Biochemical instrumental analysis - 6

Dr. Maha Al-Sedik2015

CLS 332

Osmosis:

If two aqueous solutions with different concentrations of particles

are separated from each other by a semipermeable membrane, then

water will move across the membrane from the solution with the

lower concentration to the solution with the higher concentration.

Factors affecting osmosis: The difference in the concentration of the particles.

The nature of permeability of the membrane.

Osmotic pressure:

The pressure which needs to be applied to a solution to

prevent the inward flow of water across a semipermeable

membrane. It is also defined as the minimum pressure

needed to nullify osmosis.

Clinical importance of osmotic pressure:It is an important factor affecting cells.

Hypertonicity is the presence of a hypertonic solution

that causes cells to shrink.

Hypotonicity is the presence of a hypotonic solution

that causes cells to swell.

Isotonicity is the presence of a solution that produces

no change in cell volume.

Osmolarity and osmolality:

Osmolarity is a measure of the number of particles in one

liter of solution.

Osmolality is a measure of the number of particles in one

Kg of solution.

e.g., 1 mole of NaCl 2 osmoles … NaCl (1 for Na + 1

for Cl).

What is the molarity of NaCl, HCL and CuCl2?

NaCL -------------------------- 2 osmoles

HCL ---------------------------- 2 osmoles

CuCL2------------------------------3 Osmoles

Think with me

Molarity = one mole of substance in a liter total

volume (total volume solution = 1000 ml).

Molality = one mole of substance in a kilogram

total wt (total weight solution = 1000 grams).

What is the difference between osmolarity and osmolality?

When we consider osmolarity is the

same as osmolality?

If the solvent is water → osmolarity means

osmolality

One liter of water = One Kg water

SO

1 mole of NaCl would weigh ----------- grams

molecular weights: Na = 23 , Cl = 35

1 mole of HCL would weight ------------ grams

molecular weights: H = 1 , Cl = 35

Think with me

1 mole of substance is its gram molecular weight

• 1 mole of NaCl would weight 58 grams (23 + 35).

• 1 mole of HCl would weight 36 grams.

How many grams of NaCl I have to put to prepare normal

saline = 0.9 molar solution NaCl

molecular weights: Na = 23, Cl = 35.

Think with me

I need 58 gm of NaCl is needed to prepare a molar solution, so,

how many grams I need to prepare 0.9 molar solution.

58 -------------------------------------------- 100

??? ------------------------------------------- 90

90 X 58??? = --------------------------- = 52.2 gm 100

What will happen if a solute is dissolved in a solvent

The following properties of the solvent change:

Osmotic pressure increases.

Vapor pressure decreases.

Boiling point increases.

Freezing point decreases.

COLLIGATIVe

These are known as colligative properties and are all related to

the total number of solute particles per mass of solvent, i.e. the

osmolality.

Any of the four colligative properties could be used as a basis for

the measurement of concentration of the substances.

The most commonly used method in the case of physiological

fluids is freezing point depression.

For example, the freezing point of salt water is lower than

that of pure water, due to the presence of the salt

dissolved in the water.

To a good approximation, it does not matter whether the

salt dissolved in water is sodium chloride or potassium

nitrate; if the molar amounts of solute are the same and

the number of ions are the same, the freezing points will

be the same.

Principle: The presence of a solute lowers the freezing point of a solution.

The decrease in the freezing point will be directly proportional to

concentration of the substance.

For example:

pure water freezes at 0°C; if one dissolves 10 grams of sodium

chloride in 100 ml of water, the freezing point goes down to −5.9°C.

Freezing Point Osmometer

Freezing Point Osmometer

Super cooled the sample by bath containing an

antifreeze solution that is maintained at about -5° C.

Inside the sample there will be thermometer to

measure FP.

The freezing point is determined and osmolality is

shown on the digital display.

The measurement value is stored in the memory.

http://www.youtube.com/watch?v=F3ZKAzpFpB8

Vapor Pressure osmometry

Vapor Pressure osmometryPrinciple:

The presence of a solute lowers the vapor pressure of a

solution at the same temperature and pressure.

The decrease in vapor pressure is directly proportional

to the concentration of substance.

Vapor Pressure and Boiling• Vapor Pressure: the pressure exerted by a vapor in

equilibrium with its liquid state. • Liquid molecules at the surface escape into the gas

phase.• These gas particles create pressure above the liquid in

a closed container.

Vapor Pressure increases with increasing temperature.

20oC80oC

As temperature increases, the amount of vapor generated by a liquid in a closed container increases.