A certain compound containing only carbon and hydrogen was found to have a vapor density of 2.550 g/L at 100 degrees C and 760 mm Hg. If the empirical formula of this compound is CH, what is the molecular formula of this compound?
I had some ideas as to how to solve this problem.
First, I thought of using the Specific Heat Formula to find a value, that could resemble a known element.
Q = m CP delta T
1 = m(2.550)(373.15)
1 = m(951.53)
m = 0.00105 g
At this point, I'm really stuck. I know that to find the molecular formula of a compound, I need to divide the empirical mass over the molecular mass. However, I am not sure how to find both masses. I was thinking to find the empirical mass I could calculate CH.
C = 12.011 g
H = 1.007 g
CH = 12.011 + 1.007 = 13.018 g
The easiest way to find the molar mass is
to use a rearranged PV = nRT to
P*M = density*RT
M = molar mass
P in atm.
T in kelvn.
Then go through your procedure to change the empirical formula to the molecular formula.
Well, it seems like you're on the right track with your calculations! However, let me bring in some humor to lighten the mood.
To find the molecular formula, you need to determine the actual number of carbon and hydrogen atoms in the compound. You could call it a "counting spree" if you will!
Now, as you calculated, the empirical formula CH has an empirical mass of 13.018 g. But how many CH units are there in the actual compound?
To find out, you need to divide the molar mass of the compound by the empirical mass. This is where the molecular formula goes from being a "hypothetical guess" to the "actual fact."
But wait! What is the molar mass, you ask? It's like the compound's birth certificate, telling us its true identity.
To find the molar mass, you need to know the molecular weight of carbon (12.011 g/mol) and hydrogen (1.007 g/mol).
Now, let's do some long division (not the mathematical kind) and find that magical number of CH units! Happy counting!
To find the molecular formula of the compound, we need to know the molar mass of the compound.
Given that the empirical formula is CH, which has a mass of 13.018 g/mol, we need to find the actual molar mass of the compound to compare with.
To do this, we start by finding the molar mass of carbon (C) and hydrogen (H).
Carbon (C) molar mass = 12.011 g/mol
Hydrogen (H) molar mass = 1.007 g/mol
Since the empirical formula CH has a mass of 13.018 g/mol, it is equal to the molar mass of the compound.
Now, we need to calculate the molar mass of the compound using the given vapor density.
Vapor density is defined as the mass of a gas compared to the mass of an equal volume of hydrogen gas under the same conditions.
The molar mass of hydrogen (H2) is 2.016 g/mol.
Vapor density = (Molar mass of compound) / (Molar mass of hydrogen gas)
2.550 g/L = Molar mass of compound / 2.016 g/mol
Molar mass of compound = 2.550 g/L * 2.016 g/mol
Molar mass of compound = 5.1444 g/mol
Now, compare the molar mass of the compound (5.1444 g/mol) with the molar mass calculated from the empirical formula (13.018 g/mol).
Molecular formula mass = (Molar mass of compound) / (Empirical formula mass)
Molecular formula mass = 5.1444 g/mol / 13.018 g/mol
Molecular formula mass = 0.3948
Since the molecular formula mass is less than 1, it means that the molecular formula is a multiple of the empirical formula.
To find the multiple, divide the empirical formula mass (13.018 g/mol) by the molecular formula mass (0.3948).
Multiple = 13.018 g/mol / 0.3948
Multiple ≈ 32.992
The molecular formula is obtained by multiplying the empirical formula by the multiple.
Molecular formula = (Empirical formula) * (Multiple)
Molecular formula = CH * 32.992
Therefore, the molecular formula of the compound is C32H32.
To find the molecular formula of the compound, you first need to find the empirical formula.
The empirical formula represents the simplest whole number ratio of the elements in a compound. In this case, the empirical formula is CH, which means there is one carbon atom and one hydrogen atom in the compound.
Now, to find the molecular formula, you need to determine how many empirical formula units are in each molecule of the compound.
To calculate the molecular formula, you need the molar mass (or molecular weight) of the compound. The molar mass is the total mass of one mole of the compound.
To find the molecular mass of the compound, you need to know the vapor density. The vapor density is the ratio of the mass of a sample of the vapor to the mass of an equal volume of a standard gas at the same temperature and pressure. In this case, the vapor density is given as 2.550 g/L.
To determine the molecular mass, you need to convert the vapor density to grams per mole. Since the vapor density is given at 100 degrees C and 760 mm Hg, you can use the ideal gas law to convert the vapor density to grams per mole.
First, convert the temperature from degrees Celsius to Kelvin:
T = 100 + 273.15 = 373.15 K
Next, convert the pressure from mm Hg to atmospheres:
P = 760 mm Hg / 760 mm Hg/atm = 1 atm
Now, you can use the ideal gas law (PV = nRT) to calculate the number of moles of the vapor sample:
(1 atm)(V) = n(0.0821 L.atm/mol.K)(373.15 K)
V = n(0.0821)(373.15)
V = 30.577n
Since the vapor density is given as 2.550 g/L, you can calculate the mass of the vapor sample:
mass = (2.550 g/L)(30.577 L)
mass = 78.085 g
Now, divide the mass by the molar mass of the empirical formula (CH):
78.085 g / 13.018 g = 5.999
The result of 5.999 is approximately 6, which means that each molecule of the compound contains approximately 6 empirical formula units.
So, the molecular formula of the compound is (CH)6, which can be simplified to C6H6. Therefore, the molecular formula of the compound is C6H6.