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Molar mass review, empirical vs molecular.notebook, Exams of Chemistry

University of Dayton (UD)Chemistry

'+ 16.00 = 31.03. Therefore the molecular formula is twice the empirical formula: C2H6O2. A sample with a molar mass of 34.00 g/mol is found to ...

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Molar mass review, empirical vs molecular.notebook December 09, 2015
Dec 7-7:31 AM
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?
Nov 16-7:26 AM
More Practice:
1) What is the molar mass of C
2
H
7
given to 3
sig figs?
2) How many mols of C
2
H
7
are in 321g?
3) What is the percent weight of C in C
2
H
7
?
4)How many grams would 0.750 mols of C
2
H
7
weigh?
pf3
pf4
pf5
pf8

Partial preview of the text

Download Molar mass review, empirical vs molecular.notebook and more Exams Chemistry in PDF only on Docsity!

Dec 7-7:31 AM

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?

Nov 16-7:26 AM

More Practice:

  1. What is the molar mass of C 2 H 7 given to 3 sig figs?

  2. How many mols of C 2 H 7 are in 321g?

  3. What is the percent weight of C in C 2 H 7?

4)How many grams would 0.750 mols of C 2 H 7 weigh?

Nov 16-7:31 AM

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 16-7:32 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 - C 2 H 2

benzene - C 6 H 6

Nov 16-7:39 AM

Solution

  1. Calculate the formula weight of C 3 H 7.
  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 C6H

Nov 16-7:37 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 16-8:46 AM

  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 CH 3 O, so the empirical formula weight is 12.01 + 3(1.008) + 16.00 = 31.03.

Therefore the molecular formula is twice the empirical formula: C 2 H 6 O 2.

Dec 7-7:33 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 7-7:37 AM

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 NH and a formula mass of 32.06 g/mol.

Dec 7-7:37 AM