Matt Katz
Chapter 6 study guide
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 Calculating mass using Atomic Mass Units (amu):
Ex. Calculate the mass, in amu, of a sample of aluminum that contains 75 atoms.
1 Al atom = 26.98 amu
 Calculating the number of atoms from the mass:
Ex. Calculate the number of sodium atoms present in a sample that has a mass of
1172.49 amu.
1 Na atom = 22.99 amu
Vocab
Atomic mass unit
Average atomic mass
Mole
Avogadro’s number
Molar mass
Mass percent
Empirical formula
Molecular formula
A small unit of mass used to describe the mass of an
atom. It is abbreviated as amu.
Most elements have different isotopes with different
masses. Because of this all elements are listed with the
weighted averages of their different masses.
The unit all chemists use in describing numbers of
atoms. It is abbreviated as (mol). Ex. It is the number
equal to the number of carbon atoms in 12.01 grams
of carbon.
6.022
> one mole of something consists of this
many units of that substance.
The mass (in grams) of 1 mol of the substance.
The simplest whole-number ratio of the atoms present
in the compound. It can be derived from the percent
composition of the compound.
The exact formula of the molecules present. It is
always an integer multiple of the empirical formula.
Questions:
1) Calculate the mass of 0.25 moles of water.
2) Calculate the moles in 124.5g of oxygen gas.
3) Calculate the molecular mass of a pure substance if 1.75 moles of the
substance has a mass of 29.792g
4)
5)
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7)
8)
Calculate the mass of 1 mole of CO2.
Calculate the mass of 1 mole of SO2.
What is the molar mass of NH4F?
What is the mass in grams of 6.02 x 1023 molecules of CO?
Calculate the mass in grams of 3.01 x 1023 molecules of F2.
9) Determine the mass, in grams, of one gold atom. One mole of gold atoms
has a mass of 197 grams.
10)
How many moles are present in each of the following:
(a) 36.0 grams of water (H2O)?
(b) 8.5 grams of ammonia (NH3)?
(c) 6.35 grams of copper?
(d) 2.16 grams of silver?
(e) 0.85 grams of silver nitrate (AgNO3)?
(f) 7.10 grams of chlorine gas?
11) What is the mass, in grams, of each of the following?
(a) 1.00 mole of sulfur dioxide?
(b) 2.5 moles of carbon monoxide?
(c) 0.10 mole of hydrogen fluoride?
(d) 0.50 mole of oxygen gas?
(e) 0.50 mole of aluminium?
(f) 0.040 mole of trisodium phosphate (Na3PO4)?