Chapter 11: The Chemistry of Solutes and Solutions

Solutions can (2)

exist in all 3 physical states

can be mixtures of solids, liquids, and gases

What is a solution?

a homogenous mixture of substances (solvent and solute(s))

what is a solvent?

the component in the greatest amount

most common is water

what is a solute?

all other components of a solution (possibly more than one)

what is an electrolyte?

dissolving in something and causing ions

what is a nonelectrolyte?

something dissolves but does not dissociate into ions

• tends to be covalent molecules

• dissolves due to IMFs like hydrogen bonds in sucrose

what is a weak electrolyte?

dissolves and sometimes makes ions; ex. acetic acid (weak acid)

what is a strong electrolyte?

dissolves in water and 100% dissociates or completely breaks apart into ions; ex. HBr (strong acid)

How do solute/solvent IMFS determine solubility?

• “like dissolves like”

• if IMFs are similar: the pair will be soluble polar-polar and nonpolar-nonpolar

• if IMFS are dissimilar: the pair will be insoluble

• dissolve when solvent-solute attraction > solvent-solvent attraction > solute-solute attraction

For an ion to dissolve in water what must occur?

• the ions must overcome forces holding them into the lattice (need input of energy or lattice energy)

• the ions must become hydrated or surrounded by water (creates order)

What is lattice energy?

the energy required to overcome the forces holding the ions together in a crystal (positive number; energy input to break a bond)

what three values is the Enthalpy of a solution based on?

1. lattice energy

2. solvent intermolecular forces

3. enthalpy of hydration

what is the equation for enthalpy of solution?

lattice energy + enthalpy of solvent (energy to split solvent) + enthalpy of hydration (energy needed to reform/organize)

what is entropy?

• the amount of disorder

• processes with an increase in entropy happen spontaneously

• upon mixing a solution solute/solvent molecules spreading increase entropy (S)

What are miscible liquids?

they dissolve in all proportions ex. ethanol and water (both polar)

what are immiscible liquids?

they form distinct separate phases ex. gasoline (nonpolar) and water polar

As nonpolar tail increases in length, how is solubility affected?

decrease in solubility as increase in length

• solute-solute attraction grows (tail-tail) velcro

• solute-solvent attraction stays same (head-head)

What is an unsaturated solution?

• [solute]>solubility

• all added solid is dissolved

• more solute can be dissolved still

what is a saturated solution?

• no more solute will dissolve

• some undissolved solid is often present

• [solute] is constant or in dynamic equilibrium

what is a supersaturated solution?

have more solute dissolved than the equilirbium

form when:

• the salt is dissolved at a high temp

• the solution is slowly cooled

As temp increases solubility… (solid and liquid)

also increases

talk about why (kinetic energy)

As temp increases solubility… (gas and liquid)

decreases because ??

• its in equilibrium

As pressure increases solubility… (gas and liquid)

pressure of gas ABOVE liquid (vapor pressure? increases,

What is Henry’s law?

S_g (solubility) = k_H (henry’s law constant) P_g (partial pressure of that gas)

What is a mass fraction?

mass of solute / total mass of solution

What is a weight percent?

mass fraction x 100%

What is a (m/v)% or (w/v)%?

mass solute / volume (mL) solution

• used for medical and pharmaceutical concentrations

• often assume water density 1.0 g/mL and 100mL of solution unless told otherwise

what are parts per million, billion, and trillion?

mass solute / mass solution x 10 ^ ..

• hundred = 10²

• million (ppm) = 10^6

• billion (ppb) = 10^9

• trillion (ppt) = 10^12

so up by 3 for m, b, t or number of zeros

What is a mole fraction?

• the number of moles of one component divided by the moles of all components of the solution

• X_A = moles of A / moles of A + moles of B

• X_B = moles of B/ moles of A + moles of B

• unity=1

What is Molarity?

M = moles of solute / liters of solution

what is molality?

moles of solute / kg of solvent

• uses solvent mass

• is temperature independent

What are colligative properties?

they depend ONLY on how much stuff there is NOT what the stuff is

• vapor pressure (Raoult’s law)

• boiling point

• freezing point depression

• osmotic pressure

what are colloids?

• large particles uniformly distributed through a solvent-like medium

• look homogenous, but microscopes show they are not

• particles are 10-1000x bigger than single molecules

• smaller though than particles in suspensions

what is Raoult’s law?

P₁(vapor pressure of solvent over solution) = X₁(mole fraction of solvent) P^’₁(vapor pressure of pure solvent0

• everything doing math with the solvent

What are the deviations from Raoult’s Law?

• if two liquids are mixed together, the total VP is the sum of the two or the top line of the graph

• INTERMOLECULAR FORCES get in the way and cause deviations. the graphs can show this

What are the three main colligative properties of electrolytes?

• vapor pressure lowering

• freezing point depression

• boiling point elevation

What do colligative properties depend on?

the number of particles in a solution or the van’t Hoff factor (i)

What increases the boiling point of a solvent?

• non-volatile solutes - VP lowered so higher T needed to get VP=externalP

What is the equation for boiling point elevation?

deltaT_b=K_b m_solutei

**delta T_b is the change in b.p. / the new bp will be higher

What lowers the freezing point of a solvent?

• adding a non-volatile solute

What is the equation for freezing point lowering/depression?

deltaT_f= K_f m_solutei

• delta T_f is change in fp, so the new fp is lower than the origional

What are some examples of deviations from expected van’t Hoff factors?

• ions attract each other in solution

• they only act as separate units at very low ion concentrations

• i is usually smaller than expected in most solutions

What is a semi-permeable membrane?

• allows passage of small “particles”

• stops large “particles”

• ex. cell membrane

What is osmotic pressure?

pressure that must be applied to stop osmosis

^ = c R T i

• c=molarity

• R=gas constant

• T= absolute temp

• i= particles

What is an isotonic solution?

[solution out] = [solution in]

No net flow

what is a hypertonic solution?

[solute out] > [solute in]

Net flow out

What is a hypotonic solution?

[solute out] < [solute in]

What is osmolarity?

a term used. in creating isotonic solutions for medical applications

M x i

What is normal osmosis?

water molecules cross the membrane diluting the brine

flow stops when pressure = osmotic pressure

What is reverse osmosis?

flow is reversed if pressure applied > osmotic pressure

pure water can be separated from bride as external pressure forces water molecules through the membrane to the pure water side