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2 years ago

The ph of a 0.175 m aqueous solution of a weak acid is 3.52. what is ka for this acid?

Chemistry

1 answer:

Naddika [18.5K]2 years ago

3 0

Hey there!

pH = - log [ H⁺ ] = 3.52

[ H⁺ ] = 10^-pH

[ H⁺] = 10^ ( -3.52 )

[H⁺] = 3.02*10⁻⁴ M

[HA] =0.175 M

Therefore:

Ka = [ H⁺]* [A⁻] / [ HA]

Ka = (3.02*10⁻⁴)² / 0.175

Ka = 9.1204*10⁻⁸ / 0.175

Ka = 5.2*10⁻⁷

Hope that helps!

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For calculating the mass of hydrogen:

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Step 1 : convert given masses into moles.

Moles of C = $\frac{\text{ given mass of C}}{\text{ molar mass of C}}= \frac{5.921g}{12g/mole}=0.493moles$

Moles of H= $\frac{\text{ given mass of H}}{\text{ molar mass of H}}= \frac{0.658g}{1g/mole}=0.658moles$

Mass of O= $\frac{\text{ given mass of O}}{\text{ molar mass of O}}= \frac{10.53g}{16g/mole}=0.658moles$

Step 2 : For the mole ratio, divide each value of moles by the smallest number of moles calculated.

For C = $\frac{0.493}{0.493}=1$

For H = $\frac{0.658}{0.493}=1$

For O= $\frac{0.658}{0.493}=1$

The ratio of C : H: O = 1: 1: 1

Hence the empirical formula is $CHO$ .

empirical mass of CHO = 12(1) + 1(1) + 1 (16) = 29

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$n=\frac{\text {Molecular mass}}{\text {Equivalent mass}}=\frac{104.1}{29}=4$

Thus molecular formula = $n\times {\text {Empirical formula}}=4\times CHO=C_4H_4O_4$

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