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The aim of the investigation is to examine the kinetics involved in the reactions between acids and metals.

Extracts from this document...

Introduction

A2 Chemistry Coursework Reactions of Metals & Acids Reema Kohli Section 1: Planning The aim of the investigation is to examine the kinetics involved in the reactions between acids and metals. The investigation focuses on determining if: * The type of acid (strong or weak) and the type of metal have an effect upon the activation energy of a reaction. * The order of the reaction changes as the concentration of the acid is varied. Several methods can be used to follow the reactant, in terms of the rate at which it disappears in the reaction. One approach is to use a colorimeter to measure the light absorbency change. This would be unsuitable for both experiments because both reacting substances do not produce any colour. An alternate approach could be to use dilation. This also would be an unsuitable method to follow the rate of the reaction because the volumes in all the systems do not change significantly. The third method involves measuring the electrical conductivity using a conductivity meter. Again, this would be of little use because there are no changes in ion concentration in the reaction. It would also therefore be of no use to measure the rate of the reaction using alternating currents A Titration (continuous rate method) method would not be suitable for the investigation. The main reason for this is because the reactant would be hard to measure due to the intense velocity at which it disappears. Another reason is that there would not be a significant change in the concentration of solute. As a result the procedure will be too rapid for the acid to be neutralised via quenching using ice. Measuring the volume of hydrogen gaseous product evolved from the reaction and subsequently collecting it into a measuring cylinder over a water bath or directly into a gas syringe can also follow the rate of the reaction. ...read more.

Middle

Sulphuric 50.42 Hydrochloric 81.11 Nitric 372.26 The results table above shows that at room temperature the nitric acid is very slow. This acid will not be viable as it is too time consuming. The sulphuric acid has the quickest time; this implies sulphuric acid has the highest rate of dissociation. In contrast to nitric acid, sulphuric acid reacts too quickly with the magnesium ribbon, which means it cannot be measured accurately. It can be finally observed that hydrochloric acid is the most suitable for the experiment as it completely reacts with the magnesium in the most suitable time. Ethanoic acid is the only weak acid available; therefore it will be used to draw comparisons to investigate the difference between strong and weak acids. The experiment was initially conducted with a 2.00M solution of hydrochloric acid at room temperature and at 60.0oC. At 60.0 oC the reading was 18.22 seconds. The intense speed of the reaction proved a disadvantage as it made the experiment hard to control. It was then decided against using this concentration. This could have been overcome by using a higher volume of acid e.g. 20.00cm3. This is an awkward measurement to use with a standard sized 10.00 cm3 pipette, as it would have to be measured twice and placed into the test tube. This will lead to more inaccuracies in the experiment. It was finally decided to use a concentration of 1.00 molar. Choosing the Length of Magnesium Ribbon: To choose the appropriate length of magnesium ribbon several different lengths were to be tested in a reaction with 10.00cm3 of 1.00M acids at room temperature (21.0 oC). The following results were obtained: Length of magnesium (cm) Time (seconds) 0.50 42.23 1.00 42.28 1.50 79.42 2.00 60.53 The results above show some anomalies, for example the 1.50 cm reacted in a longer time than with the 2.0cm. This is inconsistent with the background research that was conducted because it suggested that a longer length of magnesium ribbon would result in a slower rate of reaction. ...read more.

Conclusion

For example if the oxide layer were thinner on a piece of magnesium, it would have required fewer strokes. The overall effect of this occurring is that the magnesium strip would disappear slower then in other reactions producing inconsistent results. * The amount of magnesium ribbon varied in each reaction in terms of how much the amount of surface area to volume ratio was available for the acid to react with. * Another source of error was that it was hard to distinguish the precise timing in which the magnesium disappeared. This was because there where always excess bubbles consisting of hydrogen gas, distorting the observation and recordings of when the magnesium ribbon actually disappeared i.e. when the reaction took place * The reflex action of starting the stop clock and placing the magnesium ribbon into the appropriate acid. This can influence the rate of reaction and therefore the activation energy calculated. Possible improvements for the investigation As with all experiments there is scope for improvement. The following shows the ways, which the experiment could be improved if it was conducted again: * A wider range of temperatures could have been used in the experiment. This would have produced a more accurate line of best fit causing a more reliable gradient produced. This will then lead to more reliable calculation of the activation energy. * Another source of error, which could have been improved on, is the fact that the reflex time would have been different in each experiment. This could have been overcome by using one person to time the experiment while another observes the reactant disappearing. * Another improvement, which can be made to the investigation, is to weigh the magnesium ribbon after cutting it into 2.00cm strips. A consistent mass will mean consistent and reliable results. This will help ensure the validity of the experiment * Another improvement for the activation energy investigation is to place a extra thermometer in the water bath as well to maintain accuracy in terms of temperature. Reactions of Metals & Acids 2 Reema Kohli ...read more.

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