pH and Acidity of Ammonium Chloride (NH₄Cl) Aqueous Solution

Aqueous ammonium chloride (NH₄Cl) solution is acidic and show pH value less than seven. But aqueous NH₄Cl solution is a weak acidic solution. For acidity, ammonium ion is the reason. In the water , ammonium chloride dissociates completely to NH₄⁺ and Cl^- ions.

NH₄Cl_(aq) → NH₄⁺_(aq) + Cl^-_(aq)

In this tutorial, we will discuss following sections.

• Why ammonium chloride is acidic?
• pH Calculator of aqueous ammonium chloride solution
• Example of calculating pH of 0.1 mol dm^-3 ammonium chloride aqueous solution

Why ammonium chloride is acidic?

NH₄ ions interacts with water molecules and produce H₃O⁺ ions. Due to formation of H₃O⁺ ions, H₃O⁺ concentration is greater than OH^- concentration in aqueous solution. Therefore, NH₄Cl aqueous solution is acidic in water.

NH₄⁺_(aq) + H₂O_(l) ⇌ H₃O⁺_(aq) + NH_3(aq)

pH Calculator of aqueous ammonium chloride solution

Ka value of NH₄Cl at 25⁰C is taken as 5.55 * 10^-10 mol dm^-3.

Calculate

pH calculation of NH₄Cl

Now we are going to determine pH value of aqueous NH₄Cl solution. For a example, 0.1 mol dm^-3 NH₄Cl solution is taken. As, other data, dissociation constant (Ka) of NH₄Cl is 5.55 * 10^-10mol dm^-3.

• Initial concentration of NH₄Cl: 0.1 mol dm^-3
• Dissociated / formed concentration is taken as x
• x = [H₃O⁺_(aq)] = [NH_3(aq)]

Now, these equilibrium concentrations of compounds can be substituted in dissociation equation as below.

Because NH₄⁺ is a weak acid, it's dissociation is small. Therefore, dissociated concentration is small compared to the initial concentration of NH₄⁺. Therefore, we can simplify the dissociation equation.

• x <<< 0.1
• 0.1 - x ≈ 0.1

Now, we know the concentration of H⁺ (H₃O⁺) ions.

• x = [H₃O⁺_(aq)] = [NH_3(aq)] = 7.42 * 10^-6 mol dm^-3

Assumptions made in calculations

H₃O⁺ is given by water is neglected because dissociation of water is very low compared to NH₄⁺.

Because H₃O⁺ concentration is known now, pH value of NH₄Cl solution can be calculated.

• pH = -log[H₃O⁺_(aq)]
• pH = -log[7.42 * 10^-6]
• pH = 5.13

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Questions

Ask your chemistry questions and find the answers

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Which cation or anion will cause for the pH of NH₄Cl?

Chloride ion is stable in aqueous solution and does not participate to hydrolysis reactions. Therefore, chloride ion does not have an effect for pH value.

But, ammonium ion is not stable in water and some ammonium ions react with water molecule to form ammonia molcules and H⁺ ions. Due to formation of H⁺ ions, aqueous solution should be acidic and pH value is lower than 7.

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