Question

What is the missing coefficient in the balanced equation? What type of reaction is it? `Mg(OH)_2 + H_2SO_4 -> MgSO_4 + ?H_2O`

Answer 1

The stoichiometrically balanced equation is:

`Mg(OH)_2 + H_2SO_4 rarr MgSO_4 + color(red)2H_2O`

And this is an acid-base reaction.

Explanation:

Chemical equations are balanced with respect to mass and charge. For every reactant particle, there is a corresponding product particle. And for every reactant charge, there must be a corresponding product charge. When you come to study `"redox reactions"` we introduce the electron as a conceptual particle with a negative charge so that redox reactions can also be shown to conserve charge:

`"Reduction:"`

`O_2(g) + 4e^(-) rarr 2O^(2-)` `(i)`

`"Oxidation:"`

`Fe(s) rarr Fe^(2+) +2e^(-)` `(ii)`

And we cross multiply these individual redox reactions so that the electrons do not appear in the final redox equation:

`(i) + +2xx(ii)` gives.................

`2Fe(s) +O_2+cancel(4e^(-)) rarr 2FeO +cancel(4e^(-))`

`2Fe(s) +O_2 rarr 2FeO`

Charge is balanced, and mass is balanced. As is ABSOLUTELY required.

In the given example, we could write the net ionic equation, i.e.

`H_3O^(+) + HO^(-) rarr 2H_2O`

Are mass and charge conserved here?