Question

consider the ionic compound: cus copper ii sulfide. why is a roman numeral necessary?
a all transition elements have a roman numeral
b sulfur has an oxidation of -2
c copper has two oxidation states (+1 and +2) and the roman numeral is used to differentiate between the two.
d roman numerals are used for all ionic compounds to express the oxidation number.

question 15
what is the chemical name for the compound fe₂o₃?
a iron (ii) oxide
b iron (iii) oxide
c iron oxide
d diiron trioxide

question 16
what is the empirical formula for c₆h₆?
a ch
b c₂h₂
c c₆h₆
d c₃h₃

Explanation:

Question (about CuS roman numeral)

• Option A: Not all transition elements need a Roman numeral (e.g., some with fixed oxidation states). Eliminate.
• Option B: Sulfur's oxidation state doesn't explain why Cu needs a Roman numeral. Eliminate.
• Option C: Copper (a transition metal) has multiple oxidation states (+1, +2). The Roman numeral in CuS (Copper II Sulfide) specifies it's +2, differentiating from +1. Correct.
• Option D: Roman numerals aren't used for all ionic compounds (e.g., NaCl doesn't need one). Eliminate.

• Find Fe's oxidation state. O is -2. Let Fe's oxidation state be \( x \). For \( \text{Fe}_2\text{O}_3 \): \( 2x + 3(-2) = 0 \) → \( 2x - 6 = 0 \) → \( x = +3 \). So Fe is +3, named Iron (III) oxide.
• Option A: Iron (II) is +2, incorrect.
• Option B: Iron (III) matches +3. Correct.
• Option C: Doesn't specify oxidation state (Fe has multiple states), incorrect.
• Option D: "Diiron trioxide" is not the correct IUPAC name for ionic compounds with transition metals (uses Roman numerals for oxidation state). Eliminate.

Step1: Recall empirical formula definition

Empirical formula is the simplest whole - number ratio of atoms in a compound.

Step2: Find the ratio of C to H in C₆H₆

For \( \text{C}_6\text{H}_6 \), the ratio of C to H is \( 6:6 \). We simplify this ratio by dividing both numbers by their greatest common divisor, which is 6. So \( \frac{6}{6}:\frac{6}{6}=1:1 \). The empirical formula is \( \text{CH} \).

Answer:

C. Copper has two oxidation states (+1 and +2) and the Roman numeral is used to differentiate between the two.

Question 15 (Fe₂O₃ name)