# 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.

## pH Calculator of aqueous ammonium chloride solution

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

## 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)] = [NH3(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)] = [NH3(aq)] = 7.42 * 10-6 mol dm-3

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

Questions

### 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.

### Lewis structures

P2O5 lewis structure OH- lewis structure Ammonium ion (NH4+) lewis structure H2CO3 lewis structure