Answer to Question #344320 in General Chemistry for lisa

Question

1. What are buffers?

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2. Write equations to show the dissociation of the salts (i) ammonium chloride and (ii) sodium acetate.

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II. __________________________________________________________________

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3. Write equations to show the hydrolysis of the two salts named in Exercise 2.

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II. ________________________________________________________________

4. Calculate the pH of the ammonium chloride solution of concentration 0.1M if the acid dissociation constant/ hydrolysis constant for the NH₄⁺ ion is 5.8 x 10^-10

Answer 1

1.

Buffer is, solution usually containing an acid and a base, or a salt, that tends to maintain a constant hydrogen ion concentration. A buffer consists of a weak acid and its conjugate base or a weak base and its conjugate acid. Buffer capacity is the amount of acid or base that can be added before the pH of a buffer changes. An example of a buffer solution is bicarbonate in blood, which maintains the body's internal pH.

2.

(i) NH₄Cl => NH₄⁺ + Cl^-

(ii) CH₃COONa => Na⁺ + CH₃COO^-

3.

(i) NH₄Cl + H₂O <=> NH₄OH + HCl

(ii) CH₃COONa + H₂O <=> CH₃COOH + NaOH

4.

a)

Kdis – constant of dissociation = 5,8 * 10^-10 ;

C_M – concentration of molarity = 0,1 mol/l ;

C_M(NH₄⁺) – concentration of molarity of NH₄⁺ = X mol ;

C_M(NH₄⁺)= C_M * K_diss = 0,1 * 5,8*10^-10 = 5,8*10^-11

b) pH of solution: It is defined as negative of logarithm of hydrogen ion concentration. Mathematically:- pH = - log[H⁺] .

Substituting 5,8*10^-11 into the equation for pH we find that the 0,1 M NH₄Cl solution has a pH of -log(5,8*10^-11) = 11-log(5,8) = 11 - 0,76 = 10,24

Answer: pH= 10,24