Standardization of bench hydrochloric acid

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Experiment No.: 2

Date:

Title: Standardization of bench hydrochloric acid

Objective: To find the concentration of bench hydrochloric acid

Chemicals Required:        Bench Hydrochloric Acid (1M)

                        250cm3 Standard Sodium Carbonate Solution (0.05M)

                        Methyl Orange Indicator

Apparatus Required:        25cm3 Pipette x 1

                        Burette x 1

                        Pipette Filler x 1

                        Stand and Clamp x 1

Beaker x 2

Funnel x 1

250cm3 Conical Flask x 1

Dropper x 1

Clean White Paper x 1

Theory:        Bench Hydrochloric Acid is titrated against 25cm3 Standard Sodium Carbonate Solution.

2HCl(aq) + Na2CO3(aq) 2NaCl(aq) + CO2(g) + H2O(l)

The number of moles of Na2CO3 presented in the solution was divided by the volume of HCl(aq) used. The answer was multiplied by 2, and the result revealed the No. of Moles of HCl(aq) presented in the titre. The molarity of Bench Hydrochloric Acid could thus be calculated.

Procedure:

  1. 10 cm3 Bench Hydrochloric Acid was diluted to 100cm3 in a beaker, giving a solution of molarity around 0.1M.
  2. The burette was rinsed with the diluted hydrochloric acid solution for 2 times.
  3. The burette was filled with the diluted hydrochloric acid solution using the funnel. The initial level was recorded corrected to the nearest 0.05 cm3.
  4. The burette was securely clamped.
  5. 100cm3 Sodium Carbonate Solution was transferred into another beaker.
  6. The pipette was first washed by deionized water, and then rinsed with some sodium carbonate solution for 3 times using the pipette filler.
  7. 25cm3 sodium carbonate solution was sucked up by the pipette filler and transferred into a clean conical flask.
  8. 3 drops of methyl orange indicator was added to the conical flask.
  9. The knob of the burette was turned and the diluted hydrochloric acid solution ran from the burette into the conical flask.
  10. The conical flask was swirled and shaken slightly throughout the procedure.
  11. The color change of the solution was carefully observed. Once the solution just turned pale orange, the knob was closed and no more diluted hydrochloric acid solution flowed.
  12. The reading of the burette was recorded corrected to the nearest 0.05cm3 when the end-point was reached.
  13. The burette was refilled with diluted hydrochloric acid solution, with the initial level recorded.
  14. The conical flask was completely washed, and filled with 25cm3 sodium carbonate solution together with 3 drops of methyl orange indicator again.
  15. The solution was titrated again. When the end-point came close, the acid was added drop by drop, until the color had just changed.
  16. The new reading of the burette was recorded.
  17. Processes 13 – 16 was repeated for several times until the volumes of titre used had an average difference of less than 0.10cm3.
  18. The apparatus were washed immediately after the experiment.
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Data:

        

                                27.80+27.75+27.95

Average Volume =                 3

                    =        27.83cm3

Observation:

  1. Bench Hydrochloric Acid solution was colorless.
  2. Sodium Carbonate Solution was colourless.
  3. Burette was graduated with 500 0.1 cm3 intervals.
  4. While filling the burette, air spaces could be seen at the tip.
  5. After transferring the Sodium Carbonate Solution, there is some residual solution at the tip of the pipette.
  6. Methyl Orange Indicator solution was yellow in color before any reaction took place.
  7. Some gas bubbles evolved during the titration.
  8. During titration, the area where the Hydrochloric Acid solution contacts with the Sodium Carbonate ...

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