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To carry out a titration between a strong acid and a weak alkali, to eventually find the unknown concentration of sulphuric acid. However, the sodium carbonate (weak alkali) is solid, and you need two liquids to carry out a titration.

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Finding out How Much Acid There is in a Solution Planning: - Introduction: - During the extraction of a metal from its ore, sulphur dioxide is often produced. This is converted to sulphuric (VI) acid and is sold as a useful by-product. I am going to be given a sample of sulphuric acid which is thought to have a concentration between 0.05 and 0.15 mol dm3. I have to find out its accurate concentration by carrying out a titration between sulphuric acid and sodium carbonate. It is an acid-alkali titration. A titration is the "determination of material concentration by the successive addition of measured amounts of standard reagents to a known volume or weight of solution until a desired end point is reached." Acids and alkalis are classified as "strong" or "weak" depending on the extent to which they form ions when dissolved in water. Sulphuric acid is a strong acid which means it is completely in the form of ions in dilute solution. Sodium carbonate is a weak alkali, which means the process is only partially complete. Methyl orange is the best indicator to use to find the end point of a titration between a strong acid and a weak alkali. Na2CO3 (aq) + H2SO4 (aq) Na2SO4 (aq) + CO2 (g) One mole of sodium carbonate is needed to neutralise one mole of sulphuric acid. It has a 1:1 ratio. Aim: - To carry out a titration between a strong acid and a weak alkali, to eventually find the unknown concentration of sulphuric acid. However, the sodium carbonate (weak alkali) is solid, and you need two liquids to carry out a titration. This means I will make the sodium carbonate into a solution in order to carry out the titration, by dissolving it in distilled water. The concentration of the sodium carbonate solution is 0.1 mol dm-3 Apparatus: - * Spatula (to measure out the sodium carbonate) ...read more.


This helps make the actual titration much faster and more accurate and reliable, as I will know the exact amount of acid to use, and I will roughly know when to slow down the addition of sulphuric acid to the sodium carbonate solution to a drop. I am using the best indicator for reactions between strong acids and weak alkalis. This means the end point of my titration will be determined accurately, so that I can correctly work out the concentration of sulphuric acid. In devising my plan, I checked against another plan from the "student support coursework guidance" sheet, and my plan seems reasonable. I think it can be relied upon to produce accurate and reliable results. Implementing: - TITRATION READINGS ROUGH 1 2 3 4 5 AVERAGE TITRE Final 29.6 27.6 28.5 28.6 29 28.4 28.42 Initial 0 0 0 0 0 0 0 Amount of H2SO4 used (ml) 29.6 27.6 28.5 28.6 29 28.4 28.42 Analysing Evidence and Drawing Conclusions: - Moles = concentration x (volume/1000) What is the concentration of 250cm3 solution containing 2.65g of Na2CO3? Na2CO3 (aq) + H2SO4 (aq) Na2SO4 (aq) + CO2 (g) 1 mole of Na2CO3 neutralises 1 mole of H2SO4 1:1 Number of moles of sodium carbonate = Mass/RFM =2.65g/106 =0.025 Concentration of sodium carbonate = moles x (1000/volume) =0.025 x (1000/250cm3) =0.1M Number of moles of sodium carbonate = concentration x (volume/1000) = 0.1 x (25/1000) = 0.0025 What is the concentration of 28.43ml of H2SO4? Na2CO3 (aq) + H2SO4 (aq) Na2SO4 (aq) + CO2 (g) 1 mole of Na2CO3 neutralises 1 mole of H2SO4 1:1 I have already worked out the number of moles of sodium carbonate, and as there is a 1:1 ratio, sulphuric acid is the same number of moles. Therefore, 0.0025 moles of sulphuric acid = concentration x (25/1000) Concentration of sulphuric acid = 0.0025 x (1000/25) = 0.1M Conclusion: I can see from my results that the sodium carbonate solution and the sulphuric acid solution have the same concentration of 0.1M. ...read more.


This will ensure that my sodium carbonate solution is accurate, and will mean I can work out the concentration of sulphuric acid more accurately. However, this may be unnecessary for what I am doing, as the percentage error for the balance wasn't that high, and did not have a very significant impact on my results. A titration using a pH meter could be carried out, which is much more accurate, as the pH meter electrode is inserted in the solution, and I can read the pH and handle the burette with ease. It is better than a colour change because human error is not involved; it is all electronic and therefore more accurate. It will then be easier to work out the concentration of the sulphuric acid solution. I think I should have used a different bottle of methyl orange because the one I used was difficult to squeeze and the drops came out different sizes, leading to inaccuracies in the concentration of the green colour of my sodium carbonate solution. More acid is required to make a darker green turn clear, then a light green, so this is an extremely important change to improve my procedure. Other than that, I think I had an extremely accurate and reliable procedure as I kept the temperature constant, therefore liquid expansion was prevented, and volume readings contained no errors. Fixed errors in the measuring devices were cancelled out by using the same instruments. Some of my glassware was extremely accurate, such as the volumetric flask, and I was able to make an accurate sodium carbonate solution. The pipette was also extremely accurate as it delivered exactly 25cm3 of sodium carbonate solution into the conical flask. I also washed out all my glassware to ensure there was no contamination, and so that all the sodium carbonate was transferred properly to get an accurate solution concentration. I also shook my sodium carbonate solution after the final dilution to mix it thoroughly. I took adequate safety precautions to ensure my procedure was safe as well as accurate and reliable. Aisha Hussain Page 1 28/04/2007 ...read more.

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