ELECTROLYSIS

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List of All Important Equations For Electrolysis

Frequently Tested Topics:

  • Electrochemical series

  • Electrolytes/electrodes used during various reactions

  • Observations and products formed during electrolytic reactions

  • Equations for electrolytic reactions

  • Strong and weak electrolytes

Important Past Questions:

  • Give reasons: Although copper is a good conductor of electricity, it is a non-electrolyte. (2005, 2016)

  • Name the gas released at the cathode when acidulated water is electrolysed (2005,2018)

  • Give reason: solid sodium chloride does not allow electricity to pass through. (2005)

  • As we descend the electrochemical series containing cations, the tendency of the cations to get ________ (oxidised/reduced) at the cathode increases. (2005)

  • The _________ (higher/lower ) the concentration of an ion in a solution, greater is the probability of its being discharged at its appropriate cathode. (2005)

  • Give the term for: a liquid or solution which conducts electricity with accompanying chemical change. (2005)

  • Electrons are getting added to element Y. Which electrode will Y migrate to during electrolysis? (2005)

  • Select from the list:

Ammonia, copper oxide, copper sulphate, hydrogen chloride, hydrogen sulphide, lead bromide.

i) A solution of this compound is used as the electrolyte when copper is purified.

ii) When this compound is electrolysed in the molten state, lead is obtained at the cathode. (2006)

  • State the observation when:

i) copper sulphate solution is electrolysed using a platinum anode. (2006, 2011)​

ii) electricity is passed through molten/fused lead bromide. (2013, 2014, 2017, 2018)

iii) copper sulphate is electrolysed using copper electrodes. (2013, 2014, 2015, 2017)

  • Write equations for the reactions taking place:

i) at the cathode and anode when acidified water is electrolysed (2006)​

ii) at the cathode when electric current is passed through a soln. containing Mg2+, Fe2+ and Cu2+ ions. Which ions will be the first to be discharged at the cathode? (2008)

iii) at the cathode and anode when a metal article is electroplated with silver. (2009)

iv) at the cathode and anode during electroplating of an article with nickel. (2010)

v) at the cathode and anode during electrolysis of CuSO4 soln. using platinum cathode and carbon anode. (2011)

vi) when copper sulphate soln. is electrolysed using copper electrodes (2013, 2016)

vii) at the anode during purification of copper (2015, 2018)

viii) at the two electrodes during electrolysis of molten PbBr2 with inert electrodes. (2016)

  • Give reason: 

Electrical conductivity of acetic acid is less than that of dil.H2SO4 at a given concentration (2015)​

Conductivity of dilute hydrochloric acid is greater than that of acetic acid. (2018)

  • Name the electrolyte used during:

i) electroplating of an article with nickel (2010)​

ii) electroplating an article with silver (2014, 2017))

iii) purification of copper (2015)

  • Name the respective electrode:

i) the cathode and anode during electroplating of an article with nickel (2010)​

ii) the anode during purification of copper (2015)

  • Give reason: Sodium chloride will only conduct electricity in the fused or aq. soln. state (2012, 2016)

  • Rewrite the correct statement with the missing words:

i) Lead bromide conducts electricity. (2009)​

ii) Cations migrate during electrolysis. (2012)

  • Give reason: A soln. of AgNO3 is a good electrolyte but is not used for electroplating an article with silver. (2006, 2009, 2016)

  • What is the product:

i) at the anode in aq. soln of nickel sulphate containing Ni2+ and SO4 2- ions? (2009)​

ii) at the anode during electrolysis of acidified water using platinum electrodes? (2016)

iii) Electrolysis of aq. sodium chloride soln. will form _________ (hydrogen gas/ sodium metal) at the cathode. (2018)

  • Name the kind of particles present in:

i) sodium hydroxide solution​

ii) carbonic acid

iii) sugar soln. (2014)

  • Name the metallic ions which should be present in the electrolyte when an article made of copper is to be electroplated with silver. (2016)

  • Select the correct answer:

i) the aq. soln of the compound which contains both ions and molecules:

A) sulphuric acid B) hydrochloric acid C) nitric acid D) acetic acid (2009)

ii) a compound which during electrolysis in its molten state, liberates a reddish brown gas at the anode

A) sodium chloride B) copper [II] oxide C) copper [II] sulphate D) lead [II] bromide (2010)

iii) a pink metal is depoisted at the cathode during the electrolysis of the soln. of this salt

A) sulphur B) silver chloride C) hydrogen chloride D) copper [II] sulphate E) graphite (2009)

iv) the weak electrolyte from the following is:

A) sodium chloride soln B) dilute hydrochloric acid C) dilute sulphuric acid D) aq. acetic acid (2012)

v) an aq. electrolyte consists of the ions mentioned in the list. The ion which could be discharged most readily during electrolysis is [Fe2+, Cu2+, H1+] (2012)

vi) the metallic electrode which does not take part in an electrolytic reaction [Cu, Ag, Pt, Ni] (2012)

vii) The ion which is discharged at the anode during the electrolysis of copper sulphate solution using copper electrodes as anode and cathode. [Cu2+, OH1-, SO4 2-, H1+] (2012)

viii) when dilute sodium chloride is electrolysed using graphite electrodes, the cation which is discharged at the cathode most readily [Na1+, OH1-, H1+, Cl1-] (2012)

ix) during silver plating of an article using potassium argentocyanide as an electrolyte, the anode material should be [Cu, Ag, Pt, Fe] (2012)

x) which will act as a non-electrolyte 

A) liquid carbon tetrachloride B) acetic acid C) sodium hydroxide aq. soln. D) potassium chloride aq. soln. (2013)

xi) the particles present in strong electrolytes are:

A) only molecules B) mainly ions C) ions & molecules D) only atoms (2016)

xii) the ion that would get selectively discharged from the aq. mixture of [SO4 2-, NO3 2-, OH1-] (2017)

xiii) the ion that would get selectively discharged from the aq. mixture of [Pb2+, Ag1+, Cu2+] (2017)

xiv) the electrolysis of acidified water is an example of:

A) reduction B) oxidation C) redox reaction D) synthesis (2018)

xv) during electrolysis of molten lead bromide of the following takes place:

A) bromine is released at the cathode

B) lead is deposited at the anode

C) bromine ions gain electrons

D) lead is deposited at the cathode (2008)

  • Give one word or phrase for: electrolytic deposition of a superior metal on a baser metal. (2014)

  • State which electrode anode or cathode is the oxidising electrode. Give reason. (2014)

  • Differentiate between:

i) strong electrolyte and weak electrolyte (2 differences) (2015)

ii) electrical conductivity of copper sulphate soln. & that of copper metal (2011)

  • Give reason: electrolysis of acidulated water is considered to be an example of catalysis. (2011)

  • Give reason: 

i) during electrolysis of molten lead bromide, graphite anode is preferred to other electrodes. 

ii) electrolysis of molten lead bromide is considered to be a redox reaction. (2015)

  • Name particles present in a liquid such as kerosene that is a non electrolyte. (2017)

  • Match the following:

i) A: non-electrolyte B: strong electrolyte C: weak electrolyte D: metallic conductor

1.  molten ionic compound  2. CCl4  3. an aluminium wire  4. a soln, containing solvent molecules, solute molecules & ions formed by the dissociation of solute molecules  5. a sugar soln. with sugar molecules & water molecules  (2007)

ii) Column A: 1. ammonium hydroxide soln.  2. dilute hydrochloric acid  3. carbon tetrachloride

Column B: A: contains only ions B: contains only molecules C: contains ions & molecules (2012)

  • An electrode 'A' is connected to the positive terminal of a battery and electrode 'B' to the negative terminal.

i) give the names of the electrodes A & B.

ii) which electrode is the oxidising electrode? (2006)

  • Here is an electrode reaction:

Cu ⟶ Cu2+ + 2e-

At which electrode would such a  reaction take place? Is it an example of oxidation or reduction? (2008)

  • A metal article is to be electroplated with silver. The electrolyte selected is sodium argentocyanide.

i) what kind of salt is sodium argentocyanide?

ii) why is it preferred to silver nitrate?

iii) state one condition to ensure that the deposit is smooth, firm and long lasting. (2009)

  • Aq. soln of nickel sulphate contains Ni2+ and SO4 2- ions. Which ion moves towards the cathode? What is the product at the anode? (2009)

  • A, B & C are three electrolytic cells, connected in different ciruits. Cell A contains NaCl soln., and the bulb in the circuit glows brightly, when the circuit is completed. Cell B contains acetic acid and the bulb glows dimly. Cell C contains sugar soln., and the bulb does not glow. Give reasons for each observation. (2010)

  • M2O is the oxide of a metal 'M' which is above hydrogen in the activity series. M2O when dissolved in water forms the corresponding hydroxide which is a good conductor of electricity.

i) state the reaction taking place at the cathode

ii) name the product at the anode. (2014)

  • Name a gas which in the liquid state does not conduct electricity but conducts when dissolved in water. (2013)

  • Copy and complete the following table which refers to the conversion of ions to neutral particles.

Conversion                                        Ionic Equation                                                  Oxidation/Reduction

Chloride ion to chlorine molecule (i) ____________                                         (ii) ____________

Lead(II) ion to lead                     (iii) _____________                                     (iv) ____________

Copper sulphate soln. is electrolysed using copper electrodes as seen in the diagram.
i) which electrode to your left or right is the oxidising electrode and why?
ii) write the equation representing the reaction that occurs.
iii) state two observations for the reaction. (2013)

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