chemical properties and changes of matter

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Chemical properties and changes of matter 8 th grade

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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 Presentation

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Page 1: Chemical properties and changes of matter

Chemical properties and changes of matter

8th grade

Page 2: Chemical properties and changes of matter

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

Page 3: Chemical properties and changes of matter

Physical and chemical changes

CHEMICAL CHANGE• A change in matter that

produces one or more new substances

EXAMPLES• Burning• Combustion• Electrolysis• Oxidation• tarnishing

Page 4: Chemical properties and changes of matter

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

Page 5: Chemical properties and changes of matter

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

Page 6: Chemical properties and changes of matter

EXAMPLES

Page 7: Chemical properties and changes of matter
Page 8: Chemical properties and changes of matter

Reactants and products

• In a chemical change, there are reactants and products

• Example: (Reactants) H+ OH → H₂O (products)

Page 9: Chemical properties and changes of matter

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?

Page 10: Chemical properties and changes of matter

Law of conservation of mass –(pg. 418)

(chemical change)

• Fill it in…

Page 11: Chemical properties and changes of matter

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

Page 12: Chemical properties and changes of matter

– 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

Page 13: Chemical properties and changes of matter

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

Page 14: Chemical properties and changes of matter

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)

Page 15: Chemical properties and changes of matter

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)

Page 16: Chemical properties and changes of matter

CAUTION

• Pure substances: cannot be separated easily• Sometimes not at all

• Mixtures: can be physically separated

Page 17: Chemical properties and changes of matter

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 _____________.

Page 18: Chemical properties and changes of matter

• 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.

Page 19: Chemical properties and changes of matter

Class Work

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

Page 20: Chemical properties and changes of matter

Mixtures

• Two types of mixtures are:– Heterogeneous– Homogeneous

Page 21: Chemical properties and changes of matter

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)

Page 22: Chemical properties and changes of matter

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

Page 23: Chemical properties and changes of matter

Class work

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

Page 24: Chemical properties and changes of matter

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

Page 25: Chemical properties and changes of matter

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

Page 26: Chemical properties and changes of matter

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

Page 27: Chemical properties and changes of matter

BLOOD IS A SOLUTIONWATER IS THE SOLVENT

Page 28: Chemical properties and changes of matter

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

Page 29: Chemical properties and changes of matter

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

Page 30: Chemical properties and changes of matter

Litmus paper

Page 31: Chemical properties and changes of matter

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

Page 32: Chemical properties and changes of matter

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

Page 33: Chemical properties and changes of matter

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