THEORY:
Reaction: 2HCl + Na2CO3 ————–> 2NaCl + H₂O + CO₂
Ionically, 2H++ + CO3 — ————-> H₂O + CO₂
The normality of the given HCl solution can be determined by titrating it against the primary standard alkali solution, and by using the normality equation.
V₁N₁ = V₂N₂
Where, V₁ = volume of acid V₂ = volume of alkali
N₁ = normality of acid N₂ = normality of alkali
:. N₁ =V₂N₂/V₁
APPARATUS :
1) Burette
2) Pipette
3) Conical flask
4) Burette stand
5) Clamps
CHEMICALS:
1) Methyl orange indicator
PROCEDURE:
i) Wash the whole apparatus with water.
ii) Rinse the burette with the acid solution, and then fill it with the acid solution itself. See that the acid solution is continuous from zero mark down to the nipple without any gas or air bubble. Clamp the burette in a vertical position. Read the lower miniscus by avoiding parallax.
iii) Rinse the pipette with the given alkali solution, and pipette out 10 ml of the standard alkali into the clean conical flask, and add one or two drops of methyl orange indicator, when the solution turns yellow.
Note: Never rinse the conical flask with alkali
iv) To have an idea of the approximate titre value of the acid, first run down the acid into the conical flask rapidly (say) 1 ml at a time. Give swirling motion to the flask after each addition. Continue adding acid till the colour changes from yellow to pink. Note the reading.
v) Wash the conical flask with water. Pipette out 10 ml of the alkali as before, add 1-2 drops of methyl orange. Now. run out the acid 1 ml at a time till the reading is about 1 ml less than the previous approximate titre value.
vi) Now, add acid drop by drop swirling the flask all the while till with a last single drop, the colour just changes to light pink. This is the end point of titration.
[N.B. read the lower meniscus by avoiding parallax.]vii) Repeat the titrations till two or three concurrent readings are obtained.
Tabulate your results as follows
RESULTS:
Solution taken in the burette = HCI acid
Alkali solution taken for each titration = 10 ml
Indicator used = methyl orange
End point = from yellow to light pink.
Normality of standard alkali = N/10 (f = 1.17)
BURETTE READINGS:
| No. of obs. | Initial reading | Final reading | Vol. of acid (ml) | Mean |
| 1 | 0 | 10.8 | 10.8 ——> | (approx) |
| 2 | 10.8 | 21.4 | 10.6 | |
| 3 | 21.4 | 31.9 | 10.5 | 10.5 |
| 4 | 31.9 | 42.4 | 10.5 |
CALCULATIONS :
Acid Alkali
Vol of acid (V₁) = 10.5 ml Vol of alkali (V2) = 10 ml
Normality of acid (N₁) = ? normality of alkali (N₂) = N/10 (f = 1.17)
By applying the normality equation,
V,N, = V₂N₂
10.5 ml x N₁ = 10 ml x N/10 (f = 1.17)
or, N₁ = 10XNX1.17/10.5X10 = N/10 x10X1.17/10.5 = N/10(f = 1.114)