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Question

Is H2O2 (in solution , with no additives added ) basic ,neutral or acidic?What would be (theoretically) the pH of a 0.3M solution of H2O2 , considering that it reacts with water , forming the equilibrium $H_{2} O_{2} + H_{2} O = H_{3} O^{+} + H O O^{-}$ $H_2O_2+H_2O=H_3O^{+}+HOO^{-}$

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Answer 1 · 2018-03-11T16:56:27

Very slightly acidic. $sf(pH=6.1)$

Set up an ICE table based on $sf("mol/l")$ :

$sf(" "H_2O_2+H_2OrightleftharpoonsH_3O^++HOO^-)$

$sf(Icolor(white)(xxx)0.3color(white)(xxxxxxxxxx)0color(white)(xxxxxxx)0$

$sf(Ccolor(white)(xx)-xcolor(white)(xxxxxxxx)+xcolor(white)(xxxxx)+x)$

$sf(Ecolor(white)(x)(0.3-x)color(white)(xxxxxxxx)xcolor(white)(xxxxxxx)x$

$sf(K_a=([H_3O^+][HOO^-])/([H_2O_2])=2.4xx10^(-12))$

$:.$ $sf(x^2/(0.3-x)=2.4xx10^(-12))$

Because the value of $sf(K_a)$ is so small we can assume that $sf((0.3-x)rArr0.3)$ .

$:.$ $sf(x^2/0.3=2.4xx10^(-12))$

$sf(x=H_3O^+=8.485xx10^(-7)color(white)(x)"mol/l")$

$sf(pH=-log[H_3O^+]=-log[8.485xx10^(-7)]=6.1)$