Q4. Write the half reactions at the left and right electrodes of the Daniell cell, and the cell in NCERT’s notation.
Left electrode: Zn(s) → Zn2+(aq, 1 M) + 2e−; right electrode: Cu2+(aq, 1 M) + 2e− → Cu(s) (NCERT page 35). The cell is Zn(s)|Zn2+(aq)||Cu2+(aq)|Cu(s).
Q5. Find the standard emf of Mg(s)|Mg2+(aq)||Ag+(aq)|Ag(s).
E⊖cell = E⊖R − E⊖L = 0.80 − (−2.36) = 3.16 V (values from NCERT Table 2.1, page 37).
Q6. Which is the stronger oxidising agent, Cl2 or Br2? Which is the stronger reducing agent, Na or K?
Cl2, since its E⊖ (1.36 V) is higher than that of Br2 (1.09 V). K, since its E⊖ (−2.93 V) is lower than that of Na (−2.71 V) (NCERT Table 2.1, page 37).
Q7. Can Fe3+ ions oxidise bromide ions under standard conditions? Find E⊖cell for 2Fe3+ + 2Br− → 2Fe2+ + Br2.
No: 0.77 − 1.09 = −0.32 V (values from NCERT Table 2.1, page 37). Br2 oxidises Fe2+ instead (Example 4).
Q8. Assertion: the standard hydrogen electrode has zero potential at all temperatures. Reason: its potential is assigned by convention, not measured. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion: a single electrode potential cannot be measured, so the standard hydrogen electrode is assigned zero potential at all temperatures (NCERT page 34).
Q9. The cell Pt(s)|H2(g, 1 bar)|H+(aq, 1 M)||X2+(aq, 1 M)|X(s) has an emf of −0.44 V at 298 K. Identify the metal X, and say whether it gives hydrogen with dilute acid.
The emf is E⊖ for X2+/X, −0.44 V, which matches iron, Fe2+/Fe (NCERT Table 2.1, page 37). It is negative, so H+ ions can oxidise iron: iron gives hydrogen with dilute acid (reasoned from NCERT page 35).
Q10. In NCERT Table 2.1, which species is the strongest oxidising agent and which the strongest reducing agent? What happens to the oxidising power of the species on the left as you go down the table?
F2 (2.87 V) is the strongest oxidising agent and lithium (−3.05 V) the strongest reducing agent. Going down, the oxidising power of the species on the left decreases (NCERT page 36).