Experiment 10 (1/5)

Experiment 10

Determination of the heat of hydration of copper (II) sulphate

(Approximate Method)

Objective

To determine the heat of hydration of copper (II) sulphate at room conditions.

Theory

If anhydrous copper (II) sulphate powder is left in the atmosphere it slowly absorbs water vapour giving the hydrated copper (II) sulphate solid.

CuSO4(s)+5 H2O(l)CuSO45H2O(s)

AnhydrousHydrated

copper (II) sulphatecopper (II) sulphate

(white powder)(pale blue solid)

Heat is evolved in the reaction.

This experiment enables an approximate determination of the heat of hydration of copper (II) sulphate to be made, by application of Hess's law of Constant Heat Summation. The heat of solution of anhydrous copper (II) sulphate and that of hydrated copper (II) sulphate are determined.

Procedures

I. Determination of heat of solution of anhydrous copper (II) sulphate

a)Place 150 cm3 distilled water in a plastic beaker (or polystyrene cup) using a measuring cylinder.

b)Find the mass of a dry watch glass.

c)Place accurately, about 6.0g of anhydrous copper (II) sulphate on watch glass.

d)Record the initial temperature of the water in the plastic beaker.

e)Finely powdered the anhydrous copper (II) sulphate and then add the solid to the water in the plastic beaker.

f)Dissolve the solid as soon as possible by stirring with a glass rod.

g)Record the maximum temperature change.

h)Complete part I of the table.

II. To determine the heat of solution of copper(II) sulphate pentahydrate

Proceed as in part I but use accurately about 10 g of copper (II) sulphate pentahydrate instead of the anhydrous salt. Record the results in the table above.

Table

I
Anhydrous CuSO4 / II
Hydrated CuSO4
  1. Mass of watch glass + copper(II) sulphate (g)

  1. Mass of watch glass (g)

  1. Mass of copper(II) sulphate (g)

  1. Highest/ lowest temperature of the solution (C)

  1. Initial temperature of water (C)

  1. Change in temperature (4)-(5) (C)

Questions

1. What is Hess's law of constant heat summation?

2. How can the equations for the reactions that take place be linked to form an energy cycle?

Label the energy cycle with:

H1 = Heat of solution of anhydrous copper (II) sulphate

H2 = Heat of solution of copper (II) sulphate pentahydrate

H3 = Heat of hydration of copper (II) sulphate

3. What is the expression for the heat of hydration of copper (II) sulphate, H3, in terms of the other two thermochemical quantities, H1 and H2?

4. What is the molar heat of solution of anhydrous copper (II) sulphate, H1?

5. What is the molar heat of solution of copper (II) sulphate pentahydrate, H2

6. What value is obtained for the heat of hydration of copper (II) sulphate H3?

7. What assumptions did you make in calculating H1 and H2?

8. What are the errors in this experiment and how could they be minimized?

9. Given that

CompoundStandard enthalpy of formation (kJmol-1)

Anhydrous copper (II) sulphate-770

Hydrated copper (II) sulphate-2278

Water-286

Calculate the theoretical standard enthalpy of hydration of anhydrous copper (II) sulphate. Compare the theoretical and experimental results and give comments.

Class: F.6____ ( )

Name: ______Date: ______

Title:Experiment 10 - Determination of the heat of hydration of copper (II) sulphate

Objective :To determine the heat of hydration of copper (II) sulphate at room conditions.

Results Table

I
Anhydrous CuSO4 / II
Hydrated CuSO4
  1. Mass of watch glass + copper(II) sulphate (g)

  1. Mass of watch glass (g)

  1. Mass of copper(II) sulphate (g)

  1. Highest/ lowest temperature of the solution (C)

  1. Initial temperature of water (C)

  1. Change in temperature (4)-(5) (C)

Discussion

  1. What is Hess's law of constant heat summation?

______

______

  1. How can the equations for the reactions that take place be linked to form an energy cycle?

Label the energy cycle with:

H1 = Heat of solution of anhydrous copper (II) sulphate

H2 = Heat of solution of copper (II) sulphate pentahydrate

H3 = Heat of hydration of copper (II) sulphate

  1. What is the expression for the heat of hydration of copper (II) sulphate, H3, in terms of the other two thermochemical quantities, H1 and H2?

______

  1. What is the molar heat of solution of anhydrous copper (II) sulphate, H1?
  1. What is the molar heat of solution of copper (II) sulphate pentahydrate, H2 ?
  1. What value is obtained for the heat of hydration of copper (II) sulphate H3?

______

  1. What assumptions did you make in calculating H1 and H2?

______

______

  1. What are the errors in this experiment and how could they be minimized?

______

______

______

______

______

  1. Given that

CompoundStandard enthalpy of formation (kJmol-1)

Anhydrous copper (II) sulphate-770

Hydrated copper (II) sulphate-2278

Water-286

Calculate the theoretical standard enthalpy of hydration of anhydrous copper (II) sulphate. Compare the theoretical and experimental results and give comments.

Conclusion :