 #  What is the percent composition of N and O in NO 2 ?

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 What is the percent composition of N and O in NO 2 ?

 SI unit for the amount of a substance  A system of counting atoms/ molecules ◦ Much like we count eggs in dozens

 Named after Amedeo Avogadro  6.02x10 23  Number of atoms/ molecules in one mole of substance  If every person living on Earth worked to count the atoms in one mole of an element, and if each person counted continuously at a rate of one atom per second, it would take about 4 million years for all the atoms to be counted.

 The mass of a substance that contains exactly 6.02x10 23 particles of that substance.  Numerical value is the same as the formula mass ◦ Unit: g/mol ◦ Ex: mol mass of C= 12.01g/mol; mol mass of O= 16.00g/mol

 # of mol= g x 1 _ molar mass Ex: 24.02 g of Carbon= ? mol 24.02g x 1mol = 2.00 mol 12.01g

64.14g of sulfur is equal to how many moles? A sample is No has a mass of 90g. How many moles is this?

 # of g= mol x molar mass Ex: 1.5 mol of He= ? g 1.5mol x 4.00g = 6.0 g He 1 mol

What is the mass of 2.5 mol of CO 2 ? What is the mass of 5 mol of Ne?

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