Dissolve
dispersal of a substance into a second substance to form a solution
Solution
Homogeneous mixture of 2 or more substances in a single phase
Soluble
can be dissolved in a given solvent
Insoluble
can't be dissolved in a given solvent
Solvent
Present in greater amount
The dissolving medium
solute
Present in smaller amount
substance being dissolved
Miscible
two liquids that are soluble in each other
(depends on polarity)
Immiscible
two liquids that will not mix or blend
(depends on polarity)
Electrolyte
A substance that dissolves in water to produce a solution that conducts electrical current
(salt water)
Non Electrolyte
A substance that dissolves in water but the resulting solution does not conduct electrical current
(sugar water)
Gas in gas solution
air
Nitrogen + oxygen
gas in liquid solution
carbonated water
water + carbon dioxide
Liquid in liquid solution
antifreeze
water + ethylene glycol (TOXIC)
Solid in liquid solution
ocean water
water + NaCl
Liquid in solid solution
Dental amalgam
silver (solid) + mercury (liquid)
Solid in solid solution
steel
iron (solid) + carbon (solid)
Solvation
The process of dissolving
solute particles are surrounded by solvent molecules to form a solution
Water facts
1.) 75% of Earth's surface is water
2.) most living organisms are 70-90% water
3.) water quality in aquifers, lakes, oceans monitored by EPA and other government organizations
4.) "universal solvent" because so many things will dissolve in water
Hydration
water is the solvent
solute molecules are surrounded by water molecules
Aqueous solutions of ionic compounds
1.) Attraction between water's dipoles and the solute ions is greater than the attraction among ions in the crystal
2.) Polar water molecules attract and pull apart positive and negative ions of the solute
Aqueous solutions of molecular compounds
1.) Molecular compounds dissolve in water if they are POLAR (like water)
2.) Like dissolves like
Factors that increase the rate of solvation
1.) Increase surface area of the solute
2.) agitate the solution (disperses solute particles and brings fresh solvent in contact with solute surfaces)
3.) Heat the solution (increased kinetic energy of particles disperses solute more quickly)
Heat of solution
the amount of heat energy absorbed or released when a solute dissolves in a specific amount of solvent
Endothermic solution
heat is absorbed
solute + solvent + heat = solution
Exothermic solution
heat is released
solute + solvent = heat + solution
Solubility
The maximum amount of solvent that will dissolve in a given solvent at a specific temperature and pressure
(often expressed as g/100g solvent)
Dynamic Equilibrium
(two competing processes happen at the same time)
1.) Number of solute particles dissolving equals the number of particles recrystallizing
2.) Difficult to predict because it depends on the nature of the solute and solvent and the temperature
Saturated solution
solution contains the maximum amount of dissolved solute possible at a given temperature
Unsaturated solution
Solution contains less solute than a saturated solution
Supersaturated solution
solution that contains more dissolved solute than a saturated solution at the same conditions (unstable)
1.) Make a saturated solution at high temperature
2.) Cool it slowly
3.) Don't disturb it
Is the rate at which a solute dissolves dependent on its solubility
No! They are unrelated
Graphing solubility
Independent variable: temperature
Dependent variable: grams solute per grams solvent
On the line: amount of solute which dissolves at a temperature to form a saturated solution
Below the line: unsaturated solution
Above the line: supersaturated solution
Effect of temperature on solubility
- Difficult to predict the effect
- Solubility of most solids increases with increasing temperature
- Solubility of ALL gases decreases with increasing temperature
Effect of pressure on solubility
- Has very little effect on the solubility of liquids or solids
- Increased pressure increases the solubility of a gas in a liquid solvent
Factors increasing the solubility of gases
1.) Do NOT agitate the solution
2.) Chill the solution
3.) Increase pressure on the solution
Why do bubbles form in water before it bubbles
dissolved atmospheric gases are escaping from the solution as the rising temperature decreases their solubility
Henry's Law
The solubility of a gas is directly proportional to the pressure above the liquid it is dissolved in
S/P=S/P
Solution concentration
measure of the quantity of the solute dissolved in a given quantity of solvent or solution
Percent by mass
many solutions are prepared this way
round final answer to hundredths place
Percent by volume
Molarity
number of moles of solute dissolved in one liter of solution (mol/L)
Symbol: M
Limit is 20 molar
Stock solution
Concentrated solution (high molarity) stored in a stockroom
1.) Saves money
2.) saves storage space
3.) increases safety
4.) minimizes disposal/waste
Formula for dilution problems
(initial molarity x volume) x (final molarity x volume)
MOLES = MOLES , amount of solute doesn't change
Molality
The concentration of a solution expressed in moles of solute per kilograms of solvent (mol/kg)
limit is 20 molal and value does not change in temperature
Mole fraction
x= mole fraction
n= moles
Equipment for making a solution
- volumetric flask
- graduated cylinder (large volumes)
- graduated pipet (small volumes)
Steps to making a solution (molar solutions)
1.) Add a small amount of solvent to a volumetric flask
2.) measure out the amount of solute needed using a balance (solid solutes) or graduated cylinder/pipet (liquid solutes)
3.) Add measured solute to volumetric flask, stir or swirl to mix
4.) Add solv
when is a serial dilution used?
1.) want the solution to have a very low concentration
2.) if the solutes are toxic or you have limited $$ (uses less stock solution)
3.) range of the instrument you are using for analyses requires a smaller concentration
How is a serial dilution different
1.) glassware may be test tubes or cuvettes instead of volumetric flask
2.) Each dilution normally 1 place value more dilute (0.001 -> 0.0001)
Colligative properties
Properties which are affected by the number of solute particles but are independent of the type of particle (ions/molecules)
(It's important how many, but not what kind or particles are in solution)
Types of colligative properties
1.) vapor pressure lowering
2.) boiling point elevation
3.) freezing point depression
4.) osmotic pressure
Electrolytes and non electrolytes in aqueous solution
Soluble ionic compounds:
- dissociate (break apart into ions) in water
- form a solution that conducts electricity (electrolytes)
- produce more than one mole of ions in solution per mole of the compound
Molecular (covalent) compounds:
- dissolve in solve
Vapor pressure
the pressure exerted in a closed container by liquid particles that have escaped the liquid's surface and entered the gaseous state.
Lowering vapor pressure
adding a nonvolatile solute to a solvent lowers the solvent's vapor pressure
- Solute particles "tie up" the solvent particles via intermolecular attractions, keeping them from escaping into the vapor phase
The more ions that a solute dissociates into, th
nonvolatile solute
A solute that has little tendency to become a gas
Effects of adding a non-volatile solute
1.) lower vapor pressure
2.) higher boiling point
Attractions between solute and solvent keep solvent molecules from leaving the solution
Boiling
conversion of a liquid to a vapor (within the liquid and at its surface) when the vapor pressure in the liquid equals atmospheric pressure
Normal boiling point of water
Exactly 100 degrees C at 1 atm
How does adding a solute affect boiling point?
Because a solute lowers a solvent's vapor pressure, it also affects the boiling point
boiling point elevation
Change in boiling point = (constant)(molality)(number of particles formed)
boiling point of the solution
normal boiling point of pure solvent + boiling point elevation
freezing point depression
change in freezing point = (constant)(molality)(number of particles formed)
freezing point of the solution
freezing point of pure solvent - freezing point depression
Molar mass of a solute
(mass of solute)(constant)/(boiling point elevation)(kg of solvent)
Exothermic phase changes
release energy, molecules slow down
all bond formation
deposition, freezing, condensation
Endothermic phase changes
gaining energy, molecules move faster
sublimation, melting, boiling, evaporation, breaking bonds
Normal boiling point
the boiling point at 1 atm pressure
Normal freezing poing
the freezing point at 1 atm pressure
Triple point
the temperature and pressure at which all three phases can exist simultaneously
critical temperature
the highest temperature at which a substance can exist as a liquid, even with increasing power
critical point
critical temperature, and the pressure required to liquify the fluid at the critical temperature
supercritical fluid
beyond the critical point, the liquid and gas phases are indistinguishable
Useful as industrial solvents
effect of adding a non-volatile solute
1.) Freezing point and vapor pressure decrease
2.) Boiling point increases
Suspensions
a mixture containing particles that will settle out if left undisturbed
1.) have diameters greater than 1000 nm
2.) gravity acts on suspended particles in short time causing them to settle out and create a solid like state on the bottom of the container,
thixotropic
mixture like house paint which flows easily when mixed, but thickens to a solid-like state
Colloids
A heterogeneous mixture of intermediate size particles
1.) are between 1 nm and 1000nm in diameter
(colloid type) Solid sol
solid-solid
colored gems
(colloid type) Sol
solid-liquid
blood, gelatin
(colloid type) Solid emulsion
liquid-solid
butter, cheese
(colloid type) emulsion
liquid-liquid
milk, mayonnaise
(colloid type) solid foam
gas-solid
marshmallow, soaps that float
(colloid type) Foam
gas-liquid
whipped cream, beaten egg white
(colloid type) Aerosol
solid-gas
smoke, dust in air
(colloid type) Aerosol (2)
liquid-gas
spray deodorant, clouds
Brownian motion
liquid colloids with a random jerky movements due to polar or charges atomic groups on their surfaces which prevent them from settling out
The Tyndall Effect
The scattering of light by a colloidal suspension. Solutions never exhibit the Tyndall effect, only suspensions.