Law of Conservation of Matter Practice Problems worksheet | Live ... - Free Printable

Let's solve each problem step by step, explaining the reasoning behind each answer.

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Problem 1:

Question: A student adds 10 grams of vinegar to 7 grams of baking soda in a sealed container. Then he watches the chemical reaction that occurs. Which of these predicts the mass of the materials in the container after the reaction is complete?

- A. 70 grams
- B. 17 grams
- C. 3 grams
- D. 0 grams

Solution:
The Law of Conservation of Mass states that matter cannot be created or destroyed in a chemical reaction. The total mass of the reactants must equal the total mass of the products.

- Initial mass of vinegar = 10 grams
- Initial mass of baking soda = 7 grams
- Total initial mass = 10 + 7 = 17 grams

Since the reaction occurs in a sealed container, no mass can escape. Therefore, the total mass of the materials in the container after the reaction will still be 17 grams.

Answer: B. 17 grams

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Problem 2:

Question: Which procedure best represents the law of conservation of mass?

- a. evaporating salt water leaves 5 grams of salt
- b. burning 2 kilograms of wood leaves 0.4 kilogram of ash
- c. using filter paper to separate 2 grams of solid from 10 grams of water
- d. combining 2 grams of copper and 4 grams of sulfur to produce 6 grams of copper sulfate

Solution:
The Law of Conservation of Mass states that the total mass of the reactants must equal the total mass of the products.

- Option a: Evaporating salt water leaves 5 grams of salt. This does not conserve mass because the water vapor is not accounted for.
- Option b: Burning 2 kilograms of wood leaves 0.4 kilogram of ash. This does not conserve mass because the carbon dioxide and other gases produced are not accounted for.
- Option c: Using filter paper to separate 2 grams of solid from 10 grams of water. This is a physical separation, not a chemical reaction, so it does not demonstrate the law of conservation of mass.
- Option d: Combining 2 grams of copper and 4 grams of sulfur to produce 6 grams of copper sulfate. Here, the total mass of the reactants (2 + 4 = 6 grams) equals the total mass of the product (6 grams), demonstrating the law of conservation of mass.

Answer: d. combining 2 grams of copper and 4 grams of sulfur to produce 6 grams of copper sulfate

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Problem 3:

Question: In the chemical formula for Magnesium chloride, NaCl₄, what does the subscript 4 represent?

- a. 2 molecules of Magnesium
- b. Nothing
- c. 2 molecules of Chlorine
- d. 4 molecules of Chlorine

Solution:
The chemical formula NaCl₄ is incorrect because magnesium chloride is actually MgCl₂. However, assuming the question is about the subscript in general:

- The subscript in a chemical formula indicates the number of atoms of that element in one molecule.
- In NaCl₄, the subscript 4 would indicate 4 chlorine atoms per molecule.

Answer: d. 4 molecules of Chlorine

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Problem 4:

Question: Which model demonstrates the Law of Conservation of Matter?

[Models A, B, C, D are shown in the image]

Solution:
The Law of Conservation of Matter states that the total number of atoms of each element must be the same before and after a chemical reaction.

- Model A: 1 atom + 2 atoms → 3 atoms. This conserves the total number of atoms.
- Model B: 1 atom + 2 atoms → 1 atom. This does not conserve the total number of atoms.
- Model C: 2 atoms + 2 atoms → 2 atoms. This does not conserve the total number of atoms.
- Model D: 2 atoms + 2 atoms → 4 atoms. This conserves the total number of atoms.

Both Models A and D conserve the total number of atoms, but Model A is the correct choice because it shows a balanced reaction with the correct number of atoms on both sides.

Answer: A

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Problem 5:

Question: Which sample equation best illustrates the law of conservation of mass?

- a. 8 grams reactant U + 3 grams reactant V → 5 grams product W
- b. 12 grams reactant X + 10 grams reactant Y → 22 grams product Z
- c. 5 grams reactant E + 5 grams reactant F → 20 grams product G + 5 grams product H
- d. 10 grams reactant Q + 9 grams reactant R → 90 grams product S + 90 grams product T

Solution:
The Law of Conservation of Mass states that the total mass of the reactants must equal the total mass of the products.

- Option a: 8 + 3 = 11 grams (reactants) ≠ 5 grams (products). Does not conserve mass.
- Option b: 12 + 10 = 22 grams (reactants) = 22 grams (products). Conserves mass.
- Option c: 5 + 5 = 10 grams (reactants) ≠ 20 + 5 = 25 grams (products). Does not conserve mass.
- Option d: 10 + 9 = 19 grams (reactants) ≠ 90 + 90 = 180 grams (products). Does not conserve mass.

Answer: b. 12 grams reactant X + 10 grams reactant Y → 22 grams product Z

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Problem 6:

Question: The students placed an antacid tablet in a ziplock bag. The mass of the tablet, 30 grams, and the bag, 40 grams. Then they carefully added 30 grams of water and quickly sealed the bag. The tablet began to fizz and soon disappeared. The bag was filled with gas. If the total mass of the bag + tablet + water was 130 grams before the reaction, what was the total mass of the bag + liquid + gas after the reaction was completed?

- A. 70 grams
- B. 30 grams
- C. 130 grams
- D. 160 grams

Solution:
The Law of Conservation of Mass states that the total mass of the system remains constant if the system is closed. Since the reaction occurs in a sealed bag, no mass can escape.

- Initial total mass = mass of bag + mass of tablet + mass of water = 40 + 30 + 30 = 130 grams
- After the reaction, the mass of the system (bag + liquid + gas) must still be 130 grams.

Answer: C. 130 grams

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Problem 7:

Question: A cube of water measured at 200 grams. The cup of water was placed in the freezer. What is the mass of the frozen cup of water?

- A. 250 grams
- B. 150 grams
- C. 200 grams
- D. 300 grams

Solution:
The Law of Conservation of Mass states that the mass of a substance does not change during a physical change (such as freezing). Freezing water changes its state from liquid to solid but does not change its mass.

- Initial mass of water = 200 grams
- Mass of frozen water = 200 grams

Answer: C. 200 grams

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Final Answers:

1. B. 17 grams
2. d. combining 2 grams of copper and 4 grams of sulfur to produce 6 grams of copper sulfate
3. d. 4 molecules of Chlorine
4. A
5. b. 12 grams reactant X + 10 grams reactant Y → 22 grams product Z
6. C. 130 grams
7. C. 200 grams

Boxed Final Answer:
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\boxed{B, d, d, A, b, C, C}
\]