Experiment One – Collecting data for the determination of ΔH₁

• Weigh approximately 4g of anhydrous Copper (II) Sulfate in a dry stoppered weighing bottle

• Record the precise mass of Copper (II) Sulfate

• Construct a suitable table to allow results to be recorded every minute over a 15-minute period

• Using a 25ml measuring cylinder, place 25ml of distilled water into the insulated cup and record the initial temperature (t = o)

• Start the timer and record the temperature every minute, ensuring you are stirring the liquid continuously

• At the fourth minute add the anhydrous Copper (II) Sulfate rapidly to the water and continue to stir. But do not take the temperature

• At the fifth minute record the temperature and do this every minute up to 15 minutes

• Plot a graph with temperature on the y axis against time

• Draw 2 separate lines of best fit. Line one which joins the points before the addition. Line two which joins the points after the addition

• Extrapolate both lines to the point of 4 mins

• Use your graph to determine the temperature change at the fourth minute

Experiment 2 – Collecting data for the determination of ΔH₂

• Weight out approximately 6.2g of Copper (II) Sulfate-5-water into a dry stoppered weighing bottle

• Construct a suitable table of results to allow the recording of the temperature at 1-minute intervals up to a total of 15 minutes

• Using a 25ml measuring cylinder, measure 24mls of distilled water into an insulated cup

• Record the temperature of the water and start the stopwatch

• Take the temperature every minute whilst continuously stirring the water

• At minute 4, add the Copper (II) Sulfate-5-water quickly and continue to stir

• At the fifth minute, record the temperature and do this every minute up to minute 15

• Plot a graph with the temperature on the y axis against time

• Draw 2 separate lines of best fit. Line one joining the points up to 4 minutes. Line 2 which joins the points after the addition

• Extrapolate both lines to minute 4

• Use your graph to determine the temperature change at the fourth minute

Analysing the data:

Heat change = mass x specific heat capacity x temp change

Heat change = M x C x ΔT

Note : Specific heat capacity (SHC) of cup negligible compared to the mass of water

Note: SHC of the aqueous solution can be considered to be the same as water

For both experiments you will need the mass of water in (g). Density of water 1g/cm³ the mass is therefore the same as the volume used, which in both cases was 25g

You will need the temp change in K from the graph

SHC for water – 4.18 JK^-1 g^-1

Value obtained for heat change will be in J. convert to KJ by dividing 1000 Calculate the enthalpy changes for ΔH₁₁ and ΔH₂₂ in KJ/Mol, using the masses for the solids Use two values of ΔH₁ and ΔH₂ and apply Hess’s Law and calculate ΔH₃ for the hydration of CuSO₄

Theory:
Hess’s Law:

Enthalpy change for a chemical reaction is independent of the route taken

This means that the enthalpy change for the overall process will be the same independent of the steps taken

Take the following reaction –

A + B → C + D

The enthalpy change to form products C + D directly will be the same as the sum of the enthalpy changes for the production of C + D by an undirect route, where there will be intermediate products formed