TEKS
• describe heterogeneous and
homogeneous mixtures.[.6D]
• explain the similarities and
differences between heterogeneous
and homogenous mixtures.[.6E]
• identify chemical examples of pure
substances and mixtures.[.6F]
Basic Chemistry
Principles
Tuesday
Pure Substances
• Can be formed from elements or
compounds
• Consist of only one component with
definite physical and chemical
properties
• Have the same composition
throughout
– Example: O2 or pure water
Elements
• Are pure substances consisting of
one type of atom
• Cannot be broken down or changed
into another substance
• Combine with other elements to
form compounds
Compounds
• Are substances composed of two or
more elements in specific ratios
and bonded together through
chemical forces
– Example: Carbon dioxide is always
composed of one carbon atom and two
oxygen atoms
• Are classified as either covalent
or ionic
Common Compounds
• Salt -Sodium chloride- NaCl
• Baking Soda -Sodium bicarbonate –
NaHCO3
• Caffeine – C8H10N4O2
• Aspartame – C14H18N2O5
Mixtures
• Are substances held together by physical
forces
– this means individual molecules are near each
other without altering their chemical
structure
• Can be homogeneous or heterogeneous
Mixtures & Pure Substances
Example
• Tap water contains molecules which
are not water molecules,
making it a
mixture
• Distilled
water contains
only water molecules making it a
pure substance
Homogeneous Mixture
• Homogeneous: mixtures which are
the same throughout, with
identical properties throughout
the mixture
• Is also called a solution
Heterogeneous mixture
• Heterogeneous: mixtures which have
different properties when sampled
from different areas
• Different types of heterogeneous
mixtures
– Colloid
– suspension
Colloid
• A colloid is a
homogenous mixture
that contains large
Particles
Example: Milk
Suspension
• A type of heterogeneous mixture
whose particles settle out over
time and can be separated from the
mixture on standing
MATTER
yes
MIXTURE
yes
no
Can it be physically
separated?
Is the composition
uniform?
PURE SUBSTANCE
no
Homogeneous
Mixture
Heterogeneous
Mixture
Solutions
Suspensions
Colloids
yes
Can it be chemically
decomposed?
Compound
no
Element
Wednesday
Physical
and
Chemical
Properties of Matter
Properties
Chemical
Properties
Reactions in the
presence of
Water, Air, Acid,
Base
What happens
when heated
Physical
Properties
Intensive Properties
Do NOT depend on the
amount
________________
E.G Color, Taste,
Melting/Boiling Point,
Luster, Hardness
Extensive Properties
Depends on the
amount
_______________
Mass, Volume,
Length, Shape
Physical Changes
• Are any changes not involving a change
in a substance’s chemical identity
• Occur when objects undergo a change that
does not change their chemical nature
• Involves a change in physical properties
– physical properties include the following:
•
•
•
•
•
•
•
texture
shape
size
color
volume
mass
weight
Common Physical Changes in
Food
• Include the following:
– cutting
– mashing
– boiling
– melting
– freezing
Freezing
• Involves storing a food below the
freezing point of water
– safest temperature of freezer storage is
below 0°F
• Results in water transforming from a
liquid state to a solid
• Can have adverse effects on food quality
– texture change, especially if food is not
frozen quickly
– altered color
– freezer burn if exposed to air
– increased food preparation time to account
for defrosting time
Chemical Changes
• Occur when bonds are broken and
new bonds are formed between
different atoms
• Take place in everyday food
production
• Include the following common
food reactions:
– Non-enzymatic browning
– leavening
– fermentation
Non-Enzymatic Browning
• Is browning caused by heat
degradation of sugars or by the
reaction between reducing sugars
and a free amino group
• Is commonly found in foods
• Increases when there is a rise in
temperature and with a rise in pH
above 6.8
Leavening
• Gives breads, cakes, muffins,
pancakes and other foods the
ability to rise and increase in
volume
• Occurs mainly during cooking
• Involves a water or gas expanding
for rising to occur
Leavening
• Agents include:
– baking powder
– baking soda
– baker’s ammonia
– potassium bicarbonate
– yeast
– sourdough starter
Fermentation
• Is the conversion of
carbohydrates to alcohols and
carbon dioxide or organic acids
using yeasts or bacteria under
anaerobic conditions
• Implies the action of
microorganisms is desirable
• Is used in preservation
techniques to create lactic acid
in sour foods or for use in
pickling foods
Separating Mixtures
• Because mixtures are
physically combined,
the processes are
used to separate them are
based on the difference in
physical properties of the
substances.
• 4 methods for separation
Filtration
• Uses a
porous
barrier to
separate a
solid from a
liquid
Distillation
• Based on differences in
boiling points of the
substances
• Heat mixture until
substance with lowest
boiling point boils to a
vapor which is then
condensed into a liquid
Crystallization
• Results in formation of
pure solid particles of
a substance from a
solution containing
the dissolved
substance
Chromatography
• Separates the components
of a mixture (called the
mobile phase) on the basis
of the tendency of each to
travel or be drawn across
the surface of another
material (called the
stationary phase)
3.4 Elements and
Compounds
TEKS
• 4. (D) Classify matter as pure
substances or mixtures through
investigation of their properties.
Chapters
Goals & Objectives
• Explain the Periodic Table of the
Elements
• Identify and explain how chemical
symbols, formulas and equations are
used in food science
• Discuss elements, compounds, mixtures
and formulas
• Compare elements and compounds
• Analyze chemical and physical changes
in food
• Examine the occurrence of specific
chemical reactions