chemical properties and changes of matter
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Chemical properties and changes of matter. 8 th grade. Physical and chemical changes (page 303). PHYSICAL CHANGE. EXAMPLES. Dissolving Bending Breaking cutting Changing state of matter. Appearance or form of a substance changes No new substance is produced. - PowerPoint PPT PresentationTRANSCRIPT
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Chemical properties and changes of matter
8th grade
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Physical and chemical changes(page 303)
PHYSICAL CHANGE
– Appearance or form of a substance changes
– No new substance is produced
EXAMPLES• Dissolving• Bending• Breaking• cutting• Changing state of matter
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Physical and chemical changes
CHEMICAL CHANGE• A change in matter that
produces one or more new substances
EXAMPLES• Burning• Combustion• Electrolysis• Oxidation• tarnishing
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Chemical changes
• Combustion- Combining a fuel with oxygen produces new substances– Ex: burning natural gas on a gas stove. • When it burns, the methane in the natural gas
combines with oxygen in the air to form carbon dioxide and water vapor.
• Electrolysis-Using electricity to break a compound into elements– Ex: Breaking water into hydrogen and oxygen
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Chemical changes
• Oxidation-Combining a substance with oxygen– Ex: Rusting (combining iron with oxygen)
• Tarnishing-Combining a bright metal with sulfur, (or another substance), which produces a dark coating on the metal– Ex: brass tarnishing
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EXAMPLES
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Reactants and products
• In a chemical change, there are reactants and products
• Example: (Reactants) H+ OH → H₂O (products)
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Law of conservation of mass
• The law of conservation of mass states that mass is neither created nor destroyed during a chemical of physical change.– Ex: evaporation of water-does water disappear?– Ex: Does a piece of paper weigh less when it is
shredded into pieces?
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Law of conservation of mass –(pg. 418)
(chemical change)
• Fill it in…
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How do you know a chemical change has taken place??? (pg. 419)
• Some signs that a chemical change has taken place:– 1. Release of energy- chemical changes occur when
bonds between atoms break. • Breaking a bond requires energy• Forming a bond releases energy
• Exothermic reaction-energy is released (as heat)• Endothermic reaction-energy is absorbed
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– 2. Color change (brown apple)– 3. Smell/odor (rotten food)– 4. Release of gas (bubbles)– 5. formation of a precipitate• A precipitate is a solid that forms from a liquid during a
chemical reaction.– Ex: curdled milk
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Class work
• Identify the following as a physical or chemical change:– Ripping a piece of paper– Burning a piece of paper– Painting a house– Rusting– Dissolving salt in boiling water– Cutting you hair
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How do elements combine?
• An element is the simplest substance. It cannot be broken down.– Ex: Carbon (C), Oxygen, (O), Hydrogen, (H)
• Elements combine to form compounds• A compound is a substance made of two or
more elements– Ex: water (H₂O), carbon dioxide (CO₂)
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Pure substances, mixtures and solutions (pg. 391)
• A pure substance is a single kind of mater with a specific make-up– EX: water, sugar, salt– Ex: elements and compounds are pure substances
• A mixture is two or more substances that are together in the same place, but their atoms are not chemically bonded– Ex: salt water, cookie dough– Ex: air (mixture of nitrogen, oxygen and other gases)
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CAUTION
• Pure substances: cannot be separated easily• Sometimes not at all
• Mixtures: can be physically separated
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Let’s look at an example
• To make cookies you would need the following ingredients: salt, water, sugar, and baking soda.
• Salt, water, sugar and baking soda are all _____________.
• When you combine the salt, water, sugar and baking soda to make cookie dough, you get a _____________.
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• The cookie dough, (mixture), could be separated back into water, salt, baking soda and sugar.
• The pure substances, however cannot be separated….only by a chemical reaction.
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Class Work
• Identify the following as a mixture or a pure substance– Sand– Trail mix– Carbon dioxide– Flour– Gold– soil– Lemonade– rock
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Mixtures
• Two types of mixtures are:– Heterogeneous– Homogeneous
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Mixtures
• A heterogeneous mixture is a mixture in which you can see the different parts and easily separate them.– Example: trail mix (peanuts, pretzels, raisins)
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Mixtures
• A Homogeneous mixture is a mixture in which you cannot easily see the parts so separating the mixture is more difficult.– Ex: sugar in lemonade
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Class work
• Identify the following mixtures as homogeneous or heterogeneous:– Chicken noodle soup– Coffee– Blood– Orange juice with pulp– Creamy peanut butter
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Classification of mixtures(page 397)
• Mixtures are classified based on the size of their largest particles:
• They can be:– 1.Solutions– 2.Colloid– 3.particles
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Solution
• A solution is a mixture containing a solvent and at least one solute.
• Solvent: does the dissolving• Solute: gets dissolved by the solvent
• Solute can be a liquid, solid or gas
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Examples of solutions/solvent and solutes
• Grape juice is a solution– The water is the solvent– The sugar and other ingredients are the solutes
• Blood is a solution– Water is the solvent– Platelets, plasma, red and white blood cells are
the solute
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BLOOD IS A SOLUTIONWATER IS THE SOLVENT
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Acids, bases and salts(page 378)
• Acids-– React with metals
• They are corrosive because they wear away the metal– Taste sour
• Citrus fruit contains citric acid (lemons and grapefruit)– Turn blue litmus paper red
• Litmus paper is an indicator. Indicators is a compound that changes color when it comes in contact with an acid.
• Common examples: hydrochloric acid, citric acid, sulfuric acid
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Bases
• Bases• Common bases: ammonia, baking soda,
sodium bicarbonate– Taste bitter• Tonic water contains the base quinine
– Do not react with metals– Feel slippery• Shampoo and soap
– Turn red litmus paper blue
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Litmus paper
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salt
• When you mix and acid and a base together, a reaction occurs called neutralization. – The result of this reaction is the formation of a
SALT• Many types of salt exist
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pH Scale
• Acids and bases can be measured using the pH scale.
• We can tell how acidic or how basic a substance is• The pH scale ranges from 0 to 14– The lower the pH, the more acidic– The higher the pH, the more basic– pH 7 is neutral
• so a pH lower then 7 is acidic and a pH higher then 7 is basic• Water is neutral• Salt is neutral
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pH of common substances
• Battery acid pH = 1.0• Lemon juice pH= 2.0• Vinegar pH = 2.2• Apples pH = 3.0• Baking soda pH = 8.3• Blood pH = 7.4