10. a 20.00 ml sample of 0.150 mol/l ammonia (nh3(aq)) is titrated to the equivalence point by 20.0 ml of a solution of 0.150 mol/l of the strong acid hydroiodic acid (hi (
a) write a balanced equation for the titration reaction.
b) what is the ph of the ammonia solution before the titration begins?
c) what is the ph at the equivalence point?

Explanation:

a) Balanced equation

The balanced chemical equation for the titration is

b) pH at start

For simplicity, let's use B as the symbol for NH₃.

The equation for the equilibrium is

(i) Calculate [OH]⁻

We can use an ICE table to do the calculation.

                      B + H₂O ⇌ BH⁺ + OH⁻

I/mol·L⁻¹:     0.150               0         0

C/mol·L⁻¹:       -x                 +x       +x

E/mol·L⁻¹:  0.150 - x            x          x

Check for negligibility:

(ii) Solve for x

(iii) Calculate the pH

(c) pH at equivalence point

(i) Calculate the moles of each species

                 B    +    HI   ⇌   BH⁺ + I⁻

I/mol:       3.00    3.00         0

C/mol:    -3.00   -3.00     +3.00

E/mol/:       0          0          3.00

(ii) Calculate the concentration of BH⁺

At the equivalence point we have a solution containing 3.00 mmol of NH₄I

Volume = 20.00 mL + 20.00 mL = 40.00 mL

(iii) Calculate the concentration of hydronium ion

We can use an ICE table to organize the calculations.

                      BH⁺+ H₂O ⇌ H₃O⁺ +  B

I/mol·L⁻¹:     0.0750                 0        0

C/mol·L⁻¹:        -x                     +x      +x

E/mol·L⁻¹:   0.0750 - x             x         x

(iv) Calculate the pH

The titration curve below shows the pH at the beginning and at the equivalence point of the titration.

the product of the pressure and volume is also constant