does it really matter? yes! it is chemistry, isn’t it! unit 2
TRANSCRIPT
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