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Primary and Secondary Standard solutions in chemistry (titration & colorimetry)

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Introduction

Primary standards, such as potassium hydrogen phthalate (KHP) (C8H5KO4), display unique characteristics such as high purity, maintain stability during storage within a long period of time whether in solid or liquid form, large molar mass as calculated to be 204 (RMM), low reactivity with the surrounding air, high stoichiometry and low hygroscopicity (property of absorbing water from its surroundings), which makes them ideal in making precise assessments of the unknown concentration of a known chemical. Secondary standards such as sodium hydroxide (NaOH) do not have the properties listed above, therefore it is low in purity, it is highly liable in absorbing the water molecules (H2O) from the atmosphere, it has high reactivity, it?s concentration changes over time, has lower molar mass known to be 40 (RMM). They are used in standardisations by comparing against primary standards. Primary standards are high in purity; whereas secondary standards have a low purity. Primary standards such as potassium hydrogen phthalate (C8H5KO4) remain stable when stored and the concentration does not alter over time whether it is in solid form or liquid form; however, secondary standards, for e.g. sodium hydroxide (NaOH), does not remain stable and the concentration changes rapidly over time. The primary standard, potassium hydrogen phthalate for example, has a higher molar mass (204 RMM) than the secondary standard, sodium hydroxide (40 RMM) ...read more.

Middle

Therefore, the calculations for the estimation of sodium hydroxide concentration will be inaccurate, which means that the concentration could be higher or lower than it is in actuality. Colorimeter Errors 1. The absorption-concentration graph for the calibration curve of identifying manganese in manganin wire could have been drawn inaccurately. Hence, this will directly give an inaccurate result as to what the concentration of manganese will be in manganin wire. 1. If the calibration of the colorimeter is not done before making any measurements, it will give the wrong result of the wavelength of the rose wine samples. Hence, the absorbance cannot be measured accurately and an inaccurate result for the actual concentration of the rose wine will occur. 1. If the serial dilutions for rose wine are performed incorrectly, meaning excess water remained in the test tubes and burette initially, before even beginning the serial dilutions, due to washing them with distilled water, the rose wine samples added into the test tubes will be extra diluted. Therefore, the absorbance of the coloured compounds will be slightly reduced and when drawing out the calibration curve, it will correspond to the inaccurate rose wine concentration. Improvements for Colorimetry: Instead of using a hand-drawn calibration curve, it could have been drawn on a computer program ?Excel? to ensure the accuracy of the graph and hence the calibration curve. ...read more.

Conclusion

Therefore, the volume measurements of the solution in the burette is quite reliable, due to being repeated. The preparation of Potassium Hydrogen Phthalate as a standard solution was carried out accurately (it was shaken until the potassium hydrogen phthalate dissolved properly) and therefore this allowed to gain an accurate result in the concentration of Sodium Hydroxide, which was 1.11627 molar. The results obtained for the rose wine concentration percentage was 4% for sample A, 46% for sample B, and 84% for sample C. All the absorbance values found for each of the samples -A, B and C- were within the range of the serial dilutions absorbance. Preparing a serial dilution allowed the results of concentration to be more reliable and therefore more accurate, as when forming a graph of calibration curve for the rose wine samples, the line of best fit was drawn much more accurately. The manganese concentration in manganin wire was identified as 9%, however it was to be about 12%. This could be due to the calibration curve being drawn inaccurately for the manganese sample. Using a computer program such as ?Excel? in drawing the calibration curve could have improved the result of concentration for the manganese sample, as it would make the line of best fit for the calibration curve graph much more accurate. Overall, the results gained were not ?entirely? accurate, however by repeating certain parts of the techniques, the reliability of the technique was increased as well as the accuracy. ...read more.

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