Tag: extraction of metals by electrolysis

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Multiple choice chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

On passing one friday of electric charge through a dilute solution of an acid, the volume of hydrogen obtained at S.T.P. is :

  1. 22400 ML.

  2. 1120 mL

  3. 2240 mL

  4. 11200 ML.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

One Faraday (96500 C) of charge deposits or releases 1 gram equivalent of a substance. For H2 gas (n=2), 1 Faraday releases 0.5 moles of H2. Volume at STP = 0.5 * 22400 mL = 11200 mL.

Multiple choice chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

Electrolysis rules of Faraday's states that mass depends on electrodes is proportional to:-

  1. $m \propto I^2$
  2. $m \propto Q$
  3. $m \propto Q^2$

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Faraday's first law of electrolysis states that the mass of a substance deposited is directly proportional to the quantity of electricity (charge Q) passed through the electrolyte.

Multiple choice chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

The process of electrolysis is used in:

  1. extraction of metals

  2. electroplating

  3. refining of metals

  4. all of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Answer is D.
Electrolysis has wide applications in industries. Some of the important applications are, as follows, 
(i) Production of hydrogen by electrolysis of water. 
(ii) Manufacture of heavy water. 
(iii) The metals like K, Mg, Al, etc., are obtained by electrolysis of fused electrolytes. 
(iv) Non-metals like hydrogen, fluorine, chlorine are obtained by electrolysis. 
(v) In this method pure metal is deposited at cathode from a solution containing the metal ions, etc. 
(vi) Compounds like NaOH, KOH, white lead, etc. are synthesised by electrosynthesis method.
(vii) Electroplating: The process of coating an inferior metal with a superior metal by electrolysis is known as electroplating. 
Hence, the options A, B and C are correct.

Multiple choice chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

Electromeric effect involves the completer transfer of 

  1. $\sigma $ electorn
  2. $\pi $ electron

  3. proton
  4. Both $\sigma $ and $\pi $ electrons
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The electromeric effect is a temporary effect that involves the complete transfer of a shared pair of pi electrons to one of the atoms joined by a multiple bond on the demand of an attacking reagent. Sigma electrons are not involved in this process.

Multiple choice chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

The most durable metal plating on iron to protect against corrosion is:

  1. tin plating

  2. zinc plating

  3. copper plating

  4. nickel plating
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Metal plating protects the iron against corrosion by forming a sacrificial layer. This metal layer itself gets oxidize instead of iron and thus protects the iron itself. 


For a metal to be used as plating, its oxidation should be preferred over iron and thus should have lower reduction potential than iron. 

Among the given options, zinc has a lower reduction potential than iron and thus can be used for plating. The process is called galvanization.

Hence, option B is correct. 

Multiple choice chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

In the electrolysis of molten $Al _2O _3$ with inert electrodes:

  1. Al is oxidized at anode to $Al^{3+}$
  2. $O _2$ gas is produced at anode
  3. $O^{2-}$ is reduced at cathode
  4. $O$ is oxidized at anode
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The electrodes are inert so that they do not involve the electrode reactions but transfer electrons through them. Since the silvery metal i.e. $Al$ is produced at cathode.

At cathode: $Al^{3+}+3e^- \longrightarrow Al$
At anode, $O _2$ bubbles off.
At anode; $2O^{2-}\longrightarrow O _2+4e^-$
The cell reaction: $2Al _2O _3\longrightarrow 4Al+3O _2$