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Empirical and Molecular Formulas

Empirical and Molecular Formulas

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Chemistry

9th - 12th Grade

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Sara Geitner

Used 173+ times

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8 Slides • 8 Questions

1

Topic 8: Empirical and Molecular Formulas

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Empirical and Molecular Formulas

  • Molecular Formula: The true number of atoms of each element in the formula of a compound

  • Empirical Formula: The lowest whole number ratio of atoms in a compound.

    • Molecular formula = (empirical formula)n

    • Molecular formula = C6H6 = (CH)6

    • Empirical formula = CH

3

Empirical and Molecular Formulas

To go from a molecular formula to an empirical formula we divide the subscripts by the greatest common factor.

Ex. If the molecular formula is C2H2O4, What is the empirical formula?

1.    Determine the greatest common factor _______

2.    Divide subscripts by that factor to get the empirical formula __________________

4

Multiple Choice

A chemical formula that shows the actual # and kinds of atoms present in one molecule of a compound is called_________

1

ionic formula

2

covalent formula

3

empirical formula

4

molecular formula

5

Multiple Choice

What is the empirical formula for C4H6?

1

CH

2

CH3

3

C2H3

4

C4H6

6

Multiple Choice

Which pair has the same empirical formula?
1

NaCrO4 and Na2Cr2O7

2

C2H4O2 and C6H12O6

3

C3H6Oand C2H6O2

4

CH4 and C2H6

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Formulas (continued)

  • Formulas for ionic compounds are ALWAYS empirical (lowest whole number ratio).

  • Examples: NaCl, MgCl2, Al2(SO4)3, K2CO3

8

Formulas for molecular compounds MIGHT be empirical (lowest whole number ratio)

  • Molecular: H2O Empirical: H2O

  • Molecular: C6H12O6 Empirical: CH2O

9

Multiple Choice

What is the empirical formula for N2S3?

1

NS

2

N3S2

3

N2S3

10

Multiple Choice

C2H6O

Which is the correct empirical formula

1

CHO

2

C2H6O

3

C4H14O2

4

None

11

Multiple Select

Which of the following compounds are both an empirical AND molecular formula (check all that apply)

1

C6H12O6

2

C12H22O11

3

H2O2

4

S2O4

5

H2O

12

Try These

Formula GCF Empirical

H2O2

Fe2(SO4)3

Na2B4O7

6 NaCl

2 C4H5N2O

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Fill in the Blank

We can also calculate the molecular formula given the molecular mass and empirical formula.

            What is the molecular mass of HO (in grams)?

14

Fill in the Blank

What is the molecular mass of H2O2 (in grams)?

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What is the GCF which allows you to switch from HO to H2O2? ______________

What is the difference in mass between HO & H2O2? ___________________

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The GCF which we multiply each atom to find the molecular formula will be the same as the multiple which allows us to switch from the empirical formula mass to the molecular formula mass.

Ex. Empirical formula of a substance is CH2O. Molar mass is 180 g. What is the molecular formula?

1. Empirical mass ________________

2. Molecular mass/ empirical mass = ______(this is our multiple)

3. Multiply empirical formula by the multiple

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Topic 8: Empirical and Molecular Formulas

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