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Gnoma [55]
3 years ago
6

Calculate the ph at the equivalence point for the titration of 0.230 m methylamine (ch3nh2) with 0.230 m hcl. the kb of methylam

ine is 5.0× 10–4.
Chemistry
1 answer:
Vlad1618 [11]3 years ago
8 0

Answer: The pH at the equivalence point for the titration will be 0.65.

Solution:

Let the concentration of [OH^-] be x

Initial concentration of [CH3NH_2], c = 0.230 M

        CH_3NH_2+H_2O\rightleftharpoons CH_3NH_3^++OH^-

at eq'm  c-x                         x                    x

Expression of K_b:

K_b=\frac{[CH_3NH_3^+][+OH^-]}{[CH_3NH_2]}=\frac{x\times x}{c-x}=\frac{x^2}{c-x}

Since ,methyl-amine is a weak base,c>>x so c-x\approx c.

K_b=\frac{x^2}{c}=5.0\times 10^{-4}=\frac{x^2}{0.230 M}

Solving for x, we get:

x=1.07\times 10^{-2} M

Given, HCl with 0.230 M , it dissociates fully in water which means [H^+] = 0.230 M

[OH^-]=[H^+] will result in neutral solution, since [OH^-]

Remaining [H^+] after neutralizing [OH^-]ions

[H^+]_{\text{left in solution}}=[H^+]-[OH^-]=0.230-1.07\times 10^{-2}=0.2193 M

pH=-log{[H^+]_{\text{left in solution}}=-log(0.2193)=0.65

The pH at the equivalence point for the titration will be 0.65.

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Acetic acid weighs 60g contains 40% carbon, 6.67% hydrogen, and 55.33% oxygen. Calculate it’s molecular formula.
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C₂H₄O₂ is the molecular formula of acetic acid

Explanation:

Acetic acid have a molecular wight of 60 g/mol.

The correct mass percentages for acetic acid are 40% carbon, 6.67% hydrogen and 53.33 % oxygen.

To find the molecular formula knowing the elements mass percentages we use the following algorithm:

we divide each percentage by the atomic weight of the element

for carbon 40 / 12 = 3.33

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now we divide each value obtained by the smallest value, which is 3.33

for carbon 3.33 / 3.33 = 1

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30x g/mol = 60 g/mol (given by the problem)

x = 2

so the molecular formula for acetic acid is C₂H₄O₂

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molecular formula

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