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Find the [OH−] of a 0.32 M methylamine (CH3NH2) solution. (The value of Kb for methylamine (CH3NH2) is 4.4×10−4.) Express your answer to two significant figures and include the appropriate units.

Answer :

sebassandin

Answer:

[tex][OH^-]=0.01165M[/tex]

Explanation:

Hello,

In this case, for the dissociation of methylamine:

[tex]CH_3NH_2(aq)+H_2O(l)\rightleftharpoons CH_3NH_3^+(aq)+OH^-(aq)[/tex]

We can write the basic dissociation constant as:

[tex]Kb=\frac{[CH_3NH_3^+][OH^-]}{[CH_3NH_2]}[/tex]

That in terms of the reaction extent [tex]x[/tex], turns out:

[tex]Kb=\frac{x*x}{[CH_3NH_2]_0-x}[/tex]

[tex]4.4x10^{-4}=\frac{x^2}{0.32M-x}[/tex]

That has the following solution for [tex]x[/tex]:

[tex]x_1=-0.01209M\\x_2=0.01165M[/tex]

Yer 0.01165M is valid only as no negative concentrations are eligible. It means that it is the concentration of hydroxyl ions in the solution:

[tex][OH^-]=0.01165M[/tex]

Best regards.

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