What are the uses of limestone and the reaction between calcium metal and water?

8. a)

• Manufacture of glass
• Water softening

b)
Limestone ($\text{CaCO}_3$)

9. a) Gas F is hydrogen ($\text{H}_2$).

b)
The reaction between calcium metal and water produces calcium hydroxide, $\text{Ca(OH)}_2$.

$$\text{Ca}(s) + 2\text{H}_2\text{O}(l) \rightarrow \text{Ca(OH)}_2(aq) + \text{H}_2(g)$$

Calcium hydroxide is a strong base, but it has low solubility in water. This means that only a small amount of it dissolves to produce hydroxide ions ($\text{OH}^-$), resulting in a solution that is weakly alkaline.