ch 13 solutions

Question 1

energies of solutions and equation5

Answer 1

• The overall energetics of solution formation has 3 components:Hsoln=H1+H2+H3
• H1: separation of the solute particles from one another. Endothermic.
• H2: separation of solvent molecules to accommodate the solute. Endothermic.
• H3: attractive interactions between solute and solvent. Exothermic
• The three enthalpy sums can add to be positive or negative, so formation of a solution can be either exothermic or endothermic.

Question 2

why do ionic solutes not dissovle in nonpolar liquids

Answer 2

A solution will not form if Hsoln is too endothermic. H3 should be comparable in magnitude to H1+H2. Reason why ionic solutes do not dissolve in nonpolar liquids=non polar molecules would experience weak attractive interactions with ions that would not compensate for energies required to separate ions.

Question 3

factors involved in spontaneous process3

Answer 3

-Energy. Processes in which the energy content of the system decreases ted to occur spontaneously. Change tends to occur in the direction that leads to a lower energy of the system. However, some endothermic processes occur spontaneously these result in dispersed state of the components
-Entropy. Processes occurring at a constant temperature in which the randomness or dispersal in space (entropy) of the system increases tend to occur spontaneously. Distribution of each component into a larger volume.
-Gases spontaneously mix and expand unless restrained by their containers, or IMFs/
MAIN IDEA: in most cases, formation of solutions is favored by the increase in entropy that accompanies mixing. A solution will form unless solute-solute/solvent-solvent interactions are too strong relative to solute-solvent interactions.

Question 4

crystallization

Answer 4

opposition of solution process. As concentration of solute particles increases, chances of colliding with surface of solid and becoming attached to solid increases. Solute+solvent solution

Question 5

saturated2

Answer 5

• Dynamic equilibrium where the rates of dissolving and crystallizing become equal
• Amount of solute needed to form a saturated solution in a given quantity of solvent is the solubility of that solute

Question 6

unsaturated

Answer 6

dissolving less solute than that needed to form a saturated solution

Question 7

supersaturated

Answer 7

Dissolving greater amount of solute at high temp, and then cooling solution and having it still be dissolved

Question 8

factors affection solubility

Answer 8

• Solute-solvent interactions: the stronger the attractions between solute and solvent molecules (higher molecular mass), the greater the solubility. (like dissolves like)
• Pressure: solubility of the gas increases in direction proportion to its partial pressure above the solution.
• Temperature: the solubility of most solid solutes in water increases as the temperature of the solution increases. The solubility of gases in water decreases with increasing temperature.

Question 9

miscible

Answer 9

Pairs of liquids that mix in all proportions are miscible, those that do not dissolve in one another are immiscible

Question 10

alcohols3

Answer 10

• organic compounds that contain the OH polar bond attached to a C atom. They are miscible with water and polar liquids
• As number of carbon atoms in an alcohol increases, the polar OH group becomes a smaller part of the molecule, and behaves more like a hydrocarbon. Solubility of alcohol in water decreases, but the solubility of the alcohol in a nonpolar solvent increases.
• To increase the solubility of a substance in water, you can increase the polar groups it contains. (increasing number of OH groups)

Question 11

henrys law

Answer 11

Sg=kPg Sg=solubility of the gas in the solution phase (Expressed as molarity). Pg=partial pressure of the gas over the solution, k=proportionality constant known as the henry’s law constant (varies with each solute-solvent pair and with temp)
Because when pressure increases, the rate at which gas molecules enter the solution increases, so the concentration of solute molecules at equilibrium increases in proportion to the pressure.

Question 12

dilute vs concentrated

Answer 12

Solution with small concentration=dilute. Solution with large concentration=concentrated.

Question 13

mass percentage

Answer 13

Mass%component=Mass of component in soln/total mass of soln*100%

Question 14

ppm

Answer 14

parts per million
ppm of component=mass component in soln/total mass of soln*106.
1ppm corresponds to 1 mg of solute per liter of solution.

Question 15

ppb

Answer 15

parts per billion

ppb of component=mass component in soln’total mass of soln*109

Question 16

mole fraction

Answer 16

Mole fraction of a component of a solution (X)= moles component/ total moles of compound. Mole fractions have no units. The sum of the mole fractions of all components in a solution must equal 1.

Question 17

molarity vs molality3

Answer 17

• Molarity (M)=moles solute/liters soln
• Molality (m)= moles solute/kg of solvent
• Molarity depends on the volume of solution, molality depends on the mass of solvent. When water is solvent, molality and molarity are numerically about the same. Molality does not change with temperature, but molarity does.

Question 18

colligative properties

Answer 18

depend on the quantity (concentration) but not the kind/identity of the solute particles.4 colligative properties: decrease in freezing point, increase in boiling point, vapor-pressure reduction, and osmotic pressure

Question 19

reduction of vapor pressure

Answer 19

addition of nonvolatile liquid to a solution will lower the vapor pressure

Question 20

nonvolatile

Answer 20

no measurable vapor pressure. Adding a nonvolatile solute to a solvent always lowers the vapor pressure

Question 21

raoults law

Answer 21

reduction of vapor pressure

P=X*Pº. P=partial pressure exerted by solvent vapor, X=mole fraction of solvent, Pº=vapor pressure of pure solvent

Question 22

ideal vs real solution3

Answer 22

• Ideal solution obeys the raoult’s law. Real solutions best approximate ideal behaviour when the solute concentration is low and when the solute and solvent have similar molecular sizes and similar types of intermolecular attractions.
• If IMF between solvent and solute are weaker than between solvent and solvent and between solute and solute, solvent vapor pressure will be greater than predicted by Raoult’s law.
• When interactions between solute and solvent are exceptionally strong, the solvent vapor pressure is lower than Raoult’s law predicts

Question 23

boiling point elevation2

Answer 23

The the normal BP of a pure liquid, the VP of the solution will be less than 1 atm, so the BP of the solution is higher than that of the pure liquid.
The increase in BP relative to that of the pure solvent Tb is directly proportional to the number of solute particles per mole of solvent particles. Tb=kbm. kb=molal boiling-point-elevation constant, magnitude depends only on solvent. m=molality.

Question 24

freezing point depression

Answer 24

The triple point of the solution is at a lower temp than the pure liquid because the solution has a lower VP than the pure liquid. So, the freezing point of the soln is lower than that of the pure liquid. Tf=kfm. (kf=molal freezing point depression constant, m=molality)

Question 25

semipermeable

Answer 25

when in contact with a solution, will allow some molecules to pass through, but block larger solute molecules or ion.

Question 26

osmosis

Answer 26

the net movement of solvent is always toward the solution with the higher solute concentration (lower solvent concentration). The difference in liquid level, thus difference in pressure causes flow to cease. Applying pressure to the higher liquid level can also halt the flow

Question 27

osmotic pressure

Answer 27

-pressure required to prevent osmosis by pure solvent. pi=(n/V)RT=MRT. (M=molarity).

Question 28

isotonic

Answer 28

Two solutions are isotonic if they have identical osmotic pressure and when separated by semipermeable membrane, no osmosis occurs.

Question 29

hypo vs hyertonic

Answer 29

The solution of lower osmotic pressure is hypotonic with respect to the more concentrated solution, more concentrated solution is hypertonic

Question 30

colloids

Answer 30

• type of dispersion between particles not dispersing through a solution at all, and completely dispersed solution (intermediate type of dispersion). Dividing line between solution and heterogeneous mixtures.
• bigger particles than solute particles

Question 31

hydrophilic vs hydrophobic

Answer 31

• When dispersing medium is water, colloids may be hydrophilic (Water loving, polar) or hydrophobic(water fearing, nonpolar). Hydrophilic groups interact with water molecules while hydrophobic groups do not.
• Hydrophobic colloids can be stabilized by adsorption (to adhere to a surface) of ions on their surface which interact with water. Can also be stabilized by presence of hydrophilic groups on their surfaces (small oil drops (hydrophobic) aggregate and form oil slick on surface of water)`

Question 32

separation of colloidal particles

Answer 32

Colloidal particles are so small, so cannot be separated by simple filtration, so must be enlarged by coagulation to be filtered. Coagulation happens by heating the mixture (increases particle motion and number of collisions to increase particle size) or adding an electrolyte (neutralizes surface charges of particles, removing electrostatic repulsions that prevent them from coming together). Semipermeable membranes can separate ions from colloidal particles by dialysis