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Exam Review

19. Percent Composition:
Percent composition is used to identify the unknown or new compound. It tells you the exact percentage by mass of each element in a compound.
formula:
percent composition= part mass(mass of element)/whole mass(mass of compound) x100
a.)
Ni- (33.1/41.9)x100= 79.0%
O- (8.8/41.9)x100= 21%
b.)
1. find the molar mass of each element in the compound (use periodic table)
2. find molar mass of entire formula
3. use coefficients form chemical formula to determine how many grams of each element are in total mass of one mole of the compound

percent of hydrogen:
(8.064/180.163)x100= 4.48%

31. Mole
Using moles is a reoccurring topic throughout the trimester so heres a quick review...
1 mole=6.022x10^23
used for:
- atoms
- molecules
- ions
- formula units

calculating unknown element/molar mass:
1. moles= # atoms x (1 mole/6.022x10^23)
2. molar mass= molar mass/moles
3. use molar mass to find unknown element

Molar Volume of Gases:
1 mole gas= 22.4 L
(standard temperature and pressure)
Great job, but I don't think your answer in part b needs to be restricted to 2 sig figs.

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