Chapter 8 : SOLUTIONS Section 1 – Solutions and Other Mixtures Section 2 – How Substances...
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Transcript of Chapter 8 : SOLUTIONS Section 1 – Solutions and Other Mixtures Section 2 – How Substances...
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
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 )
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
• Salt max solubility above becomes ~ 6.15 mol/L
or M
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?