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Investigation to find out the factors affecting heat of neutralisation, and then choosing one variable, ascertain its effect on heat of neutralisation.

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Introduction

INVESTIGATION INTO THE FACTORS AFFECTING HEAT OF NEUTRALISATION PLANNING AIM: to find out the factors affecting heat of neutralisation, and then choosing one variable, ascertain its effect on heat of neutralisation. A neutralisation reaction is a reaction between an acid and a base in which the acidity or alkalinity of a substance is destroyed, ie, either removing H+ ions by reaction with a carbonate or metal base, or removing OH- ions by reaction with an acid. To get a perfectly neutral solution of pH7, the H+ and OH- ions must be in exactly equal amounts. The ionic equation for neutralisation is: H+ + OH- H2O Heat of neutralisation or enthalpy change of neutralisation is the amount of heat energy given out when one mole of hydrogen ions is neutralised by one mole of hydroxide ions. POSSIBLE INPUT VARIABLES: * Concentration of acid * Concentration of alkali * strength (pH) of acid * strength (pH) of alkali * volume of acid * volume of alkali * basicity of acid (the no of H+ ions that can be replaced to form a salt) I know that the concentration of the reagents affects the heat of neutralisation, however this is not as advanced an experiment, and would not give me much to investigate/analyse and so I shall not choose this variable. The basicity of the acid affects the heat of neutralisation too, however I shall not investigate this variable because I am told that sometimes the results for this can be unreliable. Also, as there are not many acids available to me, I may not be able to get a wide enough range of measurements to make my investigation worthwhile. The volume of the reagents also effects the heat of neutralisation, however I shall not choose this variable as again the investigation would not be so advanced, or give me as much to investigate/ analyse as my chosen variable, nor do I find it as interesting. My chosen investigation is that into how the strength (pH) ...read more.

Middle

The calculation that must be used is DH= MC , where M= mass, C= specific heat capacity, = change in temperature. * I also know form previous experiments that when using dilute solutions, one can take the specific heat capacity and density to be the same as water. The specific heat capacity for water is 4.2, and as the mass will equal the volume (true for water) this will be 60cm3 - (the combined acid and alkali volumes). * so MC = 60 * 4.2 * temp change Joules * To get my answer in KJ I must divide by 1000. * This will give me the total KJ of energy for my experiment, and I wish to know the KJmol-1 .To find this I must divide by the number of moles for one of the reagents. * To find the no. of moles of alkali: volume (dm3 ) * concentration = no. of moles. =0.03 * 2 = 0.06 so KJmol-1 = - (MC / 1000 / 0.06). (this is negative as the reaction is exothermic) METHOD 1. Set up apparatus as shown below (labelled appropriately): 2. Fill the two labelled beakers with the appropriate substances (working through in order of results table)- so firstly with HCl and NaOH. 3. Measure very carefully 30cm3 NaOH into the polystyrene cup using the measuring cylinder and pipette, both labelled "alkali". 4. Measure and record the initial temperature of the solution 5. Using the other measuring cylinder and pipette, both labelled "acid", measure 30cm 3 of HCl very accurately in the measuring cylinder. 6. Pour the acid into the cup to join the NaOH, and immediately push down the lid and stir gently. Make sure you only hold the cup at the very top. 7. Wait until the maximum temperature has been reached, and when it shows no signs of rising any further, record it. 8. ...read more.

Conclusion

However this occured by equal proportions in each experiment, and so although my results were not 100% reliable, they were very accurate relatively speaking. However there are some improvements I could make for if I ever conduct this experiment again: * Make sure I get very precise volumes as this is needed for accurate results. Perhaps I could be even more careful, using the pipette more skilfully * Perhaps I could repeat my experiments one more time to make sure that my readings are accurate as I will have more data to average, and compare. * I could use more advanced equipment to avoid heat loss such as a calorimiter. This is the most important area for improvement, as this is what caused my results to be slightly below those in the data book, resulting in slight inaccuracies. * Next time I could revert to my original method and use 2M chemicals, although my experiments did seem to be unaltered by the adjustment to 1M chemicals. Also there are a few ways in which I could extend my investigation: * Investigate some of the other variables listed in my plan, and see the effects they have on heat of neutralisation. * Take my current investigation further by investigating a wider range of weaker carboxylic acids, and seeing whether the pattern of lower heats of neutralisation with longer chain lengths continues. This would be very interesting and seems to me a very worthwhile extension * Do more research and book work to find out exactly why the carboxylic acids do get weaker with longer chain lengths. Even though my results may not have been exactly those in the data book, they were only slightly below, and all relative to one another (ie. they were lower by the same amounts proportionally). This indicates that it was the heat lost to the surroundings causing this inaccuracy, which was the same in each case, as the same equipment was being used in each case. At least this indicates that my experiment was a fair test. Altogether I think my results are relevant and noticeably >90% accurate/reliable. ...read more.

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