9. Solutions

Question 1

How do you know which substances are water-soluble?

Answer 1

all salts in Group 1; all salts containing ammonium, nitrate and acetate; all halides except F unless they're reacting with Ag, Pb or Hg; all salts with sulfate unless they're reacting with Ca, Sr, Ba, Pb
CHARGED CMPDS (as opposed to neutral cmpds) ARE MORE WATER-SOLUBLE

Question 2

How do you know which substances are water-insoluble?

Answer 2

all metal oxides unless they’re reacting with Group 1 salts and ammonium; all hydroxides unless they’re reacting with Group 1 salts, ammonium, Ca, Sr, Ba; all carbonates, sulfides, sulfites and phosphates unless they’re reacting with Group 1 salts, ammonium

Question 3

What is concentration? Units?

Answer 3

amount of solute dissolved in solvent; M (mol/L)

Question 4

How to find percent composition by mass?

Answer 4

(mass of solute/mass of soln) * 100 (in g)

Question 5

How to find mole fraction?

Answer 5

mole of target species/mole of all the species (in mol)

Question 6

How to find molarity?

Answer 6

mol of solute/L of soln (M)

Question 7

How to find molality?

Answer 7

mol of solute/kg of solvent (m)

Question 8

Know M1V1 = M2V2

Answer 8

Oh research semester…

Question 9

What is the best thing to do when solving any soln stoich?

Answer 9

Write out the balanced dissociation eqn

Question 10

What is solvation/dissolution vs hydration vs mixture?

Answer 10

Electrostatic attraction b/w solute and solvent: break intermolecular bonds b/w solute and those of solvent —> then form new intermolecular bonds b/w solute and solvent molec vs when water is the solvent of the sln vs when gas dissolves in gas

Question 11

Know how to find Ksp (solubility product). Remember that Ksp is analogous to equil constant

Answer 11

Write out balanced aq eqn for soln –> make ICE table (solids and liquids are negligible, conc only matters w/ aq state) –> Ksp = [products]/[reactants] (exponents in Ksp = coefficients in eqn) –> solve it like algebra

Question 12

What does high molar solubility mean?

Answer 12

more solute is dissolved; more ions = produced. Only temp can change solubility of solid solute

Question 13

What if soln forms a precipitate?

Answer 13

Add H3O+ and form a mega aq eqn (H3O = react, water and H-base = product)

Question 14

How to find new K if soln = dissolved in acid/base solns

Answer 14

K = Ksp x Kf

Question 15

What is the common ion effect?

Answer 15

more common ions –> more likely to react w/ reactants –> more precipitate –> less solubility

Question 16

Are slns homogeneous or heterogenous?

Answer 16

Homogenous (ie. Uniform appearance)

Question 17

Solns = based on enthalpy change. What are ideal solns?

Answer 17

When enthalpy change is zero: overall strength to make new bonds is equal to overall strength of breaking old bonds. Ideal sln = determined by Raoult’s Law

Question 18

Dilute vs concentrated soln

Answer 18

Proportion of solute to solvent = small vs Proportion of solute to solvent = big

Question 19

Ksp expressions should never have denominators

Answer 19

Yeeee. Cuz you’re dissolving a pure solid into pure water

Question 20

Ion product (IP)

Answer 20

Analogous to Q: helps determine the progress of a rxn

IP unsaturated sln, will dissolve more
IP=Keq —> equil, saturated
IP>Keq —> supersaturated sln, will precipitate

Question 21

Why do complex ions inc molar solubility?

Answer 21

Complex ions have multiple pole bonds b/w ligands and central atom —> lots of dipole-dipole interaction —> stabilizes dissolution of complex ion. They also have coordinate covalent bonding

Question 22

What happens to vapor pressure when more solute is added to solvent

Answer 22

Vapor pressure of solvent dec proportionately. You can find new vapor pressure using Raoult’s Law; then do final-initial for vapor pressure change

Question 23

Raoult’s Law

Answer 23

Know the formula. States that ideal sln behavior = observed when solute/solute, solute/solvent and solvent/solvent interactions are all very similar

Question 24

Osmotic pressure formula

Answer 24

PI = iMRT; osmotic pressure = colligative property

Question 25

How to change equil constants?

Answer 25

Change temp and/or identity of slns

Question 26

How to inc solubility of solid solutes? How to inc solubility of gases into sln?

Answer 26

Only temp can change solubility of solid solute. CHARGED CMPDS (as opposed to neutral cmpds) ARE MORE WATER-SOLUBLE
Gas solubility = directly proportional to pressure of sln and inv proportional to temp of sln