Empirical Formulas - PowerPoint PPT Presentation

About This Presentation
Title:

Empirical Formulas

Description:

Empirical Formulas How would a scientist determine the identity of a substance that they made? Percent Composition Mass of element in compound X 100% Total mass of ... – PowerPoint PPT presentation

Number of Views:215
Avg rating:3.0/5.0
Slides: 11
Provided by: CMas54
Category:

less

Transcript and Presenter's Notes

Title: Empirical Formulas


1
Empirical Formulas
2
  • How would a scientist determine the identity of a
    substance that they made?

3
Percent Composition
  • Mass of element in compound X 100
  • Total mass of compound
  • Repeat for each element in compound
  • Will add up to 100

4
Empirical Formula
  • The symbols for the elements combined in the
    compound, with subscripts showing the smallest
    whole-number ratio of the different atoms in the
    compound.
  • Ionic formula unit
  • Covalent reduced molecular formula

5
  • If you know the percent composition of a
    compound, then you can determine its empirical
    formula.
  • We do this by first assuming we have a 100.0 g
    sample so that the percentage values can be
    converted to grams.
  • We then convert the grams to moles (to account
    for atoms having different molar masses)
  • To correct for our assumption of 100.0 g we then
    divide each number of moles by the smallest
    number.

6
What is the empirical formula if a compound
contains 32.4 Na, 22.6 S, 45.0 O?
  • Mass composition (in 100.0g)
  • 32.4 g Na, 22.6 g S, 45.0 g O
  • Composition in moles
  • 32.4 g Na x (1 mol Na / 22.99 g Na) 1.41 mol Na
  • 22.6 g S x (1 mol S / 32.07 g S) 0.705 mol S
  • 45.0 g O x (1 mol O / 16.00 g O) 2.81 mol O
  • Smallest whole-number mole ratio
  • 1.41 mol Na / .705 2.00 mol Na
  • .705 mol S / .705 1.00 mol S
  • 2.81 mol O / .705 3.99 mol O

7
Percent Composition
Mass Composition
Composition in moles
Smallest whole-number mole ratio
8
  • A compounds empirical formula can also be used
    to determine its molecular formula.
  • x (empirical formula) molecular formula
  • x whole-number factor

9
Determine the molecular formula of the compound
with an empirical formula of CH and a mass of
78.11 amu.
  • Molecular formula mass 78.11 amu
  • Empirical formula mass
  • C H 12.01 amu 1.01 amu 13.02 amu
  • x (empirical formula) molecular formula
  • x (13.02 amu) 78.11 amu
  • x 78.11 amu / 13.02 amu 5.999

So CH ? C6H6
10
In the green workbook
  • Pg 67 1 b
  • Pg 77 1 a b
  • Pg 79 1 a b
  • Pg 89 1 a b
  • Pg 94 1 a b
Write a Comment
User Comments (0)
About PowerShow.com