CHEM04- QUALITATIVE CHEMISTRY JPQuitalig Republic of the Philippines
TARLAC AGRICULTURAL
UNIVERSITY Camiling, Tarlac
COLLEGE OF
AGRICULTURE AND
FORESTRY
Department of
Food Science and
Technology
CHAPTER 1
INTRODUCTION TO QUALITATIVE
CHEMISTRY
(REVIEW ON CHEMICAL
CONCEPTS)
INTRODUCTION:
Many problems in analytical chemistry begin with the need to
identify what is present in a sample. This is the scope of qualitative
analysis. Qualitative Analysis (Qualitative Analytical Chemistry) is the
determination of non-numerical information about a chemical
species, a reaction, etc. Examples would be observing that a
reaction is creating a gas that is bubbling out of a solution or observing
that a reaction results in a color change. Qualitative analysis is not as
reliable as quantitative analysis but is often far easier, faster, and
cheaper to perform.
Much of the early work in analytical chemistry involved the
development of simple chemical tests to identify inorganic ions and
organic functional groups.
Since the course includes the study of the identifying
samples, thus it is important to review some basic chemical concepts.
CLASSIFICATION OF MATTER:
Matter can be identified by its characteristic inertial and
gravitational mass and the space that it occupies. It is commonly
found in three different states: solid, liquid and gas.
CHEM04- QUALITATIVE CHEMISTRY
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• Atoms – smaller particles rather uniform bits of matter that can be
split into smaller units using fairly strong heat or electricity. Atoms
are the building blocks of elements, and is made up of yet smaller
units of matter called electrons (-) protons (+), and neutrons
• Substances - a sample of matter whose physical and chemical
properties are the same throughout the sample (uniform
properties throughout) because the matter has a constant
composition.
o Elements –all those substances that have not ever
been decomposed or separated into any other
substances through chemical reactions, by the
application of heat, or by attempting to force an
direct electric current through the sample
-can be arranged into what is called the
periodic table of elements based on observed
similarities in chemical and physical properties
among the different elements.
o Compounds – formed when atoms of two or more
elements come together and bond - can later be
broken down into the pure substances that originally
reacted to form it - composed of smaller units of
bonded atoms called molecules (e.g. water)
- Molecules of a compound are composed of the
same proportion of elements as the compound
as a whole since they are the smallest units of
that compound.
• Mixture- when two or more substances are mixed together
- can be classified into two main categories: homogeneous and
heterogeneous.
o Homogeneous mixture -one in which the composition
of its constituents is uniformly mixed throughout. A
homogeneous mixture in which on substance, the
solute, dissolves completely in another substance,
the solvent, may also be called a solution. Usually
the solvent is a liquid, however the solute can be
either a liquid, solid, or a gas.
- the particles of solute are spread evenly among
the solvent particles and the extremely small
particles of solute cannot be separated from
the solvent by filtration through filter paper
because the spaces between paper fibers
are much greater than the size of the solute
and solvent particles.
- Ex: sugar water (mixture of sucrose and water)
o Heterogeneous mixture – non-uniform mixture in
which the components separate and the composition
varies
- can be separated through physical processes (filtration)
- Ex: salad dressing, rocks, and oil and water mixtures.
- involve at least one fluid are also called
suspension mixtures and separate if they
are left standing long enough (Ex. Oil-water
mixture)
o Colloidal suspensions (colloids) -mixtures that fall
between a solution and a heterogeneous mixture
- does not spontaneously separate or settle out
as time passes and cannot be completely
separated by filtering through a typical filter
paper
Solutions: molecules ~0.1-2 nm in size
Colloids: molecules ~ 2-1000 nm in size
Suspensions: molecules greater than ~ 1000 nm in size
Most substances are naturally found as mixtures; therefore, it is up to
the chemist to separate them into their natural components. There are
many ways to remove substances from mixtures:
1. Physical property of magnetism -
Ex: separating a mixture of iron and sulfur. Iron pieces
would be attracted to a magnet placed into the mixture,
removing the iron from the remaining sulfur.
CHEM04- QUALITATIVE CHEMISTRY
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2. Filtration – process wherein a solid is separated from a
liquid by passing through a fine pored barrier such as
filter paper
Ex: separation of sand and water
3. Distillation – by boiling a solution of a non-volatile solid
dissolved in a liquid in a flask, vapor from the lower
boiling point solvent can be driven off from the solution by
heat, be condensed back into the liquid phase as it
comes in contact with cooler surfaces, and be collected
in another container.
STATES OF MATTER
1. Solids:
• Properties – have definite shape, do not flow, virtually
impossible to compress, expand if heated, but
usually less than liquids and gases.
• Particles in solids – strongly bonded to each other,
vibrate a little, but not much compared tp liquids and
gases
2. Liquid
• Properties: no definite shape, can flow to take the shape
of the bottom of a container, very difficult to
compress (virtually incompressible)
• Particles in liquids: weakly bonded to each other, break
their bonds easily, vibrate and ove more than those
in solids, move faster when heated
3. Gas:
• Properties: no fixed shaper, gases spread (or diffuse) to
completely fill a container, gases are easily
compressed.
• Gas Particles- are free, having no bonds between them,
have much more energy than those of a solid or
liquid, fly around, bouncing off each other and the
walls of the container
4. Other States of Matter
Most of these states of matter can be put into three
categories according to the degrees in varying temperature.
1. At room temperature- include liquid crystal, amorphous
solid, and magnetically ordered states 2. At low temperatures-
include superconductors, superfluids, and Bose-Einstein
condensate state of matter
3. At high temperatures- include plasma and Quark-gluon plasma.
When substances change state, it is because the spacing between
the particles of the substances is changing due to a gain or
loss of energy. For example, we all have probably observed
that water can exist in three forms with different characteristic
ways of behaving: the solid state (ice), liquid state (water),
and gaseous state (water vapor and steam). Due to water's
prevalence, we use it to exemplify and describe the three
different states of matter. As ice is heated and the particles of
matter that make up water gain energy, eventually the ice
melts in to water that eventually boils and turns into steam.
CHANGES IN MATTER
The difference between a physical reaction and a chemical reaction is
composition. In a chemical reaction, there is a change in the
composition of the substances in question; in a physical change,
there is a difference in the appearance, smell, or simple display of a
sample of matter without a change in composition
CHEM04- QUALITATIVE CHEMISTRY
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• Physical Changes are limited to changes that result in a difference
in display without changing the composition, change in physical
properties
- Luster, Malleability, Ability to be drawn into a thin wire,
Density, Viscosity, Solubility, Mass, Volume
Common Physical Changes
1. Texture -texture of a substance can differ with a physical change.
Ex. For example, if a piece of wood was sanded,
waxed, and polished, it would have a very different
texture than it initially had as a rough piece of wood
2. Color- changing of color of a substance is not necessarily an
indicator of a chemical change. However, in a chemical
reaction, a color change is usually an indicator that a
reaction is occurring.
Ex. Painting a metal object
3. Temperature - Although we cannot see temperature change,
unless if a change of state is occurring, it is a physical
change.
Ex. Hot pan – although we cannot physically see the
changing of pan's shape, color, texture or any
properties, however, if one were to touch the pan, it
would be incredibly hot
4. Shape and Size - the shape and size of an object can be
changed and the object will still remain true to its chemical
composition.
Ex. Folding paper
5. Change of State – change of state is likewise a physical change
Ex. Ice turning to water; it doesn't retain a solid
shape and now becomes a viscous fluid. The following are
the changes of state:
Solid→Liquid Melting
Liquid→Gas Vaporization
Liquid→Solid Freezing
Gas→Liquid Condensation
Solid→Gas Sublimation
If heat is added to a substance, such as in melting,
vaporization, and sublimation, the process is endothermic.
In this instance, heat is increasing the speed of the molecules
causing them move faster.
If heat is removed from a substance, such as in
freezing and condensation, then process is exothermic. In
this instance, heat is decreasing the speed of the molecules
causing them move slower.
• Chemical changes - occurs when the substance's composition is
changed. When bonds are broken and new ones are formed a
chemical change occurs.
CHEM04- QUALITATIVE CHEMISTRY
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Common Chemical Changes
The follow are all indicators of chemical reactions
1. Change in Temperature - characteristic of a chemical change.
Increase in temperature (as it does in most reactions)
indicates a chemical reaction is occurring (mixing of
reactants forming products indicates a chemical change)
2. Change in Color - Also an evidence that chemical reaction is taking
place
- There is a change in the chemical composition of the substances
Ex: Rusting of metal
The reaction above is that of the rusting of iron. 4Fe + 3O 2 + 6H2O → 4
Fe(OH)3
3. Noticeable Odor - When two or more compounds or elements
are mixed and a scent or odor is present, a chemical reaction
has taken place
Ex: Rotten egg –foul odor indicates chemical decomposition.
4. Formation of a Precipitate- one of the most common signs of
a chemical reaction taking place. A precipitate-defined to be a
solid that forms inside of a solution or another solid
Ex: soluble carbonate reacts with Barium
->formation of Barium Carbonate precipitate
Reaction: Ba2+(aq) + CO32-(aq) → BaCO3(s)
5. Formation of Bubbles - Formation of bubbles or gas indicates
chemical reaction taking place. When bubbles form, a
temperature change could also be taking place.
Ex: Na2CO3 + 2HCl → 2NaCl + H2O + CO2
