Chem 2 Quiz 2 (Chapter 11)

Solution

a mixture of substance (2 or more)

• polar or nonpolar

• homogenous

Solute

The substance that is dissolved

• present in a smaller amount - fixed

Solvent

The substance that dissolves the solute

• present in the largest amount (more than solute)

Electrolytes

Conducts electricity when in solution

• salt, ionic compounds

• dissociate in solution to produce ions

Non-electrolytes

Doesn’t dissociate

doesn’t conduct electricity

sugar, C₁₂H₂₂O₁₁, CO_2, C₂H₅OH

Why do solutions form?

The substances have similar properties (like polarity!!)

energetics - endothermic process (-Delta H)

• solution is more stable than the separate components

endothermic - possible if you add heat/stir (to dissolve substances → cold product)

Solubility

How easily a solute dissolves into a solvent

measures the ease of dissolving

Saturated solution

When as much solute as possible dissolves in solvent

Unsaturated solution

Anything less than the max (saturated) amount of solute dissolved in solvent

Supersaturated Solution

More solute dissolve than possible amount

• not stable (temporary and will become/drop to saturated again)

What is likely to dissolve what?

“like dissolves like”

polar solvent dissolves polar solutes

nonpolar dissolves nonpolar solutes

What affects solubility?

Most importantly, Polarity (“like dissolves like”)

Temperature

Pressure

Effect of temperature on Solubility

Temperature increase = solubility increase for solids and liquids solutes

for gases, as temp increase = solubility decreases

Effect of Pressure on Solubility

Increased pressure = increased solubility

Molarity

M = moles of solute/L of solution

Mass Percent

mass solute/total mass of solution x 100%

Mole Fraction

X = moles solute/total number of moles

Molality

m = moles solute/kg solvent

Vapor Pressure above a solution depends on ….

Temperature

Pressure

Nature of components (polar, nonpolar, IMF, solubility)

Raolt’s Law

Predicts vapor pressure above the solution (P_A = x_AP_A*)

P_A = vapor pressure above the solution

X_A = mole fraction (moles solute/total moles) of A in solution

P_A* = pure vapor pressure

What does Raolt’s Law assume?

Assumes that the solution is ideal (all the interactions are the same)

Negative Deviation

Observed pressures are less than predicted by Raolt’s law

stronger interactions with in the solution (molecules are staying liquid and not turning into vapor)

Positive Deviation

Observed pressures are higher than predicted by Raolt’s Law

weaker interaction in solution (easily come apart → turn into vapor)

Colligative Properties

Properties that depend on how much solute is present, but NOT the nature of the solute

• freezing point of depression

• boiling point elevation

• vapor pressure lowering

• osmotic pressure

Freezing Point Depression Definition

When a solute is added to a solvent, the freezing point gets reduced (like salt on roads)

solvent → add solute → form solution → vapor pressure above the solution goes down

Freezing Point equation

Δ T = K_fm

Δ T is the amount freezing point drops

K_f is the freezing point of depression constant

m is the molality of the solution (mole solute/kgsolvent)

Boiling Point Elevation Definition

When a solvent is added and the boiling point goes up

Boiling Point Elevation Equation

Δ T = K_bm

K_b is the boiling point constant

m is the molality (moles of solute/kg solvent)

Osmotic Pressure Definition

Pressure required to stop the flow of solvent through a semipermeable membrane

Osmotic Pressure Equation

π = MRT

π is the osmotic pressure

M is the molarity (moles of solute/liters of solution)

R is the gas constant (0.0821 L⋅atm/mol⋅K)

T is the temperature in Kelvin(!)