Investigating the Factors Affecting the Temperature Change Between Zinc and Copper Sulphate

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Investigating the Factors Affecting the Temperature Change Between Zinc and Copper Sulphate

Introduction

When zinc is added to copper sulphate solution, zinc sulphate and copper are formed. This is shown in the equations below:

Zinc + copper sulphate → zinc sulphate + copper

Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)

Grey            Blue                Colourless        Red

Metal        Solution                Solution        Solid

This can be described as a ‘redox reaction’ – a reaction which occurs when both oxidation and reduction occur together.

Oxidation is described as the gain of oxygen, the loss of hydrogen or the loss of electrons. Reduction is the opposite of this – the loss of oxygen, the gain of hydrogen or the gain of electrons. In the case of zinc reacting with copper sulphate solution, however, it is only the electrons that are transferred:

Cu+2SO4-2(aq) + Zn0(s) → Zn+2SO4-2(aq) + Cu0(s) 

ZnO – 2e- → Zn+2(aq)                           Oxidation

Cu+2(aq) + 2e- → Cu0(s)                        Reduction

Cu+2(aq) + Zn(s)  Zn+2(aq) + Cu(s)       Redox Reaction

                    Reduction

Cu+2(aq) + Zn(s) → Zn+2(aq) + Cu(s)

 

                 Oxidation

Zn has been oxidised because it has lost two electrons and Cu+2 has been reduced because it has gained two electrons.

The oxidising agent brings about oxidation and in the process, it is reduced. In this reaction, Cu+2 is the oxidising agent because it causes the Zn to be oxidised and is reduced to Cu in the process. Similarly, the reducing agent brings about reduction and is oxidised in the process. Here Zn is the reducing agent because it causes the Cu+2 to gain two electrons and so, become reduced and it was oxidised to Zn+2 in the process.

As well as a redox reaction, this chemical change can also be described as a displacement reaction. This occurs when one metal will displace another metal that is lower than it in the reactivity series of metals, as shown below:

Potassium                K        

Sodium                Na

Calcium                Ca                                

Magnesium                Mg

Aluminium                Al                        The most reactive metals are found

Zinc                        Zn          Reactivity        at the top of the series, i.e. potassium

Iron                        Fe          Decreases        and sodium, and the least reactive are

Lead                        Pb                        found at the bottom, i.e. Mercury and

Copper                        Cu                        Gold.

Silver                        Ag

Mercury                Hg

Gold                         Au

The reaction between zinc and copper can be described as a displacement reaction because zinc is more reactive than copper, and so it displaces the copper from its solution.

Chemical reactions involve the transfer of energy, which is associated with the breaking and making of chemical bonds. When bonds are broken, energy must be put in; i.e. it is an endothermic reaction. When bonds are made energy is released, and therefore it is and exothermic reaction.

When copper sulphate and zinc are reacted together, the bonds that are broken are:

Cu — SO4        

Zn — Zn

atoms     atoms

This is an endothermic reaction because energy is put in so the bonds can be broken.

The bonds that are formed are:

Zn — SO4

Cu — Cu

atoms   atoms

This is an exothermic reaction because energy is released and so, bonds are formed.

The reaction between zinc and copper sulphate solution is described as an exothermic reaction because overall, more bonds are being formed than broken and so more energy is given out than taken in.

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The concentration of copper sulphate solution is 0.5 mol/litres. One mole of copper sulphate solution can be calculated as shown below:

CuSO4

1 mole = (1 x 64) + (1 x 32) + (4 x 16)

        =     64     +      32     +      64

        =   160g

The concentration of copper sulphate solution is therefore 0.16 mol/litres because 160 grams of copper sulphate is dissolved in 1000 cm3 of water. Similarly, 0.5 mol/litres can be worked out by calculating half a mole of copper sulphate, i.e. 160  2 ...

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