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Molar Mass and Percent Composition Calculation for Elements and Compounds, Study notes of Chemistry

A step-by-step guide on how to calculate the molar mass and percent composition of elements and compounds. It includes examples for various elements and compounds such as H2SO4, NaNO2, Pt(O2)2, CaCO3, Mg(CN)2, and AlPO4.

Typology: Study notes

2021/2022

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7.1
LAST NAME________________________ FIRST NAME________________ DATE ________ PERIOD
7.1 Molar Mass of an Element and Compound
MOLAR MASS OF AN ELEMENT
What is the Mass of the following? (Use your Periodic Table)
1 mole of C
2 moles of C
1 mole of Silver
2 moles of Silver
1 mole of Gold
12 grams
2ร—12 g/mole =
24 grams
107.87 grams
2ร—108 g/mole โ‰ˆ
216 grams
196.97 grams
1 mole of Sodium
2 moles of Sodium
1 mole of Iron
2 moles of Iron
3 moles of Iron
23.00 grams
2ร—23 g/mole โ‰ˆ
46 grams
55.85 grams
2ร—56 g/mole โ‰ˆ
112 grams
3ร—56 g/mole โ‰ˆ
168 grams
CALCULATING MOLAR MASS FOR A MOLECULE/COMPOUND
The molar mass of a molecule is the molar mass of all of the parts of the molecule added together. For
example, the molar mass for a water molecule H2O is the molar mass of 2 Hydrogen and 1 Oxygen.
Mathematically this would be done in the following method:
1 molecule of water is H2O. It has 2 hydrogen atoms and a single oxygen.
H2O
Calculate the molar mass for the following compounds
H2SO4
Element
# in one
Molecule
Molar Mass of
Element
Subtotal
H
2
1.00 gram/mole
2.00 gram/mole
O
1
16.00 gram/mole
16.00 gram/mole
18.00 gram/mole
Element
# in one
Molecule
Molar Mass of
Element
Subtotal
H
2
1.01 gram/mole
2.02 gram/mole
S
1
32.07 gram/mole
32.07 gram/mole
O
4
64.00 gram/mole
64.00 gram/mole
98.09 gram/mole
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LAST NAME________________________ FIRST NAME________________ DATE ________ PERIOD 7.1 Molar Mass of an Element and Compound

MOLAR MASS OF AN ELEMENT

What is the Mass of the following? (Use your Periodic Table)

1 mole of C 2 moles of C 1 mole of Silver 2 moles of Silver 1 mole of Gold 12 grams 2ร—12 g/mole =

24 grams

107.87 grams

2ร—108 g/mole โ‰ˆ

216 grams

196. 9 7 grams

1 mole of Sodium 2 moles of Sodium 1 mole of Iron 2 moles of Iron 3 moles of Iron

23. 00 grams

2ร— 23 g/mole โ‰ˆ

46 grams

55. 85 grams

2ร— 56 g/mole โ‰ˆ

112 grams

3 ร— 56 g/mole โ‰ˆ

168 grams

CALCULATING MOLAR MASS FOR A MOLECULE/COMPOUND

The molar mass of a molecule is the molar mass of all of the parts of the molecule added together. For example, the molar mass for a water molecule H 2 O is the molar mass of 2 Hydrogen and 1 Oxygen.

Mathematically this would be done in the following method:

1 molecule of water is H 2 O. It has 2 hydrogen atoms and a single oxygen.

H 2 O

Calculate the molar mass for the following compounds

H 2 SO 4

Element # in one Molecule

Molar Mass of Element

Subtotal

H 2 1.00 gram/mole 2.0 0 gram/mole

O 1 16. 00 gram/mole 16. 00 gram/mole

18 .0 0 gram/mole

Element # in one Molecule

Molar Mass of Element

Subtotal

H 2 1.01^ gram/mole^ 2.02^ gram/mole

S 1

32.07 gram/mole 32.07 gram/mole

O 4 64.00^ gram/mole^ 64.00^ gram/mole

98.09 gram/mole

NaNO 2

Pt(O 2 ) 2

CaCO 3

Mg(CN) 2

Element # in one Molecule

Molar Mass of Element

Subtotal

Na 1 23.00^ gram/mole^ 23.00^ gram/mole

N 1 14.01^ gram/mole^ 14.01^ gram/mole

O 2 16.00^ gram/mole^^32 .00^ gram/mole

69. gram/mole

Percent Composition โ€“ Percent Composition tells a scientist the percentage that a molecule is made of each element. Notice that most of the mass of water is from the elment Oxygen so the Oxygenโ€™s percentage is the higher of the two. Remember that a percent is a fraction of the part divided by the whole.

ร— 100%

Calculate the Molar Mass and Percent Composition of the following Compounds.

EXAMPLE: Calculating the % Composition of a Water Molecule:

You try to Calculate the % Composition of Oxygen ( about 89%)

ร— ๐Ÿ๐ŸŽ๐ŸŽ% =

ร— ๐Ÿ๐ŸŽ๐ŸŽ% = ๐Ÿ–๐Ÿ–. ๐Ÿ–๐Ÿ–% ๐‘ถ๐’™๐’š๐’ˆ๐’†๐’

This means that water is about 11% Hydrogen and 89% Oxygen by mass.

1. KC 2 H 3 O 2

    1. Na 2 CO
    1. AlPO