Chapter 4

Question 1

What is the basic Stoichiometric formula used for titrations?

Answer 1

M₁V₁ / n₁ = M₂V₂ / n₂

Question 2

What does n₁ and n₂ represent in M₁V₁ / n₁ = M₂V₂ / n₂?

Answer 2

They represent the molar coefficients of the reactants from the balanced chemical equation.

Question 3

What is the formula to calculate number of moles from volume at STP?

Answer 3

Moles = Volume (dm³) / 22.4

Question 4

What is the formula to calculate number of moles from mass?

Answer 4

Moles = Given Mass / Molar Mass

Question 5

What is theoretical yield?

Answer 5

The maximum amount of product expected from a chemical reaction, based on limiting reactant.

Question 6

What is the formula for Percent Yield?

Answer 6

% Yield = (Actual Yield / Theoretical Yield) × 100

Question 7

What is a limiting reactant?

Answer 7

The reactant that gets completely used up first and limits the amount of product formed.

Question 8

If 5g of A reacts with 10g of B, and A is limiting, do you consider B’s moles in % yield?

Answer 8

No ❌ — only the limiting reactant determines theoretical yield.

Question 9

What is the molar volume of a gas at STP?

Answer 9

22.4 dm³/mol

Question 10

How many moles of O₂ are in 44.8 dm³ at STP?

Answer 10

44.8 / 22.4 = 2 moles

Question 11

In the reaction: N₂ + 3H₂ → 2NH₃, if given 2 moles of N₂ and 3 moles of H₂, which is limiting?

Answer 11

H₂ is limiting because 3 moles H₂ only react with 1 mole N₂, but 2 moles of N₂ were given.

Question 12

What is the molecular mass of H₂O?

Answer 12

(2×1) + 16 = 18 g/mol

Question 13

A compound is 98% pure. What does it mean?

Answer 13

98g of pure substance in 100g of sample

Question 14

Difference between molar mass and molecular mass?

Answer 14

🔹 Molecular mass = mass of one molecule in amu
🔹 Molar mass = mass of 1 mole in grams (same number, different unit)

Question 15

If % yield is >100%, what does it indicate?

Answer 15

Likely experimental error – like leftover impurities or measurement issues.

Question 16

What is the mass of 1 mole of uranium (U)?

Answer 16

238 g

Question 17

What’s the formula for converting moles to particles?

Answer 17

Particles = Moles × Avogadro’s number (6.022×10²³)

Question 18

What is the mass of 0.5 moles of NaCl? (Na=23, Cl=35.5)

Answer 18

NaCl molar mass = 58.5
Mass = 0.5 × 58.5 = 29.25 g

Question 19

A student got 9g of product instead of 12g. Find % yield.

Answer 19

(9 / 12) × 100 = 75%

Question 20

What does ‘conc. HCl is 37%’ mean?

Answer 20

37g HCl in 100g of solution