ESAT ESAT Chemistry 3 — Questions and Answers
Question 1: What is the empirical formula of a compound with 40% C, 6.67% H, and 53.33% O by mass?
- CH₂O (Correct answer)
- C₂H₄O₂
- CH₄O
- C₂H₂O
Correct answer: CH₂O
Dividing by atomic masses: C:H:O = 40/12 : 6.67/1 : 53.33/16 ≈ 3.33 : 6.67 : 3.33 = 1:2:1 → CH₂O.
Question 2: In ESAT Chemistry, what does the rate equation r = k[A]²[B] indicate?
- Second order in A and first order in B, third order overall (Correct answer)
- First order in both A and B
- Zero order overall
- Second order in B and first order in A
Correct answer: Second order in A and first order in B, third order overall
The rate equation shows the reaction is second order in A, first order in B, and third order overall.
Question 3: What is a buffer solution?
- A solution that resists pH change on addition of small amounts of acid or base (Correct answer)
- A solution of neutral pH
- A solution that changes colour with pH
- A solution that conducts electricity
Correct answer: A solution that resists pH change on addition of small amounts of acid or base
A buffer solution contains a weak acid and its conjugate base, resisting pH change when small amounts of acid or alkali are added.
Question 4: Which periodic trend describes the decrease in atomic radius across a period (left to right)?
- Increasing nuclear charge attracting electrons more strongly (Correct answer)
- Decreasing number of electron shells
- Increasing electron shielding
- Decreasing atomic mass
Correct answer: Increasing nuclear charge attracting electrons more strongly
Across a period, protons increase while electrons are added to the same shell, so greater nuclear charge pulls electrons closer.
Question 5: What is produced when an acid reacts with a base?
- Salt and water (Correct answer)
- Salt and carbon dioxide
- Water and hydrogen gas
- Oxide and water
Correct answer: Salt and water
An acid-base neutralisation reaction produces a salt and water as products.
Question 6: What is the standard electrode potential of the standard hydrogen electrode (SHE)?
- 0.00 V (Correct answer)
- 1.00 V
- -1.00 V
- 0.76 V
Correct answer: 0.00 V
The standard hydrogen electrode is assigned a potential of exactly 0.00 V by convention.
ESAT ESAT Chemistry 3
What is the empirical formula of a compound with 40% C, 6.67% H, and 53.33% O by mass?