Question

1. What's the concentration of hydronium ions if a water-base solution has a temperature of 25°C (Kw = 1.0x10-14), with a concentration of

hydroxide ions of 2.21x10-6 M? A. 3.1x10-6 M
B. 4.52 X10-9 M
C. 2.8x10-8 M
D. 1.6x10-9 M
​

Answer 1

B. 4.52 * 10^-9M

Step-by-step explanation:

did the test

Answer 2

B. 4.52 X10-9 M

Step-by-step explanation:

Our goal for this question is to calculate the concentration of hydronium ions
`H^+` produced by water in a vessel with a concentration of hydroxide ions of
`2.21X10^-^6~M`. So, our first approach can be the ionization reaction of water:

`H_2O_(_l_)~->~H^+~_(_a_q_)~+~OH^-~_(_a_q_)`

If we write the Keq expression for this reaction we will have:

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

Now, water is the universal solvent, so, Keq has a special name. In the equilibrium problems for water we have to use "Kw" instead of "Keq":

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

From this equation, we know the Kw value () and the concentration of the hydroxide ions ([2.21X10^-^6~M]). If we replace these values into the equation we can solve for
`[H^+]`:

`1.0X10^-^1^4=[H^+][2.21X10^-^6~M]`

`[H^+]=(1.0X10^-^1^4)/(2.21X10^-^6)=4.52X^-^9`

I hope it helps!