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Objective: To determine the concentration of a solution of sodium hydroxide by titration against a standard solution of potassium hydrogen phthalate

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Introduction

Date: 19th November, 2010-11-21 Name: Merish Farooq Experiment no.: 1 Title: Acid-base titration Objective: To determine the concentration of a solution of sodium hydroxide by titration against a standard solution of potassium hydrogen phthalate Theory: A titration between sodium hydroxide and potassium hydrogen phthalate was carried out so that the concentration of sodium hydroxide can be determined. The acid, hydrogen phthalate used in this experiment is monobasic as it only produces one mole of hydrogen ions per mole is produced. An indicator phenolphthalein is used which is colourless in acid and pink in alkaline solution. It can be used to determine the end point of the reaction, which means the complete reaction between sodium hydroxide and potassium hydrogen phthalate solution. The reaction between potassium hydrogen phthalate and sodium hydroxide can be expressed as shown: H+ (aq) + OH-(aq) --> H2O The exact concentration of sodium hydroxide can be determined by the titration reaction between the potassium hydrogen phthalate and sodium hydroxide H+ (aq) + OH-(aq) --> H2O From the above equation No of moles of H+ (aq) ...read more.

Middle

In this experiment, the potassium hydrogen phthalate was standardized before it can be used to undergo titration. This is because the potassium hydrogen phthalate was in solid form and it can be found in pure state in solid form, thus it should be standardized as it is in solid form and titration involves both the base and acid to be in liquid form. In the titration experiment phenolphthalein was used as an indicator in the experiment. It is colourless in the presence of acid and pink in alkaline solution. The hydrogen ions in potassium hydrogen phthalate causes the phenolphthalein to become colourless. The hydrogen ions present in the potassium hydrogen phthalate will react with the hydroxide ions present in sodium hydroxide to from water. The presence of OH- causes the phenolphthalein to turn pink. Once the H+ and OH- reacts to form water, the H+ ions in the hydrogen phthalate will be used up to form water with the OH- ions as shown: H+ (aq) + OH-(aq) --> H2O The excess OH- will turn the solution alkaline and thus turn to phenolphthalein slightly pink. ...read more.

Conclusion

A) the burette should be rinsed with NaOH as the burette was washed with distilled water. This causes the concentration of NaOH to become slightly dilute and causes the concentration. B) As the pipette was first washed with distilled water, if it is not rinsed with potassium hydrogen phthalate this causes further dilution to the solution and causes the concentration of the NaOH disrupted. C) The tip of the burette should be filled with NaOH as no t filling it will cause some air bubbles to form. D) This causes further dilution to potassium hydrogen phthalate and disrupts the concentration. 2. Because it is easier to check the end point of the experiment as it can be easy to check the end point once the solution turns from colourless to slightly pink. 3. If it's an 'older' burette with a glass tap then the sodium hydroxide can react with the glass jamming the tap. Modern PTFE taps do not suffer from this problem - but it is still good practice to wash out all apparatus after use anyway. Conclusion: The average volume of NaOH used is 25.45 cm3 and the concentration of NaOH used is 0.09 mol dm3 ?? ?? ?? ?? Mr faisal ...read more.

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