Saumil S. Sharma B.Sc. (Biochemistry), MBA

GSEB Standard 12 Science StreamSemester – 3 Chemistry

Part – 1

The classification of matter

What are Solutions?

• When two or more than two substances mix and form a uniform or homogeneous mixtures, such a mixture is called solution.

• By homogenous mixture we mean that its composition and properties are uniform throughout the mixture.

• Generally, the component that is present in the largest quantity is known as solvent. Solvent determines the physical state in which solution exists. One or more components present in the solution other than solvent are called solutes.

What are Solutions?

• In a homogeneous mixture the diameter of the molecular particle is 10-9 meter.

• In a homogeneous mixture the different components can be separated by physical methods like filtration, sedimentation, boiling or centrifugation etc.

• Solution is formed when solute and solvent molecules experience attractive interaction between them. For example, there is a strong attractive interaction between molecules of ethanol and water, therefore ethanol is soluble in water and forms a solution. But there is negligible attraction between the molecules of benzene and water, therefore benzene remains insoluble in water and no solution is formed.

Types of Solutions• The solutions can be found in three states; Solid, Liquid

and Gas. The solute and solvent can also be in three states. The physical state of the resulting solution can be decided on the basis of the physical states of solvent and solute.

Characteristics of Solutions

• Solution can be formed if the solute or solvent has the following characteristicsi. If the number of –OH groups in organic compound is more

in a solute, it is more soluble in water. More is the number of –OH groups, more is the solubility. For example Glycerol is more soluble in water than Ethanol.

ii. Most of the polar solutes dissolves in polar solvents. e.g. HCl in water.

iii. Most of the non-polar solutes dissolves in non-polar solvents. e.g. Naphthalene in benzene

iv. Most of the ionic solutes are soluble in water because they are ionic even in solid state. e.g. NaCl in water.

Characteristics of Solutions

• If water is solvent in the solution, the solution is known as an aqueous solution. (Aqua means water)

• If the water is not the solvent, the solution is known as non-aqueous solution.

• In a non-aqueous solution, generally benzene, ether, carbon tetrachloride etc. are used as non-aqueous solvents.

Units of Concentration

• Composition of a solution can be described by expressing its concentration. The quantitative proportion of solute and solvent are different in different solutions.

• The amount (quantity) of solute in unit volume of solution or unit weight of solvent is called concentration of solution.

• There are different ways to express concentrations of solutions. Normality, Molarity, Formality, Molality, Mole fraction, Weight fraction (% W/W) etc. are some units of concentration.

Formality

• Ionic compounds are in ionic form even in solid state and not in molecular form. Hence formula mass is taken instead of molecular mass and the concentration is known as formality.

• The sum of atomic masses of the atom, in the proportion formula of the compound is called its formula mass. e.g. compounds like potash alum, the molecular formula is K2SO4.Al2(SO4)3.24H2O hence it’s molecular mass will be 948 grams.mole-1. The proportion formula of alum is KAl(SO4)2.12H2O so the value of its proportion formula mass is 474 gram formula mass.

Formality

• At normal temperature, if one gram formula mass of the solute is dissolved in one liter of solution, it is called one formal solution and it’s formality is one. This type of concentration is called formality. It is indicated by the symbol F.

Formality

Volume percentage (% V/V)

• The volume (ml) of solute dissolved in 100 ml of solution is expressed as Volume percentage (% V/V). Such solution is called percent, proportion with reference to the volume of solute.

• For example, 10% ethanol solution in water means that 10 mL of ethanol is dissolved in water such that the total volume of the solution is 100 mL. Solutions containing liquids are commonly expressed in this unit. For example, a 35% (v/v) solution of ethylene glycol, an antifreeze, is used in cars for cooling the engine.

Volume percentage (% V/V)

Mass by Volume percentage (% W/V)

• The mass of solute dissolved in 100 mL of solution is called mass by Volume percentage (% W/V). Such solution is called percent mass, proportion with reference to the mass of solute.

• For example, 5% W/V aqueous solution of sugar means 5 grams of sugar is dissolved in 100 mL of solution.

• This unit of concentration is commonly used in fields of medicine and pharmacy.

Mass by Volume percentage (% W/V)

Parts per million (p.p.m.)

• Sometimes the amount of solute present in the solution is in very less (trace) quantities. In such conditions, the concentration is expressed as Parts per million (ppm).

• For example, the amount of oxygen dissolved in sea water, amount of pollutants in air and water etc. are expressed using this unit.

• Parts per million can be expressed in three different ways, parts per million mass to mass, parts per million mass to volume and parts per million volume to volume.

Parts per million mass to volume

• Parts per million mass to volume is the amount in milligrams of solute dissolved in one liter of solution.

• So the unit of Parts per million mass to volume can be written as mg liter-1 and also as microgram mL-1.

• Now if we express the amount of solute in grams and volume of solution in mL then;

Parts per million mass to volume

Molarity

• Molarity: Molarity (M) is defined as number of moles of solute dissolved in one litre (or one cubic decimetre) of solution

• For example, 0.25 mol L–1 (or 0.25 M) solution of NaOH means that 0.25 mol of NaOH has been dissolved in one litre (or one cubic decimetre).

Molality

• Molality: Molality (m) is defined as the number of moles of the solute per kilogram (kg) of the solvent and is expressed

• For example, 1.00 mol kg–1 (or 1.00 m) solution of KCl means that 1 mol (74.5 g) of KCl is dissolved in 1 kg of water.

Mole fraction• Mole fraction: Commonly used symbol for mole

fraction is x and subscript used on the right hand side of x denotes the component. It is defined as:

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

Solubility

• Solubility of a substance is its maximum amount that can be dissolved in a specified amount of solvent. It depends upon the nature of solute and solvent as well as temperature and pressure.

Solubility of Gases ( Solubility of Gaseous solute in Liquid solvent)

• Many gases dissolve in water. Oxygen dissolves only to a small extent in water. It is this dissolved oxygen which sustains all aquatic life. On the other hand, hydrogen chloride gas (HCl) is highly soluble in water.

• Factors which affect the Solubility of Gaseous solute dissolved in Liquid solvent to from a homogeneous solution are:

i. Nature of the gaseous solute and solventii. Effect of temperatureiii. Effect of pressure

Nature of the gaseous solute and solvent

• The solubility of gases like O2, N2 H2 etc. is less in water but more in ethyl alcohol.

• Also, the solubility of gaseous solutes like H2S, NH3 etc. is more in water as compared to their solubility in ethyl alcohol.

• So, the solubility depends upon the nature of gaseous solute and also the nature of solvent.

Effect of temperature

• The solubility of gaseous solute dissolved in a liquid solvent decrease with increase in temperature.

• With increase in temperature, the gaseous solute dissolved in a solution bubbles out and hence the solubility of a dissolved gas decreases with increase in temperature.

• Such an effect can also be explained by Le-Chatelier principle of equilibrium as under:

Effect of pressure

• The solubility of gases increase with increase of pressure. For solution of gases in a solvent, consider a system as shown in figure (a). The lower part is solution and the upper part is gaseous system at pressure p and temperature T. Assume this system to be in a state of dynamic equilibrium, i.e., under these conditions rate of gaseous particles entering and leaving the solution phase is the same. Now increase the pressure over the solution phase by compressing the gas to a smaller volume [Fig. 2.1 (b)].

Effect of pressure

• This will increase the number of gaseous particles per unit volume over the solution and also the rate at which the gaseous particles are striking the surface of solution to enter it. The solubility of the gas will increase until a new equilibrium is reached resulting in an increase in the pressure of a gas above the solution and thus its solubility increases.