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Title: Empirical Formula
Description:

Honors Chemistry
December 4, 2020

Topic Percentage Composition to Empirical Formula



Find the molar mass and % composition of zinc acetate. [Zn(CH3COO)2] ... Molar mass = 183.4 g
        5.7% Zn, 26.2% C, 3.3% H, 34.9% O

Finding the Empirical Formula from Experimental Data
    1) Get the number of grams of each element
    2) For each element, convert grams to moles
    3) Divide each number of moles by the smallest number of moles
    4) Use the ratio to write the formula

SUMMARY:
    1) % --> g
    2) g --> mol
    3) mol / mol

A compound is found to be 45.5% Y and 54.5% C.
    Find its empirical formula.

        Answer: YCl3

A compound of ruthenium and sulfur is 67.7% Ru.
    Find its empirical formula.

        Answer: Ru2S3

A sample of a compound is found to be 5.88 g silver, 0.56 g phosphorous, 1.16 g oxygen.
    Find its empirical formula.
        Answer: Ag3PO4

Molecular Formula from Empirical Formula
Divide the molecular mass of the compound by the molar mass of the empirical formula.
The molecular formula will be a multiple of the empirical formula.

Example:
       Given - Empirical formula is CH
            molecular mass of compound is 78 g/mol.

Determine the molar mass of the empirical formula
        CH = 13 g/mol
            Solve: 78 / 13 = 6
Therefore, the molecular formula is 6 (CH) = C6H6.

HW: Empirical and Molecular Formulas  pdf   II  pdf
         (find the empirical formula for each questions #1 - 10)

Shoot for the moon.
            Even if you miss it you will land among the stars.
                - Lester Louis Brown, b. 1928

Textbook:  Introductory Chemistry Concepts and Connections 4th Edition  by Corwin  (pg 238-243).
                                                 

                           
9.7  PECENT COMPOSITION (pg 238-239)
                                    Objective:  To calculate the percent composition of a compound given its chemical formula.
                           
9.8  EMPIRICAL FORMULA (pg 239-241)
                                    Objective:  T
o calculate the empirical formula of a compound given its mass composition.
                                    Objective: To calculate the empirical formula of a compound given its percent composition.
                            9.9  MOLECULAR FORMULA (pg 241-243)
                                    Objective:  To calculate the molecular formula for a compound given its empirical formula and molar mass.

Homework:
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