Question

A 25.00 mL sample of the ammonia solution
was accurately diluted to 250.0 mL. A 25.00mL
aliquot of the diluted ammonia solution was
placed in a conical flask. Indicator was then added
and the solution was titrated with 0.208 molL-1
hydrochloric acid. The indicator changed colour
permanently when 19.64 mL of the acid had been
added. Calculate the concentration of ammonia in
the original solution.

Answer 1

Answer:

1.634 molL-1

Explanation:

The mol ration between NH3 and HCl is 1 : 1

Using Ca Va / Cb Vb = Na / Nb   where a = acid and b = base

Na = 1

Nb = 1

Ca = 0.208 molL-1

Cb = ?

Va = 19.64 mL

Vb = 25.00mL

Solving for Cb

Cb = Ca Va / Vb

Cb = 0.208 * 19.64 / 25.0

Cb = 0.1634 molL-1 (Concentration of diluted ammonia solution)

Using the dilution equation;

C1V1 = C2V2

Initial Concentration, C1 = ?

Initial Volume, V1 = 25.00 mL

Final Volume, V2 =  250 mL

Final Concentration, C2 = 0.1634 molL-1

Solving for C1;

C1 = C2 * V2 / V1

C1 = 0.1634 * 250 / 25.00

C1 = 1.634 molL-1