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Calculation of Hydrolysis Constant, Degree of Hydrolysis and pH of Salt Solution

Last Updated on By Mrs Shilpi Nagpal

Salt of weak Acid and strong base

a) Hydrolysis Constant

Hydrolysis constant

Relation between kh, Kw, Ka

 

b) Degree of Hydrolysis

A‾ + H2O sign of equilibrium reactionOH‾ + HA

c                       0         0             original molar conc

c(1-h )             ch         ch          Molar conc at equilibrium

Degree of hydrolysis

salt of weak acid and strong base

c) pH

pH of salt of weak acid and strong base

 

Salt of strong Acid and weak base

a) Hydrolysis Constant

BA + H2O sign of equilibrium reaction BOH + HA

B+ + A‾ + H2O sign of equilibrium reaction BOH + H+ + A‾

B+ + H2O sign of equilibrium reaction BOH + H+

Degree of hydrolysis

hydrolysis constant

b) Degree of Hydrolysis

degree of hydrolysis of SA and WB

c) pH

B+ + H2O sign of equilibrium reaction BOH + H+

c                         0         0         original conc

c(1-h)                 ch        ch      conc at equilibrium

conc of hydrogen  = ch = (Kw /Kb.c ) ½= (Kw .c /Kb)½ = (Kw .c /Kb )½

pH = – log conc of hydrogen 

pH = -log (Kw .c /Kb )½

pH = -½ ( log Kw -log Kb + log c )

pH = ½ ( pKw -pKb – log c)

pH = 7 – ½(pKb + log c)

 

Salts of weak Acid and weak base

a) Hydrolysis constant

Hydrolysis constant

Kh = Kw / Ka .Kb

b) Degree of Hydrolysis

degree of hydrolysis

degree of hydrolysis of wa and wb

c) pH

HA sign of equilibrium reactionH+ + A‾

Ka

conc of hydrogen = Ka (HA / A‾)

conc of hydrogen  = Ka (ch / c(1-h))

conc of hydrogen = Ka (h /1-h)

√Kh = (h /1-h)

conc of hydrogen  = Ka √Kh =Ka  (Kw/ Ka .Kb)½ = (Ka .Kw /Kb)½

pH = -log conc of hydrogen

pH = – log (Ka .Kw /Kb)½

pH = -½( log Ka + log Kw -log Kb)

pH =½ (pKw +pKa -pKb)

pH = 7 + ½ (pKa – pKb)

If pKa < pKb , pH of the solution will be less than 7 and the solution will be acidic.

If pKa > pKb , pH of the solution will be greater than 7 and the solution will be basic.

If pKa = pKb , pH of the solution will be equal to 7 and the solution will be neutral.

About Mrs Shilpi Nagpal

Author of this website, Mrs. Shilpi Nagpal is MSc (Hons, Chemistry) and BSc (Hons, Chemistry) from Delhi University, B.Ed. (I. P. University) and has many years of experience in teaching. She has started this educational website with the mindset of spreading free education to everyone.

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  3. Sai Charan says

    It’s awesome.
    I have been searching for many days for these formulas.Thank u very much I will be following u from now onwards.

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