Chapters 13 & 15

1
Unit 4 Pure Substances Mixtures

• Chapters 13 15
• Cypress Creek Chemistry

2
Classifying Matter
3
Pure Substances

• Pure substances cannot be separated by physical
  means
• Elements cannot be chemically separated, listed
  on the periodic table
• Compounds can be chemically separated, made up
  of elements

4
Pure Substances

• Particle representations of
• Elements
• Compounds

5
Periodic Table

• Each square on the periodic table contains
• Name of Element
• Symbol
• First letter is upper case, second letter must be
  lower case
• Atomic Mass
• Number (usually with a decimal) indicates the
  mass (g) of 1 mole of that element
• Atomic Number

6
The Mole
7
Molar Mass of Atoms

• How do chemists count Avogadros number?
• By measuring mass (just like how they count
  aluminum cans for recycling)
• The mass (think grams) of one mole of a substance
• Atomic masses are based on the mass of carbon
• One mole of carbon contains 6.02 x 1023 atoms of
  C
• 1 carbon atom is 12.011 amu
• 1 mole of carbon is 12.011 grams

8
Molar Mass of Atoms

• The mass of 1 mole (in grams)
• Equal to the numerical value of the average
  atomic mass (get from periodic table)
• Examples
• 1 mole of C atoms 12.0 g
• 1 mole of Mg atoms 24.3 g
• 1 mole of Cu atoms 63.5 g

9
Practice

• Find the molar mass
• 1 mole of Au atoms
• 1 mole of Sn atoms

10
Chemical Formulas

• The chemical formula describes a compound using
  numbers and element symbols
• Subscripts denote number of each element in a
  compound
• Ex H2O has 2 hydrogens and 1 oxygen
• Ex Al2(SO4)3 has 2 aluminums, 3 sulfurs, and 12
  oxygens
• Coefficients act as a scalar (also called a
  multiplier)
• Ex 6H2O has 12 hydrogens and 6 oxygens
• Ex 3Al2(SO4)3 has 6 aluminums, 9 sulfurs, and 36
  oxygens

11
Molar Mass of Compounds

• The Molar Mass of a compound is the mass in grams
  of 1 mole equal to the sum of the atomic masses
• Example What is the mass of 1 mole of CaCl2?
• 1 mole Ca x 40.1 g/mol 40.1 g Ca
• 2 moles Cl x 35.5 g/mol 71.0 g Cl
• 
  111.1 g/mol CaCl2

12
Practice

• Prozac, C17H18F3NO, is a widely used
  anti-depressant that inhibits the uptake of
  serotonin by the brain. Find its molar mass.

13
Calculations with Molar Mass

• Examples
• How many grams are in 2 moles of Cu?
• 2 moles of Cu Xg
• 1 mole of Cu 63.546 g of Cu
• How many moles are in 100 g of H2O?
• 100 g of H2O Xg
• 18.015 g of H2O 1 mole of H2O

14
Practice

• The artificial sweetener aspartame (C14H18N2O5),
  commonly known as Nutra-Sweet, is used to sweeten
  diet foods, coffee and soft drinks. How many
  moles of aspartame are present in 225 g of
  aspartame?

15
Calculations with Particles/Mass

• Examples
• How many grams of CO2 are present in 3 particles
  of CO2?
• 3 particles of CO2 Xg
• 6.02 x 1023 particles of CO2 44.009 g of CO2
• How many particles are present in 12.0 grams of
  NaCl?
• 12.0 g of NaCl X particles
• 58.443 g of NaCl 6.02 x 1023 particles of NaCl

16
Practice

• Diabetics do not properly regulate insulin, which
  tells the body to take up glucose from the blood.
  What is the mass of 1.20 x 1024 molecules of
  glucose (C6H12O6)?

17
Diatomic Molecules

• Example
• How many atoms of O are present in 78.1 g of
  oxygen?
• Practice
• How many grams of Cl are present in 100 atoms of
  chlorine?

78.1 g O2 Xg
32.0 g O2 2(6.02 X 1023 atoms O)
18
Classifying Matter
19
Mixtures

• Mixtures are composed of two or more substances
  that can be separated by physical means contains
  elements and/or compounds
• Heterogeneous Mixtures not uniform throughout
• Homogeneous Mixtures uniform throughout
• Particle representations of mixtures

20
Heterogeneous Mixtures

• Heterogeneous Mixture two or more substances
  physically combined not uniform throughout
• Ex Granite, chex mix

21
Suspensions

• A suspension is a heterogeneous fluid containing
  solid particles that are sufficiently large for
  sedimentation.
• The internal phase (solid) is dispersed
  throughout the external phase (fluid) through
  mechanical
• Suspensions will eventually settle.

22
Colloids

• Colloids are suspensions of particles larger than
  individual ions or molecules, but too small to be
  settled out by gravity.

23
Colloids

• The Tyndall Effect is scattering of light
  particles used to determine whether something is
  a solution or suspension
• Click image to play clip

24
Homogeneous Mixtures

• Homogeneous Mixture two or more substances
  physically combined uniform throughout
• Know as a solution composed of
• Solute substance being dissolved (smaller
  amount)
• Solvent substance that does the dissolving
  (larger amount)
• Examples milk, kool-aid, brass

25
Daltons Law

• The total pressure of a gas mixture is the sum of
  the partial pressures of each individual gas
• Air is a mixture!

26
Daltons Law

• Ex The pressure on a tank of air with
• 20.9 atm oxygen
• 78.1 atm nitrogen
• 0.97 atm argon
• 1.28 atm water vapor
• 0.05 atm carbon dioxide
• 101.3 atm

Ptotal P1 P2 P3
27
Partial Pressure Practice

• A 3.5L tank contains 1.0 mole of O2, 0.5 mole of
  N2, and 2.0 mole of CO2 at 25oC. What is the
  total pressure of the gases in the tank.
• How to solve
• Find P for each gas using PVnRT
• O2 ? P(3.5) 1(0.0821)(298) ? 6.99
• N2 ? P(3.5) 0.5(0.0821)(298) ? 3.50
• CO2 ? P(3.5) 2(0.0821)(298) ? 13.98
• Add the pressures together
• 6.99 3.5 13.98 24.47atm 24atm

28
Mole Fraction

• The mole Fraction is ratio of the number of moles
  of the gas to the total number of moles in the
  gas mixture
• You can find the pressure of a gas in a mixture
  by multiplying the total press by the mole
  fraction.

Pgas Ptotal ? ngas
29
Mole Fraction Practice

• A gas mixture contains 5.0 moles of Ar and 3.5
  moles of NH4. This mixture has a total pressure
  of 4.25 atm. What is the partial pressure of Ar?
• How to solve
• Find the mole fraction of Ar.
• 5 / (5 3.5) 0.588
• Multiply the total pressure by the mole fraction
• Pgas 4.25 0.588 2.5 atm

30
Daltons Law of Partial Pressure (Over Water)

• http//www.kentchemistry.com/moviesfiles/Units/Gas
  Laws/gasoverwater.htm

31
Partial Pressure (Over Water)
Vapor Pressure (PH2O) of H2O at Different T Vapor Pressure (PH2O) of H2O at Different T
T (oC) P (torr)
0 4.6
5 6.5
10 9.2
12 10.5
14 12.0
16 13.6
18 15.5
20 17.5
22 19.8
24 22.4
26 25.2
28 28.3
30 31.8

• Gases collected by water displacement
• Correct for water vapor pressure by subtracting
  it from the total pressure (Ptotal)
• P(total) P(H2O) P(gas)
• Partial pressure of water is determined by
  temperature and looked up on a table

32
Partial Pressure over Water Practice

• Example 20.0 mL of O2 is collected over H2O at
  20.0oC and 780.0 torr. What is the volume of
  the dry gas at STP, given that P(water vapor)
  17.5 torrs at 20.0oC?
• How to solve
• Subtract the pressure of the water vapor out of
  the total pressure.
• 780.0 17.5 762.5 torr
• Use combined gas law to find the new volume for
  new conditions
• (762.5 20.0)/293 (760V)/273
• V 17.8 mL

33
Rate of Solution

• Rate of Solution refers to how fast a solute will
  dissolve in a solvent
• Increase rate of solution by
• Heating
• Stirring
• Crushing

34
Solubility

• Soluble means able to be dissolved
• Sugar is soluble in water
• Insoluble means unable to be dissolved
• Oil is insoluble in water
• Solubility refers to the amount of solute that
  will dissolve in a solvent
• Depends on temperature and pressure

35
Solubility

• Factors that affect solubility
• Temperature
• Solids ? temp ? solubility
• Gases ? temp ? solubilty
• Ex Coffee, thermal pollution
• Pressure
• Solids no effect
• Gases ? pressure ? solubility
• Ex Carbonated drinks

36
Types of Solutions

• Unsaturated solvent contains less solute than
  it can hold
• Saturated solvent contains the maximum amount
  of solute
• If more solute is added, it does not dissolve,
  falls out as a precipitate
• Ex Coffee and sugar
• How could you tell if your coffee was unsaturated
  or saturated?

37
Solutions Solubility Graph

• Solubility Graphs show amount of solute vs.
  temperature
• The curve itself is at saturation
• Below the curve indicates unsaturated solutions
• Anything above the curve falls out of solution
• Negative (downward) slope means it is a gas

38
Colligative Properties

• Colligative properties (physical property) depend
  on the concentration of the particles in the
  solution
• Examples
• Boiling point elevation adding salt to water for
  cooking
• Freezing point depression salting the roads
  before a freeze, antifreeze in cars, and making
  homemade ice cream
• Osmotic pressure responsible for plants cell
  wall, sturdiness

39
Colligative Properties

• How does adding a solute change physical
  properties?
• Solute particles get in the way of the solvent
  molecules
• Makes it harder for the solvent molecules to boil
  (more energy needed higher temperature)
• Makes it harder for the solvent molecules to
  freeze (need to release more energy lower
  temperature)

40
Concentration

• Concentration is the amount of solute dissolved
  in a given amount of solvent
• Described qualitatively as
• Dilute solution containing a small amount of
  solute
• Concentrated solution containing a large amount
  of solute

41
Molarity

• Molarity (M) describes concentration
  quantitatively
• The number of moles of solute dissolved in 1
  liter of a solution
• Ex molarity of IV fluids is calculated before it
  is administered to the patient
• Equation

Molarity moles of solute liters of
solution
M mol L
also written as
42
Practice

• What is the molarity of 2 mol sodium chloride in
  5 L of solution?
• How many moles of potassium bromide would be
  present in 1 L of a 3 M solution?
• What is the volume of a 1.5 M solution of
  hydrochloric acid that contains 10.0 moles?

0.4 M
3 moles
6.7 L
43
Molality

• Molality (m) also describes concentration
  quantitatively
• The number of moles of solute dissolved in 1
  kilogram of solvent
• Ex molality is calculated when making synthetic
  fabric dyes
• Equation

Molality moles of solute kg of
solvent
m mol kg
also written as
44
Molality

• What is the molality of a solution made by
  dissolving 45 g C6H12O6 in 500 g of water?
• How many grams of water are required to make a
  0.5 m solution containing 20 g NaCl?

0.5 m
700 grams
45
Separating a Mixture

• Separating a mixture - components are separated
  without changing their physical identity
• Manual Separation
• Magnetism
• Filtration
• Evaporation
• Distillation
• Centrifuging
• Chromatography

46
Manual Separation

• Decanting
• Separates two liquids of different densities
• Sifting
• Separates two solids of different particle size
• by pouring
• Sorting
• Separates two solids by picking

47
Magnetism

• Separates metals (such as iron) from a mixture

48
Filtration

• Separates solid substances from liquids and
  solutions

49
Evaporation

• Separates a dissolved solid from its solvent

50
Distillation

• Separates homogeneous mixture with different
  boiling points (heat mixture and catch condensed
  vapor)

51
Centrifuging

• Separates heavier particles (bottom of tube) from
  lighter particles (top of tube) by spinning them
  at high speeds

52
Chromatography

• Separates substances on the basis of their
  differences in solubility in a solvent -
  different substances are attracted to paper or
  gel and move at different speeds

53
Properties of Matter

• A property is a characteristic that describe
  matter or how it behaves
• Physical determined without a chemical change
• Extensive vary with amount of matter (Ex. Mass,
  volume, length, area)
• Intensive does not vary with amount (Ex.
  Density, color, odor, melting point, solubility)
• Chemical can only be determined by a chemical
  change
• Ex. Flammability, reactivity with acid, stability
  of a compound (how easily it decomposes)

54
Changes of Matter

• Physical Changes do not involve a change in
  chemical identity
• Ex boiling, freezing, melting, dissolving,
  evaporating, and crystallizing

55
Changes of Matter

• Chemical Changes new substances are formed in
  the reaction
• Ex iron rusting, copper oxidizing, wood burning,
  silver tarnishing

56
Evidence for Changes of Matter

• Color Change
• Gas produced without heating
• Precipitate formed
• New odor develops
• Large amount of heat or light produced

57
The End.

• Be Prepared for Unit 4 Test.