Apparatus Justification
Safety
- Copper sulphate is harmful if swallowed. It can also be an irritant to the eyes and the skin, so a lab coat and goggles should be used whilst handling. Care should be taken to not inhale any fumes. If any is spilt in the laboratory, water and mineral absorbent should be added to the area.
- Lead Nitrate is toxic, and is harmful by digestion and inhalation of dusts. Care must be taken to ensure it does not get in the eys, so goggles should be worn at all times. It is an irritant so if spilt on labcoat or skin, the area should be washed immediately.
Diagram
Method
- The calorimeter was set up as shown in the diagram above. This was done by placing a polystyrene cup inside a glass beaker. 25cm³ of 0.2 molar copper sulphate was measured into the calorimeter, using a 25cm³ pipette.
- A thermometer was placed in the solution, and the solution was left for one minute to adjust to room temperature. This was timed by a stopwatch.
- During this time, one gram of zinc was measured out into a small container using electronic scales. After the one minute rest, this was added to the calorimeter and the temperature was taken immediately.
- The temperature was then taken every 30 seconds, and the mixture was stirred occasionally. The results were recorded in the results table below.
For the second experiment, the method was the same as in stages 2, 3 and 4. However, in stage one, 0.2 molar lead nitrate solution is used instead. Before being re - used, all the equipment needs to be washed out with distilled water.
Results Table
Calculations
1. CuSO4 + Zn ZnSO4 + Cu
0.2 Molar
25cm³
There are 0.2 moles in 1000 cm³ of Copper Sulphate
There are 0.2/1000 moles in 1cm³ of Copper Sulphate
There are 25(0.2/1000) moles in 25cm³ of Copper Sulphate
There are 0.005 moles in 25cm³ of Copper Sulphate
Due to 1:1 ratio, 0.005 moles of Zinc would be needed to react with it
2. Pb(NO3)2 + Zn Zn(NO3)2 + Pb
0.2 Molar
25cm³
There are 0.2 moles in 1000 cm³ of Lead Nitrate
There are 0.2/1000 moles in 1cm³ of Lead Nitrate
There are 25(0.2/1000) moles in 25cm³ of Lead Nitrate
There are 0.005 moles in 25cm³ of Lead Nitrate
Due to 1:1 ratio, 0.005 moles of Zinc would be needed to react with it
0.005 x 65.4 = 3.2
0.327 grams are the minimal mass of zinc needed. As it was needed in excess, 1 gram of zinc was used.
2. In order to find the enthalpy changes for the two displacement reactions, the following equation is needed:
Q = MCΔT
In this equation:
Q = Enthalpy change
M = Mass (of solution)
C = Specific heat capacity of the surroundings
ΔT = Temperature change
Reaction 1
25 x 4.2 x 24 = -2520 J
2520/1000 = -2.52 kJ
Reaction 2
25 x 4.2 x 22 = -2310 J
2310/1000 = -2.31 Kj
The values are negative because the reactions are exothermic.
Conclusion
The results suggest that the further apart the results are in the reactivity series, the larger the enthalpy change will be. The results could be further improved in several ways:
· The heat loss could be minimalised by placing a plastic lid over the top of the calorimeter
· Using a higher grade of equipment. For example, the pipette was grade B, and more accurate results could be achieved by using a higher grade of equipment.
· Repeating both experiments and then taking mean values. This would smooth out any anomalous results.
It must be understood that the results are only accurate to a certain degree because of the equipment. The scales only weigh to 2 decimal places, and the automatically round up. This means the results could be up to 0.009 figures out.
