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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. ...read more.


9. The whole solution gradually changed from yellow to red as the titration proceeded after a certain time interval. 10. At the end-point, the whole solution becomes orange-red. 11. There was a slight difference in volumes of titre used between each titration. Results: No. of moles presented in the Na2CO3 Solution = Molarity of Na2CO3 x Volume of Na2CO3 = 0.059M 25cm3 1dm3 1dm3 1000 cm3 = 0.001475 mol. By 2HCl(aq) + Na2CO3(aq) 2NaCl(aq) + CO2(g) + H2O(l) Mol. Ratio of HCl(aq) to Na2CO3(aq) = 2 : 1 Molarity of the Titre = = = Molarity of Bench Hydrochloric Acid Solution = Molarity of Titre x 10 = 0.106M x 10 = 1.06M Conclusion: The Molarity of this sample of Bench Hydrochloric Acid Solution is around 1.06M. (corr. to 3 sig. fig.) Discussion: * Since the concentration of Bench Hydrochloric Acid Solution may vary from sample to sample, the results obtained may not be suitable for other sample. * The Hydrochloric Acid Solution was diluted in order to give a more significant result. If it was not diluted, the molarity of the titre would be so high that only a few drops of it could end the titration. The change in burette reading would be too small, and the percentage error would thus be high. * Both the burette and pipette had to be washed with water in order to remove impurities. ...read more.


The accuracy of the experiment could be increased. * * * People nowadays use screened methyl orange instead of methyl orange for titration. The purpose of a screened or mixed indicator is to produce a more pronounced colour change at the end point. These types of indicators consist of either a mixture of two indicators or a mixture of an indicator and an inert dye. Screened methyl orange is a mixture of methyl orange and xylene cyanole FF (a redox indicator), 40:56. It changes colour at pH 3.8 -- 4.1 from violet to green. * The titration should be repeated for several times in order to get a more accurate result. The data were divided to give an average so as to increase accuracy. * The color change was rapid when the titration was close to its endpoint due to the high acidity of HCl. When the solution was neutral, the pH was around 7, and the color was yellow. However, if one or two more drops of HCl was added, the pH value would immediately drop to 2 or 3, since HCl was a strong acid. * During the titration, the following took place: 2HCl(aq) + Na2CO3(aq) 2NaCl(aq) + CO2(g) + H2O(l) * Only a few gas bubbles evolved since CO2(g) was very soluble in water, giving the following: CO2(g) + H2O(l) H2CO3(aq) * As Hydrochloric Acid Solution was a strong acid that irritates the skin and eyes, it should be handled with great care. Reference: Singapore Science Centre - ScienceNet - Physical Sciences - Analytical Chemistry ...read more.

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