PPAR Lec Colligative Properties

Physical Properties of Substances

drug molecules have properties that are often divided into additive, constitutive, and colligative.

additive properties

depend on the total contribution of the atoms in the molecular or on the sum of the properties of the constituents in a solution.

• molecular weight

constitutive properties

depend on the arrangement and to a lesser extent on the number and kind of atoms within a molecule

• refractive index, optical rotation, solubility, surface and interfacial properties

colligative properties

depends mainly on the number of particles in a solution.

• osmotic pressure, vapor pressure lowering, freezing point depression, boiling point elevation

colligative properties

• On adding a solute to a solvent, the properties of the solvent are modified.

  • Vapor pressure = DECREASES

  • Freezing point = DECREASES

  • Boiling point = INCREASES

  • Osmosis is possible (osmotic pressure)

• These changes are called _______.

• They depend only on the NUMBER of solute particles relative to solvent particles, not on the KIND of solute particles.

vapor pressure

• is the pressure of the saturated vapor above a liquid resulting from the escape of the surface liquid.

• the vapor pressure of an ideal solution is dependent on the vapor pressure of each chemical component and the mole fraction of the component present in the solution.

• When a nonvolatile solute is combined with a volatile solvent, the vapor above the solution is provided solely by the solvent.

• The solute reduces the escaping tendecy of the solvent, and on the basis of Raoult’s Law.

vapor pressure

the vapor pressure of an ideal solution is dependent on the ________ of each chemical component and the mole fraction of the component present in the solution.

reason of vapor pressure lowering

• Solute particles obstruct or reduce the likelihood of evaporation, leading to fewer molecules changing from liquid to gas phase.

• The solution is more stable than a pure solvent, resulting in lower evaporation rate.

• Solute particles occupy surface area, reducing the space for solvent molecules to evaporate.

• Solute particles get in the way of solvent particles escaping into the vapor.

• The number of solvent molecules on the interface between vapor and solution is reduced in a solution.

Raoult’s Law

• The vapor pressure of a solution containing a nonvolatile solute is lowered proportional to the relative number of the solute molecules.

• Vapor pressure of a solution is less than that of the pure solvent, as expressed in _______

lowering of the vapor pressure

According to Raoult’s Law, the vapor pressure of a solvent over a dilute solution is equal to the vapor pressure of the pure solvent, times the mole fraction of solute in the solution.

manometer

used and the difference of the vapor pressure between the solution and the pure solvent.

• For dilute aqueous solutions, however, the vapor pressure lowering is so slight as to produce a serious error in the measurement.

determination of the vapor pressire of solution

• Accurate differential manometers: small differences in vapor pressure.

• The isopiestic method is used frequently for the precise determination of vapor pressures.

isopiestic method

This method is used frequently for the precise determination of vapor pressures.

boiling point

Is the temperature at which the vapor pressure of the liquid becomes equal to the external atmospheric pressure

boiling point elevation

• __________ is the increase in the boiling point of a solution over that of a pure solvent.

• The boiling point of a solution of a nonvolatile solute is higher than that of the pure solvent, (solute lowers the vapor pressure of the solvent).

boiling point

• the phenomenon that the _______ of a liquid (a solvent) will be higher when another compound is added, meaning that a solution has a higher ______ than a pure solvent.

• This happens whenever a non-volatile solute, such as a salt, is added to a pure solvent, such as water.

• The _______ can be measured accurately using an ebullioscope.

ebullioscope

the boiling point can be measured accurately using ______.

Cottrell boiling point apparatus

In the _______, the vapor and the boiling solvent are pumped by the force of ebullition through a glass tube and sprayed over the thermometer bulb to obtain an invariant equilibrium temperature.

• determination of boiling point elevation

freezing point

• the phenomenon in which the _______ of a liquid (a solvent) is depressed when another compound is added, meaning that a solution has a lower _______ than a pure solvent.

• This happens whenever a non-volatile solute is added to a pure solvent, such as water.

freezing point

• The phenomenon may be observed in sea water, which due to its salt content remains liquid at temperatures below 0°C (32°F), the ________ of pure water.

• The triple point of air-free water, at which solid, liquid, and vapor are in equilibrium, lies at a pressure of 4.58 mm Hg and a temperature of 0.0098 °C.

4.58 mmHg and 0.0098°C

The triple point of air-free water, at which solid, liquid, and vapor are in equilibrium, lies at a pressure of _____ and a temperature of _____.

escaping tendency or vapor pressure

• If a solute is dissolved in the liquid at the triple point, the _____ or _____ of the liquid solvent is lowered below that of pure solid solvent.

• The temperature must drop in order to reestablish equilibrium between the liquid and the solid

freezing point depression

• ________ is the difference in the melting points of pure water and a solution.

• The freezing point of a solution is LOWER than that of the pure solvent

beckmann and the equilibrium method

Methods for the Determination of Freezing Point Lowering

1. B

2. E

beckmann method

• It consists of a jacketed tube with a sidearm through which the test material may be introduced. A _____ thermometer is supported in the tube and extends into the test solution.

• A glass stirrer passes through a tube in the stopper and is operated manually or by means of a motor.

• The tube and jacket are supported in a vessel containing mixture of salt and ice.

Beckmann method

• In carrying out a determination, the temperature is read on the _____ differential thermometer at the freezing point of the pure solvent, water.

• A known weight of the solute is introduced into the apparatus, containing a given weight of solvent, and the freezing point of the solution is read and recorded.

liso value

is determined by the ionization properties of the solute.

Nonelectrolytes

1.8

weak electrolyte

2.0

di-divalent (divalent cation and divalent anion)

2.0

uni-univalent electrolyte (single charge on each)

3.4

uni-divalent electrolyte

4.3

di-univalent electrolyte

4.8

osmotic pressure

• is the pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane.

• The phenomenon of _______ arises from the tendency of a pure solvent to move through a semipermeable membrane and into a solution containing a solute to which the membrane is impermeable.

• All aqueous solutions of non-volatile solutes exert an ______.

osmosis

• is the movement of solvent through a semi-permeable membrane that allows only solvent to move through it.

• always takes place in the direction of that will equalize

  the conc’n of all the components on both sides of the

  membrane

isoosmotic

When osmotic pressure is equal on both sides of the membrane, the system is _____. In biological fluids, this equilibration is termed isotonic.

osmotic potential

is the opposite of water potential, which is the degree to which a solvent tends to stay in a liquid.

osmotic pressure osmometer

it is based on the principle of thistle tube.

Van’t Hoff Equation

Van’t Hoff

He concluded that there was an apparent analogy between solutions and gases and that the osmotic pressure in a dilute solution was equal to the pressure that the solute would exert if it were a gas occupying volume.

• Corresponded to the equation for ideal gas.

• Morse Equation

  • ¶= RTm

osmoregulation

is the homeostasis mechanism of an organism to reach balance in osmotic pressure.

hypertonicity

is the presence of a solution that causes cells to shrink.

hypotonicity

is the presence of a solution that causes cells to swell.

isotonic

is the presence of a solution that produces no change in cell volume.

colligative properties of biological fluids