Experiment No. 3
OBJECTIVE:
TO STANDARDIZE THE GIVEN NaOH SOLUTION BY USING N/10 STANDARD HCl SOLUTION AND EXPRESS THE CONCENTRATION IN TERMS OF MOLARITY, GRAM PER LITRE AND PERCENTAGE STRENGTH
APPARATUS REQUIRED
- conical flask
- pipette
- burette
- beaker
- glass tube
CHEMICALS REQUIRED
- Sodium hydroxide
- hydrochloric acid
- Phenolphthalein
THEORY
The provided HCl solution is standardised by using a primary standard solution of sodium carbonate. This HCl solution determines the strength of the given NaOH solution. Titration is the volumetric analysis to determine the strength of an unknown solution by using a standard solution in the presence of a third chemical substance called an indicator. During titration, the volume of one solution is known and the volume of another required solution is measured.
In the case of titration between HCl and NaOH, methyl orange and Phenolphthalein can be taken as an indicator.
HCl + NaOH \rightarrow NaCl + H_{2}OPROCEDURE
The apparatus was washed with water. The burette was rinsed with water followed by acid and filled up to the upper mark (zero). Burette is clamped into the stand. 10 ml solution of NaOH was pipetted out and kept in a conical flask. 2-3 drops of phenolphthalein were added to the conical flask and the solution became pink. Acid is gradually added to the NaOH solution from the burette a little at a time with constant shaking. At the endpoint, the solution became colourless. The process was repeated until two concurrent readings were achieved.
OBSERVATION TABLE
| S.N. | Volume of NaOH taken(ml) | Burette reading | Concurrent reading | ||
| Initial | Final | Difference | |||
| 1. | 10 | 0.0 | 10.5 | 10.5 | |
| 2. | 10 | 10.5 | 20.7 | 10.2 | 10.2 |
| 3. | 10 | 20.7 | 30.9 | 10.2 |
CALCULATION
| Base taken (Na2CO3) | Acid Taken (HCl) |
| V1 = 10ml N1 = ? | V2 = 10.2 ml N2 = N/10 |
From the Normality equation,
V1N1 = V2N2
10 x N1 = 10.2 x 1/10
N2 = 0.102 N
Normality = 0.102 N
Molarity = Normality/n = 0.102/1 = 0.102 M
Gram per litre = Normality x eq. wt. = 0.102 x 40 = 4.08 gm/lit
Percentage strength = (gm/lit)/10 = 4.08/10 = 0.408 %(w/v)
RESULT
Hence, the given basic solution (NaOH) was standardized and its concentration was found to be 0.102N
CONCLUSION
The secondary standard solution can be standardised by using the primary standard solution.
PRECAUTIONS
- Indicators should not be added in excess.
- The conical flask should not be rinsed.
- HCl should not be taken into the mouth while pipetting.
