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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

User Lesyk
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2 Answers

5 votes

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

User Uncle Dan
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2.8k points
6 votes

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.

User DimonZa
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2.9k points