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Measuring the Enthalpy Change for the reaction

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Introduction

Measuring the Enthalpy Change for the reaction between Zinc and Copper Sulphate Solution Equation: Zn(s) + Cu2+ (aq) ---------> Cu(s) + Zn2+ (aq) Results: This table shows how the temperature is affected by the reaction of Zinc and Copper Sulphate throughout the time interval (Zinc powder is added to the Copper Sulphate solution at the fourth minute). Time(minutes)� 0.02 1 2 3 4 5 6 7 8 9 10 11 12 Temperature �C � 0.2 19.2 19.2 19.2 40.2 45.0 45.2 44.6 43.8 43.2 42.4 41.8 Zinc Mass: 4.761g Observation: 1) To start with, the copper sulphate solution is transparent blue colour. 2) At the fourth minute, using the glass rod to stir the solution as the Zinc powder is placed into the solution, the colour changes into dark turquoise and the solution fizzes due to the chemical change. 3) The Zinc powder then dissolves in the solution. 4) As I stir the solution, the colour changes to grey with black precipitate. 5) Then, the solution gradually changes from grey to black with black precipitate. At the twelfth minute, the black precipitate dissolves yet the solution continues to fizz showing the chemical reaction is still taking place. After collecting the data and recording my observations, I then draw a linear graph in order to work out the temperature rise which occurred at the fourth minute. ...read more.

Middle

First of all, I will work out the maximum percentage error in using each piece of the apparatus. This is to ensure that I have include all the possible errors in the apparatus and so that I can comment on whether if the apparatus contributes in affecting the overall results. The maximum percentage error in apparatus: Error in balance = �0.001g = 0.001 X 100 4.761 = 0.02100 %( 4s.f) Error in the thermometer = �0.2 = 0.2 X 100 28.1 = 0.7117 %( 4s.f) Error in 50ml burette pipette= �0.05 = 0.05 X100 50.0 = 0.1% Overall maximum percentage error= 0.8327% = 0.833% (3s.f) Hence, after working out the maximum percentage error, I can use the figure to estimate the degree of uncertainty in my enthalpy change. The enthalpy change is -235 in 3s.f. I have decided to use 3s.f as an appropriate degree of accuracy so the maximum percentage error 0.8327% will be 0.833% in s.f. In my opinion, the maximum percentage error is small so therefore I don't think it will effect my enthalpy change to an extent as the smaller the number of the maximum percentage error, then the more accurate my enthalpy change will be. I also thought of including the error of the stopwatch but it wouldn't affect the maximum percentage error much so therefore I decided to exclude it from my calculation as the error is tiny and can be discarded. ...read more.

Conclusion

In order to see how well the performance of my results are, I will need to use the theoretical value of the enthalpy change and compare it with the value of my enthalpy change so that I can see how far my value is from the correct value. The theoretical values that I used are from the chemistry data book; JG Stark, H G Wallace, 1982, Chemistry data book, page 57. The values that are used for Copper aq and Zinc aq are: ?hf� (Cu2+ (aq)) = +64.4 ?hf� (Zn2+ (aq)) = -152.4 By using the Hess Law, I will work out the theoretical enthalpy change by using these values from the data book. ?h = -(+64.4) + (-152.4) = -216.8 Kjmol�� I will then compare my value with the theoretical value of the enthalpy change. To do this, i will work out the percentage difference between my experimental value and the theoretical value. This is to see how big the percentage difference between my value and the theoretical value as the smaller the percentage, the more accurate my value will be to the theoretical value. So first, I will work out the difference between my experimental value and the theoretical value. -216.8-(-234.916) = 18.116 Kjmol�� Then, I will use this value to find the percentage difference between my experimental value and the theoretical value. % difference: difference X 100 18.116 theoretical value = -216.8 = -8.35608% = -8.36% (3s.f) ...read more.

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