SubstancesPure and Mixtures

Physical & Chemical Changes: 

Physical & Chemical Changes Chapter 1 Modern Chemistry Students should understand examples of physical changes (state changes) and chemical changes (like decomposition). They should be able to identify mixtures and pure substances by their properties. Chemheritage.org

Physical Changes: 

Physical Changes Change in phase or state What do we call the change of a liquid substance to its gaseous phase?

Physical Changes: 

Physical Changes Change in phase or state What do we call the change of a liquid substance to its gaseous phase? Evaporation

Physical Changes: 

Physical Changes Change in phase or state What do we call the change of a liquid substance to its gaseous phase? Evaporation Liquid water always has some water vapor in the air above the surface, even if its temperature is well below the boiling point. ec.europa.eu

Physical Changes: 

Physical Changes Change in phase or state What do we call the change of a liquid substance to its gaseous phase? Evaporation Liquid water always has some water vapor in the air above the surface, even if its temperature is well below the boiling point. We know that because. . .

Physical Changes: 

Physical Changes Change in phase or state What do we call the change of a liquid substance to its gaseous phase? Evaporation We know that because. . . A cold glass held above the water collects condensed water vapor

Physical Changes: 

Physical Changes Change in phase or state What do we call the change of a liquid substance to its gaseous phase? Evaporation What do we call the all-at-once change of liquid to gas, so that bubbles of the gas form all through the liquid?

Physical Changes: 

Physical Changes Change in phase or state What do we call the change of a liquid substance to its gaseous phase? Evaporation What do we call the all-at-once change of liquid to gas, so that bubbles of the gas form all through the liquid? Boiling (boiling is a special case of “wholesale” evaporation) What’sCookingAmerica.net

Other Physical Changes: 

Other Physical Changes What do we call the change. . .

Other Physical Changes: 

Other Physical Changes What do we call the change. . . Liquid to solid?

Other Physical Changes: 

Other Physical Changes What do we call the change. . . Liquid to solid? Freezing (or solidification)

Other Physical Changes: 

Other Physical Changes What do we call the change. . . Liquid to solid? Freezing (or solidification) Gas to liquid?

Other Physical Changes: 

Other Physical Changes What do we call the change. . . Liquid to solid? Freezing (or solidification) Gas to liquid? Condensation (or liquefaction) Kefacoat.com

Other Physical Changes: 

Other Physical Changes What do we call the change. . . Liquid to solid? Freezing (or solidification) Gas to liquid? Condensation (or liquefaction) Solid directly to gas?

Other Physical Changes: 

Other Physical Changes What do we call the change. . . Liquid to solid? Freezing (or solidification) Gas to liquid? Condensation (or liquefaction) Solid directly to gas? Sublimation Example: dry ice (solid carbon dioxide) Flatrock.org.nz

Why Are these Physical Changes?: 

Why Are these Physical Changes? . . .because by reversing the energy flow, we can reverse the change! Examples

Why Are these Physical Changes?: 

Why Are these Physical Changes? . . .because by reversing the energy flow, we can reverse the change! Examples If we collect the carbon dioxide and chill it to -50 degrees C, it turns back into a solid

Why Are these Physical Changes?: 

Why Are these Physical Changes? . . .because by reversing the energy flow, we can reverse the change! Examples If we collect the carbon dioxide and chill it to -50 degrees C, it turns back into a solid If we put the liquid water into an ice tray and chill it to below 0 degrees C, it turns to ice

Is Dissolving a Physical Change?: 

Is Dissolving a Physical Change? A short demonstration Dissolve a small amount of sodium chloride (NaCl) in water Then put a few drops on a watch glass Heat the watch glass over a flame or hot plate What do you see?

Is Dissolving a Physical Change?: 

Is Dissolving a Physical Change? A short demonstration Dissolve a small amount of sodium chloride (NaCl) in water Then put a few drops on a watch glass Heat the watch glass over a flame or hot plate What do you see? Bigfoto.com

Is Dissolving a Physical Change?: 

Is Dissolving a Physical Change? A short demonstration Dissolve a small amount of sodium chloride (NaCl) in water Then put a few drops on a watch glass Heat the watch glass over a flame or hot plate What do you see? Bigfoto.com An application of energy reversed the process

A Chemical Change: 

A Chemical Change Although energy is almost always involved in chemical changes, the most dramatic change is in the substance The reactant(s) changes into the product(s) There is a permanent and irreversible change in the properties of the reactant(s) Examples: Hydrogen gas, clear, colorless, reacts with oxygen gas, clear, colorless, to form steam (gaseous water). Hydrogen is flammable; water puts out flames. Other example?

Pure substance v. Mixture: 

Pure substance v. Mixture A pure substance is the same throughout A mixture has two or more substances You cannot separate a pure substance with a physical process like heating, filtration You can separate mixtures by physical processes E.g. “Liquid” mud: filter to get out the water E.g. Air, a mixture: chill it below -100 degrees to separate oxygen, carbon dioxide, nitrogen E.g. most colored ink: use chromatography Arttoday.com

Mixtures: 

Mixtures Homogeneous v Heterogeneous Homogeneous mixtures Called solutions (sugar water) Won’t separate by filtration Looks like a single phase Heterogeneous mixtures Called sols or suspensions (mud) Separate by filtration or centrifuge You can see distinct phases (e.g. water and dirt particles) Arttoday.com

Pure Substances: 

Pure Substances Have a fixed composition Elements: all one thing E.g. lead, if pure, is 100% elemental lead E.g. oxygen, if pure, is 100% O 2 Compounds: all same composition We’ll show this in experiment later E.g. NaCl always 40% sodium; 60% chlorine E.g. Hydrogen peroxide always 5.9% hydrogen Lead gsi.ir

Read the Label: 

Read the Label Purity of chemicals varies Technical grade for manufacture CP = chemically pure USP = pharmaceutical grade ACS = analytical grade Primary standard grade = 99.99% pure How do you think cost varies with purity?