Question

Each molecule of ampicillin contains 16 atoms of carbon (plus other atoms). The mass percent of carbon in ampicillin is 55.00%. What is the molar mass of ampicillin?

A) 698.8 g/mol
B) 105.7 g/mol
C) 192.2 g/mol
D) 290.9 g/mol
E) 349.4 g/mol

do i divide the mass of carbon by the mass percent?

Answer 1

The answer is E) 349.4 g/mol

Yes, divide the mass of carbon by the mass percent
Step 1. Calculate the mass of 16 atoms of carbon in ampicillin.
Step 2. Make a proportion and divide the mass of carbon by the mass percent.

Step 1.
Atomic mass of carbon is 12.01 g/mol
Since there are 16 atoms of carbon, the mass of carbon in ampicillin will be:
16 * 12.01 g/mol = 192.16 g/mol

Step 2.
Make a proportion. 192.16 g/mol are 55%. How many grams are 100% (ampicillin mass is 100%):
192.16 g/mol : 55% = x : 100%
x = 192.16 g/mol : 55% * 100%
x = 349.38 g/mol
x ≈ 349.4 g/mol

Answer 2

First, we calculate the mass of Carbon ampicillin contains:
16 moles of atoms x 12 grams per mole
= 192 grams
192 is 55% of the total mass of ampicillin.
Total mass = 192 / 0.55
= 349 g/mol
The answer is E.