Question

Given [H3O+] = 1.00 x 10-7M
Is this acidic, basic or neutral?
How do you know?​

Answer 1

This solution is neutral.

Assumption: the solution is under room temperature, such that
`K_w = 10^(-14)`.

Step-by-step explanation:

For a solution in water,

`\mathrm{[H_3O^(+)] \cdot [OH^(-)]} = \mathnormal{K_w}`.

In other words, if
`K_w` is given, knowing the concentration (in
`\rm M`, or equivalently
`\rm mol\cdot L^(-1)`) of either
`\rm H_3O^(+)` or
`\rm OH^(-)` will imply the concentration of the other ion.

Under room temperature,

`K_w \approx 10^(-14)`.

The question states that for this solution,

`\mathrm{[H_3O^(+)]} = \rm 1.00* 10^(-7)\; M`

As a result, the concentration of
`\rm OH^(-)` in this solution will be

`\displaystyle \frac{K_w}{\mathrm{[H_3O^(+)]}} = (10^(-14))/(1.00* 10^(-7)) = 10^(-7)`.

• A solution is acidic if
  `\mathrm{[H_3O^(+)] > [OH^(-)]}`.
• A solution is basic if
  `\mathrm{[H_3O^(+)] < [OH^(-)]}`.
• A solution is neutral if
  `\mathrm{[H_3O^(+)] = [OH^(-)]}`.

In this case,
`\rm [H_3O^(+)] = 10^(-7)\; M = [OH^(-)]`. In other words, this solution is neutral.