Question

which numerical setup can be used to calculate the formula mass of c₉h₁₁no₂?

1. 9 u + 11 u + 1 u + 2 u
2. 12 u + 1 u + 14 u + 16 u
3. 9(6 u) + 11(1 u) + 1(7 u) + 2(8 u)
4. 9(12 u) + 11(1 u) + 1(14 u) + 2(16 u)

Explanation:

Step1: Recall formula mass calculation

Formula mass is sum of (atomic mass × number of atoms) for each element. Atomic masses: C = 12 u, H = 1 u, N = 14 u, O = 16 u.

Step2: Analyze \( \text{C}_9\text{H}_{11}\text{NO}_2 \)

• C: 9 atoms, each 12 u → \( 9(12\ \text{u}) \)
• H: 11 atoms, each 1 u → \( 11(1\ \text{u}) \)
• N: 1 atom, 14 u → \( 1(14\ \text{u}) \)
• O: 2 atoms, 16 u → \( 2(16\ \text{u}) \)

Step3: Match with options

Option 4 is \( 9(12\ \text{u}) + 11(1\ \text{u}) + 1(14\ \text{u}) + 2(16\ \text{u}) \), which matches the calculation.

Answer:

1. \( 9(12\ \text{u}) + 11(1\ \text{u}) + 1(14\ \text{u}) + 2(16\ \text{u}) \)