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Finding out how much acid there is in a solution.

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Finding out how much acid there is in a solution. During the extraction of a metal from its ore sulphur dioxide is often produced. This is converted to sulphuric (VI) acid. I have a sample of this acid, which is thought to have a concentration between 0.05 and 0.15moldm-3 . I have been asked to find an accurate value for its concentration. To obtain this I will use titration. By neutralizing the acid with a base, sodium carbonate, of set concentration, in the presence of an indicator, I will be able to calculate the concentration of the acid. Planning Apparatus: * 100cm� conical flask * 10cm� pipette and filler * Burette * 50cm� beaker * Funnel * Clamp stand * Glass stirring rod * White tile Solutions: * 100cm� acid solution sulphuric (VI) acid * 5.3g solid anhydrous sodium carbonate * Methyl orange indicator Method Add 500cm� distilled water to 5.3g anhydrous sodium carbonate and stir until the solid has completely dissolved. This is now a solution of 0.1moldm-3 sodium carbonate (alkali). Add 50cm� sodium carbonate to the burette using the funnel, then remove the funnel. Fill the conical flask with 10cm� sulphuric acid using the pipette. Add 5 drops of methyl orange indicator. ...read more.


RFM = 2 x 23 + 12 + 3 x 16 = 106 Moles= = 0.0251 moles (3sf) Combined with 250cm� water = 0.25 dm�. Therefore concentration in moldm� = = 0.100moldm� (3sf) Concentration of acid solution: Equation of neutralisation of sulphuric acid with sodium carbonate: Which means that the mole ratio of sulphuric acid : sodium carbonate is 1:1 Amount of sodium carbonate needed to neutralise 25cm� sulphuric acid = 27.7cm� Moles in 27.7cm� of 0.100 moldm� solution = 0.0277 x 0.1 = 0.00277 moles . Ratio : = 1:1 therefore moles = 0.00277 0.00277 moles in 25cm�. Concentration of= = 0.111moldm� (3sf) Conclusion The results obtained from my titration suggest that the concentration of the acid is 0.111moldm�. Whilst this value may not be accurate, it appears to agree with the original statement that the acid 'is thought to have a concentration between 0.05 and 0.15moldm�'. This is strong evidence to suggest that the investigation results are quite satisfactory, as they are in the expected range. The accuracy of the results is discussed in the evaluation. Evaluation There were no anomalous results obtained. As four of the results were the same titre, and all of the accurate titres were within 0.5cm� of the rough titre. ...read more.


Proposed improvements to method This investigation could be made more accurate with the use of a pH meter, rather than using a pH indicator to see when neutralisation occurs. This would eliminate the most significant source of error in the investigation (calculated to be around 1.8%). It would indicate more clearly when neutralisation occurs - methyl orange indicator changes colour from red to yellow at around pH 3.5 - 4, but a pH probe would give the exact point of neutralisation. Although this would not make a large difference in terms of titre, as the solution changes very quickly from acid to alkali as it nears neutralisation point, it would make the investigation far more reliable and not subject to individual colour perception. In order to minimise measurement errors, larger quantities of all solutions could be used, although concentrations would remain the same. This would reduce all errors, for example: 250cm� graduated flask. Error = = 0.08% 1dm� graduated flask. Error = =0.02% However, I would only consider this if more complex equipment was not available and a great deal of accuracy was required, as it would be time-consuming and would require some non-standard laboratory equipment. This would not be a worthwhile improvement if a pH probe were available. Results Titration Rough 1 2 3 4 5 Final burette reading Initial burette reading Titre ...read more.

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