Question

what is the percent composition by mass of oxygen (o) in carbon dioxide (co₂)? (use approximate atomic masses: c=12.01 g/mol, o=16.00 g/mol)
36.36%
50.00%
72.73%
27.27%
which of the following has the largest atomic molar mass?
copper
lead
gold
mercury
what is the mass, in grams, of 1.50 moles of nacl? (molar mass of nacl≈58.44 g/mol)
87.66 g
38.96 g
58.44 g
116.88 g

Explanation:

First Question: Percent Composition of Oxygen in CO₂

Step1: Calculate molar mass of CO₂

Molar mass of \( \text{CO}_2 = \text{mass of C} + 2\times\text{mass of O} \)
\( = 12.01 + 2\times16.00 = 12.01 + 32.00 = 44.01 \, \text{g/mol} \)

Step2: Calculate mass of O in CO₂

Mass of O in \( \text{CO}_2 = 2\times16.00 = 32.00 \, \text{g/mol} \)

Step3: Calculate percent composition of O

Percent composition \( = \frac{\text{mass of O in CO}_2}{\text{molar mass of CO}_2} \times 100 \)
\( = \frac{32.00}{44.01} \times 100 \approx 72.73\% \)

Recall atomic molar masses: Copper (Cu) ≈ 63.55 g/mol, Lead (Pb) ≈ 207.2 g/mol, Gold (Au) ≈ 197.0 g/mol, Mercury (Hg) ≈ 200.6 g/mol. Comparing these, lead has the largest molar mass.

Step1: Use the formula \( \text{mass} = \text{moles} \times \text{molar mass} \)

Given moles = 1.50, molar mass of NaCl = 58.44 g/mol.

Step2: Calculate mass

\( \text{mass} = 1.50 \times 58.44 = 87.66 \, \text{g} \)

Answer:

72.73%

Second Question: Largest Atomic Molar Mass