Solutions

Chem 12, 2011

Solutions – What to expect• Basics

• Terminology• Rules

• Concentration calculations• % by mass, % by volume• ppm, ppb• molarity

• Theory• Solubility curves

• Practical• Preparing solutions• Dilutions

Solutions – What are they

• General terms• Solute: the compound being dissolved• Solvent: the medium in which the solute is dissolved• Miscible: solute will dissolve in solvent• Immiscible: solute will not dissolve in solvent• Miscibility

• Definition – one compound (solute) dissolved in another (solvent)

• Classic example is solid/liquid dissolved in water, but any combination is possible

• Most of what we will study will be solutions with liquid (water) as a solvent

Solutions – Combinations• Solid in liquid - Sol• Solid in gas – Solid aerosol• Solid in solid – Solid sol• Gas in liquid - Foam• Gas in solid – Solid foam • Gas in gas - Gas• Liquid in liquid - Emulsion• Liquid in solid - Gel• Liquid in gas - Aerosol

StyrofoamShaving Cream

Kool-aid

C. Chip cookie

Chocolate milk

Hairspray

Clouds

Air

Jell-o

Dissolution (solvation)• Solvation (or dissolution) is the process

where the crystal structure of a solute is broken up into individual ions (electrolytes)

• Electrolytes• Electrically conductive• Often ionic solutions (produced via the break

down of ionic compounds)• Strong electrolyte: completely ionizes in

solution• Weak electrolyte: most does not dissolve

Note on solvation: For our purposes, the definition above is most appropriate however the breaking up of the crystal structure does not hold true for all types of solutions

Solvation (con’t)• Process

• When the forces of the solvent overcome the intermolecular forces of the solute, it will dissolve

• Ex. Water “attacks” juice crystals

• Factors affecting solvation• Polarity (like dissolves like)

• Polar is miscible in polar (immiscible in non-polar)

• Conditions: altering T, V, or P can alter a solutes ability to dissolve (alters saturation)

Saturation• Unsaturated

• A solution that contains some or none of the solute in question and thus can dissolve more of the compound into solution

• Saturated• solution contains the max amount of solute• any further solute will stay as a solid precipitate

• Supersaturated • more of the solute than usual is dissolved into the

solution• made possible by altering conditions (T, V, P)• video

Concentration• Definition

• The ratio between the amount of solute and solution

• Methods• Molarity (most common; mol/L)• m/m % (ratio of the mass of solute to mass

of solution)• m/v % (ratio of the volume of solute to

volume of solution)• ppb, ppm (for much smaller proportions;

ratio of solute to solvent

Solubility Curves• Over time, scientists have performed experiments

to determine the solubility of compounds in water• Graph shows the temperature on the x axis and

solubility on the y axis (in g/100mL)

• Factors affecting solubility• Temperature: supersaturation, boiling etc• Pressure: bubbles, pop• Volume: soup• Ion size, charge

Done through experimental collection of data

Take different amounts of solute and find the temp where they dissolve

Building a curve

Mass Temp

50g 32C

80g 47C

100g 55C

Data for KNO3

Anything that falls below the line is UNSATURATED

Anything above the line is SUPERSATURATED

Most of the curves point up – meaning?

Some point down. -Why?

• You have 10g of ammonium chloride at 80°C? What is the saturation?

• Give an example of how to make a super saturated solution of sodium sulfate?

• What is the solubility of NaNO3 at 40°C?

• At what temperature will 50g of KCl dissolve in 100g of water?

• How much will you have to add to make it ppt at 75°C?

• If you dissolve 140g KI at 15°C how much will ppt out at 5°C?

Problems