Molar mass review, empirical vs molecular.notebook
December 09, 2015
Warm up
1) Define molar mass
2) How many mols are in 24.0 grams of C
3) How much does half a mol of water weigh?
Dec 7-7:31 AM
More Practice:
1) What is the molar mass of C2H7 given to 3
sig figs?
2) How many mols of C2H7 are in 321g?
3) What is the percent weight of C in C2H7?
4)How many grams would 0.750 mols of C2H7
weigh?
Nov 16-7:26 AM
Molar mass review, empirical vs molecular.notebook
December 09, 2015
Molecular vs Empirical Formulas
Empirical formulas are the ratio of atoms in a
molecule
Molecular formulas are the COMPLETE
number of atoms in an element.
Nov 16-7:31 AM
Examples
Empirical formula of CH
This means that for every atom of carbon,
there is one atom of hydrogen.
Molecular formulas with the same ratio acetylene - C2H2
benzene - C6H6
Nov 16-7:32 AM
Molar mass review, empirical vs molecular.notebook
December 09, 2015
Other examples of different compounds with
the same empirical formula
ethylene C2H4
butene C4H8
cyclohexane C6H12
What is the common empirical formula?
Nov 16-7:35 AM
The empirical formula of hexane is C3H7. Its
molecular weight is 86.2 amu. What is the
molecular formula of hexane?
Nov 16-7:36 AM
Molar mass review, empirical vs molecular.notebook
December 09, 2015
Solution
1. Calculate the formula weight of C3H7.
2. Calculate the ratio between the molecular
weight and the empirical weight:
3. The molecular formula must be twice the
empirical formula:
(C3H7)2 or C6H14
Nov 16-7:39 AM
The compound ethylene glycol is often used
as an antifreeze. It contains 38.7% carbon,
9.75% hydrogen, and the rest oxygen. The
molecular weight of ethylene glycol is 62.07 g.
What is the molecular formula of ethylene
glycol?
Nov 16-7:37 AM
Molar mass review, empirical vs molecular.notebook
December 09, 2015
1. Calculate the empirical formula. Assume 100
g of the compound, which will contain 38.70 g
carbon, 9.75 g hydrogen and the rest oxygen
? g O = 100 g - 38.70 g C - 9.75 g H = 51.55 g
O.
2. Calculate the moles of each element
present:
3. Next calculate the ratio of molecular weight
to empircal formula weight. The molecular
weight is given. The empirical formula is CH3O,
so the empirical formula weight is 12.01 + 3
(1.008) + 16.00 = 31.03.
Therefore the molecular formula is twice the
empirical formula: C2H6O2.
Nov 16-8:46 AM
A sample with a molar mass of 34.00 g/mol is
found to consist of 0.44g H and 6.92g O.
Find its molecular formula.
Dec 7-7:33 AM
Molar mass review, empirical vs molecular.notebook
December 09, 2015
If 4.04g of N combine with 11.46g O to produce
a compound with a molar mass of 108.0 g/mol,
what is the molecular formula of this
compound?
Dec 7-7:36 AM
The empirical formula for trichloroisocyanuric
acid, the active ingredient in many household
bleaches, is OCNCl. The molar mass of this
compound is 232.41g/mol. What is the
molecular formula of trichloroisocyanuric acid.
Dec 7-7:36 AM
Molar mass review, empirical vs molecular.notebook
December 09, 2015
The molar mass of a compound is 92g/mol.
Analysis of a sample of the compound
indicates that it contains 0.606g N and 1.390g
O. Find its molecular formula.
Dec 7-7:37 AM
Determine the molecular formula of a
compound with an empirical formula of NH2
and a formula mass of 32.06 g/mol.
Dec 7-7:37 AM
Molar mass review, empirical vs molecular.notebook
Dec 7-7:37 AM
December 09, 2015