CuSO4 solution Blue aqueous
Zn powder Black powder
The copper sulfate solution had a blue colour at room temperature, but as the reaction progressed and the zinc powder was added, the warmed up solution became a dark gray colour with red-brown deposits in it.
Calculations
CuSO4 solution specific heat capacity x Temperature rise x mass of copper sulfate solution = Heat Evolved (kJ)
Trial 1
Temperature rise = max temperature rise- initial temperature
= 4.2 x (56- 19) x 25.0g = 3.89 kJ
Moles of CuSO4 solution
Molarity= moles/ volume 1 M= n/0.025 dm3 Moles= 0.025 of CuSO4 solution
Enthalpy of this reaction
-3.89/0.025 = -155.6 kJ/mol
Therefore:
Zn(s) + Cu 2+ (aq)Cu (s) + Zn 2+ (aq) ΔH = -155.6 kJ/mol
Trial 2
Temperature rise = max temperature rise- initial temperature
= 4.2 x (62- 20) x 25.0g = 4.41kJ
Moles of CuSO4 solution
Moles= 0.025 of CuSO4solution
Enthalpy of this reaction
-4.41/0.025 = -176.4 kJ/mol
Therefore:
Zn(s) + Cu 2+ (aq)Cu (s) + Zn 2+ (aq)
ΔH=-155.6 kJ/mol
ΔH=-176.4 kJ/mol
Average enthalpy change
(-155.6 kJ/mol+ -176.4 kJ/mol)/2 =-166.0kJ
The accepted value in the data book: -218kJ/mol
Error Calculation
Variables Margin of Error Error Percentage (%)
Temperature (°C) ±1.0 Trial 1
(1.0/(56-19)) x 100
= 2.70%
Trial 2
(1.0/(62-20)) x 100
= 2.38%
Average: 2.54%
Time (secs) ±1.0 Min: (1.0/30) x 100
= 3.33%