Calculate the[OH-] if the hydrogen ion concentration is4.2x 10 to teh negative nineth powerM?

Answer:
[H+][OH-] = 1.00 x 10^-14 at 25 °C
[OH-] = 1.00 x 10^-14 / 4.2 x 10^-9 = 2.38 x 10^-6 M

There is another way :
pH = - log [H+] = - log 4.2 x 10^-9 = 8.38
pOH = 14 - 8.38 = 5.62
[OH-] = 10^-5.62 = 2.38 x 10^-6 M

1*10^-14/4.2*10^-9

And theres ur OH concentration at 25 degress celcius.

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