A student is testing three fruit juice samples (X, Y, and Z) for reducing sugar content using a semi-quantitative Benedict's test. The student first prepares a set of glucose standard solutions of known concentrations: 0.5%, 1.0%, 2.0%, and 4.0%. For each standard and each fruit juice sample, the student mixes 2 cm³ of the solution with 2 cm³ of Benedict's reagent in a test tube and heats the tube in a boiling water bath. The student records the time taken for the first colour change from blue to green/yellow/orange/brick-red. A distilled water control is also tested.
The results are shown in the table below:
| Solution | Time to first colour change (seconds) |
|---|---|
| 0.5% glucose | 90 |
| 1.0% glucose | 60 |
| 2.0% glucose | 35 |
| 4.0% glucose | 15 |
| Fruit juice X | 50 |
| Fruit juice Y | 25 |
| Fruit juice Z | 80 |
| Distilled water | No colour change |
Describe how the student should carry out this semi-quantitative Benedict's test and explain how the times can be used to rank the reducing sugar concentrations in the three fruit juice samples.