F.6 Chemistry TAS/Experiment 1/P.()
Preparation of Standard solution and Standardization of Hydrochloric acid
The objective of carrying out this experiment is to determine the concentration of hydrochloric acid (HCl) by using sodium carbonate (Na2CO3) as the primary standard in volumetric analysis.
- All the apparatus are thoroughly washed by de-ionized water before the experiment.
About 1.3 g of anhydrous sodium carbonate (Na2CO3) was accurately weighted out using the method of “weighing by difference”.
The weighed carbonate was transferred to a beaker and about 100 cm3 of de-ionized water added to dissolve it with stirring of glass rod.
After dissolving, the solution was transferred to a 250.00 cm3 volumetric flask.
- The solution was then made up the mark on the neck by adding de-ionized water (add last few drops with dropper.)
- Pipette and burette are rinsed by the solution to be contained respectively.
25.00 cm3 of sodium carbonate solution was transferred to a clean conical flask using pipette and pipette filler.
- Two drops of methyl orange indicator were then added to the sodium carbonate solution.
50cm3 of hydrochloric acid are added in to the empty burette.
- The filled burette is checked without any air bubbles at the jet.
- The carbonate solution was titrated with the given dilute hydrochloric acid until the colour of solution just changed from yellow to orange.
- The titration was repeated at least three times.
Results and calculation
When hydrochloric acid reacts with sodium carbonate, carbonic acid and water are formed as shown in the following chemical equation:
CO32-(aq) + 2H3O+ (aq) → H2CO3(aq) + 2H2O(l)
At the equivalence point, the resulting solution is a mixture of sodium chloride (NaCl) and carbonic acid (H2CO3) in water. Sodium chloride is neutral while carbonic acid is acidic. An indicator with its pH range matching the pH value of the resulting solution is suitable for detection of the end point of titration. In this experiment, methyl orange is used because it changes from yellow to orange over the pH range from 5 to3.
Weighing: Mass of solid weighed = 1.3004g
Mass of solid remained in the bottle = 0.0012g
Mass of solid ( Na2CO3 ) used = 1.3004- 0.0012=1.2992g
Titration: Burette contained : HCL(aq) Indicator used : Methyl orange
Conical flask contained : Na2CO3 (aq)