Question

A 1.00 liter solution contains 0.45 M ammonia and 0.59 M ammonium perchlorate.

If 0.150 moles of calcium hydroxide are added to this system, indicate whether the following statements are true or false.

(Assume that the volume does not change upon the addition of calcium hydroxide.)

_______TrueFalse A. The number of moles of NH₃ will decrease.

_______TrueFalse B. The number of moles of NH₄⁺ will increase.

_______TrueFalse C. The equilibrium concentration of H₃O⁺ will increase.

_______TrueFalse D. The pH will increase.

_______TrueFalse E. The ratio of [NH₃] / [NH₄⁺] will increase.

Answer 1

Given data set:

We have 1 litre solution of 0.45 M ammonia and 0.59 M ammonium perchlorate.

The solution of NH3(ammonia) and NH4ClO4(ammonium perchlorate) creates a buffer since we have a weak base (NH3) and the conjugate acid (NH4+).

If 0.150 moles of calcium hydroxide is added, the OH- ions reacts with the acid (NH4+) to reduce the amount of NH4+ and thus the concentration of NH3 will increase. This can be written as:

NH4+ + OH-   NH3 + H2O

As water is being produced, the pH of the solution will be maintained.

We can observe the following :

1. The number of moles of NH3 will increase

2. The number of moles of NH4+ will change i.e it will decrease.

3. The equilibrium concentration of H3O+ will not increase

4. There is slight change in pH(not so much, but a slight change)

5. The ratio of concentration of NH3 to NH4+ will increase.

Thus, statement can be classified:

• The number of moles of NH3 will decrease --- False
• The number of moles of NH4+ will increase ---- False
• The equilibrium concentration of H3O+ will increase ---- False
• The pH will increase --- True
• The ratio of concentration of NH3 to NH4+ will increase --- True