Solved Exercise, Chem-11, Ch-10


Q.01: Multiple choice questions. For each question there are four possible answers a, b, c and d. Choose the one you consider correct.

(i) The cathode reaction in the electrolysis of dil. H2SO4 with Pt electrodes is:      

(a) Reduction

(b) Oxidation

(c) Both oxidation and reduction

(d) Neither oxidation or reduction

EXPLANATION: Cathode provides electrons to the positive ions. In this case, it is H+ ions which gain electrons and get converted into H2 gas. Thus, addition of electrons, which is called reduction, occurs at cathode.

(ii) Which of the following statements is not correct about galvanic cell?       

(a) Anode is negatively charged

(b) Reduction occurs at anode

(c) Cathode is positively charged

(d) Reduction occurs at cathode

(iii) Stronger the oxidizing agent, greater is the:  

(a) Oxidation potential

(b) Reduction potential

(c) Redox potential

(d) E.M.F. of cell

EXPLANATION: The oxidizing agent is a species which have the ability to take electrons from some other atom. It means when it is gaining electrons from a substance, it is oxidizing it but itself is being reduced. Thus, its ability to gain electrons or reduction potential must be very high in order to oxidize others.

(iv) If the salt bridge is not used between two half cells, then the voltage:

(a) Decreases rapidly

(b) Decreases slowly

(c) Does not change

(d) Drops to zero

EXPLANATION: Salt bridge prevents net accumulation of negative charge in cathode compartment and positive charge in anode compartment. If salt bridge is not applied, the zinc compartment will lose electrons and become positive, and copper compartment will gain electrons and become more negative. Thus, the potential difference between anode and cathode compartments will decrease continually and finally there will be flow of electrons. It means the cell voltage will drop to zero.   

(v) If a strip of Cu metal is placed in a solution of FeSO4:

(a) Cu will be deposited

(b) Fe is precipitated out

(c) Cu and Fe both dissolve        

(d) No reaction takes place

EXPLANATION: Cu cannot replace Fe in a solution because copper has greater reduction potential (+0.34) than iron (-0.44). For a metal to replace another metal in a solution, it must be more electropositive i.e., its reduction potential must be lower than the other.

Fill in the blank.

(i) The oxidation number of O-atom is ___________ in OF2 and is ___________ in H2O2. (+2, -1)

(ii) Conductivity of metallic conductors is due to the flow of ________ while that of electrolytes is due to flow of ________ . (electrons, ions)

(iii) Reaction taking place at the ________ is termed as oxidation and at the _________ is called as reduction. (anode, cathode)

(iv) _________ is set up when a metal is dipped in its own ions. (electrode potential)

(v) Cu metal __________ the Cu-cathode when electrolysis is performed for CuSO4 solution with Cu-cathodes. (deposits at)

(vi) The reduction potential of Zn is __________ volts and its oxidation potential is __________ volts. (-0.76, +0.76)

(vii)In a fuel cell, __________ react together in the presence of __________. (H2 & O2, KOH)

Q.03: Mark the following statements true or false.

(i) In electrolytic conduction, electrons flow through the electrolyte. (FALSE)

CORRECTION: In electrolytic conduction, ions flow through the electrolyte.

(ii) In the process of electrolysis, the electrons in the external circuit flow from cathode to anode. (FALSE)

CORRECTION: In the process of electrolysis, the electrons in the external circuit flow from anode to cathode.

(iii) Sugar is a non-electrolyte in solid form and when dissolved in water will allow the passage of an electric current. (FALSE)

CORRECTION: Sugar is a non-electrolyte in solid form and when dissolved in water will not allow the passage of an electric current.

(iv) A metal will only allow the passage of an electric current when it is in cold state. (TRUE)

(v) The electrolytic products of aqueous copper (II) chloride solution are copper and chlorine. (TRUE)

(vi) Zinc can displace iron form its solution. (TRUE)

(vii) S.H.E. acts as cathode when connected with Cu electrode. (FALSE)

CORRECTION: S.H.E. acts as anode when connected with Cu electrode.

(viii) A voltaic cell produces electrical energy at the expense of chemical energy. (TRUE)

(ix) Lead storage battery is not a reversible cell. (FALSE)

CORRECTION: Lead storage battery is a reversible cell.  

(x)Cr changes its oxidation number when K2Cr2O7 reacts with HCl. (TRUE)

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