What is the concentration of $OH^-$ ions in pure water at 20 degrees Celsius?

Question

$[OH^-]$ ion concentration .

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Answer 1 · 2018-04-23T18:11:36

$sf(8.25xx10^(-8)color(white)(x)"mol/l")$

Pure water dissociates:

$sf(H_2OrightleftharpoonsH^(+)+OH^(-))$

$sf(K_w=[H^(+)][OH^(-)]=0.681xx10^(-14))$ at $sf(20^@C)$

Since $sf([H^+]=[OH^(-)])$ we can say:

$sf([OH^(-)]=sqrt(0.681xx10^(-14))=8.25xx10^(-8)color(white)(x)"mol/l")$