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Neutralisation Investigation

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Peter Man 11Ashworth Chemistry GCSE: Coursework: Neutralisation Background information Substances that neutralise acids are called bases. Bases are alkali - they have pH's above 7; acids are acidic, and have pH's below 7. Bases that can dissolve in water are also known as alkalis. Acids Acids are compounds of non-metals with simple molecular structures. They all contain hydrogen (H) covalently bonded to other elements, like HCl, or H2SO4 (hydrochloric and sulphuric acid respectively). When an acid is dissolved in water, its molecules ionise. The hydrogen present in every acid has the potential to ionise; if it does, it becomes an H+ ion. It is the H+ ions that gives acids their acidic properties. The amount of an acid's molecules that ionise in water determines the strength of its acidity. Vinegar, for instance, is a weak acid, an only 1 in about 100,000 of its molecules ionise; on the other hand, almost all molecules of HCl ionise. This means that in an acid-base reaction involving vinegar, there are less H+ ions available to react, and so less bonds are made compared to an acid-base reaction involving HCl. Bond making is exothermic, and so less energy is given out. Stronger acids (those with a higher number of H+ particles that can dissolve in water) have a lower pH. Bases Just as all acids contain H+ ions, all alkalis contain OH- ions, and it is this OH- (hydroxide) ion that gives alkalis their alkali properties. Bases are usually oxides, hydroxides, or carbonates of metal. Ammonia is unusual in this respect, as it contains no metal element. Alkali substances are also very corrosive, and can do even more damage to living cells than acids. The neutralisation reaction NaOH(aq) + HCl (aq) NaCl(aq) + H2O(l) The above is an example of a neutralisation reaction, involving an alkali and an acid. The result is a salt and water. In every neutralisation reaction, the metal in the base (Na+ here) ...read more.


00 20 2.0 I have selected these values because these are a good range of concentrations and they will hopefully give me good results that I can analyse easily. I will repeat these measurements twice to get more reliable results. Preliminary Results Acid Water Alkali Temperature (?C) Quantity (cm3) Concentration (M) Quantity (cm3) Quantity (cm3) Concentration (M) Start Finish Change 00 0.0 20 20 2.0 21 21 0 04 0.4 16 20 2.0 21 24 3 08 0.8 12 20 2.0 21 26 5 12 1.2 08 20 2.0 21 28 7 16 1.6 04 20 2.0 21 31 10 20 2.0 00 20 2.0 21 33 12 I think that these results are very good and they are what I had expected. These results show that the higher the concentration of acid, the higher the energy rise. This means that the more the H+ ions there are, the more the energy there is. I will not change my method because my current one gives me accurate and reliable results. Obtaining Evidence Acid (cm3) Water (cm3) Alkali (cm3) Starting Temperature (?C) Finishing Temperature (?C) Temperature Change (?C) Average Temperature Change (?C) 1st 2nd 1st 2nd 1st 2nd 00 20 20 21 21 21 21 0 0 0.0 04 16 20 21 21 24 23 3 2 2.5 08 12 20 21 21 27 28 6 7 6.5 12 08 20 21 21 31 30 10 9 9.5 16 04 20 21 21 28 33 7 12 9.5 20 00 20 21 21 35 34 14 13 13.5 My preliminary experiment showed that the different concentrations and quantities I used worked well to give reliable results. The table above shows the results for both the 1st results, and the 2nd results- the repeated ones. I have then taken an average for each of the different molarities. To make my experiment more accurate, I did several things. ...read more.


I think that my results were fairly accurate, as most of them lied close to the line of best fit. If I were to do this experiment again, I would not change the way I measured things. I measured them accurately. There was one anomalous result. This is shown in the table in bold on page 4 and again it is ringed on the graph. I don't really know what had caused it- maybe I had not cleaned the polystyrene cup out before I added the new solutions. Or maybe I was too slow in putting the thermometer into the solution. I think that my results are consistent with each other. There weren't really any that were so different that I should have ignored. The anomalous result gave me a temperature change of 7 whereas when I had repeated I got a temperature increase of 12. This is a considerably large difference but I decided that I would not ignore it. I took the average like the other readings and plotted, circling it as an anomalous result. However I did ignore it when plotting the line of best fit. To extend my inquiry I can look at many things. Having looked at strong acids and alkaline (hydrochloric acid and sodium hydroxide solution) I can also look at weak acids and alkaline. However, the results should be the same except I would expect to get less energy from the weak acids/ alkaline. I could also look at mixing the tow: a weak acid with a strong alkali or vice versa. This could give some interesting results although they might not be fair. Looking at different acids and alkaline could also be done to extend my inquiry. This also links in with strong and weak acids. We could look at sulphuric acid or calcium hydroxide solution. This also links in with pH. We could use acids and alkaline of different pH's to see whether they follow the same pattern as the one we investigated. Another possibility would be looking at acids reacting with metals. ...read more.

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