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Finding Out how much Acid there is in a Solution

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Introduction

Finding out How Much Acid there is in a Solution When a metal is extracted from its ore, a waste product is often sulphur dioxide (SO2). This is then converted into sulphuric acid (H2SO4) and sold. To sell sulphuric acid, its accurate concentration must be known. In this investigation, I will use a titration method to attempt to find the accurate concentration of a sample of sulphuric acid thought to have a concentration of between 0.05 and 0.15 mol dm-3. The chemicals which I will use to do this will be solid anhydrous sodium carbonate (Na2Co3) and an indicator. Finding out How Much Acid there is in a Solution - Plan Quantities of Chemicals Required In this investigation, the chemical reaction used will be the neutralisation reaction between sulphuric acid and sodium carbonate: H2SO4 (aq) + Na2CO3 (aq) --> Na2SO4 (aq) + CO2 (g) + H2O (l) As the sodium carbonate has to be aqueous for this reaction, I will need to make up a solution of sodium carbonate before I begin the titration. I will need to choose an appropriate concentration for this solution and an appropriate volume of it to make up. As there is a 1:1 ratio between the moles of sulphuric acid and sodium sulphate used in this reaction, I should make up a solution of sodium carbonate of similar solution to that of the sulphuric acid. Assuming that the concentration of the sulphuric acid is around 0.1 mol dm-3, this will be the concentration of the sodium carbonate solution I make. Next I must decide what volume of solution to make up. Firstly I need to decide the volume of solution I will require per titration. This volume will be measures using a pipette and filler, so only set volumes, such as 10cm3, 25cm3 and 50cm3 are available. If I use 10cm3, the percentage error will be too large to produce reliable results, and if I use 50cm3, it is likely that I will need too much acid for a 50cm3 burette. ...read more.

Middle

Then I will complete the first titration, a rough titration - I will add acid from the burette into the conical flask whilst swirling the flask, stopping when I observe the colour change seen when I checked the indicator colour change. I will record the final burette reading to two decimal places in the table. I will then repeat the titration until I have three results, which are within 0.1cm3 of each other, excluding the rough titration, using the rough titration as a record to know approximately where the colour change takes place. Why this Plan will provide Reliable Results In the devising of this plan, I have taken several steps to ensure that it will provide reliable results: * I will wash out all equipment I have used to make up the sodium carbonate solution with deionised water, ensuring that no sodium carbonate is lost in the apparatus and the concentration of the sodium carbonate solution is precise. * When the sodium carbonate solution is made up, I will invert the flask at least ten times to ensure that the concentration is equal throughout the solution. * I will have a record of the colour change so that I will know exactly when the solution has been neutralised, so the concentration can be found accurately. * I will use a white tile during the titration to help me see exactly when the colour change has taken place. * I will measure all burette readings to two decimal places, to reduce the percentage error of the burette, so I can be sure that my results are accurate. * I will repeat the titration until I have three results within 0.1cm3 of each other. This will ensure that the average titre, and hence, the concentration found is accurate and does not include any anomalous results. Finding out How Much Acid there is in a Solution - Results I have now completed the practical part of my investigation; the results are shown below. ...read more.

Conclusion

* I ensured the colour for the end point was correct by keeping a sample of the initial titration, so that I measured to the same end point every time * I completed the titration using a white tile so that it was easier for me to tell exactly when the end point for the titration occurred, reducing the chance of overshooting, for example. * All values for the titration were measured to two decimal places, providing greater accuracy, and hence less potential for error in the calculations Improvements that could reduce errors Whilst I have assessed that my investigation will have produced reliable results, it was not perfect, and there are improvements that could be made to reduce errors, such as: * I could use a pH meter instead of indicator to more accurately find the end point of the titration, which would remove all procedural error from the process of finding the end point and would leave only the equipment error of the pH meter, which would be a lot smaller. * Similarly, I could use a data logger to measure the pH of my solution, which would not only give me a more accurate end point, but would show me the progression of the pH of the solution, making further titrations more accurate * To reduce the equipment error of the balance and the volumetric flask, I could weigh out more sodium carbonate and hence make a greater volume of sodium carbonate solution. Although this would probably leave some waste solution at the end, it would serve to reduce the percentage error of the balance and the volumetric flask, which are inversely proportional to the mass and the volume measured respectively. In summary, I have assessed that my investigation produced reliable results, identified and attempted to explain any anomalous results, investigated potential sources of error and looked at their possible effect on the final concentration of acid, and I have suggested some improvements that could be made to reduce these errors if I were to do this investigation again. ...read more.

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