Calcium reacts with cold water to form calcium hydroxide, $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$, and hydrogen, ${\mathrm{H}}_2$. State the oxidation number of calcium in calcium metal.

Calcium reacts with cold water to form calcium hydroxide, $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$, and hydrogen, ${\mathrm{H}}_2$. Write two half-equations, for the reaction between water and calcium  to show:

The change from calcium to calcium ions.

Calcium reacts with cold water to form calcium hydroxide, $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$, and hydrogen, ${\mathrm{H}}_2$. Write two half-equations, for the reaction between water and calcium to show:

The change from water to hydroxide ions and hydrogen.

Calcium reacts with cold water to form calcium hydroxide, $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$, and hydrogen, ${\mathrm{H}}_2$. Explain the role played by water in this reaction.