Does it really matter? Yes! it is Chemistry, isn’t it! Unit 2

What’s the Matter? Matter is anything that has shape and takes up space 3 forms that we study in chemistry –Solid: definite volume & definite shape –Liquid: definite volume, takes shape of container –Gas: indefinite volume & shape, will fill any container –Plasma: a super-heated vapor state

Properties of Matter Physical Properties – properties that can be observed without changing the chemical nature Examples –State (solid, liquid, gas, etc.) –Mass –Color, odor, taste (be careful!) –Volume –Solubility, hardness, texture

Chemical Properties Properties that are usually not visible when the matter is in isolation – only when it reacts chemically with other substances Examples –Combustibility –Decomposition (Worksheet)

Physical Changes A physical change is when a change occurs that the substance does not loose its identity Examples –Melting (Changing State) –Splitting –Fracturing –Mixing

Chemical Changes A change that occurs that changes the identity of the substance Examples –Formation of new substances –Burning –Electrolysis Energy is usually consumed or released during a chemical change (Worksheet)

Compounds, Mixtures, & Solutions Part II – when things get all mixed up…

Mix it up… Compound – when substances are chemically combined in a definite proportion by weight Mixture – a blend of two or more types of substances are mechanically combined (can be separated by ordinary, non-chemical means)

Compounds Elements combine to form compounds Compound – a substance that is chemically combined in a definite proportion by mass Sodium + Chlorine = Sodium Chloride (salt) Always one sodium per one chlorine atom Definite proportion – the ratio never changes

Pure substances A compound is an example of a pure substance Pure Substance – has a definite chemical composition – has definite chemical properties Compounds and elements are pure substances

Can it be separated? Mixture Pure substance Is it uniform composition? Can it be broken down by ordinary chemical means? Homogeneous mixture: e.g. air, apple juice, stainless steel Heterogeneous mixture: e.g., granite, wood, blood, unmixed coffee Compounds (water, salt, sucrose) Elements (gold, aluminum, oxygen, chlorine) Matter

Prefixes are the key… Homogeneous – the prefix homo means “same” therefore homogeneous mixtures are the same through out, e.g. apple juice Heterogeneous – the prefix hetero means “different”,therefore heterogeneous mixtures are different through out, e.g. raisin bran

Mixtures Mixture – a blend of two or more types of substances –Physically (or mechanically) combined – Not chemically combined; can be separated by ordinary means –Examples Salt and pepper mixed up in a bowl Sugar in water Milk Air

Types of Mixtures Solutions Suspensions Colloids

Find the solution… Solution – a mixture when one ingredient is dissolved completely in another (uniform & homogeneous) Solute – the ingredient that is dissolved Solvent – the ingredient that does the dissolving Particles that are dissolved are very small, light will shine right through Example –Sugar (solute) Hot coffee (solvent) –Alloy: a mixture of metals

Suspensions When particles are large and they settle out unless they are constantly agitated or stirred Suspensions are heterogeneous because they are not uniform in nature Examples –Soil & Water –Chocolate milk –Paint –Clouds & Fog

Colloids Mixture where the solute particles are of intermediate size –Particles will stay floating, not completely settle out –In between solution and suspension Colloids will scatter light –Known as the Tyndall Effect Examples –Clay in water –Fog –Paint –Mayonnaise

Tyndall Effect

Order! So to break it down…mixtures in order: –Suspension: heterogeneous, large particles, will settle out –Colloids: heterogeneous, medium sized particles, won’t settle out, will reflect light –Solution: homogeneous, tiny particles, does not separate, will NOT reflect light

Density The property of matter that is derived from the ratio of mass to volume D= Mass / Volume The unit is kg/m3- but it’s too BIG! The more common unit is g/cm3 Density does not depend on the size of the sample, all of the sample has the same density

Mass M Density = or D = Volume v When solving for density, you would use the formula exactly as it appeared above. Here is an example where density is the unknown, and the steps for solving the problem:

1. A student determines that a piece of an unknown material has a mass of g and a volume of 7.57 cm3. What is the density of the material, rounded to the correct number of significant digits?

First: Write the correct formula at the top of your page, and list the knowns and the unknowns. m D = v D = ? M= g V = 7.57 cm3 Second: Substitute the known values in the problem g D = cm3 Third: Calculate your answer, including units D = g/cm3 Fourth: Round to the correct number of significant figures D = g/cm3

Solving For Mass m = v x D Iron has a known density of 7.87 g/cm3. What would be the mass of a 2500 m3 piece of iron?

D = 7.87 g/cm3 m = ? v = 2500 cm3 Substitute the known values in the problem – m = 2500 cm3 x 7.87 g/cm3 Calculate the answer including units – m = 2500 cm3 x 7.87 g/cm3 m = g Round to the correct number of significant figures – m = 2.0 x 104 g

Solving For Volume m v = D Mercury has a density of 13.5 g/cm3. How much space would 50.0 g of mercury occupy?

D = 13.5 g/cm3 M = 50.0 g V = ? Substitute the known values in the problem 50.0 g v = g/cm3 Calculate your answer, including units v = cm3 Round to the correct number of significant figures v = 3.70 cm3

An important side note The law of conservation of matter and energy During any physical or chemical changes/reactions, the total amount of matter and energy remains the same Even nuclear reactions only convert matter into energy – you cannot get something from nothing