2.3; 3.1-3.6

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There are three naturally occurring isotopes of neon. Their percent abundances and atomic masses are neon-20, 90.51%m 19.99244 u; neon-21, 0.27%, 20.99395; neon-22, 9.22%, 21.99138 u. Calculate the weighted average atomic mass of neon.

The two naturally occurring isotopes of copper are copper-63, mass 62.9298 u, and copper-65, mass 64.9278. What must the percent natural abundances of the two isotopes if the atomic mass of copper is 63.546 u?

Carbon-12

Molecular mass (or molecular weight) is the sum ofthe atomic masses (in amu) in a molecule.

SO2

1S 32.07 amu

2O + 2 x 16.00 amu SO2 64.07 amu

For any molecule

molecular mass (amu) = molar mass (grams)

1 molecule SO2 = 64.07 amu

1 mole SO2 = 64.07 g SO2 3.3

How many atoms are in 0.551 g of potassium (K) ?

How many H atoms are in 72.5 g of C3H8O ?

Percent composition of an element in a compound =

n x molar mass of elementmolar mass of compound

x 100%

n is the number of moles of the element in 1 mole of the compound

C2H6O

3.5

11.5 g of ethanol is burned and 22.0 g of CO2 and 13.5 g of H2O is produced. Calculate the empirical formula of ethanol.

A sample of a compound contains 1.52 g of nitrogen and 3.47 g of oxygen. The molar mass of this compound is between 90-95 g. Determine the molecular formula and the accurate molar mass of this compound.