Some moist iron wool was placed in a test tube and the tube inverted and placed in a beaker containing water. The apparatus was left for one week .It was observed that the iron wool had rusted and the water level had raisen.No further change took place when the set-up was left for more days even though not all the iron rusted.

Question

Some moist iron wool was placed in a test tube and the tube inverted and placed in a beaker containing water. The apparatus was left for one week .It was observed that the iron wool had rusted and the water level had risen. No further change took place when the set-up was left for more days even though not all the iron rusted.

1. Explain whether rusting is a chemical or a physical change 
2. Write an expression for an approximate percentage of air used up 
3. What would be the effect on the level of the water if a larger piece of iron wool was used 
4. State the similarities between rusting and combustion 

Answer 1

1. Chemical change- a new substance is formed
2. y − x × 100%
      y
3. No effect-volume of oxygen in the test-tube remains the same.
4.  
   1. Oxygen is used
   2. Both from oxides
   3. Mass increases in both cases