Transcript Chapter 8 : SOLUTIONS

Chapter 8 : SOLUTIONS
Section 1 – Solutions and
Other Mixtures
Section 2 – How Substances
Dissolve
Section 3 – Solubility and
Concentration
1 - Solutions and Other Mixtures
Key Questions
• What is a heterogeneous mixture?
• What is a homogeneous mixture?
State Standards
• CLE.3202.1.5 : Evaluate pure substances and
mixtures
Heterogeneous Mixtures
• Does not appear uniform ( microscope needed )
• Does not have a fixed composition
– Amounts of each component vary in distinct samples
• Another example – Granite
– Mixture of minerals
– Different types of Granite
– Internet Break??
Oil and Water
• Do oil and water mix?
• Maybe but will separate quickly
– Depends on type of oil
• Immiscible or Miscible?
– Oil and Water are IMMISCIBLE
– Alcohol and Water are MISCIBLE
Suspensions
• Orange Juice – another heterogeneous mixture
• Suspensions have large particles that settle out
• Particles may also be filtered out
Colloids
• Colloids are suspensions with particles too small
to settle out – they remain suspended always
• Can scatter light
– Tyndall Effect
– FOG!!
Common Colloids
• FOG!!!!
• Emulsions: Colloids made of liquids
that do not normally mix
• Mayo ( oil droplets in vinegar )
• Milk/Cream ( oil droplets in water )
• Lotions, creams, many cosmetics
Homogeneous Mixtures
• Appear uniform even when using a microscope
– May look like pure substance but they are not
• They are Solutions – components are uniformly
spread throughout each other
• Solute – substance being dissolved
• Solvent – substance dissolving the solute
Homogeneous Mixtures
• Example – SALTWATER
• Water is SOLVENT / Salt is SOLUTE
Solutions
• Miscible liquids mix
– form solutions
– Solids not always involved
• Water is not always involved ( can mix alcohols ) in
liquid solutions
• Other states of matter can form solutions
– Solids can dissolve in other solids
– Metal ALLOYS ( Brass is Zn and Cu )
– Tooth Fillings ( used to be Ag/Hg but now are plastics )
How is Crude Oil
turned into
Gasoline?
1 - Solutions and Other Mixtures
Key Questions
• What is a heterogeneous mixture?
• What is a homogeneous mixture?
State Standards
• CLE.3202.1.5 : Evaluate pure substances and
mixtures
2 - How Substances Dissolve
Key Questions
• Why is water called the universal solvent?
• Why do substances dissolve?
State Standards
• CLE.3202.TE.3 : Explain the relationship between the
properties of a material and the use of the material
in the application of a technology
• CLE.3202.1.6 : Distinguish between common ionic
and covalent compounds
Water : A Common Solvent
• Water is called the universal
solvent because many substances
can dissolve in water
• Water can dissolve ionic
compounds
• A polar molecule has partially
charged + and – areas ( water is
polar )
– Charge is not evenly distributed in
polar molecules
Dissolving – Depends of Forces
• Polar water molecules pull ionic crystals apart
– Na+, Cl- attracted more to water “poles” than each other
• Dissolving depends on forces between particles
– Goto go.hrw.com and enter keyword “HK8SOLF2”
Like dissolves Like
• This is a rule in chemistry!!
• Water dissolves many molecular compounds
– Recall that O in water pulls electrons away from H
– This forms a Hydrogen Bond (pull H2O close together)
– Water dissolves compounds with hydrogen bonds
– Examples are alcohols, sugar, vitamin C
Like dissolves Like
• Nonpolar compounds ( liquids ) dissolve other
nonpolar compounds
• Nonpolars do not have their +/- charges separated
• Why oils do not dissolve in water
• But one oil WILL dissolve another oil
The Dissolving Process
• Kinetic Theory (molecules are always moving)
• Dissolving occurs because:
• Energy transferred from solvent to solute (collisions
upon addition of solute)
• Attractive forces between solute and solvent
The Dissolving Process
• Solutes with larger surface area dissolve faster
– What is surface area of a sphere ?
– ( 4πr2 )
• Small particles of salt will dissolve faster than a
large chunk of salt
The Dissolving Process
• Stirring or shaking helps dissolve solids faster
• Hot solvents dissolve solids faster than cold ones
• Solutes affect the physical properties of a solution
– Boiling & Melting temperature ( salted roads!! )
2 - How Substances Dissolve
Key Questions
• Why is water called the universal solvent?
• Why do substances dissolve?
3 – Solubility and Concentration
Key Questions
• What is solubility?
• What happens when you add more solute to a
saturated solution?
• How do you describe how much of a solute is in a
solution?
State Standards
• CLE.3202.Inq.3 : Use appropriate tools and technology
to collect precise and accurate data
• CLE.3202.Inq.6 : Communicate and defend scientific
findings ( LAB!! )
Solubility in Water
• The solubility of a substance is the maximum mass of a
solute that can dissolve in 100 g of solvent at a certain
temperature and standard atmospheric pressure
• Different solutes have different solubilities
•
•
•
•
Examples at 20 oC:
Salt ( NaCl ) has solubility of 35.9 g / 100 g H2O
Sodium Iodide ( NaI ) – 178 g / 100 g H2O
Iron(II) Sulfide ( FeS ) – 0.0006 g / 100 g H2O
Concentration
• Concentration is the quantity of solute that is
dissolved in a given volume of solution
• Concentrated solution has a lot of solute
• Dilute solution has small amount of solute
• Qualitative terms – would like to know a value
• Salt ( NaCl ) max solubility of 35.9 g / 100 g H2O
• This gives a concentration of 0.359 g/mL at 20 oC
Concentration
• Salt ( NaCl ) max solubility of 35.9 g / 100 g H2O
• This gives a concentration of 0.359 g/mL at 20 oC
• Molarity is a common way to express this
𝒎𝒐𝒍𝒂𝒓𝒊𝒕𝒚 =
𝒎𝒐𝒍𝒆𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒆
𝒍𝒊𝒕𝒆𝒓𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏
=
𝒎𝒐𝒍
𝑳
or M
• Salt max solubility above becomes ~ 6.15 mol/L
Saturated Solutions
• In saturated solutions, dissolved solute is in
equilibrium with undissolved solute
• So, more solute added just settles to bottom
• Unsaturated solutions can become saturated by
adding enough solute
Temperature and Pressure
• Heating a saturated solution can dissolve more
solute ( can also increase maximum solubility )
– Why solubility values given at 20 oC
• Temperature and pressure affect gas solubility
– Pressure inside sealed coke is higher then an open one
3 – Solubility and Concentration
Key Questions
• What is solubility?
• What happens when you add more solute to a
saturated solution?
• How do you describe how much of a solute is in a
solution?
Gas Solubility Lab