Temperature after 1minute (i?? C) Change in Temperature (i?? C) 1g 17 19 2 As I had decided I was going to use 40cmi??of copper sulphate solution in my experiments I was able to calculate the amount of mols of copper sulphate I was going to use, knowing that the concentration of the CuSO4 was 0. 5m/dmi??. Amount of CuSO4 (mols) = concentration x volume = 0. 5 x 0. 04 (40cmi?? = 0. 04dmi?? ) = 0. 02mols Know that I knew the amount of CuSO4 used I was able to work out the amount of powdered zinc needed to give the highest change in temperature using the calculation shown below: Amount of substance needed = mass / molar mass (Mr of Zn = 65) … therefore mass = amount x Mr = 0. 02 x 65 = 1. 3g Thus 1.
3g of zinc should give me the highest change in temperature. As I am not using exactly 1. 3g of zinc I predict that either 1. 25g or 1. 5g of zinc will show the highest change in temperature. Practical – Obtaining my evidence Apparatus: powdered zinc, copper sulphate solution, beaker, measuring cylinder, pipette, balance, 5 evaporating dishes, thermometer, polystyrene cup and lid, stop clock. Method: I measured out amounts of of the powdered zinc separately, using the balance to ensure accuracy. I put the amounts into the evaporating dishes.
Using the measuring cylinder and a pipette, I then put 40cmi?? of copper sulphate solution into the polystyrene cup, which I placed into a beaker for stability. I then added an amount of zinc, placed the lid and thermometer onto the cup and took the temperature of the solution. After a minute I took the temperature again. I repeated this process for each amount of zinc powder. I completed my experiment three times to each amount of zinc powder. I did it three times to establish an average change in temperature for the different amounts of zinc used.
Results: Experiment 1: Amount of Zinc (grams)3 Conclusion: As I predicted 1. 5g of powdered zinc gave me the highest change in temperature. After this amount the change in temperature slowly began to decrease. Between 0. 5g and 1. 5g the temperature change increased rapidly. Specific Heat Capacity of Zinc The specific heat capacity (s. h. c. ) of a material is the amount of heat needed to change the temperature of 1kg of the material by 1i?? C or 1K. Different substances take different quantities of heat energy to heat them up.
Specific heat capacity = energy released / (mass x temperature rise) As I know this equation I can rearrange it to find the energy released during a reaction. If I also know the amount of a substance used in the reaction I can calculate the specific heat capacity of it. Energy released = temperature rise x specific heat capacity x mass of solution .
76 KJ/mol (exothermic reactions are always negative) From my results I have calculated that the specific heat capacity of zinc is -32. 76. This is inaccurate as from my data book I was able to find that the correct ? H of zinc is -219KJ/mol. This inaccuracy shows that although my results followed the expected trend, they were not accurate. Analysis In my plan I predicted that either 1. 25g or 1. 5g of zinc would show the highest change in temperature. After this mass I predicted that the change in temperature would either decrease or level off. This is what happened. In my average results 1.
5g of zinc gave me the highest change in temperature and after this the increase in temperature decreased because a layer of copper formed on the zinc, thus making it less reactive. If I were to continue with my experiments I would investigate higher amounts of zinc to prove this theory completely. In all of my experiments the copper sulphate lost its blue colouring and the zinc became red in colour. The copper compounds in copper sulphate cause the solution to be blue in colour. As the zinc displaced the copper, the solution lost its colour. As the copper layer formed on the zinc it became red, as copper is a red metal.
My graphs show the general trend that I predicted and concluded on yet there were a few anomalies. I believe that these will have been caused by factors such as contamination and heat loss to the surroundings. The thermometer may also have been inaccurate. An exothermic reaction is one which gives out energy to the surroundings, usually in the form of heat and usually shown by a rise in temperature. I have successfully proved that the reaction between powdered zinc and copper sulphate is exothermic as I recognised a rise in temperature in all my experiments.
I have also shown that the reaction between zinc and copper sulphate is a redox reaction (see my plan). Evaluation The anomalies in my results prove that there were points during my investigations where my accuracy left a little to be desired. An inaccuracy occurred in my time keeping, as there was often a small difference in when I began timing e. g. when I added the zinc or when I secured the lid on top of the polystyrene cup. Overall even though my experiment was open to some inaccuracies I believe it was accurate enough to support my predictions.
To improve my results I would increase the period of timing from 1minute to 5minutes so that the temperature could be allowed to rise more. I would extend my investigations into the reaction between zinc and copper sulphate by using a finer powder of zinc, which would give it a larger surface area, to see if this would cause the temperature to rise more rapidly. I would also like to complete the experiments using better equipment to prevent heat loss to the surroundings, to see if it has an effect on my results and thus, my conclusion.
I would have liked to use better equipment in my practical but they were not available. If I had more time I could use different metals and different solutions to further test the displacement rule e. g. the reaction between magnesium and zinc sulphate. Sources: G. C. S. E Chemistry Revision Guide – Richard Parsons Show preview only The above preview is unformatted text This student written piece of work is one of many that can be found in our GCSE Patterns of Behaviour section.