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Chemistry apparatus

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Volumetric pipette (25cm 3): This was used because of its high degree of accuracy in quantitative analysis. It has an error of 0.06cm 3 if used correctly (i.e. if it is allowed to drain and retain the last drop). The percentage error = error x 100 = 0.06 x 100 Reading 25 =0.24% This is a relatively small percentage and ensures that the volume of solution measured is accurate to the highest degree. Volumetric flask (250cm 3): This is used to make standard solution of a particular volume. If a 250cm 3 volumetric flask is filled correctly i.e. the bottom of the meniscus rests on the calibration line, the error is 0.2cm 3. The percentage error = error x 100 = 0.2 x 100 Reading 250 =0.08% The percentage error is low and therefore the flask measures the volume to a high degree of accuracy. Burette: One drop from a burette has a volume of approximately 0.05cm 3. All the burette readings should include 2 decimal places in which the second figure is either 0 or 5. ...read more.


Apart from the errors and uncertainties related to the precision of the equipments used, procedural error may arise from practical techniques. This would include: � Not mixing the solution in the volumetric flask thoroughly would make the solution have uneven concentration through out. Some areas would be more concentrated than others. A lower concentration would use less volume from the burette and this would make my result lower. A higher concentration would use more burette solution and would make my result higher. � Not washing the burette and pipette with the solutions they are to contain before titrating can be a source of error as other substances may be present in the equipment. This can affect the concentrations of the solution, hence the volume of the titre used. The substances that will increase the value of the titre will make my result higher and the substances that will reduce the value of the titre will make my result lower. � The conical flask needs to be thoroughly rinsed with distilled water in between titrations. ...read more.


Moreover, this is used in most standard titrations. Making the solution of sodium carbonate to a volume of 250cm 3 in a volumetric flask made available enough solution in case I overshoot pass the end-point and need to repeat the titration. This also ensures that there is enough solution to repeat titrations so that different values of titre will be collected and the average of them taken. This ensures accuracy. Since random errors affect reproducibility, they influence both precision and accuracy. Common random errors include titration errors, proper draining of buret, removing last drop from tip, and judging the correct color at the end point, weighing errors, judging the level of liquid in volumetric glassware, and parallax error in reading instruments and volumetric glassware. Titration Errors with Acid/Base Indicators a. Systematic error (determinate error): i. Any error that affects the accuracy of the results (consistently low or high) ii. pH at color change doesn't match pH at equivalence point b. Random error (indeterminate error): i. Causes data to be scattered symmetrically around the mean or true value ii. Limitations on eye as analytical instrument iii. Depends on (b) concn of indicator (c) eye sensitivity to two colors ...read more.

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