Lab Test - ii) a dirty buret : Effect : Larger molarity of...

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Unformatted text preview: ii) a dirty buret : Effect : Larger molarity of KMnO 4 Explanation : A dirty buret could affect the volume of KMnO 4 required for titration, as other chemicals or water could mix with it. Thus, the molarity would fall since the KMnO4 could stick to the walls of the buret, so the measured volume would be larger than the actual amount of KMnO4 used. This mostly affects the accuracy of the measurement, as this cannot be attributed to randomness. iii) undershooting the end point : Effect : Greater molarity of KMnO 4 Explanation : If the end point is not reached, then less K is used than necessary, making the volume in the buret incorrect and less than needed. Thus, the molarity of KMnO 4 will be higher than expected. This mostly affects accuracy, as this error could be removed in a repeat of the experiment, meaning the error is not random. iv) the primary standard dissolved in smaller than prescribed amount of water: Effect : No effect Explanation : If the amount of water is less than prescribed, then the molarity of the solution will stay the same. This is because the same amount of KMnO 4 would be required to titrate the same amount of Na 2 C 2 O 4 in the solution. This does not affect precision or accuracy. v) few drops of titrant didnt make it into the solution : Effect : smaller molarity of KMnO 4 Explanation : If a few drops of titrant didnt make it into the solution, then the molarity will decrease due to the great recorded volume than the actual volume used. This mostly affects accuracy because this is a systematic error. It cannot be attributed to randomness. vi) reading errors : Effect : Either larger or smaller molarity of KMnO 4 Explanation : If the volume on the buret is read incorrectly, then the volume of KMnO 4 will be inaccurate. This will result in an increase or decrease in molarity, depending on the reading error. Because reading error is not duplicable and the error is random rather than systematic, the precision will be mostly affected by this type of error. i) wet primary standard : Effect : Smaller molarity of KMnO 4 Explanation : A wet primary standard affects the concentration of the Na 2 C 2 O 4 , as the weight of Na 2 C 2 O 4 will be more than the actual amount of Na 2 C 2 O 4 . This makes the moles of Na 2 C 2 O 4 decrease, making the overall molarity of KMnO 4 decrease. This mostly affects the accuracy of the measurement, as this error affects the concentration of the Na 2 C 2 O 4 and cannot be attributed to randomness. 5C...
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This note was uploaded on 01/23/2012 for the course CHEM 18a taught by Professor Dolnik during the Fall '06 term at Brandeis.

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Lab Test - ii) a dirty buret : Effect : Larger molarity of...

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