Ch 7 the mole
This presentation is the property of its rightful owner.
Sponsored Links
1 / 17

Formula Calculations PowerPoint PPT Presentation


  • 77 Views
  • Uploaded on
  • Presentation posted in: General

Ch. 7 – The Mole. Formula Calculations. A. Percentage Composition. EMPIRICAL and MOLECULAR FORMULAS. the percentage by mass of each element in a compound. 127.10 g Cu 159.17 g Cu 2 S. 32.07 g S 159.17 g Cu 2 S. A. Percentage Composition. Find the % composition of Cu 2 S.  100 =.

Download Presentation

Formula Calculations

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Ch 7 the mole

Ch. 7 – The Mole

Formula Calculations


A percentage composition

A. Percentage Composition

EMPIRICAL and MOLECULAR FORMULAS

  • the percentage by mass of each element in a compound


A percentage composition1

127.10 g Cu

159.17 g Cu2S

32.07 g S

159.17 g Cu2S

A. Percentage Composition

  • Find the % composition of Cu2S.

 100 =

%Cu =

79.852% Cu

%S =

 100 =

20.15% S


A percentage composition2

28 g

36 g

8.0 g

36 g

A. Percentage Composition

  • Find the percentage composition of a sample that is 28 g Fe and 8.0 g O.

 100 =

78% Fe

%Fe =

 100 =

22% O

%O =


A percentage composition3

A. Percentage Composition

  • How many grams of copper are in a 38.0-gram sample of Cu2S?

Cu2S is 79.852% Cu

(38.0 g Cu2S)(0.79852) = 30.3 g Cu


A percentage composition4

36.04 g H2O

147.02 g H2O

A. Percentage Composition

  • Find the mass percentage of water in calcium chloride dihydrate, CaCl2•2H2O?

24.51%

H2O

%H2O =

 100 =


B empirical formula

CH3

B. Empirical Formula

  • Smallest whole number ratio of atoms in a compound

C2H6

reduce subscripts


B empirical formula1

B. Empirical Formula

1. Find mass (or %) of each element.

2. Find moles of each element.

3. Divide moles by the smallest # to find subscripts.

4. When necessary, multiply subscripts by 2, 3, or 4 to get whole #’s.


What how can i remember

What ??????????How can I remember?

  • There is a poem to help

  • Percent to Mass

  • Mass to Mole

  • Divide by Small

  • Multiply ‘til Whole

  • Sometimes the mole values are still not whole numbers so multiply by the smallest factor that will make them whole numbers


B empirical formula2

1.85 mol N

1.85 mol

B. Empirical Formula

  • Find the empirical formula for a sample of 25.9% N and 74.1% O.

25.9 g N

1 mol N

14.01 g N

= 1.85 mol N

= 1 N

74.1 g

1 mol

16.00 g

= 4.63 mol O

= 2.5 O


B empirical formula3

N2O5

B. Empirical Formula

N1O2.5

Need to make the subscripts whole numbers

 multiply by 2


Example of determining empirical formula

Example of Determining Empirical Formula

  • Ex. What is the empirical formula of a compound that is 25.9% nitrogen and 74.1% Oxygen?

  • 25.9g N1 mol N = 1.85 mol N

  • 14.0g N

  • 74.1g O1 mol O = 4.63 mol O

  • 16.0g O

  • Divide each element by the lowest number of

  • moles in the compound:

  • 1.85 mol N = 1 mol N

  • 1.85

  • 4.63 mol O = 2.50 mol O

  • 1.85

  • Now find the lowest common denominator.

  • 1 mol N x 2= N22.5 mol O x 2 = O5

  • Therefore, N2O5 is the empirical formula


  • Practice problems

    Practice Problems

    Calculate the empirical formula for a compound that is 94.1% O and 5.90%H

    Calculate the empirical formula for a compound that is 79.8% C and 20.2% H


    C molecular formula

    C2H6

    C. Molecular Formula

    • “True Formula” - the actual number of atoms in a compound

    CH3

    empirical

    formula

    ?

    molecular

    formula


    C molecular formula1

    C. Molecular Formula

    1. Find the empirical formula.

    2. Find the empirical formula mass.

    3. Divide the molecular mass by the empirical mass.

    4. Multiply each subscript by the answer from step 3.


    C molecular formula2

    28.1 g/mol

    14.03 g/mol

    C. Molecular Formula

    • The empirical formula for ethylene is CH2. Find the molecular formula if the molecular mass is 28.1 g/mol?

    empirical mass = 14.03 g/mol

    = 2.00

    2(CH2) C2H4


    Example of molecular formula

    Example of Molecular Formula

    Calculate the molecular formula of the compound whose Molar mass is 60.0g and empirical formula is CH4N.


  • Login