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 ConcentrationKey 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?

Gas Solubility Lab