Method of Assay if caustic soda with Sodium Carbonate

1. ASSAY OF NAOH SOLUTION
ASSAY OF NAOH SOLUTION
Lecturer Luma Amer
Department of Pharmaceutical
Chemistry/Collage of pharmacy
1 st stage: 2stlab.

2. Lab. 2
Assay of NaOH Solution
Lab. 2
Assay of NaOH Solution
NaOH (secondary standard solution) because it is a
hygroscopic , so in BP. , NaOH solution contains not less than
97.5 %(w ⁄ w) of total alkali calculated as NaOH , and not
more than 2.5 %(w ⁄ w) of Na2CO3.
Chemical formula NaOH ,molar mass 40.00 g/mol.
Very soluble in water; freely soluble in ethanol , Sodium
Hydroxide occurs as a white lumps having various shapes
including pellets, flakes, and rods, or as a white powder.
Sodium Hydroxide solution is strongly alkaline.

3. so we have to do titration of two step, and we have to
add BaCl2 in the first titration, why?
so we have to do titration of two step, and we have to
add BaCl2 in the first titration, why?

4. procedure
procedure
1 N HCl
10 ml of NaOH sol. + 5 ml BaCl2 sol.
+ 5 ml D.W.+ 1-2 drop (ph.ph.)
1. First titration
NaOH +HCl → NaCl + H2O
Turbid pink sol.→ Turbid colorless
Calculate V1 ≡ V of HCl ≡ NaOH

5. 2. Second titration
1 N HCl
To the same conical flack add 3 drop
of BPB
Na2CO3 + 2HCl→ 2NaCl + H2O + CO2
Bluish violet → yellow
Calculate V2 ≡ V of HCl ≡ for Na2CO3
V T = V1+ V2

6. Chemical Factor : it is the weight of substance
which is chemically equivalent to 1ml of
standard solution.
Calculation of the chemical factor:
1.first titration (for the reaction of HCl with
NaOH):
NaOH +HCl → NaCl + H2O
1eq wt. NaOH ≡ 1eq wt. HCl
1× 40g NaOH ≡ 1L 1N HCL (standard sol.)
N = eq wt./V(l)
40/1000g NaOH ≡ 1ml of 1N HCl
0.04g NaOH ≡ 1ml 1N HCL chemical
factor for first titration.

7. 2. Second titration ( for the reaction of 2HCl with
Na2CO3 ):
BaCl2 + H2O + CO2→ 2HCl + BaCO3
2NaCl + H2O + CO2→ 2HCl + Na2CO3
2eq wt. of HCl ≡ 1M wt. of BaCO3 ≡ 1 M wt. Na2CO3
1 M wt. Na2CO3 ≡ 2 eq wt. of HCl
1/2 M wt. Na2CO3 ≡ 1 eq wt. of HCl
½(106) Na2CO3 ≡ 1L of 1N HCl
53 g Na2CO3 ≡ 1L of 1N HCl
53/1000 g Na2CO3 ≡ 1ml of 1N HCl
0.053 g Na2CO3 ≡ 1ml of 1N HCl (chemical factor
for the second titration).