution S2, using the information in step 5. Give your answer in g per dm3.
[2]
ii)
State a conclusion for the reducing sugar investigation.
5 marksi)
State one variable that was kept constant in the reducing sugar investigation.
[1]
ii)
The method used to estimate the concentration of reducing sugar in grapes contains potential sources of error.
State one source of error and suggest an improvement to minimise the error.
[2]
iii)
2 marksGrapes develop in large groups attached to their parent plant. As they develop, grapes increase in size and ripen.
Fig. 3 shows one group of grapes.
Fig. 3
A student suggested that the concentration of reducing sugars in grapes changed as the grapes developed and ripened.
Describe how the method used in steps 3 to 12 could be modified to determine if there is a change in the concentration of reducing sugars in grapes during development.
9 marksSome students placed eight grapes, that had been picked at different ages, into water. They measured the change in the volume of the grapes after 24 hours.
Table 2 shows the results of this investigation.
Table 2
| Age of grapes when picked / days | Starting volume of grapes / cm3 | Final volume after 24 hours / cm3 | Percentage change in volume |
| 12 | 5.0 | 5.5 | 10 |
| 24 | 7.6 | 8.5 | 12 |
| 36 | 12.0 | 13.7 | 14 |
| 48 | 17.0 | 19.7 | 16 |
| 60 | 22.0 | 26.0 | 18 |
| 72 | 25.0 | 30.0 | 20 |
| 84 | 30.0 | 36.6 | |
| 96 | 36.0 | 45.0 | 25 |
| 108 | 42.0 | 54.6 | 30 |
| 120 | 55.0 | 74.3 | 35 |
Calculate the percentage change in the volume of grapes aged 84 days.
Write your answer in Table 2.
Show your working.
[2]
Plot a line graph on the grid of the age of the grapes against the percentage change in volume.
[4]
Describe the trends shown by the results in Table 2 and your graph.
[2]
State the variable that was changed (independent variable) in this investigation.
[1]
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