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The titrimetric determination of the concentration of sodium hydroxide

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The titrimetric determination of the concentration of sodium hydroxide 29.1.2010 Abstract Sodium hydroxide is a base often used in titrimetric analysis of drugs. Its concentration is required to be volumetric standard (VS). This means that the exact concentration must be determined by titration before it is used. The "volumetric standard" is defined by the British Pharmacopoeia (BP). "Ascertain the exact concentration immediately before use in the following manner. Titrate 20ml of the solution with 0.1M hydrochloric acid VS using the indicator prescribed in the assay in which the solution is to be used"1 In the BP, standardised solutions are written in italics e.g. 0.1M sodium hydroxide VS . Key Words Burette: a long vessel with a tap at the bottom which is used to measure accurately the volume of a solution added. The scale can be read to an accuracy of half a division e.g. ...read more.


Materials * Burette & Stand * Bulb pipette (10ml) and filler * Conical Flask (100ml) * Beaker (100ml) * White Tile * Funnel * Hydrochloric acid (0.5 mol dm-3 ) * Sodium Hydroxide (approx 0.4mol dm-3 ) * Distilled water * Methyl orange indicator Method Illustration showing how to set up equipment for titration, reading the meniscus and a sample results table. * The equipment was set up as illustrated * 20ml of sodium hydroxide was pipetted into the 100ml conical flask and approximately 3 drops of methyl orange indicator were added * The flask was placed over the mouth of the burette and the burette was filled with 0.5 M HCl and the volume mark was noted to 2 d.p. (measurement was taken at the bottom of the meniscus) * HCl was added to the conical flask containing the sodium hydroxide 0.5ml at a time whilst swirling to mix the reagents. ...read more.


Concentration = moles / volume 0.01689 dm3 x 0.5 mol dm-3 =8.445 x 10-3 mol 8.445 x 10-3 mol /0.02 dm3 = 0.422 mol dm-3 Discussion The accuracy of the experiment was perceived to be quite good. The results were very close together, the percentage difference was only 1.066%. The values obtained in this experiment were very close to values obtained in the class. Although the 3 values obtained were very similar, if one was very different, it could be omitted as it would skew the average. The burette was read fairly accurately however it was difficult to read on occasion because the scale was only marked up with tenths and not hundreds of a millilitre. Conclusion The purpose of this experiment was to determine the exact concentration of sodium hydroxide through a titration experiment. The concentration of NaOH was determined to be 0.422 mol dm-3. 1 British Pharmacopoeia. Vol IV.2008. Appendix I B. A134. MHRA.London ?? ?? ?? ?? ...read more.

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