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: O 2 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 – NaHCO 3 Caffeine – C 8 H 10 N 4 O 2 Aspartame – C 14 H 18 N 2 O 5

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 Can it be physically separated? Homogeneous Mixture Heterogeneous MixtureCompoundElement MIXTUREPURE SUBSTANCE yesno Can it be chemically decomposed? noyes Is the composition uniform? noyes Colloids Suspensions Solutions

Wednesday

Physical and Chemical Properties Properties of Matter Chemical 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 Intensive Properties Do NOT depend on the amount ________________ E.G Color, Taste, Melting/Boiling Point, Luster, Hardness 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 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