Question

5. At 20°C, the water autoionization constant, Kw, is 6.8 ´ 10–15. What is the H3O+ concentration in neutral water at this temperature? A. 6.8 × 10–7 M B. 3.4 × 10–15 M C. 6.8 × 10–15 M D. 8.2 × 10–8 M E. 1.0 × 10–7 M

Answer 1

Answer: The concentration of
`H_3O^+` in neutral water is
`8.2* 10^(-8)M`

Step-by-step explanation:

The chemical equation for the ionization of water follows:

`2H_2O\rightleftharpoons H_3O^++OH^-`

The expression of
`K_w` for above equation, we get:

`K_w=[H_3O^+]* [OH^-]`

We are given:

`K_w=6.8* 10^(-15)`

`[H^+]=[OH^-]=x`

Putting values in above equation, we get:

`6.8* 10^(-15)=x* x\\\\x=8.2* 10^(-8)M`

Hence, the concentration of
`H_3O^+` in neutral water is
`8.2* 10^(-8)M`

Answer 2

Step-by-step explanation:

Let us assume that the concentration of [
`OH^(-)` and
`H^(+)` is equal to x. Then expression for
`K_(w)` for the given reaction is as follows.

`K_(w) = [OH^(-)][H^(+)]`

`K_(w) = x^(2)`

`6.8 * 10^(-15) = x^(2)`

Now, we will take square root on both the sides as follows.

`\sqrt{6.8 * 10^(-15)} = \sqrt{x^(2)}`

`[H^(+)] = 8.2 * 10^(-8)` M

Thus, we can conclude that the
`H_(3)O^(+)` concentration in neutral water at this temperature is
`8.2 * 10^(-8)` M.