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Chemistry

Making electricity

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When metals form ions, they give away one or more electrons. Some metals, such as lithium or sodium, lose their electrons very easily. Other metals for example silver or gold do not give away electrons easily.The electrochemical series is a list of metals arranged in rank order of how easily the metal atoms lose electrons. The Electrochemical series in your data booklet will help you with this revision bite.

Think about the following points before you move on.What particles are inside atoms? What electric charges do they have? How do metals conduct electricity? How do ionic solutions conduct electricity?

Electricity from pairs of metals (General)

When metals give away their electrons, they do so with a certain force. This force is measured in volts. When two different metals are connected together in a cell, the metal with the higher force pushes its electrons on to the other metal. Look at what happens in a cell that is made from magnesium and copper in a beaker of ammonium chloride solution:

Electricity from pairs of metals. A strip of copper and a strip of magnesium metal are connected up to a voltmeter. Both strips are dipped in ammonium chloride solution.

The two metals produce an electric current. The magnesium is higher up the Electrochemical series than copper, so the magnesium can push away its electrons more strongly than copper. Electrons flow along the wire and through the voltmeter from the magnesium to the copper. This is the electric current. Remember that electrons cannot move through solutions.

The voltmeter measures the force that pushes the electrons through the wire. If you replaced the magnesium in this cell with other metals you would obtain different voltage readings. By arranging the metals in order of their voltage readings, you can build up the electrochemical series.

 

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The further apart the metals are in the electrochemical series, the higher the voltage. Electrons flow along the wire from the metal higher in the electrochemical series to the metal lower down.

To understand how electricity is made from pairs of metals you needto know these words:

  • Acell is an arrangement where electricity is generated from a chemical reaction.
  • An Electrolyte is a liquid that conducts electricity. In the magnesium/copper cell the electrolyte is an ionic solution - ammonium chloride in water. The electrolyte completes the circuit in the cell.

Example question

Now try to answer these short questions. When you are ready, look at the answers.

Question

Look at the pairs of metals and decide which way the electrons flow in each case. (General level knowledge)

  • a) Tin and silver
  • b) Iron and magnesium
  • c) Aluminium and copper
  • d) Lead and zinc
Answer
  • a) Electrons flow from tin to silver
  • b) Electrons flow from magnesium to iron
  • c) Electrons flow from aluminium to copper
  • d) Electrons flow from zinc to lead

This is testing knowledge at General level. You don't have to memorise the electrochemical series - it will be in your data booklet.

Question

The voltages between pairs of metals can be used to place them in an electrochemical series. Each metal is connected to the copper in turn. The experimental results are shown below. (Credit level problem solving)

Voltmeter with copper metal attached to one lead and strip of test metal attached to other lead and placed on top of copper strip, separated by filter paper soaked in ammonium chloride solution

MetalVoltageDirection of electron flow
10.6metal → copper
20.2copper → metal
30.9metal → copper
40.4copper → metal

a) Which is the most reactive metal?

b) Which is the least reactive metal?

c) Which pair of metals would give you the highest voltage if connected together?

d) What would the voltage be with the metals in part c?

Answer

a) Metal 3 is most reactive because it gives the highest voltage. Notice also that it pushes electrons on to the copper. This means that it is more reactive than the copper.

b) Metal 4 is the least reactive. Copper forces its electrons on to both metal 2 and metal 4, but it does so with more force with metal 4. This means that metal 4 is further down the electrochemical series than metal 2.

c) Metals 3 and 4 would give the highest voltage as they are the furthest apart in the electrochemical series.

d) The highest voltage would be 1.3V. Metal 3 has 0.9V of a force stronger than the copper. Copper has a force 0.4V stronger than that of metal 4. This means that the force between metals 3 and 4 is the sum of these two forces.

This is testing Credit level skills. You only need to write your answer to the questions. The explanations are not required unless they are specifically asked for.

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