IB DP Chemistry -Reactivity 3.2 Electron transfer reactions - IB Style Questions For HL Paper 1A -FA 2025

IBDP Chemistry HL Paper 1A & 1B - All Chapters

Question

Ammonia (NH3) and nitrous acid (HNO2) are nitrogen compounds. What are the oxidation states of nitrogen in these compounds?
 NH3HNO2
(A)+3+3
(B)–3–3
(C)+3–3
(D)–3+3
▶️ Answer/Explanation
Detailed solution

NH3: H is +1 each, so \(x + 3(+1) = 0\) ⇒ \(x = -3\).
HNO2: H is +1, O is –2 each, so \(1 + x + 2(-2) = 0\) ⇒ \(x – 3 = 0\) ⇒ \(x = +3\).
✅ Answer: (D)

Question

Which change involves oxidation of N?
A. \( \mathrm{NH_3} \rightarrow \mathrm{N_2} \)
B. \( \mathrm{NO_2} \rightarrow \mathrm{NO} \)
C. \( \mathrm{N_2} \rightarrow \mathrm{AlN} \)
D. \( \mathrm{NO_2} \rightarrow \mathrm{N_2O_4} \)
▶️ Answer/Explanation
Detailed solution

Markscheme: A

Oxidation occurs when the oxidation state of an element becomes more positive.

1. Oxidation state of N in \( \mathrm{NH_3} \):
H has oxidation state \( +1 \). So for \( \mathrm{NH_3} \): \[ \mathrm{N} + 3(+1) = 0 \quad \Rightarrow \quad \mathrm{N} = -3 \]

2. Oxidation state of N in \( \mathrm{N_2} \):
Elemental nitrogen has oxidation state \[ \mathrm{N} = 0 \]

Nitrogen goes from \( -3 \) to \( 0 \), which is an increase in oxidation state. This means nitrogen is oxidized.

Thus, the change that involves oxidation of nitrogen is:

✅ Answer: (A)

Question

Which combination describes an electrolytic cell?
OptionEnergy changeSpontaneity
Achemical to electricalnon-spontaneous
Belectrical to chemicalnon-spontaneous
Cchemical to electricalspontaneous
Delectrical to chemicalspontaneous
▶️ Answer/Explanation
Detailed solution

An electrolytic cell:

  • uses electrical energy
  • to drive a non-spontaneous chemical reaction

This means the energy conversion is:

electrical → chemical

and the process is:

non-spontaneous

Only option B matches both requirements.

✅ Answer: (B)

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