Question

1. A 125mL Erlenmeyer flask has a measure volume of 152 mL. A 0.177 g sample of an unknown vapor occupies the flask at 97.8°C a pressure of 748 torr. Assume ideal gas behavior. a. How many moles of vapor are present? b. What is the molar mass of the vapor? 2. a) If the volume of the flask is mistakenly recorded as 125mL in Question 1, what is the reported molar mass of the vapor? b) What is the percent error caused by the error in the recording of the volume of the flask? Mdifference x100 %error = Machal

Answer 1

1)

a)

Given:

P = 748.0 torr

= (748.0/760) atm

= 0.9842 atm

V = 152.0 mL

= (152.0/1000) L

= 0.152 L

T = 97.8 oC

= (97.8+273) K

= 370.8 K

find number of moles using:

P * V = n*R*T

0.9842 atm * 0.152 L = n * 0.08206 atm.L/mol.K * 370.8 K

n = 4.917*10^-3 mol

Answer: 4.92*10^-3 mol

b)

mass(solute)= 0.177 g

use:

number of mol = mass / molar mass

4.917*10^-3 mol = (0.177 g)/molar mass

molar mass = 36.0 g/mol

Answer: 36.0 g/mol

Only 1 question at a time please