Unit 2 Lecture 3 Mass Percent Emp Mol Formulas 2
Mass Percent
&
Empirical and
Molecular Formulas
Unit 2 Lecture 3
Mass Percent
The percentage by mass of an element in a compound or a component in a substance
Mass % element = (# of atoms) (element’s atomic mass) x100 formula weight of compound
Mass % component=
( mass of component )
x100
total mass of substance
A component could be a compound or an element in a substance or mixture (for example, water in a hydrate).
Example 1:
1. What is the mass percent of each element in
Ilmenite (FeTiO3)?
Fe= 36.81%
Ti= 31.56%
O = 31.64%
Does this equal 100%?
Example 2:
A tablet contains 0.025 mg of vitamin D. The entire tablet has a mass of 0.115g. Calculate the mass percent of vitamin D in the tablet.
0.022% vitamin D
Example 3:
A sample of potassium permanganate
(KMnO4) is known to contain some impurities. It is found that K+ makes up
19.24% of the entire mass of the impure sample. All of the K+ comes from the
KMnO4 compound. Find the mass percent of KMnO4 in the sample.
77.77%
Molecular & Empirical
Formulas
Molecular Formula
Chemical formulas that provide the actual number of each type of atom in a molecule
Empirical Formula
Chemical formulas that provide the relative number of each type of atom in a molecule (a ratio in its simplest form).
Notice in the examples empirical formulas are written as the smallest whole number ratios of one atom to another, whereas molecular shows actual number (sometimes they can be the same as empirical).
Common Name
Molecular Formula
Empirical Formula
Hydrogen peroxide
H2 O 2
HO
Ethylene
C 2 H4
CH2
Glucose
C6H12O6
CH2O
Water
H2 O
H2 O
Steps for Finding Empirical
Formula from Mass Percent
Values
1. Use the % composition as if it were in
grams...like it was a 100 gram sample.
2. Convert from grams to # of mol of each
element.
3. Divide each # of mol by the smallest # of mol
and round to find the simplest whole-number ratio. Example 4:
A sample of caffiene was found to contain
49.5% carbon, 28.9%
&
Empirical and
Molecular Formulas
Unit 2 Lecture 3
Mass Percent
The percentage by mass of an element in a compound or a component in a substance
Mass % element = (# of atoms) (element’s atomic mass) x100 formula weight of compound
Mass % component=
( mass of component )
x100
total mass of substance
A component could be a compound or an element in a substance or mixture (for example, water in a hydrate).
Example 1:
1. What is the mass percent of each element in
Ilmenite (FeTiO3)?
Fe= 36.81%
Ti= 31.56%
O = 31.64%
Does this equal 100%?
Example 2:
A tablet contains 0.025 mg of vitamin D. The entire tablet has a mass of 0.115g. Calculate the mass percent of vitamin D in the tablet.
0.022% vitamin D
Example 3:
A sample of potassium permanganate
(KMnO4) is known to contain some impurities. It is found that K+ makes up
19.24% of the entire mass of the impure sample. All of the K+ comes from the
KMnO4 compound. Find the mass percent of KMnO4 in the sample.
77.77%
Molecular & Empirical
Formulas
Molecular Formula
Chemical formulas that provide the actual number of each type of atom in a molecule
Empirical Formula
Chemical formulas that provide the relative number of each type of atom in a molecule (a ratio in its simplest form).
Notice in the examples empirical formulas are written as the smallest whole number ratios of one atom to another, whereas molecular shows actual number (sometimes they can be the same as empirical).
Common Name
Molecular Formula
Empirical Formula
Hydrogen peroxide
H2 O 2
HO
Ethylene
C 2 H4
CH2
Glucose
C6H12O6
CH2O
Water
H2 O
H2 O
Steps for Finding Empirical
Formula from Mass Percent
Values
1. Use the % composition as if it were in
grams...like it was a 100 gram sample.
2. Convert from grams to # of mol of each
element.
3. Divide each # of mol by the smallest # of mol
and round to find the simplest whole-number ratio. Example 4:
A sample of caffiene was found to contain
49.5% carbon, 28.9%