5 Electrolysis Flashcards
Electrolysis (split)
Electro -> Electricity -> Flow of electrons
Lysis -> Pertaining to(maybe referring to the ions and electrons)
Describe an electrolytic cell:
- A non-conducting vessel
2. Containing the electrolyte (Aq or Fused)
Electrolytic cell must have a conducting vessel.
True or False.
False.
Anode is connected to the ____ terminal.
Cathode is connected to the _____- terminal of the battery.
Positive. Negative.
Define electrolysis
- Decomposition of a chemical compound
- Aqeous or Fused State
- Passage of direct electric current
- Results in discharge of ions as neutral atoms in respective electrodes.
Electrolysis is a physical or chemical change?
It is also a ____ reaction.
Chemical Change. Redox.
Electrolytes are always _____.
But its examples are not always this.
Ionic Compounds
Idiotic
Define Electrolytes:
Chemical compounds which conduct electricity in fused or aq state, due to the flow of current through it.
Define non-electrolytes:
Chemical compounds which do not conduct electricity in the fused or aq state.
Do ont undergo chemical decomposition.
NOn-Electrolytes are always _____.
But its examples are not always this.
Covalent compounds
Particles in Electrolytes
Ions only, Ions and Molecule only
Particles in non-electrolytes
Molecules
Examples of electrolytes:
All strong + weak electrolytes.
Examples of non-electrolytes:
Non-polar covalent compounds and aq solution of non-polar covalent compounds
Strong electrolytes:
- Electrolytes that allow large amount of electricity to pass through it.
- Good conductors of electricity
- Almost completely dissociated.
Particles in strong electrolytes are ___-.
Particles in weak electrolytes are ___-.
Ions only.
Ions and Unionized molecules.
Examples of strong electrolytes
All strong acids and bases and salts of strong acids.
Examples of weak electrolytes
All weak acids and bases and salts of weak acids.
Electrolytic cell definition. (device)
Device -> Electrolysis carried out.
Electrodes.
Electrolytic solution.
Electrylitic cell is also called
Voltameter.
Why electrodes?
They allow the current to enter or leave the current?
Electrodes can be (material)
Metal or Carbon
When are graphite or Carbon electrodes used
When the products formed reacts with the metallic electrode.
Depending on the connection to the battery, they are classified as
Anode or Cathode
Anode gets ____ and Cathode gets ____.
Oxidised; Reduced;
What are ions?
Atoms which carry a positive or negativ charge and become free and mobile when electric current is passed through an aq soln. of the comp.
Ions can be
Anions and Cations
Postulates of Arrhenius:
- Electrolyte on dissolving -> Free cations and anions and allow the flow of electricity
- = degree of dissociation -> extent to which it breaks up into ions.
- But amount of electricity -> Conc. of ions in the sol.
- All ions are responsible for the flow of current.
- No. of positive ions = No. of Negative ions. => Solution is electrolytic equillibrium.
Passage of current causes cations and anions to
Migrate
Preferential discharge depends on
the position in the electrochemical series.
Electrons gained and lost in the respective electrodes are
Equal
Products are formed in the respective
Respective electrosed itself
Exchange of electrons takes place in
Surface of the electrodes.
Elements liberated in cathode?
Hydrogen and Metals -> Electropositive elements
Elements liberated in anode?
Non-Metals -> Electronegative elements.
What is electrolytic dissociation?
Process due to which an ionic compound (in L or Aq) ->
Dissociates in the passage of electric current through it.
There is an equillibrium only in the number of charged particles. True or False.
False. An equillibrium is also established in the ions produced and unionized molecules.
Electrolytic dissociation takes place in __.
Involves __.
Electrovalent compounds
Seperation of ions already present.
Ionization takes place in ____.
it involves ____.
Covalent compounds.
Formation of charged ions from the molecules which are not in the ionic state.
Mg -> Mg2+ +2e- is ionization.
Yes. It may also involve atoms changing into ions.
Solid NaCl IS
Non-electrolyte.
Which energy is gained by the NaCl to break the ionic bond?
Kinetic energy.
Polar covalent compounds are ____.
Non- electrolytes in gas state. Ionize in Aq state.
HCl/NH3 in liquid state is ___. HCl/NH3 (aq) is ______.
Non-electrolyte! Electrolyte.
All good conductors are electrolytes.
False. Ex: Cu.
Metals are good conductors in _____ and ____- state.
Solid and Molten.
Is there a transfer in matter in metallic conduction?
No. No transfer of matter.
Electrolysis was first explained by ______ in ______ and he belonged to ___.
Avante Arrhenius; 1887; Sweden;
Transfer of electrons in ___ is ___.
But the transfer of ions in ____ is
not a chemical reaction
a chemical reaction.
Copper metal doesnt undergo
Chemical decomposition
Strenghtness of the electrolytes on the basis of
Degree of dissociation.
Which type of acids ionized on dissolution in water?
Mineral.
Give the chemical formula of the following and also classify them as weak or strong electrolytes:
- Formic Acid
- Lead acetate
- C.COOH
2. (CH3COO)2Pb
Carbonates, Bicarbonates and Acetates are
Weak electrolytes.
( Ca, Mg and NH4 )
Weak electrolytes.
Electrochemical series:
- Ease with which metal lose their electrons and form ions.
2. Arranged in a series.
Electrochemical series is also called
Metal reactivity series.
Electrochemical series:
Depending on the ease with which metals _____ and form ions.
Depending on the ease with which non-metals ___ electrons and form ions.
Lose electrons;
Gain Electrons;
Lower the position in the electrochemical series ->
More easily discharged. (both for ions and anions)
Ease of ___ decreases as one goes down and __ increase as one goes up, in the case of cations.
Reduction; Oxidation;
Ease of ___ decreases as one goes down and __ increase as one goes up, in the case of anions.
Oxidation; Reduction;
Preferential discharge ->
It is also known as selective discharge of ions.
Factors effecting selective discharge ->
- The position (lower the greater)
- The concentration (Higher the greater)
- Nature of electrode.
Dependency on position in electrochemical series ->
Lower the position of the ions, greater the tendency to be liberated.
Concentration of the ions, increases the __ of the ion being discharged. Give an example.
The probability.
Example:
Dilute vs Con. NaCl Solution.
In con. NaCl solution’s electrolysis, Na is preffered over H due to concentration.
True or False.
False. Despite the conc. H+ is preffered.
In con. NaCl solution’s electrolysis, OH- is preffered over Cl- due to concentration.
True or False.
False. Cl- is more concentrated.
Which is an example for the change in preferential discharge due to concentration?
Cl- is discharged instead of OH-.
Nature of electrodes determines the _____.
Preferential ion which will be discharged at the electrode.
Examples of Inert Electrodes:
- Iron
- Platinum
- Graphite
GIP
Examples of Active electrodes:
- Copper
- Nickel
- Silver
NiCopSi
_ electrodes lose electrons and form ions. The anions migrating are not discharged.
Active.
Which part of the electrolytic equation changes if we change from active to inert electrode>O
Anode reaction. Cathode reaction remains the same.
Name the following in the electrolysis of molten lead bromide:
- Cell
- Electrolyte
- Electrode
- Temperature
- Current
- Product at cathode and Anode
- Silica Crucible
- Molten Lead Bromide
- Graphite/Iron and Graphite
- 380 degree (mp of PbBr2)
- 3 Amperes
- Cathode -> Lead Metal; Anode -> Bromine vapors;
Lead metal is deposited as ____.
Silvery grey deposit.
Bromine vapors are ____.
Reddish brown fumes.
Why is the crucible made out of silica in Molten lead bromide electrolysis.
- Withstands High temperature
- Non-reactive
- Non-conductor of electricity.
Why is Crucible heated and why is it heated even after the Lead bromide comes to its molten state?
To make it an electrolyte.
Maintain lead bromide in the molten state :)
Why should electrode be inert?
Why should it be made out of graphite?
in molten lead bromide electrolysis.
- They shouldnt take part in the reaction -> Prevent teh discharge of the respective ions.
- Graphite anode is preffered, as it is unaffected by bromine vapors.
Is graphite preffered in anode or cathode for electrolysis of molten lead bromide?
Anode made of graphite is preffered.
If it is XY compound, then Y is discharged always as ______
Gas or Vapor state.
Name the following in the electrolysis of Acidified water:
- Cell
- Electrolyte
- Electrode
- Temperature
- Current
- Product at cathode and Anode
- The electrodes are placed in 2 inverted test tubes so as to collect the gas.
- Acidified water (dil. H2SO4)
- Platinum Foil
- Room temp.
- 3 amps
- Cathode -> Hydrogen(2 volumes); Anode -> Oxygen (1 volume);
Pure water is a
Non-electrolyte. Consists almost of molecules only.
How can water be electrolytically decomposed?
Addition of traces of Dil. H2SO4
Electrolysis of acidulated water is an example of
Catalysis
Why not nitric acid be used?
It is volatile.
It may decompose the NO3- Radical and may tend to interfere with the electrolytic reduction.
Why is the current passed for a prolonged period of time?
For the purpose of accurate comparison.
This ensure saturation of the gases in the electrolyte as solubilituy of Oxygen and Hydrogen is different.
Comment on the concentration of the substances during electrolysis
Concentration of SO4 2- increases at the anode and decreases at the cathode.
Total concentration of H2SO4 molecules remains the same.
____ has low discharge potential than ___. (water)
OH-; SO4 2-
Lower the position in the electrochemical series, ____ the discharge potential.
Lower;
Why does the total concentration of H2SO4 remains the same?
Because H+ and OH-ions actually discharged at the electrode respectively.
___H+ is required to produce ___ OH-
For _____ molecule of water, ___ molecules of H2 and ___ molecules of O2 are libterated
4, 4, 2, 2 and 1
2H 2 ->
2H + 2H -> H x 4
4OH ->
2H2O + O2
Fused NaOH discharges ___ and ___.
Aq NaOH discharges ___ and ___.
Na+ and OH-
Hydrogen (2 volumes) and Oxygen (1 volume)
In a strong acid HX, Ions present are
In a weak acid HX, Ions present are
- H3O+, X- and Minimum Undissociated molecules of HX.
2. H3O+, X- and Undissociated molecules of HX.
H2O dissociates into **
H+ and OH-
H2O dissociates into 2H+ AND O2-.
True or False.
FALSE!!!
Name the following in the electrolysis of Copper sulphate:
- Cell
- Electrolyte
- Electrode
- Temperature
- Current
- Product at cathode and Anode
- Normal
- Aq Cu(SO4) (H2SO4 maybe added)
- Copper and Copper (active)
- Normal
- 3 Amps
- Cathode -> Cu metal; Anode -> Nil (Cu2+ Ions formed)
To change the inert electrode, what only needs to be changed?
Anode
Why is H2SO4 dil added to copper sulphate?
- Enhances conductivity
- Prevents hydrolysis of the electrolyte
(Common ion effect)
____ ions are formed at the anode if copper electrodes are used and ____ is formed if platinum or carbon is used, as ___ ions are discharged. Also give the equation of anode with platinum anode.
Copper; Oxygen; OH-
(OH-) - (e-) -> OH x 2
[2OH -> H2O +[O] ]
4OH - 2H2O + O2
If copper is active electrode then there is a loss in
Mass in the electrode (anode)
The blue copper of aq. Copper sulphate
- Vanished when platinum electrode.
2. Stays the same when copper electrode is used.
Copper is a ___ colored metal.
Brownish-Pink
If copper anode is used ___ and ___ are spectator ions.
SO4 2- and OH-
Reason for the change in color when platinum electrodes or used.
Blue Cu2+ discharged are not replaced at the anode.
Name the 3 applications of electrolysis:
- Electroplating of metals
- Electrorefining of metals
- Extraction of metals -> Electrometallurgy.
What is electroplating?
Process of deposition of a superior metal on the surface of a baser betal.
Example of superior and baser metal:
Superior -> Nickel, Silver, Chromium and Gold.
Baser - Iron, Copper, Brass
Reasons for electroplating:
- Prevents corrosion/rusting of the base metal;
2. Makes the article attractive and gives it an “expensive “ appearence.
Why is nickel/chromium electroplated ?
Why is Silver or Gold electroplated?
For the prevention of corrosion of the base metal.
To make the article attractive and gives it an expensive appearence.
Conditions of electroplating:
- Article -> Kept at cathode
- Metal to be plated on the article -> Kept at anode.
- Electrolyte must contain the ions of metals used for electroplating.
- Low current long time.
- DC is used; AC is not used.
Name the number of electrons in the balanced equation for the following:
- Lead Bromide (molten)
- Acidified Water (dil. H2SO4)
- CuSO4 (aq dil.H2SO4)
- 2 electrons;
- 1 electron x 4
- 2 electrons
Always in the first step, electrons to be added or subracted are
The charge number; only then do addition or multiplication;
Give the reasons for the following:
1. Article -> Kept at cathode
2. Metal to be plated on the article -> Kept at anode.
Anode has to be replaced periodically.
3. Electrolyte must contain the ions of metals used for electroplating.
- Metal is always deposited at the cathode.
- The metal anode continuously dissolves as ions in solution and is hence replaced periodically.
- The electrolyte dissociate -> into the ions of the metals -> Which migrate and are deposited on the article.
Give the reasons for the following:
- Low current long time.
- DC is used; AC is not used.
- Higher current -> uneven deposition of the metal;
Lower current -> Smooth, Firm, Uniform and Long
lasting. SMULF - AC causes discharge and ionization to alternate at the cathode thus giving no effective coating.
Name the following in the electroplating of Nickel:
- Electrolyte
- Electrode
- Product at cathode and Anode
- NiSO4
- Article to be electroplated and Plate and Block of Nickel metal.
- Ni metal deposited on the “article” at the cathode.
NIL (Ni2+), Diminished in weight
Ions formed in the active anode are considered to be products.
False.
Nickel has a ___ position in electrochemical series than H2
Lower. Thats why it is discharged in preference to Hydrogen.
Name the following in the electroplating of Silver:
- Electrolyte
- Electrode
- Product at cathode and Anode
- Aq solution of Sodium Argento Cyanide
- Cleaned article to be electroplated and Plate or Block of Silver.
- Ag deposited and Nil (Ag1+ formed);
Dissociation of Sodium Argento Cyanide:
Na+ + Ag+ + 2CN-
What is electrorefining:
It is process by which metals containing impurities are purifies electrolytically -> Give a pure metal.
Conditions of Electrorefining:
- Item to be refined in placed at the anode.
- Thin sheet of the pure substance that is being purified is placed at the Cathode.
- The metals which are not extracted through electrometallurgy use this method.
Name the following in the electrorefining of Copper:
- Electrolyte
- Electrode
- Product at cathode and Anode
1.
Which metals are generally refined by electrolysis?
All metals below Al except for Iron:
Zn, Lead, Copper, Silver and Hg
Al2O3 is extracted by electrometallurgy. Why?
It is highly stable and Al has strong affinity for Oxygen.
Why highly electro-positive elements need not be electrolysed?
They are extracted by electrolysis and hence need not be refined further.
___ dimisished in mass.
Anode.
The impurities present in impure copper is called
Anode mud or Slime
Anode mud or slime contains ->
Gold and Silver as impurities.
Method of extraction of metals depends on the
position of the metals in the activity series.
Metals extracted by electrolysis are
K. Na, Ca, Mg and Al
Metals extracted by Reducing agents are
Zn, Iron, Pb and Cu
Metals extracted by thermal decomposition are
Hg and Ag
The balanced equation of electrorefining of copper has ___ number of electrons.
2 electrons.
