solutions, osmosis & water

Question 1

define mixture

Answer 1

2 or more substances dispersed throughout one another but whos constituent parts are the same as their original i.e. they have not chemically interacted.

e.g. air is a mixture of gases.

Question 2

define solution

Answer 2

A homogenous mixture of 2 or more substances - even distribution of all particles in the mixture and more complex techniques are needed to separate them.

not a simple mixture because there is some chemical reaction i.e. ions have formed in water.

Question 3

define a suspension…

Answer 3

A mixture of hetergenous mixture of 2 or more substances.
the particles are much larger than those in a solution and usually one substance is heavier than the other and with time will settle.
this may take seconds to years depending on the suspension

Question 4

define emulsion

Answer 4

a liquid-liquid colloidal system
mixture of 2 or more immiscible liquid (these are liquids that cannot combine to form homogenous mixture e.g. oil and water)

need to be stirred to maintain otherwise will separate to individual componets with time.

Question 5

what is an alloy?

Answer 5

a solution of 2 or more metals - i.e. a solid soluition.

(usually solution is a solid in a liquid but alloys are example of solid in solid)

Question 6

how does particle size vary in solution vs suspension?

Answer 6

solution - very small particles - dont settle out of solution

suspension - larger particles, settle out of solution with time.

Question 7

what is a colloid ?

Answer 7

small particles i.e. the solvent phase
and external phase - the larger paricles

Not quite a suspension but particles are bigger than solution

e.g. smoke - solid particles in gaseous air.
e.g. an emulsion

Question 8

what is an emulsifier?

Answer 8

A substance that stabilises an emulsion to prevent the separation process for longer.

e.g. surfactants - Surfactants bind electrostatically to the surface of the particles, and interact electrostatically with the other substance too to maintain their contact.

Question 9

describe how a mixture of propofol is maintained?

Answer 9

propofol is a lipid as an emulsion in water.

Egg and soya lecithin are added as emulsifiers to stabilise this emulsion.

Question 10

what are the properties of water?

Answer 10

water has unique properties due to its polar nature - slightly positive H and slightly negative O, meaning it forms H bonds between its molecules

this makes it
- a good solvent - electrostatic forces between water and solute particles.
- higher boiling point than predicted for its size
- higher latent heat of vaporisation
- higher surface tension
- ice has a lower density than water.

Question 11

what is the shape of a water molecule?

Answer 11

non-linear
due to 2 lone pairs on Oxygen

oxygen is electronegative and so becomes slightly negative in charge
H is therefore left slightly positive.

Question 12

why is ice less dense than water?

Answer 12

in water H bonds are breaking and forming all the time and hence water particles can move past one another and are not kept rigidly at a H bond distance.

in ice there are fixed H bonds holding the lattice whereby each water molecule is packed but this is limited by distance of H bonding.

Question 13

define solubility?

Answer 13

the ability for a solute to dissolve in a solvent.
can be measured as the max mass of solute per unit volume of solvent
e.g. mg/ml

at a constant temperature and pressure.

Question 14

what factors affect solubility?

Answer 14

the nature of solute and solvent
i.e. polarity - more polar the more likely to make electrostatic interactions and dissolve

pressure - henrys law
temp
- solid in liquid = as temp increases, solubility increases
- gas in liquid = as temp increases, solubility decreases.

Question 15

what is the Bunsen solubility coefficient

Answer 15

this is a measure of solubility of gas in a liquid

the volume of gas that dissolves in one unit volume of liquid

at standard temperature and pressure - 1atm and 0 degree C

Question 16

what is the ostwald solubility coefficient ?

Answer 16

this is a measure of solubility of gas in a liquid

the volume of gas that dissolves in one unit volume of liquid

not at a standard temp/pressure but at a specified temp/pressure.

more useful for clinical practice where standard temp and pressures are not present.

Question 17

define osmosis

Answer 17

physical process describing the movement of water across partially permeable membrane from area of low to high concentration

(from higher to lower water potential i.e. less negative to more negative)

Question 18

define osmolarity

Answer 18

the amount of osmotically active particles per litre of solution

Question 19

define osmolality

Answer 19

the amount of osmotically active particles per kg of solvent

Question 20

define an osmole

Answer 20

one osmole = amount of particles equal to avogadros constant (6.02 x 10^23)

Question 21

define osmotic pressure

Answer 21

the hydrostatic pressure exerted by osmotically active particles in a sealed system on one side of partially permeable membrane.

can be measured as the hydrostatic pressure required to oppose the movement of water by osmosis.

Question 22

what happens to osmolarity and osmolality as temperature changes?

Answer 22

increase in temp will reduce the volume of solution but not the mass of solvent

hence osmolarity changes with temp

osmolality does not.

Question 23

how much pressure does 1 osmole of solute exert?

Answer 23

101.325 kpa / 1atm pressure
when dissolved in 22.4L of solvent
at 0 degrees

Question 24

what is tonicity ?

Answer 24

A term used when comparing the osmolarity of 2 solutions.

i.e. hypotonic - one solution has a higher (less negative) water potential than the other. Or lower osmolality

Question 25

what is the vant hoff equation?

Answer 25

Osmotic pressure (π)= iMRT

I = van’t hoff factor
M = molarity - molar concentration
R = universal gas constant = 8.31 J/K/mole
T = absolute temp in kelvin

Question 26

what is the vant hoff factor?

Answer 26

denoted by i in the vant hoff equation
a measure of how many osmotically active particles a solute will give
e.g. NaCl = 2 however not quite 2 because doesnt all fully dissociate

Question 27

what drug works osmotically and describe its action?

Answer 27

mannitol - an unmetabolised sugar

it increases the osmolarity of the blood
doesnt cross BBB (initially)
hence allows water to be drawn from cerebrum to reduce oedema

freely filtered at kidneys but not absorbed - hence draws water into renal tubules via osmosis.

Question 28

what are colligative properties?

Answer 28

properties of a solution that vary with the osmolarity of the solution.

these include..
osmotic pressure
boiling point
freezing point
vapour pressure

Question 29

how does boiling point vary with osmolality?

Answer 29

increased osmolarity i.e. more number of solute particles will increase the boiling point.

0.52 degrees increase per osmole of solute per kg of solvent

e.g. adding salt to pan of boiling water - increases the boiling point hence water will be hotter to cook the pasta.

Question 30

how is vapour pressure of solvent altered by osmolality?

Answer 30

Decreases with increased molar concentration.

explained by Raoults law but also to understand… As solute is added, it takes up space, fewer solvent molecules at the surface to evaporate and hence lower solvent vapour pressure.

reduction by 0.04 kpa per osmole per kg of solvent

Question 31

how does freezing point vary with osmolality?

Answer 31

freezing point is depressed by 1.86 degrees for every osmole of solute per kg of solvent

i.e. freezing salty water requires lower temp than water.

this is because the solute particles will disrupt a nice lattice forming

Question 32

what is Raoults law? how is this related to vapour pressure as osmolarity increases.

Answer 32

states that the partial pressure of a solute in solution is proportional to the molar concentration

the total vapour pressure of the solution is a sum of the component vapour pressures of each solvent.

hence if solute conc increases the partial pressure of that solute increases hence the partial pressure of the solvent decreases - partial pressure is a percentage. e.g. if 2part of Na Cl and 8 parts water - partial pressure is 80% for water. if more NaCl is added - now 4 parts to 6 parts water so pp of water 60%

Question 33

explain in terms of vapour pressure how the boiling point of a solution be decreased with increased osmolarity?

Answer 33

adding solute will increase osmolarity
this will drop vapour pressure of the liquid.
boiling point occurs when vapour pressure = atmospheric pressure.

hence lowering vapour pressure means further from atmospheric pressure.
so increases boiling point.

also can be thought of as…
fewer particles at the surface to evaporate and boil off when solvent present

Question 34

what is an osmometer?

Answer 34

A device that measures the osmolarity of a solution.
it uses colligative properties to do this

Question 35

how does an osmometer work?
draw a diagram.

Answer 35

solvent is supercooled to bring it below its freezing point. (-7 degrees)

then slowly mixed/mechanical stimulus to allow it to slowly freeze.

as molecules freeze they will release energy which will warm the mixture.

the temp of the mixture will plateau at its freezing point. this can be measured by a thermometer

compare freezing point to that of pure solvent i.e. water. can calculate how much it has been depressed by to measure the osmolarity of solution.

drawing the graph:
- temp on x axis, time on y axis.
- at 0 start at room temp
- supercooling - rapid drop to -7 degrees
- then gradual rise to freezing point
- plataeu at freezing point

Question 36

how is the cooling of an osmometer achieved?

Answer 36

peltier effect
- absorption of heat at the junction of 2 dissimilar metals

(opposite of seebeck effect)

Question 37

what is reverse osmosis?

Answer 37

use of pressure to force water against its osmotic gradient across semipermeable membrane

method used to produce fresh water from sea water

need a dense polymer membrane which permits water and not solutes and can withstand the high pressures.

requires high energy/ force

Question 38

what is surface tension?

Answer 38

intermolecular forces at a surface of a liquid which resist forces acting upon the surface. intermolecular forces throughout the liquid but in the centres this is cancelled out by molecules next to it whereas a the edge, the forces are net inwards to help keep the liquid together.

measured as N/m

arises because of intermolecular forces within a liquid that attract one another and require energy to break e.g. in water this is H bonds.

Question 39

what is meant by water has cohesive property?

Answer 39

water molecules tend to stick together due to intermolecular forces acting between them.

this explains why a droplet of water stays together

Question 40

how can surface tension be applied to forces within an alveoli?

Answer 40

using la place law we can measure pressure in alveolus in relation to its radius and surface tension.
la place law P=2T/r

2 alveoli with equal surface tension but one is smaller than the other…

hence smaller one will need more pressure to open than a larger one and hence also have high pressure when open.
this means pressure gradient created - and small alveoli will empty into large

Question 41

what is la-place’s law?

Answer 41

relates pressure in a sphere to its surface tension

P=2T/r
P= pressure, T is wall tension, r is radius

for a tube the equation is P = T/r