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"Finding out how much acid there is in a solution"

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Introduction

Anna Galloway As Level Investigation "Finding out how much acid there is in a solution" PLAN I will carryout an acid-base titration to determine the concentration of hydrochloric acid (HCl); I will do this by making up a solution of sodium carbonate (Na2CO3) of known molarity. I will then citrate the unknown molarity of acid into the sodium carbonate; from these results it will enable me to calculate the molarity of the unknown acid. The reaction: Sodium carbonate + hydrochloric acid sodium chloride +water + carbon dioxide Na2CO3(aq) + 2HCl(aq) NaCl(aq) + H2O(l) + CO2 Planning to make the sodium carbonate solution: I already know that the approximate concentration of the hydrochloric acid is around 0.2mol/dm, from the above balanced chemical equation I know that 2 moles of hydrochloric acid react with 1 mole of sodium carbonate; therefore I will make a solution of sodium carbonate of 0.1 mol/dm^3. Half that of the approximate molarity of the hydrochloric acid, I have made it 0.1 mol/dm^3 so to keep the volumes of solutions being titrated of a sensible amount as regard to the size of glass wear available. Calculations: Sodium carbonate salts relative formula mass: Na2CO3 . 10H2O = 106 . ...read more.

Middle

4).I will use the same number of drops of indicator to ensure same degree of colour change 5).I will use the same glass wear each time (so using same calibrations for measurement) 6). I will wash glass wear in corresponding solutions to ensure no cross contamination 7).I will record all measurements to 0.05 cm^3 to limit error 8).I will measure to the meniscus each time 9).I will use a pipette and volumetric flask rather than measuring cylinder because it increases accuracy 10).I will repeat experiments until I get concordant results to with in 0.1cm^3 What safety precautions must I observe? 1).I am working with acid/alkaline so must wear goggles 2).I will also wear a lab coat to protect my clothing 3).I must be careful to slowly pour liquids, so to avoid spillage on myself and work area (which could be potentially hazardous due to nature of chemicals use) 4).I will tie my hair back to stop it hindering my work RESULTS Titration Rough 1 2 3 4 5 Initial burette reading cm^3 8.1 8.1 17.85 16 2.45 2.9 Final burette reading cm^3 32.35 31.35 41.5 39.05 26.05 26.45 Titre cm^3 24.25 23.25 23.65 23.05 23.60 23.55 Coherent results Titration 2 4 5 Initial burette reading cm^3 17.85 2.45 2.90 Final burette reading cm^3 41.50 26.05 26.45 Titre cm^3 23.65 23.60 23.55 Calculations (molarity * volume) ...read more.

Conclusion

of glass wear/measurement could have contributed to the calculated molarity of the unknown concentration of hydrochloric acid being out by as much as 2.75 %. This could result in the true molarity lying between 0.21 mol/dm^3 and 0.219 mol/dm^3. Although there was a possible added error, which could not be accounted for in the figures - this being the point at which the experiment stopped (i.e. the exact point at which the indicator changed from one colour to the other). When researching indicators I came across another indicator which could possibly be better, bromothymol blue which had a useful range of 6.0 -7.0 pH, which distinctly changes in colour from blue to yellow, this may have been a better indicator to have used because it is nearer than methyl-orange to neutral, i.e. more accurate amounts of data collected. I am quite confident in my results, although I have identified errors within the experiment, possible error of +/- 1.35%, this sounds like a large error for a small quantity, however realistically this could be less; this being because of conducting repeats - this minimises the total error. Also I washed glass wear before and between procedures in the substance/solution which was to be used in it, this limited cross contamination which could have effected results from occurring, thus limiting error. ...read more.

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