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zvonat [6]
2 years ago
11

A 20.0 mL of 0.27 M solution of the salt NaA has a pH of 8.70.

Chemistry
1 answer:
zlopas [31]2 years ago
3 0

Answer:

a) 3.969

b) 3.489

Explanation:

a) Calculate the pk, value of the acid HA

PH of salt hydrolysis

P^{H} = 1/2 ( pkw + pka + logC )

8.7 * 2 =  14 + log ( 0.27 )  + Pka

∴ Pka = 3.9686  ≈  3.969

b) Calculate the PH of a solution containing 0.3 M HA and 0.1 M NaA

PH = Pka + log ( salt / acid )

    = 3.9686 + log ( 0.1 / 0.3 )

    =  3.9686 - 0.48  = 3.489

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Answer:

1.12g/mol

Explanation:

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ΔT = Kf*m*i

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<em>ΔT = 13.4°C - (-12.82) = 26.22°C</em>

<em>m is molality of the solution</em>

<em>Kf is freezing point depression constant of benzonitrile (5.35°Ckgmol⁻¹)</em>

<em>And i is Van't Hoff factor (1 for all solutes in benzonitrile)</em>

Replacing:

26.22°C = 5.35°Ckgmol⁻¹*m*1

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As the mass of the solvent is 100g = 0.100kg:

4.9mol/kg * 0.100kg = 0.490moles

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<em>This result has no sense but is the result by using the freezing point of the solution = 13.4°C. Has more sense a value of -13.4°C.</em>

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