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]

Basic Basic Chemistry Chemistry PrinciplesPrinciples

TuesdayTuesday

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

ColloidColloid

• A colloid is a

homogenous mixture

that contains large

Particles

Example: Milk

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

Wednesday

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

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 3.4 Elements and CompoundsCompounds

TEKS• 4. (D) Classify matter as pure substances or mixtures through investigation of their properties.

ChaptersChapters

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