EmSAT Chemistry 2 — Questions and Answers
Question 1: What is the molarity of a solution containing 58.5 g of NaCl dissolved in 1 liter of solution? (Molar mass of NaCl = 58.5 g/mol)
- 0.5 M
- 1 M (Correct answer)
- 2 M
- 58.5 M
Correct answer: 1 M
Molarity = moles of solute / liters of solution. Moles of NaCl = 58.5 g / 58.5 g/mol = 1 mol. Molarity = 1 mol / 1 L = 1 M.
Question 2: According to Le Chatelier's Principle, what happens when pressure is increased on the reaction N₂ + 3H₂ ⇌ 2NH₃?
- Equilibrium shifts to the left
- Equilibrium shifts to the right (toward fewer moles of gas) (Correct answer)
- No change occurs
- The reaction stops
Correct answer: Equilibrium shifts to the right (toward fewer moles of gas)
Increasing pressure shifts equilibrium toward the side with fewer moles of gas. The left side has 4 moles (1 + 3) while the right has 2 moles, so equilibrium shifts right, producing more NH₃.
Question 3: What type of reaction is: 2Na + Cl₂ → 2NaCl?
- Decomposition
- Synthesis (combination) (Correct answer)
- Single replacement
- Double replacement
Correct answer: Synthesis (combination)
This is a synthesis (combination) reaction where two reactants (sodium and chlorine) combine to form a single product (sodium chloride).
Question 4: What is the oxidation state of sulfur in H₂SO₄?
- +2
- +4
- +6 (Correct answer)
- -2
Correct answer: +6
In H₂SO₄: H is +1 (×2 = +2), O is -2 (×4 = -8). For the compound to be neutral: +2 + S + (-8) = 0, so S = +6.
Question 5: What distinguishes an exothermic reaction from an endothermic reaction?
- Exothermic reactions are always faster
- Exothermic reactions release heat energy to surroundings, endothermic reactions absorb heat (Correct answer)
- Endothermic reactions produce more products
- There is no difference
Correct answer: Exothermic reactions release heat energy to surroundings, endothermic reactions absorb heat
Exothermic reactions release energy (negative ΔH) and increase surrounding temperature, while endothermic reactions absorb energy (positive ΔH) and decrease surrounding temperature.
Question 6: How many valence electrons does oxygen have?
- 2
- 4
- 6 (Correct answer)
- 8
Correct answer: 6
Oxygen is in Group 16 (VIA) of the periodic table, so it has 6 valence electrons in its outer energy level (electron configuration: 2, 6).
EmSAT Chemistry 2
What is the molarity of a solution containing 58.5 g of NaCl dissolved in 1 liter of solution? (Molar mass of NaCl = 58.5 g/mol)