EmSAT EmSAT Chemistry 3 — Questions and Answers
Question 1: What is the oxidation state of sulfur in H₂SO₄?
- −2
- 0
- +4
- +6 (Correct answer)
Correct answer: +6
In H₂SO₄: H is +1 (×2 = +2), O is −2 (×4 = −8). For the molecule to be neutral: +2 + S + (−8) = 0, so S = +6.
Question 2: What is a redox reaction?
- A reaction involving only acids
- A reaction where electrons are transferred between species (Correct answer)
- A reaction producing water only
- A reaction at constant temperature
Correct answer: A reaction where electrons are transferred between species
A redox (reduction-oxidation) reaction involves the transfer of electrons between chemical species. One species is oxidized (loses electrons) and another is reduced (gains electrons).
Question 3: Which element is reduced in: Zn + CuSO₄ → ZnSO₄ + Cu?
- Zinc
- Sulfur
- Copper (Correct answer)
- Oxygen
Correct answer: Copper
Cu²⁺ gains 2 electrons to become Cu (solid). Gaining electrons is reduction. Zinc is oxidized (loses electrons) to become Zn²⁺.
Question 4: What is the rate of a chemical reaction?
- The energy released
- The change in temperature
- The change in concentration of reactants/products per unit time (Correct answer)
- The pressure during reaction
Correct answer: The change in concentration of reactants/products per unit time
Reaction rate is defined as the change in concentration of reactants or products per unit time. It tells us how quickly a reaction proceeds.
Question 5: Which factor does NOT affect reaction rate?
- Temperature
- Concentration
- Catalyst
- Color of the reactants (Correct answer)
Correct answer: Color of the reactants
Reaction rate is affected by temperature, concentration, catalyst presence, and surface area. The color of reactants is not a factor that affects how fast molecules react.
Question 6: What is a catalyst?
- A substance consumed in a reaction
- A substance that increases activation energy
- A substance that speeds up a reaction without being consumed (Correct answer)
- A product of the reaction
Correct answer: A substance that speeds up a reaction without being consumed
A catalyst speeds up a chemical reaction by providing an alternative pathway with lower activation energy. Crucially, it is not consumed in the reaction and can be reused.
EmSAT EmSAT Chemistry 3
What is the oxidation state of sulfur in H₂SO₄?