Section 1: Chemistry

Section 1: Chemistry

Unit 1 – Matter • What is matter? • Matter is anything that has mass and takes up space. • Can matter change? • Yes – e.g. snow melting, water boiling

Properties of Matter • What do we mean by the properties of an object? • A property is simply a characteristic that we can use to describe something. • There are physical properties and chemical properties.

1.2 Physical Properties of Matter • A physical property does not involve a substance becoming a new substance. • There are many types of physical properties that you may want to describe • Colour - red, green, blue, …? • Texture – smooth, fine, coarse, …? • Taste – sour, salty, sweet, …?

1.2 Other Physical Properties of Matter • States of matter at room temperature • Solid, liquid, plasma, or gas • Hardness is the measure of the resistance of a solid to be scratched or dented. • Malleable is the opposite of brittle. Glass and dried clay are examples of things that are brittle. Aluminum foil is malleable. Gold is malleable since it can be hammered into thin sheets.

Copper isductilesince it can be pulled into wires. • Melting and boiling points. • What is the boiling point of water? The melting point of ice? • Crystal form. Example, salt. • Solubility is the ability of a substance to dissolve in a solvent such as water. Salt is soluble while pepper is not. • Density- mass per unit volume

1.2 Chemical Properties of Matter • A chemical propertydescribes the behaviour of a substance as it becomes a new substance. • Combustibility - If a substance is combustible or flammable, it will burn when exposed to a flame. A substance that will not burn is described as nonflammable. • List some materials that are combustible. • List some materials that are nonflammable.

Combustion • During combustion, a substance reacts rapidly with oxygen and releases energy. • The energy may be in the form of heat and light • Many substances can act as fuels. E.g. wood, diesel oil, and kerosene.

Combustion: The Fire Triangle • The fire triangle is a convenient way to remember the three components of any combustion reaction. • Removing any one of these makes the triangle incomplete and puts out the fire.

Reaction with acid • Reaction with acid. The ability of a substance to react with acid is a chemical property. • Name some substances that react with acids such as vinegar. • Would you drink acid? • Look at the side of a Coke can.

Corrosion • Corrosion is the slow chemical change that occurs when a metal reacts with oxygen from the air. This chemical reaction forms a new substance called an oxide. • Different kinds of corrosion: • Rusting • Aluminum corrosion • Silver tarnish

Rusting • Rusting is a chemical change that involves iron, oxygen from the air, water, and salt or other minerals that may be dissolved in water. • Where do we normally see rust? • What can we do to prevent rust?

Aluminum Corrosion • Aluminum has a chemical property similar to iron in that it reacts with oxygen to form an oxide. • The aluminum oxidethat forms is strong and it is unaffected by water.

Silver tarnish • Unlike iron and aluminum, silver does not react with oxygen but it does react with sulphur. • Sulphur is found in • Mustard • Eggs • Acid rain • Silver sulphide causes silver to develop a black coating. • The black layer is annoying but it can be removed by polishing the silver.

Preventing Corrosion • There are many ways to prevent corrosion: • Painting metal prevents oxygen from getting at the metal • Use plastic instead of steel • Cathodic protection – using one metal to attract corrosion (oxygen) from another.

Density • A quantitative physical property of matter • Which is heavier: a 12 inch bar of gold or a pillow full of feathers?

A 12 inch bar of gold weighs more than a pillow full of feathers even though the pillow takes up more space? Why? • Gold is more dense. It has more matter per unit volume.

Density is the amount of matter per unit volume of that matter. • Density (D) = Mass (m) / Volume (V ) • If you know any two of the three variables (D, m, V), you can solve for the third. • m = DV V = m / D

Sample density question #1 • If a rock has a mass of 49 g and occupies a volume of 7 cm3, what is the density? D = m / V = 49 g / 7 cm3 = 7.0 g/ cm3

Solve these sample density questions 1. An object has a mass of 250 g and occupies a volume of 14.5 cm3, what is the density? 2. A piece of wood occupies a volume of 46 cm3 and it has a mass of 100 g. What is the density of the wood? 3. An unknown metal has a density of 2.6g/cm3 and a mass of 15 g. How much volume does this piece of meal occupy. 4. A sample of a particular liquid has a density of 6.85 kg/L and it occupies a volume of 3.4 L. How much does this particular sample weigh?

Answer to question #1 • D = m/V D = 250 g/14.5 cm3 D = 17.24 g/cm3

Answer to question #2 • D = m/V D = 100g / 46 cm3 D = 2.17g/cm3

Answer to question #3 • D = m/V V = m/D V = 15g / 2.6 g/cm3 V = 5.77 cm3

Answer to question #4 • D = m/V M = DV M = 6.85 kg/L x 3.4 L M = 23.29 kg ** Note that volume can be expressed as cm3, m3, ml, or even L.

Approximate Densities of Some Common Materials

Water is denser than ice! • Why is this so important? • It means that ice floats in water instead of sinking. Think of the poor fish if this was not the case. • Why is ice less dense than water? • When water freezes, it expands which means that the same mass of water is spread over a greater volume.

Homework • Answer questions 2, 3, 4 on page 25 of the text.

WHMIS • WHMIS (Workplace Hazardous Material Information System) • These symbols are found on products to indicate exactly why and to what degree a product is dangerous

Assignment #1 • Create a simple map of your home and indicate where you would have found products with some of the hazardous household product symbols that we have discussed.

1.7 Physical and Chemical Changes • A burning candle – what happens? • As the candle burns, the wax melts (a solid becomes a liquid), and then it hardens (a liquid becomes a solid). These are physical changes. • The wax also combusts producing heat and light. This chemical change involves the wax becoming carbon dioxide, water, and energy.

What is a physical change? • In a physical change, the substance involved remains the same substance, even though it may change state or form. When candle wax melts, it is still wax. • Changes of state – melting, boiling, freezing, condensing, and dissolving – are physical changes. • Most physical changes are easy to reverse.

What is a chemical change? • In a chemical change, the original substance is changed into one or more different substances that have different properties. • As candle wax melts, some of the wax particles combine with oxygen to produce water vapour, carbon dioxide, heat, and light, but it is still wax. • A chemical change always involves the production of new substances. Examples include burning, cooking, and rusting. • Most chemical changes are difficult to reverse.

Clues That a Chemical Change Has Happened • A new colour appears. • Heat or light is given off. • Bubbles of gas are formed. • A solid material forms in a liquid. (Precipitate) • The change is difficult to reverse.

Homework • Answer questions 2 and 3 on page 30.

Section 1: Chemistry