Experiment 2 –Standardization of Bench Hydrochloric Acid
- Objective
Determine the concentration of a given bench hydrochloric acid of about 0.1M.
- Chemicals and Apparatus
- Standard Solution of Sodium Carbonate (Na2CO3)
- Hydrochloric Acid of about 0.1M
- Methyl Orange Indicator Solution
- Conical Flask
- Pipette Filler
- 25 mL Pipette
- 250 cm3 Beaker
- Burette
- 250 cm3 Volumetric Flask
- Filter Funnel
- Plastic Washbottle
- Glass Rod
- Dropper
- Deionized water
- Method
Hydrochloric acid is a strong acid and can react with weak base sodium carbonate according to the equation below:
2HCl + Na2CO3 → 2NaCl + H2O + CO2
To determine the concentration of the bench hydrochloric acid, which is about 1 M, the acid is titrated against a standard sodium carbonate solution. Methyl orange is used to indicate the completion of the reaction, as its colour will change from yellow (in alkaline solution) to pale orange when the equivalence point (also known as stoichiometric point) has reached.
- Procedure
- Rinse the burette with water and then with the diluted hydrochloric acid.
- Fill the burette with the acid to rinse and fill the tip.
- Record the initial reading in the “Trial” column of the Results Table, and round it off to the nearest 0.05 cm3, which is approximately one drop.
- Use a pipette filler to rinse the pipette with water and the sodium carbonate solution. 25.0 cm3 of sodium carbonate solution is then carefully transferred to a clean 250 cm3 conical flask. Note that this first flask is usually taken as a trial run as the end-point is probably overshot.
- Run the diluted hydrochloric acid from the burette into the flask. The flask is swirled until the colour of solution has just changed from yellow to pale orange. The final burette reading was recorded.
- Refill the burette with the acid, and take down the initial reading again.
- Transfer another 25.0 cm3 of the standard solution to a clean conical flask with 3 drops of the methyl orange indicator solution added.
- Titrate the solution to the end-point carefully. Add the alkali drop by drop into the flask when the end-point is near and the colour is about to change from yellow to pale orange.
- Repeat the above 3 steps for at least 3 times, with the readings recorded down in the Results Table.
- Empty the burette and wash it thoroughly immediately right after the titration.
- Calculation
- Results Table
- Average Titre Used = = 27.25 cm3
-
2HCl + Na2CO3 → 2NaCl + H2O + CO2
Mole Ratio of HCl to Na2CO3 = 2:1
Let M1 and V1 be the Molarity and Volume of HCl
Let M2 and V2 be the Molarity and Volume of Na2CO3
=
=
∴M1 = = 0.1028 M - The molarity of the diluted hydrochloric acid solution is 0.103 M.
- The molarity of the bench hydrochloric acid solution is 1.030 M.