calculate the molar mass of an unknown whose mass was 0.846 g, and occupied a volume of 354 cm3 at a pressure of 752 torr and a temperature of 100 degrees celcius.
I came up with .0114 moles, I want to know if this is correct.
yes and no. Yes, n = number of moles = 0.0114 but that isn't the molar mass which is the question.
n = grams/molar mass will get that for you if you solve for molar mass.
To determine the molar mass of the unknown substance, we can use the ideal gas law equation, PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant, and T is the temperature.
First, let's convert the given values to the appropriate units:
- The pressure is given as 752 torr. We need to convert it to atm by dividing by 760 torr/1 atm, which gives 0.989 atm.
- The volume is given as 354 cm3. We need to convert it to liters by dividing by 1000 cm3/1 L, resulting in 0.354 L.
- The temperature is given as 100 degrees Celsius. Since the ideal gas law requires Kelvin temperature, we need to add 273.15 to convert it. Thus, 100 Celsius + 273.15 = 373.15 K.
Next, let's rearrange the ideal gas law equation to solve for n, the number of moles:
n = (PV) / (RT)
Substituting the values into the equation:
n = (0.989 atm * 0.354 L) / (0.0821 L·atm/mol·K * 373.15 K)
n = 0.3471 / 30.607
n ≈ 0.01135 moles (rounded to five significant figures)
Therefore, your calculation of approximately 0.0114 moles is correct.
Now, to determine the molar mass of the unknown substance, we can use the formula:
Molar Mass (g/mol) = Mass (g) / Moles (mol)
The mass of the unknown substance given is 0.846 g, and the number of moles calculated is approximately 0.0114 moles.
Molar Mass = 0.846 g / 0.0114 mol
Molar Mass ≈ 74.21 g/mol (rounded to two decimal places)
So, the molar mass of the unknown substance is approximately 74.21 g/mol.