1. An interesting phenomenon often occurs when the fire is warmed in winter: water drops drop on the red-hot iron plate above the coal stove, and the water drops suddenly disappear, but the water drops are gone. There has been a chemical change, iron+water+iron oxide+hydrogen. Put a red-hot iron bar into water, collect the generated gas, and do it for several times, so that the collected gas is ignited and crackles, indicating that hydrogen is generated. Then the oxygen in the water combines with iron to form black ferroferric oxide.