Quiz II Review Guidance: Ionic Bonding, Chemical Reactions, Stoichiometry, and Redox

Q1. Draw a Lewis Dot Diagram for P2.

Background

Topic: Covalent Bonding & Lewis Structures

This question tests your understanding of how to represent molecules using Lewis dot diagrams, specifically for diatomic phosphorus (P2), showing valence electrons and bonding.

Key Terms and Concepts:

• Lewis Dot Diagram: A visual representation of valence electrons around atoms and bonds in a molecule.

• Octet Rule: Atoms tend to form bonds to achieve eight electrons in their valence shell.

• Phosphorus (P): Has 5 valence electrons.

Step-by-Step Guidance

1. Determine the number of valence electrons for each phosphorus atom. Phosphorus is in group 15, so each atom has 5 valence electrons.

2. Calculate the total number of valence electrons for the P2 molecule: $2 \times 5 = 10$ electrons.

3. Arrange the two phosphorus atoms side by side and decide how many bonds are needed to satisfy the octet rule for each atom.

4. Place bonding pairs (shared electrons) between the atoms, then distribute the remaining electrons as lone pairs to complete the octet for each atom.

Try solving on your own before revealing the answer!

Final Answer:

The Lewis dot diagram for P2 shows a triple bond between the two phosphorus atoms, with each atom having one lone pair:

$\cdot\cdot\text{P}\equiv\text{P}\cdot\cdot$

Each phosphorus atom shares three pairs of electrons (triple bond) and has one lone pair, satisfying the octet rule.

Q2. Balance the following equation and classify the reaction it represents as combination, decomposition, single-replacement, or double replacement. Fe + CdCl2 → FeCl3 + Cd

Background

Topic: Balancing Chemical Equations & Reaction Types

This question tests your ability to balance a chemical equation and identify the type of reaction (combination, decomposition, single-replacement, or double replacement).

Key Terms and Concepts:

• Balancing Equations: Ensuring the same number of atoms of each element on both sides of the equation.

• Reaction Types:

  • Combination: Two or more substances form one product.

  • Decomposition: One substance breaks into two or more products.

  • Single-replacement: An element replaces another in a compound.

  • Double replacement: Two compounds exchange ions.

Step-by-Step Guidance

1. Write the unbalanced equation: $\text{Fe} + \text{CdCl}_2 \rightarrow \text{FeCl}_3 + \text{Cd}$

2. Count the number of atoms of each element on both sides.

3. Adjust coefficients to balance the number of Fe, Cd, and Cl atoms.

4. Once balanced, examine the reactants and products to determine which reaction type fits (look for an element replacing another in a compound).

Try solving on your own before revealing the answer!

Final Answer:

Balanced equation: $3\text{Fe} + 2\text{CdCl}_2 \rightarrow 2\text{FeCl}_3 + 3\text{Cd}$

This is a single-replacement reaction because iron (Fe) replaces cadmium (Cd) in cadmium chloride (CdCl2).

Q3. Describe what happens when CaCl2 and NaOH are added to the same beaker of water. What, if anything, dissolves, and what, if anything, precipitates? Write the net ionic equation.

Background

Topic: Solubility & Precipitation Reactions

This question tests your understanding of solubility rules, precipitation reactions, and writing net ionic equations.

Key Terms and Concepts:

• Solubility: Whether a compound dissolves in water.

• Precipitate: An insoluble solid formed in a reaction.

• Net Ionic Equation: Shows only the species that change during the reaction.

• CaCl2 and NaOH: Both are soluble in water.

Step-by-Step Guidance

1. Write the formulas for the reactants: $\text{CaCl}_2$ and $\text{NaOH}$.

2. Predict the products by exchanging ions: Ca2+ with OH-, Na+ with Cl-.

3. Determine solubility of the products using solubility rules. Ca(OH)2 is only slightly soluble and will precipitate; NaCl is soluble.

4. Write the balanced molecular equation, then the complete ionic equation, and finally the net ionic equation by removing spectator ions.

Try solving on your own before revealing the answer!

Final Answer:

CaCl2 and NaOH both dissolve in water. When mixed, Ca(OH)2 precipitates, and NaCl remains dissolved.

Net ionic equation:

$\text{Ca}^{2+} (aq) + 2\text{OH}^- (aq) \rightarrow \text{Ca(OH)}_2 (s)$

This shows the formation of the insoluble Ca(OH)2 precipitate.

Q4. Chemical treatment of zinc sulfide, ZnS, with oxygen, O2, gives zinc oxide, ZnO, and sulfur dioxide gas, SO2. (a) Write a balanced equation for the reaction (b) If 10.0 g of ZnS is combined with excess oxygen, what is the theoretical yield of each product, in grams?

Background

Topic: Stoichiometry & Chemical Equations

This question tests your ability to write balanced equations and use stoichiometry to calculate theoretical yields.

Key Terms and Formulas:

• Stoichiometry: Calculating quantities of reactants and products.

• Molar Mass: Mass of one mole of a substance.

• Theoretical Yield: Maximum amount of product formed from given reactant.

• Key formula: $\text{grams of A} \rightarrow \text{moles of A} \rightarrow \text{moles of B} \rightarrow \text{grams of B}$

Step-by-Step Guidance

1. (a) Write the unbalanced equation: $\text{ZnS} + \text{O}_2 \rightarrow \text{ZnO} + \text{SO}_2$

2. Balance the equation by adjusting coefficients.

3. (b) Calculate the molar mass of ZnS.

4. Convert 10.0 g ZnS to moles using its molar mass.

5. Use the balanced equation to find the mole ratio between ZnS and each product.

6. Set up the calculation to convert moles of ZnS to moles of ZnO and SO2, then to grams using their molar masses.

Try solving on your own before revealing the answer!

Final Answer:

(a) Balanced equation: $2\text{ZnS} + 3\text{O}_2 \rightarrow 2\text{ZnO} + 2\text{SO}_2$

(b) Theoretical yield for each product (from 10.0 g ZnS):

ZnO: $6.82$ g SO2: $4.98$ g

These values are calculated using stoichiometry and molar masses for ZnS, ZnO, and SO2.

Q5. Determine if the following reaction is a redox reaction. If so, which substance is the oxidizing agent, and which is the reducing agent? Sn + HNO3 → SnO2 + NO2 + H2O

Background

Topic: Redox Reactions & Oxidation States

This question tests your ability to assign oxidation states, recognize redox reactions, and identify oxidizing and reducing agents.

Key Terms and Concepts:

• Redox Reaction: Involves transfer of electrons; oxidation and reduction occur.

• Oxidation State: Number assigned to an atom to indicate its degree of oxidation.

• Oxidizing Agent: Causes oxidation, is reduced.

• Reducing Agent: Causes reduction, is oxidized.

Step-by-Step Guidance

1. Assign oxidation states to each atom in the reactants and products.

2. Identify which atoms change oxidation state from reactants to products.

3. Determine which substance is oxidized (increase in oxidation state) and which is reduced (decrease in oxidation state).

4. Identify the oxidizing agent (the substance that is reduced) and the reducing agent (the substance that is oxidized).

Try solving on your own before revealing the answer!

Final Answer:

This is a redox reaction.

Sn is oxidized (reducing agent), HNO3 (specifically the nitrogen in NO3-) is reduced (oxidizing agent).

Sn goes from 0 to +4; N goes from +5 in NO3- to +4 in NO2.