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# Determine whether the rate of the reaction changes as the concentration is varied, and find out what effect changing the type of acid used (strong or weak) will have on the activation energy.

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Introduction

THE RATES OF REACTION OF METALS WITH ACID AIM OF EXPERIMENT 1 To determine whether the rate of the reaction changes as the concentration is varied. AIM OF EXPERIMENT 2 To find out what effect changing the type of acid used (strong or weak) will have on the activation energy. SCIENTIFIC KNOWLEDGE Factors, which have an effect on the rate of a reaction Temperature - when the temperature is increased the rate of the reaction will decrease. This is because at higher temperatures molecules have more energy to move and collide with enough energy to react, so the reaction will be quicker. Concentration- if the concentration is increased then the rate will decrease. This is because there are more molecules within the same volume so they are more likely to collide and react, so the reaction will happen more quickly. Surface area - When the surface area of a substance is increased the rate of that reaction will decrease as the molecules of the reacting substance will have a greater surface to react on and so more molecules can collide at the same time, as a result the reaction will be quicker. Volume - if the volume is decreased then the rate will decrease this is because there are the same amount of molecules within a smaller space so when the molecules move they are more likely to collide and react, resulting in a faster reaction. When investigating one of these factors all others must remain constant in order to obtain accurate results. Activation Energy This is the minimum amount of kinetic (movement) energy required by molecules in order to overcome the repulsion between them and start reacting. The aim of experiment 2 is to find out the effect of using different types of acid (strong or weak) on the activation energy. When the concentration is increased the rate of a reaction decreases this is because, there are more molecules to reach the required energy and start reacting, so the reaction will be faster. ...read more.

Middle

Measure the time taken to produce 30 cm� of gas and record. Repeat for concentrations of 1, 1.3, 1.5 and 2. Do three runs for each different concentration and calculate the average. METHOD FOR OBTAINING DIFFERENT CONCENTRATIONS OF ACID USING 1M HCl For 0.1M - In a 10 cm� measuring cylinder place 1 cm� of acid then add pure water up to 10 cm�. For 0.3M - In a 10 cm� measuring cylinder place 3 cm� of acid then add pure water up to 10 cm�. For 0.5M - In a 10 cm� measuring cylinder place 5 cm� of acid then add pure water up to 10 cm�. Using 2M HCl For 1.5M - In a 10 cm� measuring cylinder place 7.5 cm� of acid then add pure water up to 10 cm�. RESULT I found from the preliminary experiment that the amount of reactants used were too small to produce a sufficient amount of gas to measure an accurate initial rate. The concentrations of 0.1M and 0.3M were too low to produce a sufficient amount of gas. To improve the final experiment I will use concentrations ranging from 0.5M - 2M HCl I will also use three magnesium strips to ensure a sufficient reaction occurs and enough gas is produced to measure the initial rate. EXPERIMENT 2 METHOD Measure 10 cm� of HCl using a measuring cylinder. Pour into a boiling tube and place in the water bath. Measure the temperature of the water heat if necessary to 20�C. Measure the temp of the acid to ensure it is the same. Once correct temperature is reached add 2 magnesium strips to the acid and immediately start the stop clock. Measure the time taken for all the magnesium to react. Repeat for temperatures of 30, 40, 50 and 60�C and again using CH CO H for each of the temperatures. Do three runs for each different temperature and calculate an average. ...read more.

Conclusion

61 19.33 63 18.05 EVALUATION AND CONCLUSIONS EXPERIMENT 1 The results indicate that when the concentration of the HCl was doubled from 0.5-0.1M, the rate roughly halved. When the concentration was increased from 1.0-2.0M, the rate was roughly divided by eight. These results suggest that the order of the reaction increases as the concentration increases. EXPERIMENT 2 The results suggest that when a stronger acid was reacted with magnesium the activation energy was lower than when a weaker one was used. The results of the previous experiments may have some inaccuracies due to errors during experimental procedures. In experiments 1 and 2, a measuring cylinder inverted in water was used to measure the amount of gas given off over a certain amount of time. This was a fairly accurate procedure, however it is quite subjective, which was possibly the main source of error in measurements, throughout the investigation. In experiment 2 the temperature of the solution surrounding the test tubes containing the reactants, was heated to different temperatures in order to make comparisons of activation energy. Although the temperatures were measured several times and averages were recorded, there is a strong possibility that the temperature did not remain constant throughout the experiments, this may have caused slight inaccuracies in the final results, however this would probably have effected each run in a similar way and so have little effect on the final outcome. The resolutions of the apparatus used play a part in how accurate the final results are. For instance the inverted measuring cylinders only measure to 0.1cm�, limiting their accuracy to this range. The thermometer used in experiment 2 only measured to the nearest degree, again limiting the accuracy to this range. Despite some experimental errors affecting the final results, I would say they were fairly reliable, as repeats were taken and averages recorded. Also, the results seem to indicate that the initial predictions based on scientific knowledge were correct, therefore suggesting that any errors made didn't have a major effect on the final results ...read more.

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