Question

If a solid sample of Ca(OH)2 is titrated with HBr(aq) what is the sum of the coefficients of the balanced chemical equation for this titration? Write the equation in molecular form to determine the coefficients.

Answer 1

Chemical Equation:

`\text{Ca}(\text{OH})_2 \; (s) + 2 \; \text{HBr} \; (aq) \to \text{Ca}\text{Br}_2 \; (aq) + 2 \; \text{H}_2\text{O} \; (l)`

Hence the sum of all four coefficients would be six.

Calcium hydroxide
`\text{Ca}(\text{OH})_2` dissolves in water to produce hydroxide ions
`\text{OH}^(-)`. Calcium hydroxide can thus act as a base.

Bromine is found in group seventeen of the periodic table and is a halogen element. Molecules of hydrogen bromide
`\text{HBr}` contain hydrogen atoms bonded to bromine atoms. These molecules would thus ionize when dissolved in water to release hydrogen ions
`\text{H}^(+)` and therefore act as acids.

Acids would neutralize bases in an aqueous solution. Hydrogen ions would combine with hydroxide ions to produce water.

Calcium hydroxide dissolves to produce calcium ions
`\text{Ca}^(2+)` in addition to hydroxide ions. Similarly, hydrogen bromide dissolves to produce bromide ions
`\text{Br}^(-)` in addition to hydrogen ions. The mixture would contain both calcium ions and bromide ions. It would thus behave as a solution of the salt calcium bromide
`\text{Ca}\text{Br}_2`.

Thus the reaction would produce two species:

• Calcium bromide
  `\text{Ca}\text{Br}_2`, and
• Water
  `\text{H}_2\text{O}`

Balance the reaction through the conservation of atoms. For example, start by assuming one as the coefficient of calcium bromide. Both sides of the equation shall thus contain one calcium atom and two bromine atoms. There would be one formula unit of calcium hydroxide and two hydrogen bromide molecules on the reactant side. The formula unit of calcium hydroxide contains two oxygen atoms, which corresponds the production of two water molecules.