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Week 10

Finding atomic mass, formula mass, and molar mass

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Finding atomic mass and atomic weight

The atomic mass or atomic weight of an element is the average mass of an atom of that element. To find the atomic mass of an element look on your periodic table. The units are atomic mass units (amu)

The atomic mass of phosphorus is 30.97amu

To the nearest whole number it is 31 amu

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What is the atomic mass of chlorine? ________________

Finding molecular weight or formula mass

To find the molecular weight (also called formula mass), add the average atomic masses of all the atoms in the molecule. Use subscripts to determine the number of atoms of each element. Units will be amu

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What is the formula mass of glucose C₆H₁₂O₆? to nearest whole number

6(C) + 12(H) + 6(O)

6(12) + 12(1) + 6(16)

180 amu

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What is the molecular weight of water (H₂O)?

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What is the formula mass of calcium nitrite Ca(NO₂)₂?

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Finding molar mass of an element

The molar mass of an element is the mass of 1 mole ( 6.02 x 10²³ ) atoms of that element. It will have the same value as the atomic mass however the units will be grams/mole

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Finding molar mass of a compound

The molar mass of a compound is the mass of one mole (6.02 x 10²³) of molecules of that compound. It is found the same way as formula mass but the units will be grams/mole.

What is the molar mass of barium nitrate Ba(NO₃)₂ ?

1(Ba) + 2(N) + 6(O)

1(137) + 2(14) + 6(16)

137 + 28 + 96

= 261 g/mole

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