Ideal and Non-ideal solutions

 Ideal and Non-ideal solutions

Ideal solutions :What is an ideal solution in chemistry?

(In chemistry, an ideal solution or ideal mixture is a solution with thermodynamic properties analogous to those of a mixture of ideal gases. ... The vapor pressure of the solution obeys Raoult's law, and the activity coefficient of each component (which measures deviation from ideality) is equal to one)
An ideal solution is the solution in which each component obeys Raoult’s law under all conditions of temperatures and concentrations.

Properties of Ideal solutions :

ΔH_MIXING = 0

ΔV_MIXING = 0

Intermolecular attractive forces between the A-A and B-B are nearly equal to those between A-B. 
Eg. solution of benzene and toluene, solution of n-hexane and n-heptane

Non – ideal solutions :What is an Non- ideal solution in chemistry?

(A non-ideal solution is a solution whose properties are generally not very predictable on account of the intermolecular forces between the molecules. None.Non-ideal solutions by definition cannot be dealt with through Raoult's Law. Raoult's Law is strictly forideal solutions only. A non-ideal solution)
 When a solution does not obey Raoult’s law over the entire range of concentration, then it is called non-ideal solution.

Solutions showing positive deviation from Raoult’s Law :

Solvent-Solute(A-B) type of force is weaker than Solute-Solute (B-B) &  Solvent-Solvent(A-A) forces.

The vapour pressure is higher than predicted by the law

ΔH_MIXING > 0

ΔV_MIXING > 0

Eg. ethanol and acetone, carbon disulphide and acetone 

Solutions showing negative deviations from Raoult’s law :

1. Solvent-Solute(A-B) type of force is stronger than the other two.
2. The vapour pressure is lower than predicted by the law.
3. ΔH_MIXING < 0
4. ΔV_MIXING < 0

For example,phenol and aniline, chloroform and acetone etc 

What is meant by azeotropic mixture?

An azeotrope (UK /əˈziːəˌtrəʊp/, US /əˈziəˌtroʊp/) or a constant boiling pointmixture is a mixture of two or more liquids whose proportions cannot be altered or changed by simple distillation. This happens because when an azeotrope is boiled, the vapour has the same proportions of constituents as the unboiled mixture.

Raoult’s Law

 Vapour pressures of solutions of solids in liquids and Raoult’s Law

A law stating that the freezing and boiling points of an ideal solution are respectively depressed and elevated relative to that of the pure solvent by an amount proportional to the mole fraction of solute.

• a law stating that the vapour pressure of an ideal solution is proportional to the mole fraction of solvent.

(Raoult’s law for non volatile solutes)

Q-1 what happens when a non volatile solute is added to a solvent?

1.  If a non-volatile solute is added to a solvent to give a solution, the number of solvent molecules escaping from the surface is correspondingly reduced, thus, the vapour pressure is also reduced.

Q-2 Which factor effects the vapour pressure of solvent ?

1.  The decrease in the vapour pressure of solvent depends on the quantity of non-volatile solute present in the solution, irrespective of its nature.

Q-3 What does Raoult law in its general form can be stated?  

1.  Raoult’s law in its general form can be stated as, for any solution the partial vapour pressure of each volatile component in the solution is directly proportional to its mole fraction.

Q-4 How to Denote binary solution?

1.  In a binary solution, let us denote the solvent by 1 and solute by 2.

Q-5 What happens when the solute is non-volatile? 

1. When the solute is non-volatile, only the solvent molecules are present in vapour phase and contribute to vapour pressure.

Q-6 How to use  Raoult's law?

1.  Let p₁ be the vapour pressure of the solvent, x₁ be its mole fraction, p⁰₁ be its vapour pressure in the pure state. Then according to Raoult’s law
2. p₁ 𝞪 x₁ and p₁ = x₁  p⁰₁ = p_(total)

If a solution obeys Raoult’s law for all concentrations, 

its vapour pressure would vary linearly from zero to the vapour pressure of the pure solvent.

According to Raoults law, for any volatile component of the solution. Pa=P°a×Xa. Hence vapour pressure is directly proportional to the mole fraction of solute.

If gas is a solute and liquid is the solvent, then according to Henry law, Pa=KaXa. Hence partial pressure of volatile component is directly proportional to mole fractionof that component.

Hence both are identical with only different proportionality constant's.

1. Raoult's law  is a law of thermodynamics established by French chemist François-Marie Raoult in 1887. It states that the partial vapor pressure of each component of an ideal mixture of liquids is equal to the vapour pressure of the pure component multiplied by its mole fraction in the mixture.
2. Henry's law is one of the gas laws formulated by William Henry in 1803 and states: "At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid."
3. Henry's law is one of the gas laws, formulated by the British chemist, WilliamHenry, in 1803. It states that: At a constant temperature, the amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid

What is the relationship between Henry's law and Raoult's law?

Both are ideal vapor-liquid equilibrium relationships that hold for very dilute binary component mixtures.
  Henry's Law tends to approximate real behavior for the solute (i.e., lower concentration) at a very low concentration while Raoult's Law tends to approximate real behavior for the solvent in a dilute solution.
  They are both limit cases of an underlying binary vapor-liquid equilibrium relationship. 
 Unifying them basically requires that you replace the pressure terms with fugacity terms to accurately represent real gas behavior.

1. If you're familiar with chemical equilibria, it might be useful to think of the Henry's law 'constant' (not really a constant as it is dependent on temperature and ionic strength of the solution) as the equilibrium 'constant' of the reaction X(g) <-> X(aq), where X is the gas in question and is dissolving in water. (http://www.chemguide.co.uk/physi...) I.e. Henry' law constant is is the ratio of aqueous concentration to gas phase concentration of the gas AT EQUILIBRIUM.
2.  Any deviation from this, means the gas and liquid phases are not at equilibrium with respect to the particular gas and there will be a net transfer of gas molecules one way or another to move towards equilibrium (Le Chatelier's principle).
3.  Henry's law only holds for dilute solutions in single solvents (normally water).
4.  Henry's LAW basically says that the position of this equilibrium, i.e. the value of the equilibrium constant is always the same under the same conditions.
5. 
   
6. Raoult's law, as stated by one of the other answers, concerns the bulk components of a solution made up of different solvents, and their relative contributions to the total vapour pressure. In short, the total vapour pressure is the sum of the partial pressures:
7. 
   
8. vapour pressure of mixture = partial pressure of component A + partial pressure of component B +....
9. 
   
10. and each partial pressure is the product of the vapour pressure of a pure solution of the compound and the mole fraction of the compound in the solvent mixture (i.e. what proportion, by moles rather than mass, of the total mixture is made up of each particular compound):
11. 
    
12. partial pressure of A = vapour pressure of pure solution of A x mole fraction of A in mixture.
13. 
    
14. Both Henry's law and Raoult's make important assumptions about ideality of gases and solutions respectively.
15. 
    

Both laws can get into quite details and more complicated calculation, my answer just provide the base of both law. 

1. With a little more detail: 
2. Henry's law states that the solubility of a gas in a liquid is proportional to the pressure of the gas over the solution.
3. The equation is c = kP ,
4.  where c is the molar concentration in mol/L of the dissolved gas,
5.  P is the pressure (in atm) of the gas over the solution at equilibrium and k is a constant that depends only on temperature for a given gas.
6. Which means that when you want to mix a gas and a liquid,
7.  the amount of gas that will actually dissolve in the liquid is proportional to two things:
8.  the pressure of that gas at equilibrium over the solution and a constant k that changes depending on the gas and the temperature.
9.  By using the equation up there, you will find the molar concentration (mol/L) of the gas that will dissolve in the solution. 

On the other hand,

Raoult's law is used in a case where the solute (the smallest component of the solution) is non-volatile. The law considers that the vapor pressure of the whole solution will always be less than that of the pure solvent. Therefore, the vapor pressure of the solution will depends on the concentration of the solute. 

Raoult's law equation is P1 = X1 P1* (they are multiplied), where P1 is the vapor pressure of the solvent over the solution, X1 is the mole faction of the solvent in the solution and P1* is the vapor pressure of the pure solvent (if it was alone in the solution). 

Overall, the difference is that Henry's law takes care of what happen IN the solution when you have gas over it, while Raoult's law looks at what is happening OVER the solution when you mix a non-volatile solute to a solvent that has a known vapor pressure when it's pure (e.g. water). 
Henry's law will give you the molar concentration of a dissolved gas in the solution, Raoult's law will give you a vapor pressure over a solution after you mixed a solvent with a non-volatile solute. 
Hope it helped!

Raoult’s law explains partial vapour pressure of volatile component of the solution.

According to Raoult’s law,partial vapour pressure of volatile component is equal to product of vapour pressure of pure component and mole fraction of that component in the solution.

P =P⁰ X

Henry’s law explains the solubility of gas in liquid.

According to Henry’s law,pressure is directly proportional to the mole fraction of gas.

P = KH X

When KH and P⁰ are same ,then Raoult’s law becomes special case of Henry’s law. This happens in case of few ideal solutions of gas in liquid.

On the other hand,

1. Raoult's  law is used in a case where the solute (the smallest component of the  solution) is non-volatile.
2. The law considers that the vapor pressure of  the whole solution will always be less than that of the pure solvent.
3. Therefore, the vapor pressure of the solution will depends on the  concentration of the solute. 
4. 
   
5. Raoult's law equation is P1 = X1  P1* (they are multiplied),
6.  where P1 is the vapor pressure of the solvent  over the solution,
7.  X1 is the mole faction of the solvent in the  solution
8.   P1* is the vapor pressure of the pure solvent (if it was  alone in the solution). 
9. 
   
10. Overall, the difference is that Henry's  law takes care of what happen IN the solution when you have gas over it, 
11.  while Raoult's law looks at what is happening OVER the solution when  you mix a non-volatile solute to a solvent that has a known vapor  pressure when it's pure (e.g. water). 
12. Henry's law will give you the  molar concentration of a dissolved gas in the solution,
13.  Raoult's law  will give you a vapor pressure over a solution after you mixed a solvent  with a non-volatile solute. 

VAPOUR PRESSURE

 VAPOUR PRESSURE 
(the pressure of a vapour in contact with its liquid or solid form.)

Properties of solution affected by vapour pressure

• Vapour pressure of solution decreases on addition of a non-volatile solute to a volatile solvent.
• Properties of solutions affected by the decrease of vapour pressure includes-

1. Relative lowering of vapour pressure of the solvent
2. Depression of freezing point of the solvent
3. Elevation of boiling point of the solvent and
4. Osmotic pressure of the solution.

• These properties of solution depend on the number of solute particles present in the solution regardless of their nature relative to the total number of particles present in the solution. These properties are termed as colligative properties derived from a Latin word with co meaning together ligare meaning to bind

Definition

Vapour pressure of a liquid/solution is the pressure exerted by the vapours in equilibrium with the liquid/solution at a particular temperature. 

Vapour pressure ∝ escaping tendency

 Vapour pressure of liquid solutions and Raoult’s Law :

(Raoult’s law for volatile solutes)

 Raoult’s law states that for a solution of volatile liquids, the partial vapour pressure of each component in the solution is ∝ to its mole fraction.

Consider a solution containing two volatile components 1and 2 with mole fractions x₁ and x₂ respectively. 

Suppose SOLUTIONS & COLLIGATIVE PROPERTIES at a particular temperature,

their partial vapour pressures are p₁ and p₂ and the vapour pressure in pure state are  p⁰₁ and  p⁰₂.

Thus, according to Raoult’s Law, for component 1 

1. The plot of vapour pressure and mole fraction of an ideal solution at constant temperature. 
2. The dashed line I and II represent the partial pressure of the components.
3.  It can be seen from the plot that p1 and p2 are directly proportional to x1 and x2 , respectively.
4.  The total vapour pressure is given by line marked III in the figure.
5.  Mole fraction in vapour phase If y 1 and y 2 are the mole fractions of the components 1 and 2 respectively in the vapour phase then, using Dalton’s law of partial pressures: 
6. p1 = y 1 ptotal p2 = y 2 ptotal 
7. In general pi = y i ptotal

All liquids exhibit tendency for evaporation.

Evaporation takes place at the surface of liquid. If the kinetic energy of liquid molecules overcomes the intermolecular force of attraction in the liquid state then the molecules from the surface of liquid escape into space above surface. The process is called 'evaporation'. If evaporation is carried out in a closed container system then the vapours of liquid remains in contact with surface of liquid. Like gas molecules vapour of molecules also execute continuous random motion. During this motions, molecules collide with each other and also with the walls of the container, losses their energy and returns back to liquid state. This process is called as 'condensation'.
Evaporation and condensation are continues processes. Hence, after some time an equilibrium is established, at constant temperature between evaporation and condensation. At equilibrium number of molecules in vapour state remains constant at constant temperature.
"The pressure exerted by vapours of liquid on the surface of liquid when equilibrium is established between liquid and it's vapour is called VAPOUR PRESSURE of liquid."
    The vapour pressure of the liquid depends on the nature of the liquid and temperature. With increase of intermolecular force of attraction vapour pressure of liquid decrease and with rise of temperature vapour pressure of liquid increases.
  Mercury manometer may be used to determine vapour pressure of liquid.

Vapour pressure is a liquid property related to evaporation. In the liquid (or any substance) the molecules have a distribution of kinetic energies related to the temperature of the system. Because this is a distribution there will always be a few molecules that have enough kinetic energy to over come the attractive potential energy of the other molecules (the intermolecular force), and escape the liquid into the gas phase. In an open container, these molecules will wander off (diffuse) into the room and out into the atmosphere. Eventually all the liquid will evaporate.

For example-

Ice melts to form water, and water evaporates to form water vapor.The pressureexerted by the water vapor is the vapor pressure. In more general terms, vapor pressure is the pressure exerted by a gas in equilibrium with the same material in liquid or solid form.

Vapor pressure or equilibrium vapor pressure is defined as thepressureexerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. The equilibrium vapor pressure is an indication of a liquid's evaporation rate.

Vapour pressure is the pressure applied by the vapours on liquids and it has different values for different liquids, even in different conditions.

Solution Important Points

1. A solution is a homogeneous mixture of two or more substances.
2. Solutions are classified as solid, liquid and gaseous solutions.
3. The component that is having more number of moles is known as solvent.
4. Solvent determines the physical state of the solution.
5. Water is an universal solvent.
6. The concentration of a solution is expressed in terms of
- mole fraction,
- molarity,
- molality and
- in percentages.
7. Mole fraction (X) is a unitless quantity.
8. Molality (m) and mole fraction are temperature independent quantities whereas
SOLUTIONS - IMPORTANT POINTS




molarity decreases with increase in temperature.
9. The dissolution of a gas in a liquid is governed by Henry’s law, according to which, at
a given temperature, the solubility of a gas in a liquid is directly proportional to the partial
pressure of the gas.
10. As the temperature increases Henry’s law constant, KH increases so the lower is the
solubility of the gas in the liquid.
11. 11.7% w/w Helium is added to air used by scuba divers due to its low solubility in the
blood.
12. The vapour pressure of the solvent is lowered by the presence of a non-volatile
solute in the solution and this lowering of vapour pressure of the solvent is governed by
Raoult’s law.
13. According to Raoult’s law, the relative lowering of vapour pressure of the solvent over
a solution is equal to the mole fraction of a non-volatile solute present in the solution.
14. However, in a binary liquid solution, if both the components of the solution are volatile
then another form of Raoult’s law is used. Mathematically, this form of the Raoult’s law is
stated as:
p(total) = p⁰₁x₁ + p⁰₂x₂
15. Raoult’s law becomes a special case of Henry’s law in which KH becomes equal to
PA⁰ , i.e., vapour pressure of pure solvent.
16. Solutions which obey Raoult’s law over the entire range of concentration are called
ideal solutions.
17. Two types of deviations from Raoult’s law, called positive and negative deviations are
observed. Azeotropes arise due to very large deviations from Raoult’s law.
18. Azeotropes having the same composition in liquid and vapour phase and boil at a
constant temperature and therefore can’t be distilled.
19. Maximum boiling azeotropes form when solutions exhibit negative deviation from
Raoult’s law whereas minimum boiling azeotropes form when solutions exhibit positive
deviation from Raoult’s law.
20. The properties of solutions which depend on the number of solute particles and are
independent of their chemical identity are called colligative properties.
21. These are lowering of vapour pressure, elevation of boiling point, depression of
freezing point and osmotic pressure. The process of osmosis can be reversed if a
pressure higher than the osmotic pressure is applied to the solution.
22. Colligative properties have been used to determine the molar mass of solutes.
Solutes which dissociate in solution exhibit molar mass lower than the actual molar mass
and those which
associate show higher molar mass than their actual values.
23. Quantitatively, the extent to which a solute is dissociated or associated can be
expressed by Van’t Hoff factor i. Van’t Hoff factor (i) is the ratio of the observed value of
the colligative property in solution to the theoretically calculated value of the colligative
property.
(a) A non-volatile solute undergoes dissociation, then i > 1.
(b) A non-volatile solute undergoes association, then i < 1.

Strength of Solutions

1. Strength of Solutions

The amount of solute dissolved per unit solution or solvent is called Strength of solution. There are various methods of measuring strength of a solution. :

1. Mass Percentage (%w/w):
“It represents mass of a component present in 100 g of solution”

Mass% of a component = Mass of the component in the sol. *100/Total Mass of sol


2. Volume percentage (%v/v): 

“It represents volume of a component in 100 mL of solution” 

 Vol. % of a component = Vol. of component ×100 /Total vol. of solution

3. Mass by volume percentage (%w/v): 

“It represents mass of solute in grams present in 100 mL of solution” 

Mass by vol. percent = Mass of solute in gram *100/Vol. of sol.in ml  

4. Parts per Million (ppm): 

"Concentration in parts per million can be expressed as mass to mass, volume to volume and mass to volume."

Parts per Million = (No. of parts of the component/Total no. of all the components of sol.)*10⁶ 

5. Mole Fraction (x) :
“It represents the moles of a solute present in one mole of solution”

Mole fraction=No. of moles of the component/Total no. of moles all the components 

For example, in a binary mixture, if the number of moles of A and B are n_A and n_B respectively, the mole fraction of A will be

x_A =n_{A/nA + nB}

6. Molarity, M:
 “It represents moles of solute present in 1 L of solution”

 Molarity, M = Moles of solute / Vol. of sol. in L

Units of Molarity are mol/L also represented by ‘M’ or ‘Molar’. 

“Density of a solution = mass of the solution per unit volume”

  Density, d = m / V 

7. Molality, m:
“It represents moles of solute present per kg of solvent”

Molality, m = Moles of solute/Mass of solvent in kg

Units of molality are mol/kg which is also represented by ‘m’ or ‘molal’

8. Normality, N

It represents no. of equivalents of solute present in 1 L of solution.

Normality, N = No. of Equivalents of solute/Vol. of sol. in L

No. of equivalents, eq = Weight/Equivalent weight (W / E)


E=M/z(z is the valency factor)

SOME IMPORTANT RELATIONSHIPS

Dilution Law

If a solution is diluted by adding solvent to it, then the amount of solute remains constant and we can write:

M₁V₁ = M₂V₂ and N₁V₁ = N₂V₂


Molarity and Normality 

Normality = z × Molarity]


IMPORTANT : 

Mass %, ppm, mole fraction and molality are independent of temperature, whereas molarity & normality are a function of temperature. This is because volume depends on temperature and the mass does not.

Classification Solutions

 Classification of Solution

1.  Solutions which contain two components in it are called Binary Solutions. 
2. Substances which are used to prepare a solution are called as Components.
3.  The component that is present in the largest quantity is known as Solvent.
4.  Solvent determines the physical state in which solution exists.
5.  The other component present in lesser quantity in the solution is termed as Solute.
6.  Each component may be solid, liquid or in gaseous state.

Table on Types of Solutions

SOLUTIONS & COLLIGATIVE PROPERTIES

A solution is a homogeneous mixture of two or more than two components

Q 1- In normal life we rarely come across which type substance?

1. In normal life we rarely come across pure substances. 

Q-2 What do mixture contains?

1. Most of these are mixtures containing two or more pure substances.

Q-3 Their importance in life depends on what ?

1. Their utility or importance in life depends on their composition. 
2. The air around us is a mixture of gases primarily oxygen and nitrogen; 
3. the water we drink contains very small amounts of various salts dissolved in it. 
4. Our blood is a mixture of different components. 
5. Alloys such as brass, bronze, stainless steel, etc. are also mixtures. 
6.  we will consider mostly liquid solutions and their properties.