Polarisation in a simple cell

Polarisation in a simple cell

ZIMSEC O Level Combined Science Notes: Perfecting the electric cell

Voltage/Potential difference

  • The voltage between the two electrodes is dependent on the type of electrode used
  • When magnesium and copper are used the potential difference between the two electrodes is fairly high
  • Enough current flows to even light a bulb
  • If copper and zinc are used the voltage is insufficient to light the lamp
  • The current can however be read on an ammeter
  • A voltmeter can also be used to measure the voltage of the cell
  • It will show that the magnesium-zinc battery produces a higher voltage and more current than a copper-zinc cell
Negative TerminalPositive Terminal
MagnesiumCopper
ZincLead
IronIron
LeadZinc
CopperMagnesium
  • The table above shows the metals which could be used to make an electric cell
  • The least reactive metal can be used to make the positive terminal
  • The most reactive metal will be used to make the negative terminal
  • The further apart the minerals in the series the greater the potential difference (voltage)
  • For example the Magnesium-Copper cell gives the most potential difference
  • The Lead copper cell would give the least potential difference
  • A simple with a zinc plate for an electrode and
  • A copper plate for an electrode
  • and dilute sulphuric acid as an electrolyte
  • produces about 1 volt

Polarisation

  • After only a short time the cell stops working due to polarisation
  • Polarisation-this is when hydrogen bubbles collect on the copper plate of a simple electric cell and act as an insulator
  • Polarisation can be overcome by wiping the bubble off the plate at intervals
  • It can also be solved by adding a depolirising agent
  • A little potassium manganate (VII) to oxidise the hydrogen as soon as it forms

To access more topics go to the Combined Science Notes page.


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