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.

---

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. Therefore, 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. Thus, the total mass of the materials in the container after the reaction will still be 17 grams.

Answer: B. 17 grams

---

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. Let's analyze each option:

- a. Evaporating salt water leaves 5 grams of salt: This is a physical change (evaporation), not a chemical reaction. The mass of the salt remains constant, but this does not demonstrate the conservation of mass in a chemical reaction.
- b. Burning 2 kilograms of wood leaves 0.4 kilogram of ash: This is a chemical reaction where wood reacts with oxygen to form ash and other products (e.g., carbon dioxide and water vapor). The mass of the ash alone (0.4 kg) is less than the initial mass of the wood (2 kg), which means mass was lost as gases escaped. This does not conserve mass.
- c. Using filter paper to separate 2 grams of solid from 10 grams of water: This is a physical separation, not a chemical reaction. The total mass of the solid and water remains constant, but this does not demonstrate the conservation of mass in a chemical reaction.
- d. Combining 2 grams of copper and 4 grams of sulfur to produce 6 grams of copper sulfate: This is a chemical reaction where the total mass of the reactants (2 g + 4 g = 6 g) equals the total mass of the product (6 g). This demonstrates 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

---

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 general meaning of subscripts in chemical formulas:

- Subscripts in chemical formulas indicate the number of atoms of an element in a molecule.
- In NaCl₄, the subscript 4 would mean there are 4 chlorine atoms per molecule.

However, since magnesium chloride is MgCl₂, the correct formula should be used. If we assume the question is hypothetical, the subscript 4 would represent 4 chlorine atoms.

Answer: d. 4 molecules of Chlorine

---

Problem 4:

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

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. Let's analyze each model:

- A: The reactants have 1 atom of one type and 2 atoms of another type. The product has 3 atoms of one type. This does not conserve the number of atoms.
- B: The reactants have 1 atom of one type and 2 atoms of another type. The product has 1 atom of one type and 1 atom of another type. This does not conserve the number of atoms.
- C: The reactants have 1 atom of one type and 2 atoms of another type. The product has 1 atom of one type and 2 atoms of another type. This conserves the number of atoms.
- D: The reactants have 2 atoms of one type and 2 atoms of another type. The product has 2 atoms of one type and 1 atom of another type. This does not conserve the number of atoms.

Answer: C

---

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. Let's check each option:

- a. 8 grams + 3 grams = 11 grams (reactants) → 5 grams (products): Mass is not conserved.
- b. 12 grams + 10 grams = 22 grams (reactants) → 22 grams (products): Mass is conserved.
- c. 5 grams + 5 grams = 10 grams (reactants) → 20 grams + 5 grams = 25 grams (products): Mass is not conserved.
- d. 10 grams + 9 grams = 19 grams (reactants) → 90 grams + 90 grams = 180 grams (products): Mass is not conserved.

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

---

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 before the reaction must equal the total mass after the reaction. The total mass before the reaction is given as 130 grams. Since the reaction occurs in a sealed container, no mass can escape or enter the system. Therefore, the total mass after the reaction must also be 130 grams.

Answer: C. 130 grams

---

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.

Answer: C. 200 grams

---

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. C
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:
\boxed{B, d, d, C, b, C, C}