2a: Determining the enthalpy change between zinc and copper sulfate Flashcards
What are the two equations for this reaction full equation and ionic equation
full: Zn(s) + CuSO4(aq) = ZnSO4(aq) + Cu(s)
ionic: Zn(s) + Cu(2+)(aq) = Zn(2+)(aq) + Cu(s)
what do sulfate ions act as (SO4(2-))
Spectator ions
What is the procedure for this practical
1: use a safety pipette to transfer 25 cm³ of copper sulfate into a polystyrene cup [colorimeter] place the cup in a beaker for stability
2: Using a digital balance way out 2grams of zinc metal powder in a weighing boat since the zinc is an excess there is no need to be too accurate.
3: call a thermometer in the solution and record the initial temperature to the nearest 0.1°C, when t=0
4: set a solution of a starring rod and record the temperature of the solution at one minute intervals for the next three minutes, until t=3
5: At exactly 4 minutes add all of the zinc powder to the solution in the polystyrene cup whilst stirring. do not record the temperature at this point.
6: Record the temperature for the next 10 minutes every minute.
7: during this time continue to stir the reaction mix well
How do we put a graph in this experiment [what goes on the X and Y axis]
Y axis: temperature [degrees Celsius]
X axis: Time [minutes]
plot the graph but do not plot a point for t=4
How do we analyze the graph plotted and how do we calculate the overall enthalpy change delta H
draw a line of best fit through the temperatures for the first three minutes. Draw a second line of best fit through the cooling points. Make sure to extrapolate both of the lines to t=4. this will establish the maximum temperature rise and therefore the temperature change in this reaction. Find the overall enthalpy change using q=mc deltaT. Unfold this reaction use the most of the limiting reagent which is copper sulfate.
Comment on the main sources of uncertainty in this experiment
uncertainties with the equipment [pipette/thermometer]
heat could have been lost to air in the surroundings
heat could have been lost to the equipment
Suggest improvements that could be made to increase the accuracy of this experiment
We could add a lid to the polystyrene cup to help prevent heat loss to the surroundings
Why was an excess of zinc used
to make sure all of the copper sulfate had enough reactant to react with so the copper sulfate could react fully
why was the temperature not recorded at t=4
This is when we added the sink to the copper sulfate, so there would’ve been hardly any time for the zinc to react
