does it really matter? yes! it is chemistry, isn’t it!

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 space3 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 substancesExamples– Combustibility– Decomposition(Worksheet)

Physical Changes

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

Chemical Changes

A change that occurs that changes the identity of the substanceExamples– 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 compoundsCompound – a substance that is chemically combined in a definite proportion by massSodium + Chlorine = Sodium Chloride (salt)

Always one sodium per one chlorine atomDefinite proportion – the ratio never changes

Pure substances

A compound is an example of a pure substancePure 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 juiceHeterogeneous – 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

SolutionsSuspensionsColloids

Find the solution…

Solution – a mixture when one ingredient is dissolved completely in another (uniform & homogeneous)Solute – the ingredient that is dissolvedSolvent – the ingredient that does the dissolvingParticles that are dissolved are very small, light will shine right throughExample– 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 stirredSuspensions are heterogeneous because they are not uniform in natureExamples– 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 volumeD= Mass / VolumeThe unit is kg/m3 - but it’s too BIG!The more common unit is g/cm3Density does not depend on the size of the sample, all of the sample has the same density

                 Mass                           MDensity = --------------     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 5.854 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 = -------                                                                   vD = ?M= 5.854 gV = 7.57 cm3 Second: Substitute the known values in the problem                                                                 5.854 g                                   D = ------------                                                                 7.57 cm3   Third: Calculate your answer, including units D = 0.77331571994 g/cm3   Fourth: Round to the correct number of significant figures D = 0.773 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 cm3Substitute 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 = 19675 gRound to the correct number of significant figures– m = 2.0 x 104 g

Solving For Volume

mv = -------

DMercury 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 = ---------                                                                    13.5 g/cm3    Calculate your answer, including units v = 3.70370370. . . cm3  Round to the correct number of significant figuresv = 3.70 cm3

An important side note

The law of conservation of matter and energyDuring any physical or chemical changes/reactions, the total amount of matter and energy remains the sameEven nuclear reactions only convert matter into energy – you cannot get something from nothing