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Finding out how much acid there is in a solution.

Extracts from this document...

Introduction

Finding out how much acid there is in a solution - Chemistry Coursework PLAN Aim: The purpose of this experiment is to find an accurate concentration of sulphuric acid (H SO ) using titration with anhydrous sodium carbonate (Na CO ). I am told that the concentration of sulphuric acid is between 0.05 mol dm , but the task is to find out the exact concentration. The followng equation shows a reaction between sulphuric acid and sodium carbonate solution. Na CO (aq) + H SO (aq) Na SO (aq) + CO (g) This equation is a neutralization reaction. 1 mole of sodium carbonate reacts with 1 mole of sulphuric acid (see equation). When reacting together, both solutions will have the same number of moles. From reliable sources, I have been able to determine which of the various indicators to use in the titration. I found that methyl orange was the most suitable due to the fact that the titration to be carried out is between sulphuric acid (strong acid) and sodium carbonate (weak alkali). Firstly I will have to prepare a solution of sodium carbonate that will be used in the titration with sulphuric acid. It can be seen from the formula that it takes one mole of sodium carbonate to neutralise 1 mole sulphuric acid. Molecular mass of Sodium carbonate = (23X2) + (12) + (16X3) = 106g Molecular Mass of Sulphuric Acid = (2X1) + (32) + (16X4) = 98g It would take 106 grams of sodium carbonate to neutralise 98 grams of sulphuric acid if their molar concentrations were equal. As the exact concentration of sulphuric acid is not known an accurate prediction cannot be made. But the concentrations of the solutions are similar, therefore it should take roughly an equal amount of each substance in order that neutralisation occurs. This helps to determine the volume of the sample of sodium carbonate to be used. ...read more.

Middle

This is combined with 250 cm� water, we can convert this to dm� as 1000cm� = 1dm�. So, 250cm� = 0.250dm� (3sf) 1000 We then rearrange equation 1 as shown below and plot in the known amounts to receive the concentration. No of moles = Concentration Volume (dm�) So, the concentration in moldm-� is: 0.0250 = 0.100 moldm-� (3sf) 0.250 Concentration of sodium carbonate = 0.100 moldm-� (3sf) (b) Concentration of acid solution We are already aware that the concentration of the acid solution is between 0.05 and 0.15 mol/dm�. The equation for the neutralization of sulphuric acid with sodium carbonate is as follows: H2SO4 (aq) + Na2CO3 (aq) Na2SO3 (aq) + H2O (l) + CO2 (g) This shows that the mole ratio of sulphuric acid : sodium carbonate is 1 : 1. Therefore, we can say that The average concordant results of sulphuric acid used are: 39.25 + 39.30 + 39.20 = 117.75 3 = 39.25 If the concentration of Na2CO3 is 0.100 dm�, we can now work out the moles of H2SO4 using equation 1. This is because the ratio of Na2CO3 and H2SO4 is 1:1, therefore they both have equal volumes of 0.1 dm�, and hence, we can now use this in equation 1 to find the number of moles of H2SO4. Moles of H2SO4 = 0.100 dm� 0.025 Moles of H2SO4 = 0.100 � 0.025 = 0.0025 moles. We convert the average titre to dm� before inserting it into the equation: 39.25 = 0.03925 1000 Using equation 1 once again, we divide the number of moles by the volume to receive the concentration of acid solution in mol/dm�. 0.0025 0.03925 = 0.06370 moldm� (3sf) Concentration of sulphuric acid = 0.06370 moldm� (3sf) Evaluation From the results in the titration, the calculations suggest that the concentration of sulphuric acid is 0.0637mol/dm�. Despite the value not being precisely accurate, it seems to be in agreement with the initial statement that the acid is thought to have a concentration between '0.05 and 0.15moldm�'. ...read more.

Conclusion

This is to ensure that I can immediately stop the titration once the solution changes colour. Swirling the flask is very important; this is to ensure that all of the sodium carbonate solution and sulphuric acid is fully blended. It is also valuable because by mixing the solution together, I would be able to identify the change of colour. If the flask was not swirled, the colour change would not be clear and therefore the titre would be undoubtedly inaccurate. When starting a new titration I would have to fully wash the volumetric flask that contains the sodium carbonate solution so that it does not affect the new experiment and hence modify the results. Other equipment that could have been used in order to identify the change in colour for neutralisation is a light detector. A beam of light could have been shone through the volumetric flask. This would reduce human error and therefore make the results more reliable. Practising using the equipment for the titration would assist to reduce human error such as practising using the tap on the burette, reaching the meniscus line, reading the burette etc. Environmental control should have also been considered, such as evaporation of the liquid or temperature fluctuations. In order to overcome this, I would need a thermometer to ensure all liquids are about the same temperature. This is because temperature can affect the rate of reaction, and thus speed up or slow down reactions more than others. On the whole, the results that I obtained fitted within the specification of between .05 and 0.15moldm�. From my investigation, I found the concentration of the acid solution to be 0.0637mol dm-3, this shows that this amount of concentration of sulphuric acid was needed to neutralise the sodium carbonate solution. These results obtained are to a certain extent reliable and accurate. However, if I were to repeat the experiment overall, I would use the techniques as mentioned in my evaluation. By Farshea Saail ...read more.

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