Quick Review Flashcards - Click to flip and test your knowledge!
Question
Define 'electrolysis' based on its chemical effect.
Answer
The decomposition of a chemical compound in the aqueous or fused state by the passage of a direct electric current.
Question
What term describes compounds that conduct electricity when dissolved in water or in a molten state and undergo chemical decomposition?
Answer
Electrolytes.
Question
Which particles are the sole constituents of non-electrolytes like sugar or alcohol?
Answer
Molecules only.
Question
How does the degree of dissociation differ between strong and weak electrolytes?
Answer
Strong electrolytes are almost completely dissociated, whereas weak electrolytes are only partially dissociated.
Question
Identify the primary particles present in a solution of a strong electrolyte.
Answer
Mainly ions.
Question
Why does a bulb glow dimly when testing a weak electrolyte in an electrolytic cell?
Answer
Because weak electrolytes allow only small amounts of electricity to flow through them.
Question
Give an example of a common non-electrolyte liquid used as a solvent.
Answer
Carbon tetrachloride ($CCl_{4}$).
Question
To which terminal of a battery is the anode connected?
Answer
The positive terminal.
Question
To which terminal of a battery is the cathode connected?
Answer
The negative terminal.
Question
Explain why the cathode is referred to as the 'reducing electrode'.
Answer
Because reduction (gain of electrons) takes place at the cathode as cations receive electrons.
Question
Explain why the anode is referred to as the 'oxidising electrode'.
Answer
Because oxidation (loss of electrons) takes place at the anode as anions donate electrons.
Question
Identify the type of ions that migrate towards the anode during electrolysis.
Answer
Anions (negatively charged ions).
Question
Identify the type of ions that migrate towards the cathode during electrolysis.
Answer
Cations (positively charged ions).
Question
What name is given to the separation of ions already present in an electrovalent compound like $PbBr_{2}$?
Answer
Electrolytic dissociation.
Question
What name is given to the formation of charged ions from polar covalent molecules like $HCl$?
Answer
Ionisation.
Question
Contrast the charge carriers in metallic conduction with those in electrolytic conduction.
Answer
Metallic conduction involves the flow of electrons, while electrolytic conduction involves the flow of ions.
Question
Why is sodium chloride a non-conductor in its solid state?
Answer
The ions are not free but are held together by strong electrostatic forces of attraction.
Question
Under what condition does sodium chloride become a good conductor of electricity?
Answer
When it is in a molten (fused) or aqueous solution state.
Question
How does the concentration of ions in a solution affect its electrolytic conductivity?
Answer
The amount of electricity conducted depends upon the concentration of ions in the solution.
Question
State the characteristic product formed at the cathode when metallic ions are discharged.
Answer
Metals (or Hydrogen gas).
Question
According to the electrochemical series, which ions are discharged with the greatest difficulty at the cathode?
Answer
Ions of metals at the top of the series, such as $K^{1+}$ and $Ca^{2+}$.
Question
According to the electrochemical series, which metal ions are discharged most readily at the cathode?
Answer
Ions of metals at the lower end of the series, such as $Cu^{2+}$ and $Ag^{1+}$.
Question
List the three factors that influence the selective discharge of ions.
Answer
Relative position in the electrochemical series, concentration of ions, and the nature of the electrode.
Question
When comparing concentrated $NaCl$ and dilute $NaCl$, why are chloride ions preferentially discharged at the anode in the concentrated solution?
Answer
Due to the higher concentration of $Cl^{1-}$ ions compared to $OH^{1-}$ ions.
Question
Define an 'inert electrode' in the context of electrolysis.
Answer
An electrode that does not take part in the electrolytic reaction, such as graphite or platinum.
Question
Define an 'active electrode' in the context of electrolysis.
Answer
An electrode that participates in the reaction, such as copper, nickel, or silver.
Question
Why is a silica crucible used for the electrolysis of molten lead bromide?
Answer
Because it is non-reactive, withstands high temperatures, and is a non-conductor.
Question
Identify the observation at the cathode during the electrolysis of molten lead bromide.
Answer
A silvery grey deposit of lead metal.
Question
Identify the observation at the anode during the electrolysis of molten lead bromide.
Answer
Reddish brown vapours of bromine gas.
Question
In the electrolysis of acidified water, what is the role of the added dilute sulphuric acid?
Answer
It acts as a catalyst to facilitate the dissociation of water into ions.
Question
State the volume ratio of Hydrogen to Oxygen produced during the electrolysis of acidified water.
Answer
$2:1$.
Question
During the electrolysis of acidified water, why is dilute sulphuric acid preferred over nitric acid?
Answer
Nitric acid is volatile and may decompose, interfering with the electrolytic reaction.
Question
In the electrolysis of aqueous copper sulphate using copper electrodes, what happens to the anode?
Answer
The copper anode ionises and dissolves, losing mass as $Cu^{2+}$ ions enter the solution.
Question
Why does the blue colour of copper sulphate solution remain unchanged when using active copper electrodes?
Answer
For every copper ion discharged at the cathode, a copper ion is added to the solution from the anode.
Question
What is the product at the anode during the electrolysis of aqueous copper sulphate using platinum electrodes?
Answer
Oxygen gas.
Question
Define 'electroplating'.
Answer
The electrolytic process of depositing a superior metal onto the surface of a baser metal or article.
Question
To which electrode is the article to be electroplated always connected?
Answer
The cathode.
Question
What is the requirement for the anode during electroplating?
Answer
It must be made of the pure metal that is to be deposited on the article.
Question
Why must direct current ($DC$), rather than alternating current ($AC$), be used for electroplating?
Answer
Because $AC$ causes discharge and ionisation to alternate at the cathode, resulting in no effective coating.
Question
State one reason why a low current for a longer time is used in electroplating.
Answer
To ensure a smooth, firm, uniform, and long-lasting deposition.
Question
Identify the electrolyte used for electroplating an article with nickel.
Answer
Aqueous solution of nickel sulphate ($NiSO_{4}$).
Question
Identify the electrolyte used for electroplating an article with silver.
Answer
Sodium silver cyanide (sodium argentocyanide) solution, $Na[Ag(CN)_{2}]$.
Question
In the electrorefining of copper, what material is used for the anode?
Answer
A thick block of impure copper.
Question
In the electrorefining of copper, what material is used for the cathode?
Answer
A thin sheet of pure copper.
Question
What is 'anode mud' in the context of copper refining?
Answer
Insoluble impurities like gold and silver that settle down below the anode.
Question
Which method is used to extract highly electropositive metals like Potassium, Sodium, and Aluminium?
Answer
Electrolysis of their fused (molten) salts.
Question
State the Ionic Equation for the reaction at the cathode during the electrolysis of molten lead bromide.
Answer
$Pb^{2+} + 2e^{-} \rightarrow Pb$.
Question
State the final reaction occurring at the anode during the electrolysis of molten lead bromide.
Answer
$Br + Br \rightarrow Br_{2}$.
Question
What are 'spectator ions'?
Answer
Ions present in the electrolyte that migrate to the electrodes but are not discharged.
Question
In the electrolysis of acidified water using platinum electrodes, which ion is discharged at the anode?
Answer
The hydroxyl ion ($OH^{1-}$).
Question
What defines the 'degree of dissociation' of an electrolyte?
Answer
The extent to which an electrolyte dissociates or breaks up into ions.
Question
Identify the type of bonding typically found in electrolytes.
Answer
Ionic (electrovalent) bonding.
Question
Why is graphite usually preferred as an anode over platinum in some electrolytic processes?
Answer
Because graphite is unaffected by reactive vapours like bromine.
Question
During electroplating with silver, why is sodium silver cyanide preferred over silver nitrate?
Answer
Because the migration of $Ag^{1+}$ ions from the complex salt is slow, resulting in a more even deposition.
Question
Name the device in which electrolysis is carried out.
Answer
The electrolytic cell or voltameter.
Question
What happens to the impurities that are more electropositive than copper during electrorefining?
Answer
They ionise and remain in the electrolytic copper sulphate solution.
Question
State the equation for the formation of hydronium ions when $HCl$ is added to water.
Answer
$H^{+} + H_{2}O \rightarrow H_{3}O^{+}$.
Question
Why does metallic conduction not result in any new products?
Answer
Because there is no transfer of matter during the flow of electrons.
Question
What is the specific product at the cathode during the extraction of aluminium from pure alumina?
Answer
Aluminium metal ($Al$).
Question
In the electrochemical series for anions, which ion is the most difficult to oxidise?
Answer
Sulphate ion ($SO_{4}^{2-}$).