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Chemical properties and changes of matter

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.

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Chemical properties and changes of matter

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  1. Chemical properties and changes of matter 8thgrade

  2. 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

  3. Physical and chemical changes CHEMICAL CHANGE EXAMPLES Burning Combustion Electrolysis Oxidation tarnishing • A change in matter that produces one or more new substances

  4. 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

  5. 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

  6. EXAMPLES

  7. Reactants and products • In a chemical change, there are reactants and products • Example: (Reactants) H+OH → H₂O (products)

  8. 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?

  9. Law of conservation of mass –(pg. 418)(chemical change) • Fill it in…

  10. 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

  11. 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

  12. 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

  13. 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)

  14. 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)

  15. CAUTION • Pure substances: cannot be separated easily • Sometimes not at all • Mixtures: can be physically separated

  16. 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 _____________.

  17. 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.

  18. Class Work • Identify the following as a mixture or a pure substance • Sand • Trail mix • Carbon dioxide • Flour • Gold • soil • Lemonade • rock

  19. Mixtures • Two types of mixtures are: • Heterogeneous • Homogeneous

  20. 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)

  21. 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

  22. Class work • Identify the following mixtures as homogeneous or heterogeneous: • Chicken noodle soup • Coffee • Blood • Orange juice with pulp • Creamy peanut butter

  23. 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

  24. Solution • A solution is a mixture containing a solventand at least one solute. • Solvent:does the dissolving • Solute: gets dissolved by the solvent • Solute can be a liquid, solid or gas

  25. 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

  26. BLOOD IS A SOLUTIONWATER IS THE SOLVENT

  27. 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

  28. 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

  29. Litmus paper

  30. 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

  31. 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

  32. 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

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