# Homework Help: Density of a gas

1. Nov 7, 2009

### moe darklight

1. The problem statement, all variables and given/known data
Assuming ideal gas behaviour, what would be the density of gaseous ethane (C2H6) at 30. °C and 771 mmHg?

2. Relevant equations

Ideal gas laws.
I'm using:
Density = MP/RT (M is g/mol)

3. The attempt at a solution

This is one of the questions due online by Sunday night. They're marked by the computer, and we get only a limited number of tries. Anyway, this is my answer and how I arrived at it:

-- M = 2*16+6*1.008 = 38.048 g/mol
-- T = 30 + 273.15 = 303.15 K
-- P = 771/760 = 1.014 atm
-- R = 0.0821 atm*L/mol*K
=> d = MP/RT = (38.048*1.014)/(0.0821*303.15) = 38.43/24.88 = 1.54 g/L

I've tried rounding to 2 digits, to 3 digits... every possible combination. I've gone over the numbers a bazillion times and it keep telling me I'm wrong, and I have 1 try left. What am I doing wrong?

2. Nov 7, 2009

### moe darklight

zomg. neevermind. C = 16 ?? glah :yuck::yuck::yuck:. this is the sort of stupid mistake that ends up costing me the A.

no soup for me.