COLLIGATIVE PROPERTIES Flashcards
1
Q
- What is a Solute?
A
- the dissolved substance
2
Q
- What is a Solvent?
A
- the substance that is doing the dissolving
3
Q
- In solid-liquids solutions, what is the solute and what is the solvent?
A
- the solute is the solid that dissolves in the solvent
- the solvent is a liquid
4
Q
- In liquid-liquid solutions, what is the solute and what is the solvent?
A
- the solute is the liquid found in the smaller amount
- the solvent is the liquid that is present in higher
amounts
5
Q
- What is meant by “Like dissolves like”?
A
- polar solvents dissolve polar solutes
- non-polar solutes dissolve in non-polar solvents
EG: water and oil are not an example of like dissolves
like
: water is polar
: oil is non-polar
: the one cannot dissolve in the other
6
Q
- What are the two units of concentration we focus on in this topic?
A
- Mole Fraction (X)
- Molality (m)
7
Q
- What is Molarity defined as?
A
- it is the moles of the solute
DIVIDED - by the litres of the solution
- the litres of the solution consist of the volume of the solute and the volume of the solvent mixed together
8
Q
- What are the advantages of Molarity (M)?
A
- it is convenient for titrations
- it makes use of simpler stoichiometric calculations
9
Q
- What are the disadvantages of Molarity (M)?
A
- it is dependent on temperature
- this is because the volume of the solution is involved in
the equation - it will only be valid for the temperature that the
solution was made at
10
Q
- What is the Mole Fraction (X) defined as?
A
- it is the moles of the component
DIVIDED - by the total moles in the solution
11
Q
- What are the advantages of the Mole Fraction (X)?
A
- it is independent of temperature
- it does not depend on the volume of the solution
- it is convenient for gas mixtures
- it can also be used for liquid-liquid solutions
12
Q
- What is Molality (m) defined as?
A
- it is the moles of the solute
DIVIDED
by the kilograms of the solvent
13
Q
- What are the advantages of Molality (m)?
A
- it is independent of temperature
14
Q
- What unit is often used to convert to Molarity (M)?
A
- the density of a solution
15
Q
- When are Molarity and Molality similar?
A
- when the dilute water solutions are similar
16
Q
- When are Molarity and Molality different?
A
- when you use a solvent with a very different density from water
17
Q
- What does 1 Litre of water weigh?
A
- it weights 1kg
- 1000 grams
18
Q
- What is the derivative of the word Colligative?
A
- the word has a latin origin
- it means the number/amount of particles
19
Q
- What do Colligative Properties depend on?
A
- they depend on the amount (number of particles) of the solute that is placed on the solution
- they do not depend on the type of solute
- the more particles present in the solute:
- the greater the effect of the colligative properties
20
Q
- What are 4 Colligative Properties?
A
- Vapour Pressure Lowering
- Boiling Point Elevation
- Freezing Point Depression
- Osmotic Pressure
21
Q
- The left flask has a lid on top of it.
It is a closed container.
it contains pure water.
What happens to the water inside under normal circumstances?
A
- some water molecules will evaporate
- they will float above the liquid surface
- this creates a small vapour pressure
22
Q
- The flask on the right contains a water and sugar
solution.
What do the pink particles in the image represent?
A
- the sugar molecules
23
Q
- What exists in the sugar and water solution?
What is the result of these?
A
- intermolecular forces
(ion dipole forces) - these are found between the sugar and the water molecules
- these forces make it difficult for the water molecules to
exit the liquid phase - the rate of the evaporation decreases
24
Q
- What does a decreased rate of evaporation result in?
A
- there are fewer water molecules that evaporate
- this decreases the vapour pressure
- this vapour pressure is found in the region above the
liquid - this is called Vapour Pressure Lowering
25
Q
- What is the equation to work out the actual vapour pressure of a solution?
A
P solution = X solvent x P solvent
26
Q
- What is the equation to work out of Vapour Pressure lowering?
A
▵ P solution = X solute x P solvent
- X Solute:
- this increases as more solute is added
- it can be written as a mole fraction of the solute
- this will cause a decrease in the vapour pressure
27
Q
- What is X solvent in this equation?
A
IF WE HAVE A PURE SOLVENT:
- X solvent = 1
- the vapour pressure is P solvent
- this is the vapour pressure of a pure solvent
28
Q
- What happens if we start to add more solute?
A
- the X solvent starts to decrease
- the X solvent now have a value lower than 1
- this will decrease the water pressure of the solution
- it will be below that of the pure solvent
- this is known as Vapour Pressure Lowering
29
Q
- What does this equation give us?
A
- the actual amount by which the vapour pressure is lowered
30
Q
- What is X Solute in this equation?
What are its values?
A
- it is the mole fraction of the solute
IF THERE IS NO DISSOLVED SOLUTE:
- then X Solute = 0
- there is no vapour pressure lowering
IF WE START ADDING MORE SOLUTE:
- X Solute will have a value of between 0 and 1
- the vapour pressure lowering will start to increase
31
Q
- What happens when ionic solids dissolve?
A
- they produce more particles than when non-ionic substances dissolve in water
32
Q
- Give us an example of when an ionic solid dissolves in water?
A
NaCl→ Na⁺ (aq) + Cl⎺ (aq)
1 mol → 1 mol + 1 mol
→ there are 2 moles of particles
33
Q
- What is the Van’t Hoff factor?
A
- it has the symbol : i
- it is the total number of particles produced when a solute dissolves
34
Q
- What happens when a solute is added to a solvent?
A
- there are new interactions that form
- these form between the solute and the solvent
particles - these new particles make it more difficult for the solvent particles to escape to the has phase
35
Q
- What is the result of when a solute is added to a solvent?
A
- the boiling point of the solution becomes higher than the boiling point of the pure solvent
- this is known as BOILING POINT ELEVATION
36
Q
- What happens when we cool a pure solvent below its freezing point?
A
- we form highly structured crystal lattices
- the liquid freezes
37
Q
- What happens when we cool a solvent that has solute particles present within it?
A
- these particles interfere with the formation of the crystal lattice
- the freezing process now requires an even lower temperature to take place
- this is known as FREEZING POINT DEPRESSION
38
Q
- What increase the range between the normal boiling point and the new boiling point?
This factor has the same effect on the difference between the normal freezing point and new freezing point.
A
- adding a solute
- the more ions you add, the greater range there will be
- it will have a bigger effect
NB: Kb an Kf are always slightly different
: ▵Tb ≠ ▵Tf
39
Q
- How do we calculate the Change in the Boiling
Point?
(Boiling Point Elevation)
A
▵Tb = Kb x m x i
40
Q
- How do we calculate the Change in the Freezing
Point?
(Freezing Point Depression)
A
▵Tf = Kf x m x i
41
Q
- What do the constants used to calculate the boiling point elevation and the freezing point depression depend on?
A
- the nature of the solvent
- they do not depend on the nature of the solute
42
Q
- What can be seen going on in the left container in the diagram?
A
- there are two-sugar water solutions present
- they are separated by the semi-permeable
membrane - the solution on the left side is less concentrated than the solution on the right side
43
Q
- What does a semi-permeable membrane allow for?
A
- it allows the passage of water molecules through it
- it does not allow the passage of the solute particles
- these are too large to go through the pores of the
membrane
44
Q
- What do two solutions that have different concentrations represent?
A
- order
45
Q
- What is the natural tendency for this system?
A
- the entropy should increase
- the water molecules will migrate from the left side to the ride side of the permeable membrane
- this is done to decrease the concentration of the right-side solution
- until it is equal to the concentration on the left side
- THIS PROCESS IS CALLED OSMOSIS
46
Q
- What is Osmotic Pressure?
A
- it is the pressure required to prevent Osmosis from taking place
47
Q
- How is Osmotic Pressure Calculated?
A
π = i x M x R x T
- π = pi
- i = Van Hoff’s Factor
- M = concentration
- RT = given temperature
48
Q
- What is seen on the left side and the right of the container in the diagram?
A
LEFT SIDE:
- pure water
RIGHT SIDE:
- glucose and water solution
49
Q
49 What does the Initial State Diagram Represent?
A
- it represents order
- the natural tendency is to increase the entropy in the system
50
Q
- What does the need to increase the entropy of a system result in?
A
- the water molecules will migrate through the semi-permeable membrane
- this movement is from the left side to the right side
- this is OSMOSIS
51
Q
- What does the Equilibrium diagram represent?
A
- the water molecules will pass from the left side to the right side
- they do this through the semi-permeable membrane
- the level of the right column will begin to rise at this stage
- the osmotic pressure is related to the difference in the heights of the two columns
52
Q
- What can be seen in the External Pressure Applied diagram?
A
- there is an external pressure being applied to the
glucose-water side - this pressure is equal to the calculated osmotic
pressure of this solution - the external pressure prevents osmosis from taking place
- this is the definition of Osmotic Pressure
53
Q
- What is the Application of lowering the freezing point of ice?
A
- it keeps the ice as liquid water in the road
- it does this over a larger range of T
- this prevents the road from freezing over
54
Q
- What is the Application of reverse osmosis?
A
- it produces distilled water from seawater
55
Q
- What is the Application of Protein Molar Masses?
A
- they can be calculated from the results of experiments that involve colligative properties
56
Q
- What is Reverse Osmosis?
A
- the applied pressure will increase the osmotic pressure
- this will exceed to osmotic pressure of Sea Water
- the water from the solution that involves a solute will
move to the pure/distilled solution that is without
solute - it will move from a place of lower concentration to a place of higher concentration
57
Q
- Why is salt added to icy roads?
A
- it melts the ice
- this prevents the freezing of roads
- the freezing/melting point of water is 0°C
- the water will freeze into ice when the temperature
drops below this point - the water will stay in liquid form when the temperature
is above this point
WHEN WE ADD SALT TO ICE:
- it lowers the melting point
- this causes solid ice to melt at temperatures below 0°C
- the salt dissociates in the water
- this produces NaCl ions
- this makes it harder for the water molecules to bond
together again to form ice
58
Q
- Read through this summary.
Does everything make sense?
A
- yes
