11. If the pH of a solution increases from 2.0 to 4.0, the H3O^ + ion

concentration

O

a decreases by a factor of 2.

b. decreases by a factor of 100.

c. increases by a factor of 3.

O

d. increases by a factor of 1000,

A. Decreases by a factor of 2

Explanation:

The pH of a solution is equal to - log10 c, where c is the hydrogen ion concentration in moles per litre.

If - log10c = 2.0

C = 10^-2

If - log10c = 4.0

C = 10^-4

Therefore, it can be seen that the hydrogen ion concentration decreased by a factor of 2

Option B. decreases by a factor of 100

Explanation:

To obtain the right answer to the question, let us calculate the concentration of the hydronium ion, [H3O+] in both cases.

For pH = 2,

pH = - Log [H3O+]

2 = - Log [H3O+]

-2 = Log [H3O+]

[H3O+] = antilog (-2)

[H3O+] = 1x10^-2M

For pH = 4,

pH = - Log [H3O+]

4 = - Log [H3O+]

-4 = Log [H3O+]

[H3O+] = antilog (-4)

[H3O+] = 1x10^-4M

Now, we shall determine the ratio of [H3O+] in pH 4 to that of pH 2. This is illustrated below:

[H3O+] in pH 4 : [H3O+] in pH 2 = > 1x10^-4 / 1x10^-2 = 0.01 = 1x10^-2

From the above, we can thus say that:

[H3O+] in pH 4 = 1/100 [H3O+] in pH 2

Therefore, the [H3O+] decrease by 100