Question

question 4: this question has two parts. first answer part a. then answer part b. part a: which chemical reaction supports the claim that mass is conserved? a na + cl₂ → nacl b na + 2cl₂ → 2nacl c 2na + cl₂ → 2nacl d na₂ + 2cl₂ → na₂cl₂ part b: which statement best supports the answer to part a? a the mass of salt molecules is equal to the mass of chlorine molecules. b the mass of molecules in the product differs from the mass of chlorine. c the number of reactant molecules equals the number of product molecules. d the number of chlorine and sodium atoms on both sides of the reaction are equal.

Explanation:

Step1: Recall law of mass - conservation

The law of mass - conservation states that in a chemical reaction, the total mass of the reactants is equal to the total mass of the products, which is reflected by having the same number of each type of atom on both sides of the chemical equation.

Step2: Analyze each reaction in Part A

• For A: $\text{Na}+\text{Cl}_2

ightarrow\text{NaCl}$, there are 2 Cl atoms on the left - hand side and 1 Cl atom on the right - hand side, so it is not balanced.

• For B: $\text{Na}+2\text{Cl}_2

ightarrow2\text{NaCl}$, there are 4 Cl atoms on the left - hand side and 2 Cl atoms on the right - hand side, so it is not balanced.

• For C: $2\text{Na}+\text{Cl}_2

ightarrow2\text{NaCl}$, there are 2 Na atoms and 2 Cl atoms on both the left - hand side and the right - hand side. This reaction is balanced and supports the law of mass conservation.

• For D: $\text{Na}_2 + 2\text{Cl}_2

ightarrow\text{Na}_2\text{Cl}_2$, sodium does not exist as $\text{Na}_2$ in this context and the compound $\text{Na}_2\text{Cl}_2$ is not a correct formula for sodium chloride.

Step3: Analyze statements in Part B

• Option A: The mass of salt molecules is not equal to the mass of chlorine molecules in the reaction $2\text{Na}+\text{Cl}_2

ightarrow2\text{NaCl}$, so this statement is incorrect.

• Option B: If the mass of molecules in the product differs from the mass of chlorine, it violates the law of mass conservation, so this statement is incorrect.
• Option C: It is not just the number of molecules that matters for mass conservation, but the number of atoms of each type. For example, in some reactions, the number of molecules can change while mass is still conserved. So this statement is incorrect.
• Option D: In a balanced chemical equation like $2\text{Na}+\text{Cl}_2

ightarrow2\text{NaCl}$, the number of chlorine and sodium atoms on both sides of the reaction are equal, which is a key aspect of mass conservation.

Answer:

Part A: C. $2\text{Na}+\text{Cl}_2
ightarrow2\text{NaCl}$
Part B: D. The number of chlorine and sodium atoms on both sides of the reaction are equal.