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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.
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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 2ร12 g/mole =
24 grams
107.87 grams
2ร108 g/mole โ
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
46 grams
55. 85 grams
2ร 56 g/mole โ
112 grams
3 ร 56 g/mole โ
168 grams
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.
Calculate the molar mass for the following compounds
Element # in one Molecule
Molar Mass of Element
Subtotal
18 .0 0 gram/mole
Element # in one Molecule
Molar Mass of Element
Subtotal
32.07 gram/mole 32.07 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
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 Oxygenโs percentage is the higher of the two. Remember that a percent is a fraction of the part divided by the whole.
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%)