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Acid-base Titration

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Introduction

S.6A Karen Kwok (8) 11th, September, 2002. Chemistry Laboratory Report Title: Acid-base Titration Date: 11th, September, 2002. Objective: (1) To determine the concentration of the unknown Sulphuric acid solution. (2) To learn how to use the pipette and burette skillfully. Result: The solution will change from yellow to orange when it is neutralized. 1st 2nd Final burette reading (cm3) 34.75 44.60 Initial burette reading (cm3) 9.55 19.25 Volume of sodium carbonate solution (cm3) 25.20 25.25 Calculation: The volumes of 0.0500M sodium carbonate required for neutralization are: 25.20 cm3, 25.25 cm3. Therefore the average volume of 0.0500 M sodium carbonate required for neutralization: = 25.20 + 25.25 2 cm3 =25.23 cm3 Na2CO3 (aq) + H2SO4 (aq) ´┐ŻNa2SO4 (aq)+ CO2 (g)+H2O (l) ...read more.

Middle

Why do we use methyl orange? Ans: If we use phenolpthlein as indicator, the solution will turn from pink to colourless, however, the solution which is neutral or acidic remain as colourless, therefore it is not easy for us to determine the end point,we cannot obtain an accurate volume of acid used. But when we use methyl orange, the solution will turn from yelow to pale orange. When the solution is neutral, it remain pale orange, when it is acidic, it will turn red, therefore, it is easy for us to determine the end point, so that we can obtain a more accurate result. (p.t.o. to continue) For strong acid (H2SO4) with weak base (Na2CO3), the pH at the equivalence point is always less than 7 because of the acidity of the conjugate acid of the weak base. ...read more.

Conclusion

in the solution has been exactly consumed by the titrant base (or acid). End point is the point at which indicator changes its colour, it occurs when the stoichiometric amount of acid has been added to the base. However as it is not easy for us to obtain an accurate value for end point, therefore it will be a little bit different from the equivalence point. 3. Why can phenolphthalein and methyl orange be used as the indicator when sodium hydroxide solution is titrated with standard sulphuric acid solution? Ans.: Because according to the titration curve for strong acid with strong base, the pH range for methyl orange (3.1-4.4) and the pH range of phenolpthalein (8.3-10.0) is very near to the equivalence point, therefore we can use both phenolpthalein and methyl orange as the indicator when sodum hydroxide solution is titrated with standard sulphuric acid solution. Titration curve for strong acid with strong base ...read more.

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