Basic Concepts in Chemistry Physical Properties. Physical Properties A characteristic of a substance...
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Transcript of Basic Concepts in Chemistry Physical Properties. Physical Properties A characteristic of a substance...
Basic Concepts in ChemistryPhysical Properties
Physical Properties
A characteristic of a substance that you can observe and measure without changing
the identity of the substance.
Number vs. Quantity
• Quantity - number + unit
UNITS MATTER!!
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Types of measurement
Quantitative- can be measured and assigned a particular value.use numbers to describe- melting point - viscosity is a measure of how easily a fluid flows.- 4 meters,- 100 0C
Qualitative- can be observed and described without detailed measurements.
- the colour of aluminum is grey.- Hydrogen sulfide has a characteristic odour of rotten eggs.- Greenish-yellow gas could be a warning that chlorine gas is present.- extra large- hot
Scientists prefer
QuantitativeQuantitative - easy to check
• Easy to agree upon, no personal bias
• The measuring instrument limits how good the measurement is.
Examples of Qualitative Physical Properties
Property Examples
Colour Colourless, red, black
Odour Sweet, pungent, mouldy
State Solid, liquid, or gas
Texture Rough, smooth, bumpy
Lustre Shiny, dull
malleability Soft, pliable, hard
Quantitative Physical Properties
Property DescriptionViscosity Resistance to flow
Melting point Temperature of melting
Boiling point Temperature of boiling
Solubility Ability to dissolve in another substance
Hardness Ability to scratch another material
Conductivity Ability to conduct electricity or heat
Density Ratio of mass to volume
States of Matter
Gas, Liquid, and Solid
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 441
Gas Liquid Solid
Some Properties of Solids, Liquids, and Gases
Property Solid Liquid Gas
Shape Has definite shape Takes the shape of Takes the shape the container of its container
Volume Has a definite volume Has a definite volume Fills the volume of the container
Arrangement of Fixed, very close Random, close Random, far apartParticles
Interactions between Very strong Strong Essentially noneparticles
• To evaporate, molecules must have sufficient energy to break Intermolecular (IM) forces. Change of state from a liquid to a gas.
• Molecules at the surface break away and become gas.
• Only those with enough Kinetic energy (KE) escape.• Breaking IM forces requires energy. The process of
evaporation is endothermicendothermic.• Evaporation is a cooling process.• It requires heat.
Evaporation
Change from gas to liquid
Achieves a dynamic equilibrium with vaporization in a closed system.
What is a closed system?
A closed system means matter can’t go in or out. (put a cork in it)
Condensation
Energy Changes Accompanying Phase Changes
Solid
Liquid
Gas
Melting Freezing
Deposition
CondensationVaporization
Sublimation
Ene
rgy
of s
yste
m
Brown, LeMay, Bursten, Chemistry 2000, page 405
Melting / Boiling Point
Boiling pointof water
Freezing pointof water
Absolutezero
Celsius
100Celsiusdegrees
100oC
0oC
-273oC
Melting Point - change of state from solid to liquidMelting point: the temperature at which a solid turns into a liquid.Boiling point: the temperature at which a liquid turns into a gas.Boiling point of water is 100 0C.
Definitions
• Solution - Solution - homogeneous mixture
Solvent Solvent - present in greater amount
Solute Solute - substance being dissolved
Solutions
• What the solute and the solvent are determines–whether a substance will dissolve. –how much will dissolve.
• A substance dissolves faster if it is stirred or –The particles are made smaller. shaken.–The temperature is increased.
Why?
Solution = Solute + Solvent
• Solute - gets dissolved
• Solvent - does the dissolving– Aqueous (water)
– Tincture (alcohol)
– Amalgam (mercury)
– Organic• Polar• Non-polar
Dental filling
Nightmare on White StreetChem Matters, December 1996
Solution Definitionssoluti
on:
alloy:
solvent: the substance that dissolves the solute
water salt
a homogeneous mixture
-- evenly mixed at the particle level
-- e.g., salt water
a solid solution of metals
-- e.g., bronze = Cu + Sn; brass = Cu + Zn
“will dissolve in”
refers to two gases or two liquids that forma solution; more specific than “soluble”
-- e.g., food coloring and water
miscible:
soluble:
Types of Solutions
Solute Solvent Solution
Gaseous Solutions
gas
liquid
gas
gas
air (nitrogen, oxygen, argon gases)
humid air (water vapor in air)
Liquid Solutions
gas
liquid
solid
liquid
liquid
liquid
carbonated drinks (CO2 in water)
vinegar (CH3COOH in water)
salt water (NaCl in water)
Solid Solutions
liquid
solid
solid
solid
dental amalgam (Hg in Ag)
sterling silver (Cu in Ag)Charles H.Corwin, Introductory Chemistry 2005, page 369
As size , rate
As To , rate
3. mixing
Factors Affecting the Rate of Dissolution
1. temperature
2. particle size
4. nature of solvent or solute
More mixing, rate
Classes of Solutionsaqueous solution:
water = “the universal solvent”
solvent = water
amalgam: solvent = Hg
e.g., dental amalgam
tincture: solvent = alcohol
e.g., tincture of iodine (for cuts)
organic solution: solvent contains carbon
e.g., gasoline, benzene, toluene, hexane
Non-Solution Definitions
insoluble: “will NOT dissolve in”
e.g., sand and water
immiscible: refers to two gases or two liquids that will NOT form a solution
e.g., water and oil
suspension: appears uniform while being stirred, but settles over time
Solubility
Water
HOT
A B
AFTERBefore
Water
COLD
Water
HOT
Add 1 drop of red food coloring
Miscible – “mixable”
two gases or two liquids that mix evenly
Experiment 1:
Water
COLD
A B
Solubility
Water Water
Oil
T30 sec
AFTER
Before
Add oil to water and shake
Immiscible – “does not mix”
two liquids or two gases that DO NOT MIX
Experiment 2:
T0 sec
Solubility vs. Temperature
Timberlake, Chemistry 7th Edition, page 297
KI
NaNO 3
KN
O 3
Na 3PO 4
NaCl
Temperature (oC)
Sol
ubili
ty (
g so
lute
/ 10
0 g
H2O
)200
180
160
140
120
100
80
60
40
20
020 40 60 80 100
Pure water does not conduct an electric current
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 215
Source ofelectric power
Purewater
Ionic Solutions conduct a Current
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 215
Source ofelectric power
Free ionspresent in water
Electrolytes
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.
(a) Nonelectrolyte (b) Weak electrolyte (c) Strong electrolyte
Electrolytes
Timberlake, Chemistry 7th Edition, page 290
ElectrolytesElectrolytes - solutions that carry an electric current
NaCl(aq) Na+ + Cl- HF(aq) H+ + F-
strong electrolyte weak electrolyte nonelectrolyte
Solubility and the Environment
Chemical Stewardship
• Be responsible in how you dispose of and use chemicals.
• Chemical pollution can travel far – and harm organisms.
Frog with three legs – it hasmutated from chemical exposure.
Early Warning Signs…
=
Contamination of water where frog lives causes mutations.
Canary dies in the mine from bad air (cyanide). This is clue for minersto leave the mine…alive.
Pfiesteria
Fish sores from infection by pfiesteria.
Pfiesteria organism
Solvents
Solvents at the hardware store
Density
• Density is an INTENSIVEINTENSIVE property of matter.
- does NOT depend on quantity of matter. - color, melting point, boiling point, odor, density
• Contrast with EXTENSIVEEXTENSIVE
- depends on quantity of matter.- mass, volume, heat content (calories)
Styrofoam Brick
Styrofoam Brick
?It appears that the brick is ~40x more dense than the Styrofoam.
MMMM
VV= =DD
VVDD
BrickBrickStyrofoamStyrofoam
Styrofoam Brick
Which liquid has the highest density?
52
3
1
4
Coussement, DeSchepper, et al. , Brain Strains Power Puzzles 2002, page 16
least dense 1 < 3 < 5 < 2 < 4 most dense
Cube Representations
1 m3 = 1 000 000 cm3
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 119
Volume and DensityRelationship Between Volume and Density for Identical Masses of Common Substances
Cube of substance Mass Volume Density Substance (face shown actual size) (g) (cm3) (g/cm3)
Lithium
Water
Aluminum
Lead
10 19 0.53
10 10 1.0
10 3.7 2.7
10 0.58 11.4
Density
D
M
Vensity
ass
olume
D = MV
M = D x V
V = MD
Volume
Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 41
6 cm
3 cm
2 cm
1 cm
4 cm4 cm
2 cm
2 cm2 cm
Volume
Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 41
V = length x width x height
V = 2 cm x 2 cm x 2 cmV = 8 cm3
Volume = length x width x height
Volume = 6 cm x 2 cm x 3 cm
6 cm
3 cm
2 cm
1 cm
4 cm
Volume = 36 cm3
Volume =
Volume = 28 cm3
8 cm3
-
Density of Some Common Substances
Density of Some Common Substance
Substance Density (g / cm3)
Air 0.0013* Lithium 0.53 Ice 0.917 Water 1.00 Aluminum 2.70 Iron 7.86 Lead 11.4 Gold 19.3
Density of Some Common Substance
Substance Density (g / cm3)
Air 0.0013* Lithium 0.53 Ice 0.917 Water 1.00 Aluminum 2.70 Iron 7.86 Lead 11.4 Gold 19.3
*at 0oC and 1 atm pressure
Consider Equal Volumes
The more massive object(the gold cube) has the_________ density.
Equal volumes…
…but unequal masses
aluminum gold
GREATER
Density = Mass
Volume
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 71
Consider Equal MassesEqual masses……but unequal volumes.
The object with the larger volume (aluminum cube) has the density.
aluminum
gold
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 71
smaller
Christopherson Scales
Two ways of viewing density
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 71
Equal volumes…
…but unequal masses
The more massive object(the gold cube) has thegreater density.
aluminum gold
(A)
Equal masses……but unequal volumes.
(B)
gold
aluminumThe object with the larger volume (aluminum cube) has the smaller density.
O2-
H+
H+H2O
++
Water Molecule
Water is a POLAR molecule
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.
Water molecules “stick” together to
create surface tension to support
light weight objects.
Water Molecule
• What is a polar molecule?
• How does the polarity of water effect this molecule?
O
H
H
Hydrogenbond
• Hydrogen bonds occur
between two polar molecules, or between different polar regions of one large macro-molecule.
• One “relatively” negative region is attracted to a second “relatively” positive region.
OH
H
H
NH
H
Electronegativeatoms
Hydrogen bond
Reviewing ConceptsReviewing ConceptsPhysical Properties
• List seven examples of physical properties.
• Describe three uses of physical properties.
• Name two processes that are used to separate mixtures.
• When you describe a liquid as thick, are you saying that it has a high or low viscosity?
Reviewing ConceptsReviewing ConceptsPhysical Properties
• Explain why sharpening a pencil is an example of a physical change.
• What allows a mixture to be separated by distillation?