Questions on Law of Conservation of Mass
Multiple Choice Questions
1. What does the Law of Conservation of Mass state?
A) Mass can be created but not destroyed
B) Mass is always decreasing
C) Mass cannot be created or destroyed
D) Mass increases during a chemical reaction
2. Who is credited with establishing the Law of Conservation of Mass?
A) Isaac Newton
B) Albert Einstein
C) Antoine Lavoisier
D) Dmitri Mendeleev
3. In a chemical reaction, the mass of the products is ______ the mass of the reactants.
A) Less than
B) Equal to
C) Greater than
D) Unrelated to
4. Which of the following is an example of the Law of Conservation of Mass?
A) Burning wood and the ashes weigh more
B) Dissolving salt in water and mass remains constant
C) Melting ice and gaining mass
D) Evaporating water and losing all mass
5. When wood burns, it seems to weigh less. Why does this not violate the Law of Conservation of Mass?
A) Some mass disappears
B) Gases released are not measured
C) Mass becomes energy
D) Ash is heavier than wood
6. Which process follows the Law of Conservation of Mass?
A) A nuclear explosion
B) Baking a cake
C) Dissolving sugar in water
D) Photosynthesis
7. What must be true in a closed system during a chemical reaction?
A) Temperature decreases
B) Energy disappears
C) Mass remains constant
D) Mass increases
8. Which best describes a closed system in terms of mass conservation?
A) Matter can enter and exit
B) Only energy is allowed to escape
C) No matter enters or leaves
D) Mass is lost over time
9. Which situation would violate the Law of Conservation of Mass?
A) Weighing an open container before and after boiling
B) Measuring both reactants and products in a sealed flask
C) Comparing mass before and after dissolving a substance
D) Conducting a reaction in a closed container
10. Why might mass appear to be lost during a reaction in an open container?
A) Measurement error
B) Gas escapes into the air
C) Atoms are destroyed
D) Some reactants vanish
11. Which equation shows the conservation of mass?
A) H₂ + O₂ → H₂O₂
B) 2H₂ + O₂ → 2H₂O
C) C + O₂ → CO
D) Na + Cl → NaCl₂
12. The total mass before and after a chemical reaction is 250g. This demonstrates:
A) Law of Acceleration
B) Law of Conservation of Energy
C) Law of Conservation of Mass
D) Law of Thermodynamics
13. Which is NOT a requirement to verify mass conservation in an experiment?
A) Use accurate scales
B) Ensure a closed system
C) Record observations
D) Use flammable chemicals
14. What happens to atoms during a chemical reaction according to the Law of Conservation of Mass?
A) They disappear
B) They multiply
C) They rearrange
D) They lose mass
15. In a balanced chemical equation, the number of atoms of each element is:
A) More on the product side
B) Less on the reactant side
C) Equal on both sides
D) Randomly distributed
16. Burning 5g of magnesium in a sealed container produces white ash. What is the total mass after the reaction?
A) Less than 5g
B) More than 5g
C) 5g
D) 0g
17. Why is a sealed container important when demonstrating mass conservation?
A) It makes the reaction faster
B) It prevents heat loss
C) It ensures gases don't escape
D) It blocks light
18. If 10g of hydrogen reacts with 80g of oxygen to form water, what is the total mass of the water formed?
A) 70g
B) 90g
C) 100g
D) 110g
18. Which statement is true about chemical reactions and mass?
A) New atoms are created
B) Some mass is destroyed
C) Mass is converted to light
D) Mass is conserved
20. If mass appears to change during an experiment, what is the most likely reason?
A) The law is wrong
B) An error in measurement or setup
C) Atoms ceased to exist
D) Gravity changed
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Answer Key
- C) Mass cannot be created or destroyed
- C) Antoine Lavoisier
- B) Equal to
- B) Dissolving salt in water and mass remains constant
- B) Gases released are not measured
- C) Dissolving sugar in water
- C) Mass remains constant
- C) No matter enters or leaves
- A) Weighing an open container before and after boiling
- B) Gas escapes into the air
- B) 2H₂ + O₂ → 2H₂O
- C) Law of Conservation of Mass
- D) Use flammable chemicals
- C) They rearrange
- C) Equal on both sides
- C) 5g
- C) It ensures gases don't escape
- B) 90g
- D) Mass is conserved
- B) An error in measurement or setup
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