RPAL Conservation of Mass 1 — Questions and Answers
Question 1: Which law states that matter is neither created nor destroyed in a chemical reaction?
- Law of Definite Proportions
- Law of Conservation of Mass (Correct answer)
- Law of Multiple Proportions
- Law of Conservation of Energy
Correct answer: Law of Conservation of Mass
The Law of Conservation of Mass states that the total mass of reactants equals the total mass of products in a chemical reaction.
Question 2: In a sealed container, 10 g of reactant A reacts completely with 5 g of reactant B. What is the total mass of products formed?
- 5 g
- 10 g
- 15 g (Correct answer)
- 20 g
Correct answer: 15 g
By conservation of mass, the total mass of products equals the total mass of reactants: 10 g + 5 g = 15 g.
Question 3: A balanced chemical equation demonstrates conservation of mass because:
- It has the same number of molecules on both sides
- It has the same number of atoms of each element on both sides (Correct answer)
- It has the same number of coefficients on both sides
- It has the same number of compounds on both sides
Correct answer: It has the same number of atoms of each element on both sides
A balanced equation has equal numbers of each type of atom on both sides, ensuring mass is conserved since atoms are not created or destroyed.
Question 4: If 4 g of hydrogen reacts with 32 g of oxygen to form water, what mass of water is produced?
- 28 g
- 32 g
- 36 g (Correct answer)
- 40 g
Correct answer: 36 g
By conservation of mass, 4 g H₂ + 32 g O₂ = 36 g H₂O, since total reactant mass equals total product mass.
Question 5: Which of the following best describes what happens to atoms during a chemical reaction?
- Atoms are created from energy
- Atoms are destroyed to release energy
- Atoms are rearranged to form new substances (Correct answer)
- Atoms fuse together to form heavier atoms
Correct answer: Atoms are rearranged to form new substances
In chemical reactions, atoms are rearranged — bonds are broken and formed — but atoms themselves are neither created nor destroyed.
Question 6: A student burns 12 g of carbon in excess oxygen and collects 44 g of CO₂. How much oxygen was consumed?
- 12 g
- 22 g
- 32 g (Correct answer)
- 44 g
Correct answer: 32 g
By conservation of mass: mass of O₂ = mass of CO₂ − mass of C = 44 g − 12 g = 32 g.
Question 7: Why does an open container experiment sometimes appear to violate conservation of mass when a substance burns?
- Mass is destroyed during combustion
- The reaction creates new matter
- Gas-phase products like CO₂ escape into the atmosphere (Correct answer)
- The scale measurement is always wrong
Correct answer: Gas-phase products like CO₂ escape into the atmosphere
In an open system, gaseous products like CO₂ and water vapor escape, making the remaining solid or liquid mass appear to decrease, but total mass is still conserved.
RPAL Conservation of Mass 1
Which law states that matter is neither created nor destroyed in a chemical reaction?