AP Chem - Chapter 11 - Solutions Flashcards
What is a solution
a homogenous mixture
what is the difference between a solvent and a solute
a solvent does the dissolving, a solute gets dissolved
what are the different ways to find concentration
molarity mass percent volume percent mole fraction molality
what is the equation for molarity (M)
moles solute/liters solution
what is the equation for mass percent (%m/m)
mass solute/mass solution x 100
what is the equation for volume percent (%v/v)
volume solute/volume solution x 100
what is the equation for mole fraction (weird x)
moles solute/total moles
what is the equation for molality (m)
moles solute/kg solvent
what is the difference between molarity and molality
molarity changes slightly with temperature, molality doesn’t
what is the general rule of thumb with solubility
like dissolves like
how do you determine the polarity of a molecule
structure
electronegativity and bond polarity
what are the three steps in solution formation
breaking up the solute
breaking up the solvent (overcoming intermolecular forces)
allowing the solute and solvent to interact and mix
is breaking up the solute (step 1) endo or exothermic
endothermic
is breaking up the solvent (step 2) endo or exothermic
endothermic
is allowing the solute and solvent to interact and mix (step 3) endo or exothermic
exothermic
what is the heat of solution
the sum of the heat values for each step
heat of solution = heat step 1 + heat step 2 + heat step 3
what are the factors that affect solubility
structure
pressure
temperature
how does structure affect solubility
structure determines polarity, which determines solubility
polar will dissolve in polar, nonpolar in nonpolar
how does pressure affect solubility
pressure significantly increases the solubility of a gas
what is henry’s law
the amount of gas dissolved in a solution is directly proportional to the pressure of the gas above the solution
when does Henry’s law hold true
only when there is no chemical reaction between the solute and the solvent
how does temperature affect solubility
most solids dissolve better in warm liquids
gasses dissolve better in cold liquids
what is thermal pollution
when factories use water and then put it back put its warm so gasses can’t dissolve as well in it so living things in the pond suffocate.
when are the magnitude of the molarity and molality almost the same
in very dilute aqueous solutions
what is a nonvolatile solute
one that has no tendency to escape from solution into the vapor phase
how does the presence of a nonvolatile solute affect the vapor pressure of a solvent
it lowers it
why will a nonvolatile solute lower the vapor pressure of a solvent
because the solvent is occupied with interacting with the solute, so less is available to evaporate
what does the lowering of vapor pressure depend on
the number of solute particles present in the solution
what is an ideal solution
a liquid to liquid solution that obeys Raoult’s Law
in solutions where both solute and solvent are volatile, describe the vapor pressure if the solvent/solute have weak interactions (dissimilar IMFs)
vapor pressure will be higher than expected
in solutions where both solute and solvent are volatile, describe the vapor pressure if the solvent/solute have strong interactions (similar, very strong IMFs)
Vapor pressure will be lower than expected
what can we assume about the IMFs between the solute and the solvent when the energy of formation of solution is large and negative
the IMFs are strong
there will be a negative deviation from Raoult’s law
what can we assume about the IMFs between the solute and the solvent when the energy of formation of solution is positive
IMFs are weaker than those among the molecules in the pure liquids
there will be a positive deviation from Raoult’s Law
what are colligative properties
properties of a solution that depend only on the number, and not on the identity, of the solute particles
How does the presence of a nonvolatile solute affect the freezing point of a solution
It depresses it (lowers it
When does the normal boiling point of a liquid occur
At the temperature where the vapor pressure of a liquid equals exactly 1 atm
How does a nonvolatile solute affect the boiling point of the solvent
It elevates it
Why does the presence of a nonvolatile solute elevate the boiling point of the solvent
Because VP is lowered when we add a solute, so we need to add more energy (higher temperature) to get more solvent to evaporate so the VP will be equal to the atmospheric pressure and be able to boil
Why does the presence of a non volatile solute lower the freezing point of the solvent
Solvent is busy interacting with the solute, so we have to remove even more energy to get the solvent to go from a liquid to a solid
Why is putting salt on the roads not always effective in keeping them from freezing
Because if the outside temperature is lower than the freezing point of the resulting salt solution, ice forms anyway
What is osmosis
The flow of solvent into the solution through the semipermeable membrane
What is osmotic pressure
The pressure that must be applied to a solution to stop osmosis
How does water tend to move/diffuse
From areas of high concentration to low concentration
Why is osmotic pressure particularly useful?
Because a small concentration of solute produces a relatively large osmotic pressure
What are isotonic solutions
Solutions that have identical osmotic pressures
When does reverse osmosis occur
If a solution in contact with pure solvent across a semipermeable membrane is subjected to an external pressure larger than its osmotic pressure
What does reverse osmosis cause
A net flow of solvent from the solution to the solvent
What does the semipermeable membrane act as in reverse osmosis
A “molecular filter” to remove solute particles
What does the van’t Hoff factor (little i thing) account for
The fact that ionic compounds ionize and produce more particles in solution
How can you find the expected value for i
By noting the number or ions per formula unit (i.e. NaCl would be 2, K2SO4 would be 3, etc)
Is the expected value of the van’t Hoff factor always what actually happens?
No
Why is the expected value for the van’t Hoff factor not always true
Ion pairing
What is ion pairing
When dissolved ions in a solution find each other swimming around and hang out for a bit and thus count as a single particle
Why do higher concentrations of solute lead to a lower value of the van’t Hoff factor
There’s more of a chance for ion pairing because there is a higher concentration of ions
A salt solution sits in an open beaker. Assuming constant temperature and pressure, the vapor pressure of the solution…
Decreases over time
When is ideal behavior for a solution often observed
When the solute-solute, solvent-solvent, and solute-solvent reactions are very similar
2 liquids from a solution and release a quantity of heat. How does the pressure above the solution compare to that predicted by raoult’s law?
It will be less
Why will a nonpolar solute and a highly polar solvent not produce a solution (mix)
Because a large amount of energy would have to be expended
