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.

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Chemical properties and changes of matter

Chemical properties and changes of matter

8thgrade


Physical and chemical changes page 303

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


Physical and chemical changes

Physical and chemical changes

CHEMICAL CHANGE

EXAMPLES

Burning

Combustion

Electrolysis

Oxidation

tarnishing

  • A change in matter that produces one or more new substances


Chemical changes

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


Chemical changes1

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


Examples

EXAMPLES


Reactants and products

Reactants and products

  • In a chemical change, there are reactants and products

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


Law of conservation of mass

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?


Law of conservation of mass pg 418 chemical change

Law of conservation of mass –(pg. 418)(chemical change)

  • Fill it in…


How do you know a chemical change has taken place pg 419

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


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


Class work

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


How do elements combine

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)


Pure substances mixtures and solutions pg 391

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)


Caution

CAUTION

  • Pure substances: cannot be separated easily

    • Sometimes not at all

  • Mixtures: can be physically separated


  • Let s look at an example

    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 _____________.


    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.


    Class work1

    Class Work

    • Identify the following as a mixture or a pure substance

      • Sand

      • Trail mix

      • Carbon dioxide

      • Flour

      • Gold

      • soil

      • Lemonade

      • rock


    Mixtures

    Mixtures

    • Two types of mixtures are:

      • Heterogeneous

      • Homogeneous


    Mixtures1

    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)


    Mixtures2

    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


    Class work2

    Class work

    • Identify the following mixtures as homogeneous or heterogeneous:

      • Chicken noodle soup

      • Coffee

      • Blood

      • Orange juice with pulp

      • Creamy peanut butter


    Classification of mixtures page 397

    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


    S olution

    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


    Examples of solutions solvent and solutes

    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


    Blood is a solution water is the solvent

    BLOOD IS A SOLUTIONWATER IS THE SOLVENT


    Acids bases and salts page 378

    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


    Bases

    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


    Litmus paper

    Litmus paper


    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


    Ph scale

    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


    Ph of common substances

    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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