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 Salt max solubility above becomes ~ 6.15 mol/L 𝒎𝒐𝒍𝒂𝒓𝒊𝒕𝒚= 𝒎𝒐𝒍𝒆𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒆 𝒍𝒊𝒕𝒆𝒓𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏 = 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