[Farid]

Could u help me witch this  task?

prepared 2 solutions, where concentration of [H+] was:
a) 4 * 10 ^-9
b) 8 *10    ^-5
How many times the concentration of [OH-] is bigger  in a) then in b).

[Sam (NG)]

Use the equation for the Equilibrium constant of the self ionisation of water (K_w) to find the concentration of OH^- ions in each case:

K_w=[H⁺][OH^-]

K_w=10^-14

[Farid]

a) [OH-] =2,51 * 10^-6
b) [OH-] = 1,25 *10 ^-10

And i think a is 20080 times bigger than b, but in my book there is write: anwser is 20 000.
So, i don't where is mistake? Did i make it, ore mistake is in book.

[Sam (NG)]

Check your concentration for (a), it is slightly wrong (think about what number you get if you divide 10 by 4).  Once you have this correct then you will get the answer in your book.

[Farid]

Thank youvery much . Yes, in a there is 2,5 * 10^-6, and now the result is good.
 Thanks again