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TEKSTEKS
• 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]
Pure SubstancesPure 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
ElementsElements
• 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
CompoundsCompounds• 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 CompoundsCommon Compounds
• Salt -Sodium chloride- NaCl• Baking Soda -Sodium bicarbonate – NaHCO3
• Caffeine – C8H10N4O2
• Aspartame – C14H18N2O5
MixturesMixtures
• 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 Mixtures & Pure Substances ExampleExample
• Tap water contains molecules which are not water molecules,making it a mixture
• Distilled water containsonly water molecules making it a pure substance
Homogeneous MixtureHomogeneous Mixture
• Homogeneous: mixtures which are the same throughout, with identical properties throughout the mixture
• Is also called a solution
Heterogeneous mixtureHeterogeneous mixture
• Heterogeneous: mixtures which have different properties when sampled from different areas
• Different types of heterogeneous mixtures– Colloid– suspension
SuspensionSuspension
• A type of heterogeneous mixture whose particles settle out over time and can be separated from the mixture on standing
MATTER
Can it be physically separated?
Homogeneous Mixture
Heterogeneous Mixture Compound Element
MIXTURE PURE SUBSTANCE
yes no
Can it be chemically decomposed?
noyesIs the composition uniform?
noyes
Colloids
SuspensionsSolutions
Physical and Chemical Physical and Chemical PropertiesPropertiesProperties of MatterProperties of Matter
Chemical PropertiesChemical
Properties
Reactions in the presence of
Water, Air, Acid, Base
What happens when heated
Reactions in the presence of
Water, Air, Acid, Base
What happens when heated
Physical Properties
Physical Properties
Intensive PropertiesDo NOT depend on the
amount________________
E.G Color, Taste, Melting/Boiling Point, Luster, Hardness
Intensive PropertiesDo NOT depend on the
amount________________
E.G Color, Taste, Melting/Boiling Point, Luster, Hardness
Extensive Properties Depends on the
amount_______________Mass, Volume, Length, Shape
Extensive Properties Depends on the
amount_______________Mass, Volume, Length, Shape
Physical ChangesPhysical 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 Common Physical Changes in FoodFood
• Include the following:– cutting– mashing– boiling– melting– freezing
FreezingFreezing• 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 ChangesChemical 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 BrowningNon-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
LeaveningLeavening
• 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
LeaveningLeavening
• Agents include:– baking powder– baking soda– baker’s ammonia– potassium bicarbonate– yeast– sourdough starter
FermentationFermentation
• 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 MixturesSeparating 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
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 3.4 Elements and CompoundsCompounds
TEKS• 4. (D) Classify matter as pure substances or mixtures through investigation of their properties.
Goals & ObjectivesGoals & 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
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