Representative Particles
Whatever type of particle that is being
examined.
•Atom – any single element that is part of
the overall compound.
•Ion – an atom or group of atoms that has a
net charge
•Molecule – a group of atoms that have been
chemically combined. There is no net charge
on a molecule.
Determine how many atoms, ions and
molecules are in each example:
Pb(NO3)2
molecule
ions
atoms
5 (NH4)2SO4
molecules
ions
atoms
compound
7 NaCl
3 K2CO3
8 AgNO3
5 Ca3(PO4)2
6(NH4)2CO3
Atoms Ions
molecules
The size of an atom, ion or molecule is too
small to deal with on an individual basis in
the lab. Therefore, normally in chemistry we
deal in moles of atoms, ions or molecules. A
mole can have multiple definitions:
1 mole = 6.022 E 23 (Avogadro’s number)
= atomic weight in grams
= 22.4 liters (for gases only)
Molar Mass – the mass, in grams, of 1 mole
of any substance. It is found by taking the
atomic weight from the periodic table, and
rounding to one place past the decimal.
The molar mass of each of the following:
Be = 9.0 grams
Cr = 52.0 grams
Cl = 35.5 grams
S = 32.1 grams
O = 16.0 grams
Calculate the molar mass of the following:
BeCl2, BeSO4, Cr(ClO3)3, Cr2(SO4)3 and (NH4)3PO4
BeCl2 :
BeSO4 :
Cr2(SO4)3 :
(NH4)3PO4 :
Particles
6.022 E23
The Flux Capacitor
Moles
22.4
Volume
1 mole = 6.022 E23 (particles)
= molar mass (grams)
= 22.4 (liters)
Mass
molar mass
What is the mass of 1.75 mole of NaCl?
1.75 mol NaCl
58.5 g NaCl = 102 g NaCl
1 mol NaCl
How many moles of AgNO3 is 57.3 grams?
What is the volume of 0.258 moles of CH4?
1. How many moles of FeSO4 is 2.57 grams
of FeSO4?
2.How many molecules are in 2.57 grams of
FeSO4?
3.How many moles of oxygen are in 2.57
grams of FeSO4?
4.How many ions are in 2.57 grams of
FeSO4?
1. 0.0169 mol FeSO4
2. 1.02 E22 molc FeSO4
3. 0.0677 mol O
4. 2.04 E 23 ions
How many atoms are in 17.3 grams of Fe2O3?
3.26 E 23 atoms
What is the mass of 1.16 E 21 molecules of Fe2O3?
0.307 g Fe2O3
1. What is the mass of 617 molecules of
MgSO4?
2.What is the volume of 18.7 grams of O2?
3.How many Freon molecules are in 0.1573
liters of Freon?
4.How many oxygen atoms are in 16.3 g of
CuClO3?
5.What is the volume of 76.3 grams of
mercury vapor?
1. What is the volume of 16.3 g of O2?
2.How many molecules are there in 63.75
liters of CO2?
3.What is the mass of 9.47 E 25 molecules
of CH4?
4.a. How many moles of PCl3 are in 16.8
grams of PCl3?
b. How many atoms are in 16.8 g of PCl3?
5. What is the mass of 27.9 liters of NH3?
1. What is the volume of 4.35 E 18 molecules of
SO2?
2. How many atoms are in 15.3 liters of propane
gas, C3H8?
3. What is the mass of 3.92 liters of HCCl3?
4. How many oxygen atoms are in 16.3 grams of
K2Cr2O7?
5. What is the mass of 8.15 E 24 molecules of
CCl4?
6. How many grams of HClO4 can be made from
9.13 E 24 oxygen atoms?
% Composition - % by mass of each element in a
compound
• What is the % of each element in K2CrO4?
1. Calculate the molar mass
2 (39.1) + 52.0 + 4 (16.0) = 194.2 grams
2. Take the mass of each element and divide by
the molar mass of the compound, and then
multiply by 100%
% K = 78.2/194.2 x 100% = 40.3 %
% Cr = 52.0/194.2 x 100 % = 26.8 %
% O= 64.0/194.2 x 100 % = 33.0 %
The total % should be between 99.8 – 100.2 %
•What is the % composition of C3H8?
%C=
%H=
What is the % composition of NaHSO4?
% Na =
%S=
%H=
%O=
How many grams of sodium are in 4.76
grams of NaHSO4?
0.912 g Na
How many grams of oxygen are in 4.76
grams of NaHSO4?
2.54 g O
Empirical Formula – lowest ratio of elements
in a compound
Molecular Formula – Actual number of
elements in a compound
MM = molecular mass
EM = empirical mass
MM/EM = whole number. Multiply subscripts
of the empirical formula by the whole
number to get the molecular formula.
To get the empirical formula from the
molecular formula, reduce the subscripts.
What is the molecular formula of a
compound with a molecular mass of 60.0
grams, and an empirical formula of CH4N?
EM = 12.0 + 4 (1.0) + 14.0 = 30.0 grams
MM/EM = 60.0/30.0 = 2
2 x (CH4N) = C2H8N2
Emp
formula
C2HCl
MM
(g)
181.5
CH2O
180.0
CH
78.0
HO
34.0
CH4
16.0
EM
(g)
MM/EM
Molc.
formula