The diagram shows apparatus used to measure oxygen uptake by germinating mung bean seeds. The capillary tube contains a coloured drop. Potassium hydroxide i...
Question 1 Report
The diagram shows apparatus used to measure oxygen uptake by germinating mung bean seeds. The capillary tube contains a coloured drop. Potassium hydroxide is placed in the tube labelled X. At the start, the drop is at 0 mm. After 15 minutes it has moved to the 18 mm mark. The student seals all joints with petroleum jelly before starting the experiment.
(a) Name the chemical placed in X. [2]
(b) Explain why this chemical is needed in the apparatus. [2]
(c) Calculate the mean distance moved by the coloured drop each minute. [2]
(d) Describe why petroleum jelly is used on the joints. [2]
Answer Details
(a) X contains potassium hydroxide solution, KOH. [2]
(b) Potassium hydroxide absorbs carbon dioxide produced by the seeds. Therefore, any decrease in gas volume, shown by movement of the coloured drop, is due only to oxygen being used in respiration. [2]
(c) \[\text{mean distance per minute}=\frac{18\text{ mm}}{15\text{ min}}=1.2\text{ mm min}^{-1}\] The drop moves at 1.2 mm per minute. [2]
(d) Petroleum jelly makes the joints airtight. This prevents air entering or leaving the apparatus and altering movement of the coloured drop. [2]
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