Q.1. Identify the oxidizing agent and the reducing agent in the following reaction
H2S + HNO3 → NO + S + H2O
AnswerAnswer: In the reaction HNO3 is an oxidizing agent since it itself gets reduced from +5 to +2. While H2S is an reducing agent since it itself gets oxidized from –2 to 0.
Q.2. In a binary compound of two non–metals, the positive oxidation state is assigned to which metal?
AnswerAnswer: Less electronegative metal amongst the two.
Q.3. What is the oxidation number of C in C6H6?
AnswerAnswer: It is –1.
Q.4. What does negative electrode potential signify ?
AnswerAnswer: It signifies that electrode has larger tendency to loose electrons than hydrogen electrode.
Q.5. At what concentration of Cu2+ (aq), will its electrode potential become equal to its standard electrode potential?
AnswerAnswer: At 1 M concentration.
Q.6. Why is anode called oxidation electrode whereas cathode is called reduction electrode?
AnswerAnswer: At anode, loss of electrons takes place, i.e., oxidation takes place whereas at cathode, gain of electrons takes place, i.e., reduction takes place therefore cathode is called reduction electrode and anode is called oxidation electrode.
Q.7. Zn rod is immersed in CuSO4 solution. What will you observe after an hour? Explain your observation in terms of redox reaction.
AnswerAnswer: Zn + CuSO4 → ZnSO4 + Cu
The blue colour will get discharged and reddish brown copper metal will get deposited.
Q.8. Why can CuSO4 solution not be stored in an iron vessel?
AnswerAnswer: It is because E°Fe2+/Fe = – 0.44 V which is lower than that of Cu
E°cell = E°Cu2+/Cu – E°Fe2+/Fe = + 0.34 V – (– 0.44 V) = 0.78 V.
Since, E°cell = + ve, DG = – ve, i.e., reaction will take place.
We cannot store CuSO4 in an iron container.
Q.9. Fe decomposes steam while Cu does not, why?
AnswerAnswer: Fe is more reactive than hydrogen, it has lower reduction potential than hydrogen whereas Cu has higher reduction potential than H2.
Q.10. What is meant by inert electrolyte used in salt bridge?
AnswerAnswer: Inert electrolyte is an electrolyte which does not react with any of the solution present in two half cells.
Q.11. What is oxidation state of Cr in CrO5 and why?
AnswerAnswer: Cr has + 6 oxidation state because it has 6 valence electrons, therefore, can form 6 covalent bonds.
Q.12. What is meant by oxidation potential of an electrode?
AnswerAnswer: Oxidation potential measures the tendency of an element or anion to lose electrons.
Q.13. What is relationship between standard oxidation potential and standard reduction potential?
AnswerAnswer: Both are equal in magnitude but opposite in sign.
Q.14. Find the oxidation number of Cl in HCl, HClO, ClO4 – , and Ca(OCl)Cl.
Q.15. Find the oxidation number of sulphur in S2O72–.
AnswerAnswer: + 6, 2x – 14 = –2 ⇒ 2x = 12
⇒ x = + 6.
Q.16. Arrange the following in order of increasing oxidation number of iodine. I2, HI, ICl.
AnswerAnswer: I2 has oxidation number zero, in HI. iodine has oxidation number–1.
In ICl, iodine has oxidation number + 1.
HI, I2, ICl is order of increasing oxidation number.
Q.17. Does the redox reaction in a cell go to completion?
AnswerAnswer: No, it is not completed.
Q.18. What happens when a silver plate is dipped in copper sulphate solution?
AnswerAnswer: No change will be noticed.
Q.19. What is electronation?
AnswerAnswer: The process in which gain of electrons takes place is called electronation.
Q.20. Is the valency of an element, same as its oxidation number?
AnswerAnswer: No. they are not always same.
Q.21. In the reaction given below which species is called a spectator ion and why?
AnswerAnswer: SO42- ion is the spectator ion as it does not participate in the reaction.
Q.22. What is a redox couple?
AnswerAnswer: Refer textbook
Q.23. What is a disproportionation reaction? Give one example.
AnswerAnswer: Refer textbook
Q.24. What is the function of platinum electrode?