This investigation is about using aluminium to remove copper ions from waste solution. Fig. 1 shows an insulated beaker fitted with a temperature probe. The...
Question 1 Report
This investigation is about using aluminium to remove copper ions from waste solution. Fig. 1 shows an insulated beaker fitted with a temperature probe. The student adds aluminium granules to copper sulfate solution and records the temperature every minute. Table 1 gives the results. The reaction produces copper metal and aluminium sulfate solution.
| time / min | temperature / degrees C |
|---|---|
| 0 | 20.2 |
| 1 | 24.7 |
| 2 | 27.9 |
| 3 | 29.1 |
| 4 | 28.8 |
(a) Record the temperature change at the maximum temperature. [1]
(b) Describe the evidence that the reaction is exothermic. [1]
(c) Give one observation, other than temperature, expected when aluminium reacts with copper sulfate solution. [1]
(d) Use the formula Q = mcΔT to calculate Q for 100 g of solution. [2]
Fig. 1 shows a student measuring the temperature change when magnesium reacts with dilute hydrochloric acid in a polystyrene cup. The cup contains 50.0 cm3 of acid. The student records the highest temperature after adding the metal. Assume that 1.0 cm3 of solution has a mass of 1.0 g and that the specific heat capacity of the solution is 4.2 J g-1 degrees C-1.
| measurement | value |
|---|---|
| initial temperature | 21.5 degrees C |
| highest temperature | 35.0 degrees C |
(a) Record the temperature change. [1]
(b) Use the table to calculate the energy transferred to the solution. [2]
(c) Give the sign of the energy change for the reaction. [1]
Answer Details
Aluminium and copper sulfate
(a) Temperature change at the maximum = 29.1 °C − 20.2 °C = 8.9 °C. [1]
(b) The temperature increases, showing that energy is transferred to the solution. This is evidence that the reaction is exothermic. [1]
(c) Brown-pink copper metal forms. Alternatively, the blue solution becomes paler or aluminium dissolves. [1]
(d) Q = mcΔT = 100 g × 4.2 J g-1 °C-1 × 8.9 °C = 3738 J, or 3.74 × 103 J. [2]
Magnesium and hydrochloric acid
(a) Temperature change = 35.0 °C − 21.5 °C = 13.5 °C. [1]
(b) 50.0 cm3 of solution has a mass of 50.0 g.
Q = 50.0 g × 4.2 J g-1 °C-1 × 13.5 °C = 2835 J, or 2.84 × 103 J. [2]
(c) The energy change is negative, because the reaction is exothermic. [1]
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