At a remote climbing centre, a medic makes warm glucose solution for a walker who has become exhausted. The medic first checks how quickly glucose dissolves...
Question 1 Report
At a remote climbing centre, a medic makes warm glucose solution for a walker who has become exhausted. The medic first checks how quickly glucose dissolves in water. Fig. 1 shows the equipment used. For each trial, the medic used 5.0 g of glucose, stirred the mixture at the same speed and recorded the time when no solid could be seen.
| Temperature of water / °C | Time for glucose to dissolve / s |
|---|---|
| 10 | 214 |
| 25 | 108 |
| 40 | 54 |
| 60 | 32 |
The final drink has a volume of 500 cm3. It must contain 10 g of glucose. Water is the solvent and glucose is the solute in this solution.
(a) Name the substance that dissolves in the water. [1]
(b) Describe the pattern shown by the results in Table 1. [2]
(c) Explain why glucose dissolves more quickly when the temperature of the water is increased. [3]
(d) Use the information to work out the concentration of glucose in the drink, in g/dm3. [2]
(e) Write two control variables, other than water temperature, for this investigation. [2]
Answer Details
(a) The substance that dissolves is the solute. Here, the solute is glucose. [1]
(b) As water temperature increases, the time for glucose to dissolve decreases. For example, it falls from 214 s at 10 °C to 32 s at 60 °C. [2]
(c) At a higher temperature, water particles have more kinetic energy and move faster. They collide with the glucose surface more frequently and successfully, so glucose particles leave the solid and disperse through the water more quickly. [3]
(d) Convert the volume: \(500\text{ cm}^3=0.500\text{ dm}^3\). \[\text{concentration}=\frac{10\text{ g}}{0.500\text{ dm}^3}=20\text{ g/dm}^3\] [2]
(e) Any two suitable control variables are the mass of glucose, volume of water, stirring speed, surface area or particle size of glucose, container used, or the method used to decide when the glucose has dissolved. Keeping these constant makes temperature the only variable affecting dissolving time. [2]
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