effect of electric current on sunstances by otieno Domnic

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Effect of Electric Current on Substancesform 2
chemistry

• By Domnic Otieno
• Sega girls High-siaya

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KNEC Specific objectives

• a) define the terms conductor and non-conductor
  electrolyte and non - electrolyte
• b) classify solutions and molten substances as
  electrolytes and non-electrolytes
• c) distinguish between electrolytes and
  non-electrolytes in terms of the particles they
  contain
• d) explain the process of electrolysis and define
  the terms anode and cathode
• e) state the products of electrolysis of a binary
  electrolyte
• f) state some applications of electrolysis.

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Effect of Electric Current on Substances

• Define the following terms
• Conductor
• substances which allow electric current to pass
  through

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Sample1 To determine the products of
electrolysis of molten Lead(II)chloride

• (i)Decomposition of electrolyte into free ions
• PbCl2 (l) -gt Pb 2(l) 2Cl-(l)
• (Compound decomposed into free cation and anion
  in liquid state)
• (ii)At the cathode/negative electrode(-)
• Pb 2(l) 2e -gt Pb (l)
• (Cation / Pb 2 gains / accepts / acquires
  electrons to form free atom)
• (iii)At the anode/positive electrode()
• 2Cl-(l) -gt Cl2 (g) 2e
• (Anion / Cl- donate/lose electrons to form free
  atom then a gas molecule)
• (iv)Products of electrolysis therefore are
• I.At the cathode grey beads /solid lead metal.
• II.At the anode pale green chlorine gas.

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sample 2To determine the products of
electrolysis of molten Zinc bromide

• (i)Decomposition of electrolyte into free ions
• ZnBr2 (l) -gt Zn 2(l) 2Br-(l)
• (Compound decomposed into free cation and anion
  in liquid state)
• (ii)At the cathode/negative electrode(-)
• Zn 2(l) 2e -gt Zn(l)
• (Cation / Zn2 gains / accepts / acquires
  electrons to form free atom)
• (iii)At the anode/positive electrode()
• 2Br-(l) -gt Br2 (g) 2e
• (Anion / Br- donate/lose electrons to form free
  atom then a liquid molecule which change to gas
  on heating)
• (iv)Products of electrolysis therefore are
• I.At the cathode grey beads /solid Zinc metal.
• II.At the anode red bromine liquid / red/brown
  bromine gas.

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Discuss the effect of electric current on molten
lead(II) bromide
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QUESTION
a) State the observation that would be made in
the crucible when the circuit is switched on.
(1mark) b) Write an ionic equation for the
reaction at anode. (1mark) c) Give a reason why
this experiment should be performed in the fume
chamber. (1mk)
a)Greenish-yellow gas liberated at anode (1) //
Brown coating forms on the cathode b) 2Cl(l)- ?
Cl2(g) 2e-(1) c) The chlorine gas produced is
poisonous (1)
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Electrolysis of aqueous solutions
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Ionic compound
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observations

• Bulb light due to presence of free ions in
  molten lead (II) bromide which conduct
  electricity.
• Anode red brown fumes Br- ions are discharged
  there to form bromine
• Cathode formation of grey beads/solid as Pb2
  are discharged there to form lead metal

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Discussions

• During electrolysis of a molten substances the
  solid is heated so that it can melt and make ions
  free
• Ions in molten state are usually in liquid
  states. The positive ions (cations) migrate
  towards the cathode (negative electrode) while
  the negative (anions) migrate towards the anode
  (positive electrode).
• Electrons are produced at anode and leave the
  electrolyte through the anode, moves through the
  connecting wire (external circuit), and re-enter
  the electrolyte through the cathode.
• Electrons conduct electricity through the
  connecting wire (external circuit) while free
  ions conduct electricity in the electrolyte

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Discussion

• The setup below can be used to show the effect of
  an electric current on molten lead (II) bromide.
• When an electric current is passed through lead
  (II) bromide it is decomposed into lead metal and
  bromine fumes.
• This process of decomposing an electrolyte by
  passing an electric current through it is called
  electrolysis.
• Molten lead (II) bromide is an example of a
  binary electrolyte. This is because its melt
  contains Lead (II) ions and Bromide ions only.
• Note that the experiment must be carried out in a
  fume chamber. This is because Bromine fumes
  produced are very poisonous

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DISCUSSION

• Lead (II) iodide and lead (II) bromide do not
  conduct an electric current in solid state
  because their ions are held firmly by strong
  electro-static forces and this cannot move.
• However they conduct in molten state because
  melting weakens the electrostatic forces thus
  enabling the ions to move and thus conduct the
  electric current.
• Sugar and sulphur do NOT conduct electricity both
  in molten and solid state because they have
  molecular structures and lack charged particles
  to conduct the electric current.
• Some substances conducts electricity in both
  molten and aqueous state. Others do NOT.

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discussion

• Aqueous solutions of salts, bases and dilute
  acids conduct electricity. Sodium chloride,
  copper (II) chloride and dilute hydrochloric acid
  conduct electricity. Sugar and urea do NOT
  conduct electricity.
• An aqueous solution or melt which conducts an
  electric current and is decomposed by it are
  called electrolytes.
• Aqueous or molten solutions that do NOT conduct
  an electric current are called non-electrolytes.

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APPLICATIONS

• 1.Extraction of metals such sodium, magnesium and
  aluminium by electrolysis of their molten
  compounds.
• Extraction of Aluminium

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• 2. Purification of metals such as copper

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• 3.Electroplating Electroplating is the process
  of coating a metal with another metal using an
  electric current.
• During electroplating, the cathode is made of
  the metal to be coated/ impure.
• Importance improve their appearance(add their
  aesthetic value)and prevent/slow
  corrosion(rusting of iron).
• Electroplated watch

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• 4.Manufacture of pure chemicals such as sodium
  hydroxide.

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DEFINITIONS OF TERMS

• Electrolysis process in which a chemical
  substance in molten or in aqueous state is
  decomposed when an electric current is passed
  through
• Electrolyte substance in molten or aqueous state
  allows electric current to pass through and is
  decomposed by it.
• Non-electrolyte substances whether in molten or
  aqueous state do not allow electric current to
  pass through.
• Binary electrolyte an electrolyte which contains
  two ions only

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• THE END