7. The table shows information about some oxides.
| Oxide | Structure | Effect of water |
|-------|-------------------|------------------------------|
| | Simple molecular | Dissolves to form an acid |
For which of the elements nitrogen, phosphorus, sulfur and silicon could this information about their oxides be correct?
A) Phosphorus and sulfur only
B) Nitrogen and silicon only
C) Nitrogen, phosphorus and sulfur only
D) Nitrogen, phosphorus, sulfur and silicon
8. The table contains information about four substances.
Which substance is an ionic compound?
| | State at room temperature | Conducts electricity at room temperature | Conducts electricity when molten | Conducts electricity when in aqueous solution |
|-----|---------------------------|-----------------------------------------|---------------------------------|----------------------------------------------|
| A | Liquid | X | X | |
| B | Solid | ✓ | ✓ | Insoluble |
| C | Solid | ✓ | ✓ | |
| D | Solid | X | | ✓ |
9. An ionic compound has the formula Al₂O₃.
What are the charges on the ions?
A) Al⁺ O⁻
B) Al²⁺ O²⁻
C) Al²⁺ O³⁻
D) Al³⁺ O²⁻
10. Which equation is correct for the reaction between carbon dioxide and magnesium hydroxide?
A) CO₂ + Mg(OH)₂ → MgCO₃ + H₂O
B) CO₂ + 2Mg(OH)₂ → 2MgCO₃ + 2H₂O
C) 2CO₂ + Mg(OH)₂ → MgCO₃ + H₂O
D) 2CO₂ + Mg(OH)₂ → 2MgCO₃ + H₂O
Answer (2)
For question 7, the correct answer is C) Nitrogen, phosphorus, and sulfur only. For question 8, it is Substance C as the ionic compound. For question 9, the correct charges on the ions in Al₂O₃ are Al³⁺ and O²⁻. For question 10, the correct equation is A) CO₂ + Mg(OH)₂ → MgCO₃ + H₂O.
;
For Question 7:
The table indicates that the oxide dissolves in water to form an acid and has a simple molecular structure. In chemistry, oxides of nonmetals such as nitrogen, phosphorus, and sulfur typically exhibit this behavior. Nitrogen dioxide (NO₂), phosphorus pentoxide (P₄O₁₀), and sulfur dioxide (SO₂) are examples where these oxides dissolve in water to form acids like nitric acid, phosphoric acid, and sulfurous acid, respectively. Silicon dioxide, however, has a giant covalent structure and does not dissolve in water to form an acid. Therefore, the correct option is C) Nitrogen, phosphorus, and sulfur only.
For Question 8:
An ionic compound at room temperature is usually a solid, and it conducts electricity when molten and when dissolved in aqueous solution. From the table, substance C is a solid that conducts electricity when molten. Therefore, the correct feature we are looking for in an ionic compound, like its ability to conduct electricity when dissolved in water, is seen with substance C. Thus, substance C represents an ionic compound.
For Question 9:
For the ionic compound Al₂O₃, aluminum forms Al³⁺ ions and oxygen forms O²⁻ ions. This balance of charges (2 Al³⁺ and 3 O²⁻ ions) maintains neutrality in the compound. Therefore, the correct charges on the ions are D) Al³⁺ and O²⁻.
For Question 10:
The reaction between carbon dioxide and magnesium hydroxide can be balanced as follows:
Magnesium hydroxide, Mg(OH)₂, reacts with carbon dioxide, CO₂, to form magnesium carbonate, MgCO₃, and water. The unbalanced reaction is:
CO₂ + Mg(OH)₂ → MgCO₃ + H₂O
This is option A, which is already balanced, showing that magnesium from Mg(OH)₂ combines with carbonate from CO₂ while matching reactants and products stoichiometrically. Therefore, the correct equation is A) CO₂ + Mg(OH)₂ → MgCO₃ + H₂O.
