A chemist investigated the rate of reaction between copper(II) carbonate and dilute nitric acid by monitoring the total mass of the reaction flask. Carbon dioxide gas was allowed to escape through a cotton wool plug.
Their results are shown in the table below:
| Time (t t\,t in seconds) | Mass of flask (m m\,m in grams) |
|---|---|
| 0 | 250.00 |
| 20 | 248.65 |
| 40 | 247.70 |
| 60 | 247.10 |
| 80 | 246.75 |
| 100 | 246.55 |
| 120 | 246.45 |
| 140 | 246.45 |
| 160 | 246.45 |
Explain why the chemist could have stopped recording measurements at 120 seconds.
