CHEMISTRY 59-320
ANALYTICAL CHEMISTRY
Fall - 2010
Lecture 2
0-2 General steps in a chemical
analysis
• An analysis involves several steps and
operations which depend on:
the particular problem
your expertise
the apparatus or equipment available.
• The analyst should be involved in every
step.
Sample questions
#1: The steps in a chemical analysis are
(a) 1. Formulate the question.
2. Select the analytical procedure.
3. Sample.
4. Prepare the sample.
5. Make replicate measurements of the sample.
(b) 1. Select the analytical procedure
2. Sample.
3. Prepare the sample.
4. Make replicate measurements of the sample.
5. Make a clear and complete written report of your findings.
(c) 1. Formulate the question.
2. Select the analytical procedure.
3. Sample.
4. Prepare the sample.
5. Make replicate measurements of the sample.
6. Make a clear and complete written report of your findings.
#2: When performing an analysis a chemist often uses a
standard solution. What is a standard solution?
(a) A solution that complies with standards established
by the Environmental Protection Agency.
(b) A solution that has a concentration of a chemical that
is known to a high degree of certainty.
(c) A solution that is prepared from a chemical that has
been designated as a primary standard.
#3: In a random heterogeneous material,
(a) differences in composition occur randomly and on a
fine scale.
(b) large regions have obviously different compositions.
(c) samples are collected by taking portions from the
desired number of segments chosen at random.
Chapter 1: Measurements
1-1
SI Units
Using prefixes as multipliers
We customarily use prefixes for every third power of ten, e.g. 10-9.
10-6, 10-3 …
Converting between units
Example: Express the energy 20 Calories in terms of ? kilojoules (kJ)
1-2 Chemical concentrations
A few concepts
• Solution: homogeneous mixture of two or more
substances.
• Solute: a minor species in a solution.
• Solvent: the major species in a solution.
• Concentration: how much solute is contained in
a given volume or mass of solution or solvent.
• Strong & weak electrolytes.
1-2 Chemical concentrations (Continued)
Molarity and Molality:
Molarity (M) is the number of moles of a
substance per liter of solution.
Molality (m) is concentration expressed as
moles of a substance per kilogram of solvent.
Problem 1-14. What is the formal concentration (expressed
as mol/L = M) of NaCl when 32.0 g are dissolved in water
and diluted to 0.500 L?
Answer: The molecular mass of NaCl is 58.44 g/mol
The moles of sale in 32.0 g are 32.0 g /58.44(g/mol)
= ……
1.3 Preparing solutions
• Preparing a solution with a desired molarity
• Dilution
Mcon Vcon  M dil Vdil
Problem 1-32: A bottle of concentrated
aqueous sulfuric acid labeled 98.0wt %
H2SO4, has a concentration of 18.0 M. How
Many millilitres of reagent should be diluted to
1.000 L to give 1.00 M H2SO4?
Solution:
1.4 Stoichiometry Calculation
One must make sure that the reaction equation is
balanced!!
Stoichiometry Calculation (2)
• Problem 1-34: How many millilitres of 3.00
M H2SO4 are required to react with 4.35 g
of solid containing 23.2% Ba(NO3)2 if the
reaction is Ba2+ + SO42- →BaSO4(s)?
• Answer:
Chapter 2: Tools of the Trade
• 2.1 Safe, ethical handling of chemicals
and waste
-- Chemical experimentation creates hazards!
-- The primary safety rule is to familiarize yourself with
the hazards and then to do NOTHING that you consider
to be dangerous.
-- Minimize waste production and RESPONSIBLY
dispose of waste.
-- Recycling chemicals.
-- Clean spills immediately.
-- Label all vessels to indicate what they contain.
What safety information can be
obtained from the following label?
2.2 The lab notebook
• State what you did and what you observed
in a way that it can be understood by a
stranger.
• Record the names of computer files where
programs and data are stored.
• Copy important data into your notebook.
(Computers may crash and become
garbage at any time).
2.3 Analytical balance
• Tare: the mass of an empty vessel that is used
to receive the substance to be weighted .
• Sensitivity: the smallest increment of mass that
can be measured.
• Chemicals should NEVER be placed directly on
the weighting pan
• Handle the vessel you are weighting with a
paper towel so that the tare value does not
change.
Principle of operation (1)
Principle of operation (2)