Chemistry 2.3
Math in Chemistry:
 the atomic mass unit is today defined as 1/12 of



the mass of a carbon-12 atom. That figure is
exactly 1.66053873 · 10 E−24 grams.
Avogadro's number = 6.0221415 × 10E23
What do you get when you multiply these two
quantities?
1 atomic mass unit (amu).
Solving for Formula or Molecular
Mass:
1.
2.
3.
Determine the number of atoms of each
element from the formula.
Find the atomic mass of each element,
and multiply it by the number of atoms of
that element.
Add the total mass for each element to
determine the formula mass.
Sample Problems

What is the gram formula mass of:
 NaHCO3
 Al2(SO4)3
 C12H22O11
Percent Composition:

Using subscripts and atomic mass, one
can find the percent of a certain element
or component by mass.
Hydrates:
Water molecules are shown as parts of the
formula.
 CuSO4 · 5H2O
 Treat the water molecules as a single unit.

Sample problems:
1.
2.
What is the percentage of oxygen in
glucose?
What is the percentage, by mass of
water in sodium carbonated crystals,
Na2CO3 · 10 H2O?
The Mole:


Avogadro's number = 6.0221415 E23
Based on the number of atoms in 12.00
grams of Carbon-12 (amu =12g/mol)
Dimensional Analysis:

Using the formula:
Molar Mass = grams/moles
 Grams = MM x moles
 Moles = grams/MM

Sample problems:
What is the total mass of 0.75 mol of SO2?
 What is the number of moles of KCl
(MM=74g) present in 148 grams of KCl?
 How many grams are there in 2 moles of
sulfuric acid?

Finding Molecular Formulas from
Empirical Formulas:
Using the molecular mass and the
empirical formula, one can determine the
molecular formula.
 Ex/ What is the molecular formula of
glucose ( MM = 180g/mol, empirical
formula=CH2O)?

Solving problems using Balanced
Equations:

Equation must be balanced, and then the
stoichiometric coefficients can be used to
determine quantity of reactants and
products.
Sample Problems:

How many liter of carbon dioxide gas will
be produced from the complete
combustion of 30.0 liters of ethane?
Phase Change:
Solid (s), liquid (l), and gas (g).
 Melting, freezing:
 Condensation, vaporization (or boiling):
 Sublimation, deposition:

Temperature and Heat:
a measure of average kinetic energy
 Where on the heating curve can you show
the difference between heat and
temperature?
 The heating curve in reverse is called a
cooling curve.
 K = ˚C + 273.
 Heat is measured in Joules or calories.

Problems with Specific Heat (c):
How much heat is absorbed or released
by a substance in a specific reaction?
 Use the formula q = mc∆T

q = heat (joules)
 m = mass of substance
 c = specific heat capacity of a substance
 ∆T = final temp – initial temp

Sample Problems:

How many joules are absorbed when 50.0
g of water are heated from 30.2 ˚C to
58.6 ˚C?
Heat of fusion and vaporization:
The amount of heat per gram to change a
substance from solid to liquid (heat of
fusion) at 1 atm.
 The amount of heat per gram to change a
substance from liquid to gas (heat of
vaporization) at 1 atm.
 Endo or Exo?
 What about freezing and condensation?

Sample problem:

How many joules of energy are required to
vaporize 423 g of water at 100 ˚C and 1
atm?
Behavior of Gases

Kinetic Molecular Theory (KMT)
Gas particles do not occupy volume.
 Gas molecules do not exert attractive forces
on each other.
 Gaseous material have completely elastic
collisions (no loss of energy).

Ideal Gas
An ideal gas is one that follows the
guidelines of the KMT.
 Deviations from an Ideal Gas:

Low temperatures cause gas molecules to
attract each other.
 High pressure causes gas molecules to have
significant volume.

Combined Gas Law:
Gas Volume
1 mole of gas molecules at Standard
Temperature and Pressure (STP), 0˚C
and 1 atmosphere will occupy 22.4 liters of
volume.
 The ideal gas equation shows us this
relationship:

PV =nRT
 1atm x 22.4L=1molx0.0821x273K

Separation Techniques:

Filtration:
 Based
on particle size and density, filtrate and
residue.

Distillation:
 Based

on different boiling points of substances.
Chromatography:
 Based
on polarity and attraction of molecules to
medium. Paper, Column, and Gas.