A student investigated the synthesis of iron oxide by heating iron wool in a crucible with a lid.
Their results are shown in the table below.
| Experiment | Mass of iron wool used / g | Mass of iron oxide formed / g | Mass of oxygen gained / g |
|---|---|---|---|
| 1 | 0.14 | 0.20 | 0.06 |
| 2 | 0.28 | 0.40 | 0.12 |
| 3 | 0.42 | 0.60 | 0.18 |
| 4 | 0.56 | 0.80 | 0.24 |
| 5 | 0.70 | 0.90 | 0.20 |
| 6 | 0.84 | 1.20 | 0.36 |
The result for experiment 5 is anomalous. The masses of the reactants and products were all measured accurately on a balance.
Suggest one experimental reason for this anomalous result.
