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Investigate the effect that concentration has on a reaction on these factors: Temperature rise, Heat evolved, and Heat given off due to the neutralization between Hydrochloric Acid and Sodium hydroxide solution.

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Introduction

NAME: ASHLEY FERNANDES CLASS: SENIOR 5 'B' CHEMISTRY 'ENERGY CHANGES' COURSEWORK 13. 03. 04 INTRODUCTION Aim- to investigate the effect that concentration has on a reaction on these factors: * Temperature rise * Heat evolved * Heat given off due to the neutralization between Hydrochloric Acid and Sodium hydroxide solution. Neutralization takes place when acids react with substances called bases. When they react their acidity is cancelled out, and the reaction always produces a salt and water. The base can be soluble (when called an alkali) or insoluble like copper (II) oxide. Neutralization can be used for: * Treating insect bites (that are acidic) * Making fertilizers and other salts in industry. * Reducing the acidity in soil, to make it better for plants to grow and live in it. The heat of neutralization is the heat change when 1 mole of the acid used is neutralized. That is, it is the heat given out when water molecules are produced from one mole of acid. Following is the ionic equation that is stated for the neutralization reaction that we will carry out in the lab. NaOH(aq) + HCL(aq) --�> NaCL(aq) +H2O(l) Na+ + OH- + H+ + CL- --�> Na+ + CL- + H2O H+(aq) + OH-(aq) --�> H2O(l) Hence, Na+(aq) + CL-(aq) --�> NaCL(s) When the hydrochloric acid is mixed into the sodium hydroxide solution, the ions react with the various other ions present in the solution. In this increased (in volume) solution, the spectator ions are Na+ and CL-, as the ions of H+ and OH- react to form H2O. These spectator ions (Na+ and CL-) do not react to form a salt until the Water is formed from the H+ and OH- ions. In this reaction all four ions present, form bonds between each other, hence a lot of energy is given out. The reaction is said to given out a lot of energy, and hence reactions that give out energy are called exothermic. ...read more.

Middle

Temperature (oC) Volume of acid added (cm3) Temperature (oC) 0 24.6 0 24.8 5 29.6 5 29.5 10 33 10 32.9 15 35.2 15 35.1 20 36.5 20 36.9 25 35.4 25 35.9 30 34.4 30 34.9 35 33.6 35 33.9 40 33 40 33 NAME: ASHLEY FERNANDES CLASS: SENIOR 5 'B' CHEMISTRY 'ENERGY CHANGES' COURSEWORK ANALYSIS In the introduction of the coursework, I had said that if the concentration is doubled or tripled, the temperature rise and heat evolved will also double or triple. This is because when the concentration doubles, there are double the number of hydroxide and hydrogen ions in solution and therefore double the amount of bonds will be made. And when double the amount of bonds are made, it means that the Temperature Rise and the Heat Evolved will also be doubled. But the Heat of Neutralization will remain the same since it is only the heat change when 1 mole of H+ ions is neutralized, producing one mole of water molecules. (Reference to the predicted graphs of the effects of Temperature Rise, Heat Evolved and Heat of Neutralization, on concentration again which I had predicted previously in the introduction) Hence in order to test if my predictions are correct, I conducted an analysis on the readings and compared the different readings (Temperature Rise, Heat Evolved and Heat of Neutralisation), with the different concentrations (the whole section of Analysis). Below are tables in which I have calculated the average temperature of the two experiments, done for each concentration: 0.8M Volume of acid added / cm3 Temperature / oC 1st Test 2nd Test Average 0 23.8 23.6 23.7 5 26.4 25.6 26.0 10 27.6 26.9 27.25 15 28.2 27.8 28.0 20 28.8 28.4 28.6 25 28.4 28.1 28.25 30 28.0 27.7 27.85 35 27.5 27.3 27.4 40 27.0 26.9 26.95 1.2M Volume of acid added / cm3 Temperature / oC 1st Test 2nd Test Average 0 24.1 24 24.05 5 27.4 27.8 27.6 10 29.4 30.1 29.75 15 30.6 31.7 ...read more.

Conclusion

Hence to get very accurate readings, I should have waited for a few seconds or so, in order to let the reactants react properly and the then read the thermometer. A stirrer could also have been used to mix the reactants in proportion as well. Other possible precautions in the future: The plastic cup should have been covered with a lid and a hole in it to fit the thermometer into. This would have drastically reduced the heat lost due to convection currents. This would have probably resulted in very accurate readings. The cup should have been insulated, put into another cup or maybe even made of another material such as polystyrene, in order to reduce the heat lost due to conduction. The following procedure to carry out the experiments is improved: 1. Measure out, and then fill 20 cm3 of alkali in the cup. Add 5 cm3 of acid and then measure the temperature. 2. Then throw out the solution, clean the cup dry and then add 10 cm3 of acid to 20 cm3 of alkali. Then note down the temperature. 3. After this again throw out the solution, clean the cup dry and continue in the same manner each time, adding 5 cm3 of acid. This method would also produce excellent results. But to carry out this method is not suitable as it is a waste of acid, alkali and also of time. Another method to have very accurate results would be to make sure that the above precautions are taken and that the thermometer is replaced with a 'Data logger'. This data logger automatically notes the temperature readings when called upon to, of a solution. This method however is quite expensive and is usually not carried out in a school laboratory and therefore it proves to be unnecessary. With this coursework, I have hence achieved a good success rate since most of my predictions nearly match the obtained values and graphs. ...read more.

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