Question

!miller, z. chemistry a_section 1_fall 25/26 / unit 5 - chemical reactions
which of these describes the law of conservation of mass?
○ mass$_{reactants}$ < mass$_{products}$
○ mass$_{reactants}$ = mass$_{products}$
○ mass$_{reactants}$ ≈ mass$_{products}$
○ mass$_{reactants}$ > mass$_{products}$

1. choose the best answer.

for their lab report, students must describe a chemical reaction in words.
which of the following would represent the correct word equation for this equation?
cu (s) + agno₃ (aq) → cu(no₃)₂ (aq)+ag (s)
○ solid copper and silver (iii) nitrogen oxide, dissolved in water, react to form aqueous copper (ii) nitrate and solid silver.
○ solid copper and silver nitrite, dissolved in water, react to form aqueous zinc nitrite and solid silver.
○ solid copper and silver nitrate, dissolved in water, react to form aqueous copper (ii) nitrate and solid silver.
○ solid copper and silver nitrate, dissolved in water, react to form aqueous copper nitrate and solid silver.

Explanation:

First Question (Law of Conservation of Mass)

The law of conservation of mass states that in a closed system, the total mass of reactants before a chemical reaction is equal to the total mass of products after the reaction. So we check the options:

• \( \text{Mass}_{\text{reactants}} < \text{Mass}_{\text{products}} \): Incorrect, as mass isn't created.
• \( \text{Mass}_{\text{reactants}} = \text{Mass}_{\text{products}} \): Correct, matches the law.
• \( \text{Mass}_{\text{reactants}} \approx \text{Mass}_{\text{products}} \): Incorrect, it's an equality, not approximation (in ideal conditions).
• \( \text{Mass}_{\text{reactants}} > \text{Mass}_{\text{products}} \): Incorrect, as mass isn't destroyed.

1. Analyze reactants: \( \text{Cu}(s) \) is solid copper, \( \text{AgNO}_3(aq) \) is silver nitrate (aqueous, dissolved in water).
2. Analyze products: \( \text{Cu(NO}_3\text{)}_2(aq) \) is copper(II) nitrate (aqueous), \( \text{Ag}(s) \) is solid silver.
3. Check options:

• Option 1: Incorrect, \( \text{AgNO}_3 \) is silver nitrate, not "silver (III) nitrogen oxide".
• Option 2: Incorrect, products have copper, not zinc; reactant is silver nitrate, not silver nitrite.
• Option 3: Close, but "copper (II) nitrate" is correct, but the option's formatting (like the "II" in parentheses) might be a typo, but the key is reactants and products. Wait, no—wait the fourth option: "Solid copper and silver nitrate, dissolved in water, react to form aqueous copper nitrate and solid silver." Wait, \( \text{Cu(NO}_3\text{)}_2 \) is copper(II) nitrate, but sometimes "copper nitrate" is used informally, but let's check:
• Correct breakdown: Reactants are solid Cu and aqueous \( \text{AgNO}_3 \) (silver nitrate). Products are aqueous \( \text{Cu(NO}_3\text{)}_2 \) (copper(II) nitrate or copper nitrate) and solid Ag. The fourth option says "solid copper and silver nitrate, dissolved in water, react to form aqueous copper nitrate and solid silver"—this matches the reactants and products (names: Cu is copper, \( \text{AgNO}_3 \) is silver nitrate, \( \text{Cu(NO}_3\text{)}_2 \) is copper nitrate, Ag is silver). The third option has a typo in "copper (II)" but the fourth is more accurate in naming (no incorrect ions or elements). Wait, let's re-express the equation: \( \text{Cu} + \text{AgNO}_3

ightarrow \text{Cu(NO}_3\text{)}_2 + \text{Ag} \). So reactants: solid copper, aqueous silver nitrate. Products: aqueous copper(II) nitrate, solid silver. The fourth option: "Solid copper and silver nitrate, dissolved in water, react to form aqueous copper nitrate and solid silver." This is correct because "copper nitrate" can refer to copper(II) nitrate (since copper has +2 here), and the reactants/products are named correctly (no wrong elements like zinc, no wrong compounds like silver nitrite or silver (III) nitrogen oxide).

Answer:

B. \( \text{Mass}_{\text{reactants}} = \text{Mass}_{\text{products}} \) (assuming the option with this is labeled as such, e.g., if the second option is B, then "B. \( \text{Mass}_{\text{reactants}} = \text{Mass}_{\text{products}} \)")

Second Question (Word Equation for \( \boldsymbol{\text{Cu}(s) + \text{AgNO}_3(aq)

ightarrow \text{Cu(NO}_3\text{)}_2(aq) + \text{Ag}(s)} \))