A student investigates the decomposition of hydrogen peroxide.
They measure the time taken to collect 40 cm340\text{ cm}^340 cm3 of oxygen gas. Without any catalyst, this time is 120 seconds.
The student investigates four substances, P, Q, R, and S, which are possible catalysts for the reaction.
| Substance | Appearance of substance | Time to collect 40 cm340\text{ cm}^340 cm3 of oxygen (s) | Other observations |
|---|---|---|---|
| P | black powder | 120 | black powder remains |
| Q | brown powder | 30 | brown powder remains |
| R | blue crystals | 25 | blue solution formed |
| S | white powder | 120 | colourless solution formed |
Which substance, P, Q, R or S, is a catalyst for the reaction?