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Aim/Objective: To determine the molarity of a given sample of Sulphuric acid by using titration

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Introduction

1) Title: VI Standardization of Sulphuric acid 2) Aim/Objective: To determine the molarity of a given sample of Sulphuric acid by using titration 3) Theory: A volumetric analysis is a method used to find out the amount of solute in a solution. It involves preparation of a primary standard, which is a solution of known molarity, and titration. When choosing a good primary standard, the requirements are that it should be cheap, stable in atmosphere and should not be hygroscopic to prevent the loss of solution. Also, it should have a high purity and high molar mass to prevent serious weighing error. In this experiment, sodium carbonate is chosen to be the primary standard, because it suits all the aforementioned criteria. Methyl orange should be used as the indicator, because in this experiment, a strong acid Sulphuric acid and a weak alkali sodium carbonate were involved. The pH of the resulting solution would be below 7, i.e. acidic. As a result, methyl orange, having a pH transition range of 3.1 to 4.4, should be used instead of the others. All the apparatus should be rinsed or washed before titration, since some dirt may be left on them in the previous experiments. They should be cleaned with tap water first. ...read more.

Middle

vi. The initial reading of the burette was taken. vii. Four drops of methyl orange indicator solution were added to the conical flask. The acid was run into the flask while the flask was swirled continuously. When an orange colour was seen, the acid was added drop by drop, until a yellow colour appeared. At this time, no more acid was added. The final burette reading was taken. viii. Other than washing the burette, procedures (ii) to (vii) were repeated for three times to obtain three consistent results. 7) Results: Trial 1 2 3 Final burette reading (cm3) 39.20 28.40 29.00 27.70 Initial burette reading (cm3) 10.25 1.70 2.70 1.15 Volume of Na2CO3 used (cm3) 28.05 26.70 26.30 26.55 Mean volume of Na2CO3 solution used to react with Sulphuric acid = (26.70+26.30+26.55)/3 =26.52 cm3 8) Calculation/interpretation: Equation of the reaction: Na2CO3 (aq) + H2SO4 (aq) � Na2SO4 (aq) + H2O (l) +CO2 (g) No. of moles of Na2CO3 dissolved: mass of Na2CO3 / molar mass of Na2CO3 = 2.654/ (23*2 + 12 + 16*3) = 2.654/106 = 0.025mol No. of moles of Na2CO3 used: 0.025 * (26.52/250) = 0.00266mol (3 sig. fig.) Ratio of no. of moles of Na2CO3 to H2SO4 = 1:1 No. ...read more.

Conclusion

Besides, after one titration, the conical flask used should be left behind as a colour sample for the next titration, because it was always difficult to distinguish between the orange and yellow colour of methyl orange at the end point. Having the previous colour sample in a conical flask could prevent confusion of whether the colour is orange or yellow. Regarding the possible errors, first of all, when doing titration, there may be some Sulphuric acid left on the inner wall of the conical flask. As a consequence, the recorded reading of Sulphuric acid used would be larger than the actual amount. Thus, the calculated molarity of Sulphuric acid would be larger. In a bid to eliminate this error, the inner wall of the conical flask should be washed by distilled water occasionally during the titration process to leash the Sulphuric acid back into the solution. Secondly, it was rather difficult to drip exactly one drop of Sulphuric acid from the burette into the conical flask at the final stage. Due to human error, usually more than one drop of Sulphuric acid was added. As a result, more practice for turning the stopcock of the burette from the horizontal position to slightly incline is essential to obtain a more accurate result. 10) Conclusion: The concentration of the Sulphuric acid was found to be 0.100M. ?? ?? ?? ?? Yu Wing Yee 6A(30) - 1 - ...read more.

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