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Investigating the energy change during neutralisation reactions

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Introduction

INVESTIGATING THE ENERGY CHANGE DURING NEUTRALISATION REACTIONS Aim In this experiment I intend to investigate how the concentration of the solution affects the energy given off in a neutralization reactions. BACKGROUND KNOWLEDGE A neutralization reaction takes place when an acid and alkali of relatively the same concentration and volume react with each other to form salt and water. Acid + Base Salt + Water HCl + NaOH NaCl + H2O An acid is a solution that contains H+ ions and an alkali is a solution that contains OH- ions. To test for acidic or alkaline solution, pH indicator is used. When pH indicator is added to an acid, the solution turns pink. And when it is added to an alkali, the solution turns violet. During neutralization reactions, the H+ ions bond to the OH- ions to form water (H2O). As the bond is being made, energy is given out; the reaction is exothermic. E.g. H+ + OH- H2O Acids/Alkalis of the same chemical nature may still be different depending on the strength or concentration. Although these two might have the same effect, they are actually quite different. > The strength of an acid means how many molecules are ionised or disassociated in the solution. If the molecules are completely ionised or disassociated in the solution, they are referred to as Strong acids. E.g. Hydrochloric acid, Sulphuric acid and nitric acid e.t.c. ...read more.

Middle

As my background knowledge states, the more concentrated the acid/alkali is, the less water is present in the solution. Therefore there will be a greater amount of strong Na-Cl bonds created in the absence of the water molecules (giving that the volume remains the same) therefore giving of a greater amount of heat. So if the concentration is not kept constant for all my experiments, my results will be unreliable. 2. The Chemical nature of the acid or alkali. The chemical nature of the acid/alkali refers to the concentration of the H+ ions and OH- ions respectively. Stronger acids have more H+ ions concentrated in the solution than weaker acids. While stronger alkali's have more OH- concentrated in the solution than weaker acids. Consequently when conducting the experiment, if the chemical natures of both the acid and alkali are not kept the same, the heat given off will also vary therefore making my results irrelevant. * I will be investigating Factor 1. APPARATUS For this experiment I will require the following equipment: * 5 test tube * A 30ml measuring cylinder * A polystyrene cup with it's cover * A beaker * A sufficient amount of cotton wool * A thermometer Before the experiments begin, I make sure that all the equipments needed are of good for use and beneficial in gaining accurate results. PREDICTION I predict that as I decrease the concentration of the solution, the amount of heat given off will decrease. ...read more.

Conclusion

As you can see from the tables, as the concentration of the acid decreases, the heat given off decreases as well. This is because there are more weak H-OH bonds being made than strong Na-Cl bonds. And strong bonds give off a greater heat. This results to an overall decrease in the temperature given off. I also noticed that my temperature to start with kept on increasing as I proceeded with the experiment. This is a flaw because of the rising temperature due to the weather at the time. Another temperature flaw occurred in my third, fourth, and fifth graph. When I added some water to the solution of Alkali, the temperature changed. This should not occur because the water should not react with the alkali and therefore not give off any heat. This fault might be because of human error or probably the temperature of the water forces the overall temperature of the solution to fall. EVALUATION Although my experiment was quite successful to a certain degree, there were a number of faults that could be minimised. For example the temperature change when water was added to the alkali. This fault could be minimised if I conducted my experiment in an enclosed and well-insulated environment. The procedure I used to conduct my experiment was quite reliable to my understandings and I believe that it was the best way to conduct the experiment. The only change I would make is the apparatus. Instead of using a normal thermometer, I would prefer to use an electrical thermometer so that human error is limited. ...read more.

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