I. How Solutions Form
How Solutions Form Definitions
Solution - homogeneous mixture
Solute – substance being dissolved
Solvent – substance doing the dissolving, present in greater amount Definitions
Solute - KMnO4 Solvent - H2O Types of Solutions
Based on state of solvent. All solid-liquid-gas combos are possible. EX: dental amalgam (alloy of silver, mercury, etc.) • liquid solute, solid solvent • solid solution Bell Ringer
What is a solution?
What is a solute?
What is a solvent? Types of Solutions
Unsaturated – not holding all the solute it can, will dissolve more. Saturated- holding all the solute it can, won’t dissolve any more. Supersaturated- holding more than theoretically possible, very unstable • Seed Crystal Dissolving
Solvation • occurs at the surface of the solute • solvent particles surround solute particles (+/- attraction) • solute particles are pulled into solution Dissolving
NaCl dissolving in water Rate of Solution
Solids dissolve faster... • more stirring • small particle size (increased surface area) • high temperature Rate of Solution
Gases dissolve faster... • no shaking or stirring • high pressure • low temperature Solutions
Solubility & Concentration Concentration
Concentrated solution • large amount of solute
Dilute solution • small amount of solute Concentration
% by Volume • usually liquid in liquid • EX: 10% juice = 10mL juice + 90mL water
% by Mass • usually solid in liquid • EX: 20% NaCl = 20g NaCl + 80g water Concentration
UNSATURATED SATURATED SUPERSATURATED SOLUTION SOLUTION SOLUTION more solute no more solute becomes unstable, dissolves dissolves crystals form
concentration Solubility
Solubility - maximum grams of solute that will dissolve in 100 g of solvent at a given temperature • varies with temperature • based on a saturated solution Solubility
Solubility Curve - shows the dependence of solubility on temperature Solubility
Solids are more soluble at... • high temperatures.
Gases are more soluble at... • low temperatures. • high pressures (Henry’s Law). Bell Ringer
What is a saturated solution? What is a supersaturated solution? What is solubility? What factors can affect solubility? Solutions
Particles in Solution POLAR MOLECULE
A molecule that has electrically charged areas. Also called a polar substance or polar compound.
+ DURACELL _ NON-POLAR SUBSTANCES
Non-polar substances do not have charged ends
DURACELL
Aqueous (Water) Solutions
Water dissolves ionic compounds and polar covalent molecules very well. • Salt is ionic- makes salt water. The rule is: “like dissolves like” Polar dissolves polar. Nonpolar dissolves nonpolar. Oil is nonpolar. • Oil and water don’t mix. STRUCTURE OF WATER
H H
O
1 molecule of water is made up of 2 hydrogen atoms bonded with 1 oxygen atom Water is Very Polar
+ H H +
O
- Universal Solvent
Why is water so good at dissolving things? Because water is a polar molecule and is shaped like a wedge, it is able to break up substances into smaller pieces (dissolve). • Water 1) breaks the + and - charged pieces apart, and 2) surrounds them.
How Ionic solids dissolve in water
These ions have been pulled away from the
main crystal structure by water’s polarity.
H
H
H
H H These ions have http://www.youtube.com/watch?v= been surrounded VTmfQUNLlMY by water, and are now dissolved! Bell Ringer
What is a polar molecule?
Why is water called the universal solvent? Hint: 2 parts to this answer Electrolytes and Nonelectrolytes
Electrolytes- compounds that conduct an electric current in aqueous solution, or in the molten state • all ionic compounds are electrolytes because they dissociate into ions (they are also called “salts”) NaCl Na1+ and Cl1- • Must have charged particles that can move.
Electrolytes and Nonelectrolytes
Do not conduct? = Nonelectrolytes. • Most are molecular materials, because they do not have ions Not all electrolytes conduct to the same degree • there are weak electrolytes, and strong electrolytes • depends on: the degree of ionization Electrolytes- conduct electricity
- + - + - +
salt acetic acid sugar
Weak Non- Electrolyte Electrolyte Electrolyte solute exists as solute exists as solute exists as ions only ions and molecules molecules only
Colligative Properties
Colligative properties - properties of solutions that depend only on solute concentration
Freezing Point Depression • solutes lower the f.p. of a solvent
Boiling Point Elevation • solutes raise the b.p. of a solvent Colligative Properties
Freezing Point Depression Colligative Properties
Boiling Point Elevation
Solute particles “get in the way.” Colligative Properties
Effect increases as the solute concentration increases.
Uses: • antifreeze • making ice cream • salting icy roads • http://www.youtube.com/watch?v=PVL24HAesnc&list=PL 8dPuuaLjXtPHzzYuWy6fYEaX9mQQ8oGr&index=23