Colligative properties of solutions

Сентябрь 8, 2022

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Colligative properties of solutions

Содержание

2. QUIZ ME NEXT 1 What is it a true solution? a pure substances in water compounds
3. QUIZ ME NEXT 2 The amount of a solute dissolved in a given amount of solvent
4. QUIZ ME 3 What is the molar concentration of solution? the number of equivalent-moles of solute
5. QUIZ ME 4 What is the molality of solution? the number of equivalent-moles of solute per
6. Nature of Solute Non-electrolytic are substances that do not form ions and do not conduct electricity
7. SOLUTION OF Electrolyte – solution that conducts electricity ionic compounds in polar solvents dissociate (break apart)
8. COLLIGATIVE PROPERTIES Colligative properties are the set of properties that depend only on the concentration of
9. 1) Vapor Pressure Lowering (1st Raoult’s Law) Related to boiling point 2) Freezing Point Depression Salt
10. The vapor pressure of water (P0) is the pressure at which water vapor is in thermodynamic
11. Vapor pressure depends on various factors: the nature of the liquid, the presence of dissolved substances
12. VAPOR PRESSURE LOWERING Pure water Aqueous solution of nonvolatile solute >
13. As solute molecules are added to a solution, the solvent become less volatile (=decreased vapor pressure).
14. The extent to which a nonvolatile solute lowers the vapor pressure is proportional to its concentration.
15. The temperature at which vapor pressure is equal to the atmospheric pressure (p0= pаtm) is called
16. The 2nd Raoult’s Law One consequence of Raoult's law is that the boiling point of a
17. ebulioscopic constant of solvent The boiling temperature of non-electrolytes solution ebulioscopic method
18. where Esvt is boiling point elevation constant, equivalent to 0.52°C/m for aqueous solutions. This means that,
19. krioscopic constant of solvent The freezing temperature of non-electrolytes solution krioscopic method
20. where Ksvt is the freezing point depression constant equivalent to -1,86°C/m for aqueous solutions. Again, for
21. Some common values for Kfreez and Eboil respectively, are:
22. In 1784, the French physicist Jean Antoine Nollet discovered that a pig's bladder filled with a
23. Jean-Antoine Nollet first documented observation of osmosis in 1748. During osmosis pure solvent diffuses through a
24. Net transfer of solvent molecules into the solution until the hydrostatic pressure equalizes the solvent flow
25. Osmotic Pressure h
26. (a) A dilute solution of glucose in water is placed in the right arm of a
27. The osmotic pressure of a solution is the pressure required to stop osmosis. The osmotic pressure
28. Molarirty units are most appropriate in calculating which of the following? QUIZ ME A) freezingpoint depression
29. Types of Solutions Based on Solute Concentration… Hypotonic (lower solute concentration) to the solution Hypertonic (higher
30. Non-electrolyte: 1 М sugar solution Electrolyte: 1 М NaCl salt solution where i is the Van’t
31. The degree of dissociation is associated with an isotonic factor by next ratio: For Electrolyte Solution:
32. If equal numbers of moles of each of the following are dissolved in 1 kg of
33. SUMMARY OF FACTS AND CONCEPTS 1. Colligative properties (or collective properties) are properties that depend only
34. 7. In electrolyte solutions, the interaction between ions leads to the formation of ion pairs. The
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QUIZ ME
NEXT
1 What is it a true solution?
a pure substances in

water

compounds in water

a heterogeneous mixture

a homogeneous mixture

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QUIZ ME
NEXT
2 The amount of a solute dissolved in a given

amount of solvent is represented by the …

Volume of the solution

Mass of the solute

Mass of the solution

Concentration of the solute

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QUIZ ME
3 What is the molar concentration of solution?
the number of

equivalent-moles of solute per 1 liter of solution

the gram of a solute per 1 milliliter of solution

the number of moles of solute per 1 kilogram of solvent

the number of moles of solute per 1 liter of solution

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QUIZ ME
4 What is the molality of solution?
the number of equivalent-moles

of solute per 1 liter of solution

the gram of a solute per 1 milliliter of solution

the number of moles of solute per 1 kilogram of solvent

the number of moles of solute per 1 liter of solution

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Nature of Solute
Non-electrolytic are substances that do not form ions and

do not conduct electricity when placed in water.

An electrolyte is a substance that, when dissolved in water form ions, as results a solution can conduct electricity:
NaCl => Na+ + Cl-
cation anion

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SOLUTION OF
Electrolyte – solution that conducts electricity
ionic compounds in polar

solvents dissociate (break apart) in solution to make ions
may be strong (100% dissociation) or weak (less than 100%)
Strong Electrolyte – all or almost all of compound dissociates; example: strong acids (H2SO4, HNO3, HClO4, HCl, HBr, HI)
Weak Electrolyte – small amount of compound dissociates; example – weak acids (HF, CH3COOH, H3PO4)

Nonelectrolyte – solution that does not conduct electricity
solute is dispersed but does not dissociate
Example: sugar (dissolves but does not dissociate), organic acids (contain carboxyl groups)

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COLLIGATIVE PROPERTIES
Colligative properties are the set of properties that depend only

on the concentration of solute particles (ions or molecules) in the solution and not the type.

In other words, it doesn’t matter if it is salt, sugar, gasoline, or tennis balls – it will behave the same way!

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1) Vapor Pressure Lowering (1st Raoult’s Law)
Related to boiling point
2) Freezing

Point Depression
Salt on the road
Anti-freeze in your radiator
And Boiling Point Elevation (2nd Raoult’s Law)
Anti-freeze in your radiator
3) Osmotic Pressure (Van’t Hoff’s Law)
Membrane diffusion
The Great Sugar Fountain

COLLIGATIVE PROPERTIES:

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The vapor pressure of water (P0) is the pressure at which water vapor is in thermodynamic

equilibrium with its condensed state.

When ↑t , ↑p0 H2O:
00C – 4,6 mm Hg
200C – 17,4 mm Hg
1000C – 760 mm Hg

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Vapor pressure depends on various factors:
the nature of the liquid,

the presence of dissolved substances in the liquid or solid.
According to Raoult's law, the vapor pressure of a pure liquid or solid is lowered by the addition of a solute.

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VAPOR PRESSURE LOWERING
Pure water
Aqueous solution of
nonvolatile solute
>

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As solute molecules are added to a solution, the solvent become

less volatile (=decreased vapor pressure).
Solute-solvent interactions contribute to this effect.

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The extent to which a nonvolatile solute lowers the vapor pressure

is proportional to its concentration. This was discovered by French chemist Francois Raoult (1830-1907).
1st Raoult’s law states that for non-electrolyte solutions, the partial vapor pressure of a solvent over a solution (P1) is equal to the vapor pressure of the pure solvent (P0) multiplied by the mole fraction of the solute (X2). This law is mathematically expressed as:

the number of dissolving solute moles

the number of solvent mole

the mole fraction

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The temperature at which vapor pressure is equal to the atmospheric

pressure (p0= pаtm) is called boiling point
The temperature at which vapor pressure of solvent in its liquid and solid phase become equal is called freezing point
at 00C water is freezing,
and at 1000C water is boiling

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The 2nd Raoult’s Law
One consequence of Raoult's law is that the

boiling point of a solution made of a liquid solvent with a nonvolatile solute is greater than the boiling point of the pure solvent. The boiling point of a liquid or is defined as the temperature at which the vapor pressure of that liquid equals the atmospheric pressure. For a solution, the vapor pressure of the solvent is lower at any given temperature. This pattern applies to the freezing point of the solution. Therefore, a higher temperature is required to boil the solution and a low temperature – to freeze the solution than the pure solvent.

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ebulioscopic constant of solvent
The boiling temperature of non-electrolytes solution
ebulioscopic method

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where Esvt is boiling point elevation constant, equivalent to 0.52°C/m for

aqueous solutions.
This means that, for example, 1 mole of sugar (non-electrolyte) in 1 kilogram of water will increase the boiling point from 100°C to 100,52°C. And Cm is the molal concentration of solute.
It is also important to note that Δtboil is a positive quantity and should be added to the boiling point of pure solvent (water), which is 100°C.

The change in boiling point is proportional to the molality of the solution:

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krioscopic constant of solvent
The freezing temperature of non-electrolytes solution
krioscopic
method

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where Ksvt is the freezing point depression constant equivalent to -1,86°C/m

for aqueous solutions.
Again, for example, 1 mole of sugar (non-electrolyte) in 1 kilogram of water will decrease the freezing point from 0°C to -1,86°C.
And since we have already established that the freezing point of the solution is less than that of the pure solvent, then Δtfreez is a negative quantity and should be subtracted from the freezing point of pure solvent (water), which is 0°C.

The change in freezing point can be found similarly:

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Some common values for Kfreez and Eboil respectively, are:

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In 1784, the French physicist Jean Antoine Nollet discovered that a

pig's bladder filled with a concentrated solution of alcohol in water expanded when it was immersed in water. The bladder acted as a semipermeable membrane, which allowed water molecules to enter the solution, but kept alcohol molecules from moving in the other direction. Movement of one component of a solution through a membrane to dilute the solution is called osmosis, and the pressure this produces is called the osmotic pressure (π).
Osmotic pressure can be demonstrated with the apparatus shown in the figure below. A semipermeable membrane is tied across the open end of a thistle tube. The tube is then partially filled with a solution of sugar or alcohol in water and immersed in a beaker of water. Water will flow into the tube until the pressure on the column of water due to the force of gravity balances the osmotic pressure driving water through the membrane.

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Jean-Antoine Nollet first documented observation of osmosis in 1748.
During osmosis pure solvent

diffuses through a membrane but solutes do not.
Osmosis is defined as the flow of water/solvent molecules through a semipermeable membrane from a region of low to high solute concentration, until equilib-
rium is established.

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Net transfer of solvent molecules into the solution until the hydrostatic

pressure equalizes the solvent flow in both directions.
Because the liquid level for the solution is higher, there is greater hydrostatic pressure on the solution than on the pure solvent .
Osmotic Pressure:
The excess hydrostatic pressure on the solution compared to the pure solvent.

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Osmotic Pressure
h

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(a) A dilute solution of glucose in water is placed in

the right arm of a U-tube, and the left arm is filled to the same height with pure water; a semipermeable membrane separates the two arms. Because the flow of pure solvent through the membrane from left to right (from pure water to the solution) is greater than the flow of solvent in the reverse direction, the level of liquid in the right tube rises. (b) At equilibrium, the pressure differential, equal to the osmotic pressure of the solution (Πsoln), equalizes the flow rate of solvent in both directions. (c) Applying an external pressure equal to the osmotic pressure of the original glucose solution to the liquid in the right arm reverses the flow of solvent and restores the original situation.

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The osmotic pressure of a solution is the pressure required to

stop osmosis. The osmotic pressure of the solution is given by:

where CM is the molarity of solution, R the gas constant (0.0821 L . atm / K . mol), and T the absolute temperature (in Kelvins).
The osmotic pressure is expressed in atm.

Van’t Hoff’s equation

Mendeleev Clapeyron equation

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Molarirty units are most appropriate in calculating which of the following?
QUIZ

A) freezingpoint depression
B) vapor pressure
C) boilingpoint evaluation

D) osmotic pressure

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Types of Solutions Based on Solute Concentration…
Hypotonic (lower solute concentration) to

the solution
Hypertonic (higher solute concentration) to the solution
Isotonic solutions are equal in their solute concentrations. We say that they are isotonic to each other.

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Non-electrolyte:
1 М sugar solution
Electrolyte:
1 М NaCl salt solution
where i is

the Van’t Hoff factor, named after Jacobus Henricus Vant’ Hoff (1852-1911), who won the very first Nobel Prize in chemistry in 1901 for his work on colligative properties of solution.
The i factor gives the number of particles per formula unit of the solute.

Na+

Cl-

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The degree of dissociation is associated with an isotonic factor by

next ratio:

For Electrolyte Solution:

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If equal numbers of moles of each of the following are

dissolved in 1 kg of distilled water, the one with the lowest boiling point will be:
NaI
B) AlCl3
C) Mg(NO3)2
D) CH3COOH
E) C6H12O6

QUIZ ME

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SUMMARY OF FACTS AND CONCEPTS
1. Colligative properties (or collective properties) are

properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.
2. The four colligative properties of a solution are vapor pressure, osmotic pressure, boiling point and freezing point.
3. The change in vapor pressure where the solute is less volatile than the solvent is regulated by Raoult’s law, which states that the vapor pressure of a solvent over a solution is equal to the mole fraction of the solvent times the vapor pressure of pure solvent.
4. The osmotic pressure of a solution is the pressure required to stop osmosis.
5. The freezing point of the solution is always less than the freezing point of the pure solvent.

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7. In electrolyte solutions, the interaction between ions leads to the

formation of ion pairs. The Van’t Hoff factor (i) provides a measure of the extent of dissociation of electrolytes in solution.
8. Solutions can be classified as hypertonic, hypotonic or isotonic depending on the concentration of solute inside and outside the cell.
9. A hypertonic solution has a higher concentration of particle than the cell causing the cell to shrink.
10. A hypotonic solution has a lower concentration of particles than the cell causing the cell to swell.
11. An isotonic solution has the same osmotic strength on both sides of the semipermeable membrane.
12. Osmosis is the spontaneous net movement of solvent molecules through a semi-permeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides.

Colligative properties of solutions

Содержание

QUIZ MENEXT1 What is it a true solution?a pure substances in

QUIZ MENEXT2 The amount of a solute dissolved in a given

QUIZ ME3 What is the molar concentration of solution?the number of

QUIZ ME4 What is the molality of solution?the number of equivalent-moles

Nature of SoluteNon-electrolytic are substances that do not form ions and

SOLUTION OF Electrolyte – solution that conducts electricityionic compounds in polar

COLLIGATIVE PROPERTIES Colligative properties are the set of properties that depend only

1) Vapor Pressure Lowering (1st Raoult’s Law)Related to boiling point2) Freezing