Electrolysis Review Flashcards

A complete set of 30 question-and-answer flashcards based on the provided lecture notes on electrolysis, covering core definitions, electrochemical series, specific electrolytic processes, and industrial applications.

What is electrolysis?

Electrolysis is the decomposition of a chemical compound (electrolyte) in the aqueous or fused state by the passage of a direct electric current, resulting in the discharge of ions as neutral atoms at the respective electrodes.

How do electrolytes and non-electrolytes differ in terms of chemical bonding?

Electrolytes are ionic compounds, whereas non-electrolytes are covalent compounds.

What type of particles are present in a weak electrolyte?

Ions and unionised molecules.

Why is the anode referred to as the oxidising electrode?

Because anions lose electrons at the anode, undergoing an oxidation reaction.

Who first explained the mechanism of electrolysis, and in what year?

Swedish chemist Avante Arrhenius in $1887$.

What is the key difference between electrolytic dissociation and ionisation?

Electrolytic dissociation is the separation of ions already present in electrovalent compounds, whereas ionisation is the formation of charged ions from molecules in covalent compounds.

Why is solid sodium chloride a non-conductor of electricity?

Its ions are not free but are held together by a strong electrostatic force of attraction.

Why is copper metal classified as a non-electrolyte even though it conducts electricity?

It does not undergo chemical decomposition due to the flow of electric current through it.

What three factors influence the selective discharge of ions during electrolysis?

1. Relative position of the cation or anion in the electrochemical series; 2. Concentration of the ions in the electrolyte; 3. Nature of the electrode.

According to the electrochemical series, which metal cation is discharged at the cathode with the most difficulty?

Potassium ion ($\text{K}^{1+}$).

Why is the crucible used during the electrolysis of molten lead bromide made of silica?

Silica is non-reactive, withstands high temperature, and is almost a non-conductor of electricity.

What temperature and electric current are required for the electrolysis of molten lead bromide?

A temperature above $380^\bullet\text{C}$ and a current of $3\,\text{A}$.

What product is observed at the cathode during the electrolysis of molten lead bromide?

Lead metal, which forms a silvery grey deposit around the cathode.

Why is a graphite anode preferred over platinum during the electrolysis of molten lead bromide?

Graphite is unaffected by the reactive bromine vapours produced at the anode.

What products are formed at the cathode and anode during the electrolysis of acidified water?

Hydrogen gas is formed at the cathode and oxygen gas is formed at the anode.

What is the volume ratio of hydrogen gas to oxygen gas liberated during the electrolysis of acidified water?

$2 : 1$ by volume.

Why is dilute sulphuric acid preferred over dilute nitric acid for acidifying water during electrolysis?

Nitric acid is a volatile acid that may decompose and its nitrate radical ($\text{NO}_3^{1-}$) may interfere with the electrolytic reaction.

What happens to the blue colour of aqueous copper [II] sulphate solution when electrolysed using active copper electrodes?

The blue colour remains unchanged because for every copper ion ($\text{Cu}^{2+}$) discharged at the cathode, a copper ion ($\text{Cu}^{2+}$) is added to the solution at the copper anode.

What product is liberated at the anode when aqueous copper [II] sulphate is electrolysed using platinum electrodes?

Oxygen gas.

What is electroplating?

Electroplating is the electrolytic process of deposition of a superior metal on the surface of a baser metal or article.

At which electrode is the article to be electroplated always placed?

At the cathode.

Why is direct current (D.C.) used instead of alternating current (A.C.) for electroplating?

A.C. current causes discharge and ionisation to alternate at the cathode, resulting in no effective coating.

Why is sodium silver cyanide preferred over silver nitrate as an electrolyte for silver electroplating?

The migration of $\text{Ag}^{1+}$ ions from the sodium silver cyanide complex solution is slow, resulting in a smooth and even deposition of silver on the article.

What electrolyte is used in the electroplating of an article with nickel?

An aqueous solution of nickel sulphate ($\text{NiSO}_4$).

In the electro-refining of copper, what materials serve as the cathode and anode?

The cathode is a thin sheet of pure copper and the anode is a thick block of impure copper.

What is anode mud in the electro-refining of copper?

Insoluble impurities such as gold and silver that settle down beneath the impure copper anode.

What happens to impurities like iron and zinc during the electro-refining of copper?

They ionise and dissolve into the electrolytic copper sulphate solution.

Which metals are generally extracted by the electrolysis of their fused salts?

Potassium ($\text{K}$), sodium ($\text{Na}$), calcium ($\text{Ca}$), magnesium ($\text{Mg}$), and aluminium ($\text{Al}$).

What is the cathode reaction during the extraction of aluminium by electrolysis of fused alumina ($\text{Al}_2\text{O}_3$)?

$2\text{Al}^{3+} + 6e^- \rightarrow 2\text{Al}$.

What product is evolved at the anode during the electrolysis of concentrated sodium chloride solution?

Chlorine gas