SOLUBILITY

ETHERS

LEARNING OBJECTIVES

1.Solubility

2.Solubility of Liquid solutions: I.Solids in liquid II. Gases in liquid

3.Factors which effect the solubility

4.Henry’s law and applications

5.Numericals on Henry’s law

SOLUBILITY • Solubility of a substance is its maximum

amount that can be dissolved in a specified amount of solvent at a specified temperature to form the saturated solution. This process is also known as dissolution. In fact solubility also one of the method to express concentration

.

SOLUBILITY OF LIQUID SOLUTIONS

•

• I. Solubility of a Solid in a Liquid

•II. Solubility of a Gas in a Liquid

I. Solubility of a Solid in a Liquid The solubility of a solid in a liquid at any temperature is defined as the maximum amount of the solid(solute) in grams which can dissove in 100g of the liquid (solvent) to form the saturated solution at that particular temperature.

. At saturated condition there exist dynamic equilibrium between dissolution and crystallization(opposite to dissolution)

Solute + Solvent ↔ Solution

Factors affecting the solubility of a solid in a liquid (i)Nature of the solute and the solvent (ii) Temperature

(i)Nature of the solute and the solvent In general, a solid dissolves in a liquid which is chemically similar to it. This is expressed by saying “LIKE DISSOLVES LIKE” i.e polar solutes dissolves in polar solvent like water, where as non-polar solutes dissolves in non-polar solvent like carbon tetrachloride

POLAR/POLAR Ex:- Sodium chloride(polar) dissolve readily in

water(polar),Naphthalene(non- polar) dissolve in carbon tetrachloride(non-polar),But Sodium chloride(polar) does not dissolve in carbon

tetrachloride(non-polar),Naphthalene(non- polar)

does not dissolve in water(polar)

NON-POLAR/POLAR

Q. “Genarally organic compounds are non-polar, but some of organic compounds like ethanol, glucose are soluble in water(polar solvent)”Give reason. Ans. Organic compounds form intermolecular hydrogen bonding with water, that is why they are soluble in water, because certain part of the organic compound possesses polarity

(ii) Temperature Most of the cases with rise in temperature solubility increases In general, if in a nearly saturated solution, the dissolution process is endothermic (DsolH > 0), the solubility should increase with rise in temperature and if it is exothermic (DsolH < 0) the solubility should decrease. These trends are also observed experimentally.

Examples(effect of temperature)

II. Solubility of a Gas in a Liquid

The solubility of any gas in a particular liquid is the volume of the gas in cc’s(converted to S.T.P) that can dissolve in unit volume(1CC) of the liquid to form the saturated solution. Factors affecting the solubility of a gas in a liquid

(i)Nature of the gas and the solvent (ii)Temperature (iii)Pressure(Henry’s law)

(i)Nature of the gas and the solvent SOLUBILITY OF A GAS IN LIQUID ALSO

BASED ON CHEMICALLY SIMILARITY

BETWEEN THE GAS AND THE SOLVENT

Ex:-Gases like hydrogen, oxygen, nitrogen. etc., dissolve in water only to a small extent whereas gases like CO2,HCl,NH3. etc.,are highly soluble. The greater solubility of the latter gases is due to their reaction with the solvent

(ii)Temperature The solubility of a gas decreases with increase in temperature as escaping tendency of gas increases

(iii)Pressure(Henry’s law)

On increasing the pressure of the gas above the solution, the solubility increases This can be understood by Henry’s law Henry’s law: “The partial pressure of the gas in vapour phase (p) is proportional to the mole fraction of the gas (x) in the solution”

p = KH x Here KH is the Henry’s law constant.

More gas is soluble as pressure is high

Less gas is soluble as pressure is low

Graphical representation of Henry’s law and Significance of Henry’s law constant

In Henry’s law equation (p = KH x) partial pressure is

directly proportional to mole fraction of the gas and

which follows y=mx form and goes through origin

Higher the value of KH at a given pressure, the lower is the olubility(x)of the gas in the liquid(i.e. KH and x are inversely proportional KH = p/ x)

Why water bodies find difficult to survive during summer?

Which law governs assimilation of oxygen in blood and in turn into tissues?

?

Numericals Intext Questions 2.6. H2S, a toxic gas with rotten egg like smell, is used for the qualitative analysis. If the solubility of H2S in water at STP is 0.195 m, calculate Henry’s law constant. Ans. Here the solubility of H2S gas is mentioned as 0.195m

i.e 0.195 moles of H2S is present in 1kg of the solvent(water)

No.of moles of water=mass of water/molar mass of water =1000/18 =55.55

Hence Mole fraction H2S gas in the solution(x)=No.of moles of H2S (No. of moles of H2S +No. of moles of water)

=0.195/(0.195+55.55) =0.0035

Pressure value given at STP is 0.987bar From Henry’s law KH=P H2S /X H2S

=0.987/0.0035=282bar

2.7 Henry’s law constant for CO2 in water is 1.67x108 Pa at 298 K. Calculate the quantity of CO2 in 500 mL of soda water when packed under 2.5 atm CO2 pressure at 298 K. Ans. Here KH= 1.67x108 Pa , p CO2 = 2.5 atm mass of CO2 = ?

From Henry’s law X CO2 =p CO2 / KH

No.of moles of CO2 = p CO2 / KH

No. of moles of CO2+ No.of moles of H2O No.of moles of CO2 = p CO2 / KH

No.of moles of H2O

(No.of moles of CO2 neglected as compared to No. of moles of water)

=2.5X101325Pa/ 1.67x108 Pa =1.517X10-3

No. of moles of H2O=500mL=500g=500/18=27.78moles

No.of moles of CO2 = 1.517X10-3 X 27.78 =42.14 X 10-3 mol

mass of CO2 = 42.14 X 10-3 mol molar mass of CO2

mass of CO2= 42.14 X 10-3 mol X molar mass of CO2

= 42.14 X 10-3 mol X44g/mol =1.854g

HOME WORK Solve the following exercise questions based

on the above topic

10. What role does the molecular interaction play in a solution of alcohol and water?

11.Why do gases always tend to be less soluble in liquids as the temperature is raised?

12. State Henry’s law and mention some important applications.

13.The partial pressure of ethane over a solution containing 6.56 × 10–3 g of ethane is 1 bar. If the solution contains 5.00 × 10–2 g of ethane, then what shall be the partial pressure of the gas?

Thank you Thank you