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Chemistry Investigation on neutralisation reaction.

Extracts from this document...

Introduction

Chemistry Investigation on neutralisation reaction Plan Neutralisation is the reaction that occurs when an acid has its acidity, that is its hydrogen ions removed by, another chemical containing OH- hydroxide ions. Chemicals that can cancel out an acid in this way are: bases (metal oxides or hydroxides), alkalis (bases that dissolve), metals (e.g. magnesium) or metal carbonates (e.g. marble chips) All of these have a similar way of removing the hydrogen from the acids (they swap it or their metal atoms) but the reactions are quite different. They will all get quite hot if the acid is strong enough, but only the last two will make bubbles. Metals form hydrogen gas, carbonates make carbon dioxide. All of them will leave a neutral chemical after the reaction has finished, if all the acid has been used up. Titration is a technique used to calculate the concentrations or amounts of substances. In an acid base titration you may have an acid that you don't know the concentration of, and a base whose concentration you do know. The technique is to measure out accurately a volume of the alkali of unknown concentration into a flask, and fill up a burette with the acid. Add some indicator solution to the acid in the flask, so that when all the acid has reacted with the base, there will be a colour change. The burette is graduated. You then open the tap on the burette and let the acid run into the flask. Once all the acid has reacted with the base, you get a colour change and you turn off the tap. ...read more.

Middle

Enthalpy is a measure of energy needed to break bonds and make new bonds. Different types of bonds need different amounts of energy and because different acids have different types of bonds in them they will need to have different amounts of energy to break them. This will affect the overall enthalpy of neutralisation. Obtaining evidence 0.1 moles/dm3 of HCl and NaOH Amount of HCL used (ml) Experiment 1 (0c) Experiment 2 (0c) Experiment 3 (0c) Average (0c) 0 18.6 21.6 21.6 20.6 5 19 21.8 21.7 20.83 10 19.2 21.9 21.8 20.97 15 19.4 22.3 21.8 21.17 20 19.5 22.3 21.8 21.2 25 19.6 22.2 21.8 21.2 30 19.5 22.3 21.8 21.2 35 19.5 22.2 21.8 21.17 40 19.4 22.1 21.8 21.1 45 19.4 22 21.7 21.03 50 19.3 21.9 21.7 20.97 Maximum rise in temperature 19.6-18.6 =1 22.3-21.6 =0.7 21.8-21.6 =0.2 21.2-20.6 =0.6 2 moles/dm3 of HCl and NaOH Amount of HCL used (ml) Experiment 1 (0c) Experiment 2 (0c) Experiment 3 (0c) Average (0c) 0 18.8 20.9 20.7 20.13 5 19.9 22.9 22.5 21.77 10 23.6 25.4 24.5 24.5 15 25.9 28.4 26.8 27.03 20 27.7 30 28.3 28.67 25 28.8 31.3 29.4 29.83 30 28.5 30.1 29.9 29.5 35 28.2 30.5 29.6 29.43 40 27.9 30.2 29.3 29.13 45 27 29.8 29.1 28.63 50 26.7 29.4 28.6 28.23 Maximum rise in temperature 28.8-18.8 =10 31.3-20.9 =10.4 29.9-20.7 =9.2 29.83-20.13 =9.7 Analysis When I mixed the acid with the alkali, a neutralisation reaction took place. This reaction was exothermic as heat was given out. The temperature went up. I added a little bit of acid at a time to a known volume and concentration of alkali. ...read more.

Conclusion

To make the experiment better I would have allowed the acid to run in to the alkali at a constant rate and get the computer to plot a graph of time against temperature change. As I know the time it takes for all the acid to run into the alkali I could then turn that graph into volume of acid against temperature change. This would be more accurate. This experiment could be repeated using different concentrations of the same acids or using other acids and alkali at different concentrations. When using different acids and alkalis it is important to workout how many moles of water are formed. If you don't then you can just measure the heat of neutralisation for a given mixture and the heat change would increase if the morality increased and the volumes remained the same. If you do know the number of moles of water produced you can find the energy change for producing 1 mole of water. In this case the heat of neutralisation will not change if you use more concentrated acids and alkalis. This is then called the Standard Enthalpy (or Heat) Of Neutralisation. The reaction between a strong acid and a strong base is the same irrespective of the acid or base used. If you look at the ionic equations they only include H+ and OH-. NaOH(aq) + HCl(aq) ? NaCl(aq) + H2O(l) Na+(aq)+OH-(aq)+H+(aq)+Cl-(aq) ? Na+(aq)+Cl-(aq)+H2O(l) From the above equation we can see that the sodium and the chlorine ions are present before and present after. So the real reaction is: OH-(aq) + H+(aq) ? H2O(l) 1 ...read more.

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This account is detailed throughout. There is relevant background theory, full explanations for steps followed and carefully worked calculations.

Marked by teacher Adam Roberts 14/10/2013

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