Tool : Study

Mixture: A mixture is a matter that contains more than one pure substance in any ratio/proportion.

A mixture is an impure form of matter.

Example:

Water in milk, lemon juice, Ginger Garlic paste, etc.,

The mixture may or may not be separated into its constituent particles by physical processes.

Substance: A matter that cannot be separated into its constituent particles by any physical process is known as a substance.

Example:

Solution: A homogeneous mixture of two or more substances is called a solution.

Example:

Tea, sugar, and common salt are dissolved in water.

Alloy: A homogeneous mixture of metals is called an alloy.

Properties of the Solution: 

• A solution is a homogeneous mixture
• Particles are extremely small, not visible to the naked eye
• The light path is invisible in solution.
• Solute particles cannot be separated by filtration

Concentration of solution: The concentration of a solution is the amount of solute present in a given quantity of the solution.

Unsaturated and Saturated Solutions: a solution in which a larger quantity of solute can be dissolved without raising its temperature, is called an unsaturated solution.

• A solution in which no more solute can be dissolved at a certain temperature, is called a saturated solution.

Solubility: The maximum amount of a solute that can be dissolved in 100 grams of a solvent at a specified temperature is known as the solubility of the solute in that solvent.

Suspension: a heterogeneous mixture of solids and liquids where the solid particles are suspended throughout the medium. 

Example: Mixture of chalk powder and water

Properties of Suspension

• Particles are visible to the naked eye

• Light path in a suspension is visible

• Particles settle down

Colloidal Solution: Colloidal Solution Is a heterogeneous mixture, but appears to be homogeneous.

Examples: Milk, soap lather, soda water, pumice stone, rubber, bread, fog, cloud, insecticide spray, butter, etc.

Properties of colloidal solutions

• Heterogeneous mixture

• Particle size is small, not visible to the naked eye

• Light path can be visible;

• Particles do not settle down

• Substances cannot be separated by filtration

Tyndall Effect: Scattering of light beam by suspended particles in the solution.

Physical and Chemical changes: 

Physical and change: The changes in which no new substances are formed are called physical changes. 

Chemical change: The changes in which new substances are formed are called chemical changes.

SEPARATION OF MIXTURES

The method of separation depends on both the type of mixture and the physical properties of its constituents. 

These are :

(i) The physical state of the constituents.

(ii) The differences in the physical properties

of the constituents, such as:

(a) boiling point 

(b) melting point

(c) density

(d) magnetic properties

(e) ability to sublime

(f) volatility

(g) solubility in various solvents.

• Evaporation: Used for separating mixtures of volatile solvents and non-volatile solutes.

Working Principle:

One component should be non-volatile. It may or may not be soluble in water.

Example: Separating salt from its solution

• Centrifugation used for separating components based on the difference in their weights.

Working Principle:

Difference in the densities of two liquids.

Example: Separating mixtures of cream from milk

• Separating Funnel: Used for separating two or more immiscible liquids.

Working Principle:

Immiscible liquids with different densities get separated into different layers if they are in the same container.

Example: Separating oil and water

Sublimation:

Sublimation is the process of converting a solid into vapour and returning it to the solid state without passing through the liquid state.

Sublimation is used to separate sublimable solids from their mixtures.

Working Principle:

One of the components can be sublime.

Example: Separating ammonium chloride from a mixture

Chromatography:

The process of separating the different dissolved constituents of a mixture by their adsorption (adsorption refers to the collection of one substance on the surface of another substance.) over an appropriate adsorbing material is called chromatography.

Chromatography is used to separate those solutes that dissolve in the same solvent.

Working Principle:

Adsorption/partition

Example: Separating the components of a dye

Distillation: 

Distillation is the process of heating a liquid to convert it into vapours and then condensing the vapours back into a liquid.

Distillation is used to separate two miscible liquids that boil without decomposition.

Working Principle:

One component should be a soluble solid in a liquid.

Example: Separating a mixture of acetone and water

Fractional distillation 

Fractional distillation is a process that involves the distillation and collection of fractions or different liquids boiling at different temperatures.

Fractional distillation is used to separate a mixture of liquids when their boiling temperatures differ by less than 25 K. 

Example: Separating different components of petroleum

Crystallization: Used to separate pure solids from a solution by forming crystals.

Working Principle:

A solid dissolved in a liquid is separated by evaporating the solvent completely by heating the mixture. 

Example: Obtaining pure crystals of copper sulphate from an impure sample.

Differences Between Mixture And Compound

Particles:

Particles are very small in size. Therefore we cannot see particles with our naked eye. 

Characteristics of the particles of matter: 

(1) All matter (elements or compounds) consists of very small particles which can exist independently and are called particles. 

(ii) The particles of matter are in a state of continuous motion and possess kinetic energy. 

(iii) There are intermolecular spaces in between the particles (molecules) of matter.

(iv) The particles (molecules) of matter attract each other with a force called intermolecular force. 

Intermolecular force is maximum in solids and least in the gases.

These material particles can be touched, moved by changing temperature or attracted by decreasing or increasing forces of attraction or repulsion.

2. States of Matter

Matter exists in three different physical states namely solid, liquid and gas.

One substance such as water can exist in all the three states such as, ice in solid state, water in liquid state and steam or vapours in gaseous state.

The state of matter depends on temperature, forces of attraction between their constituent particles etc.

3. Interconversion of Matter

All these three different states of matter are interconvertible depending upon temperature and pressure.

The state of matter can be changed by changing temperature or pressure. 

Due to change in temperature and pressure there will be a change in inter-particle space as well as force between them, resulting in change in physical state.

Examples: 

• Applying pressure and reducing temperature can liquefy gases.
• Solid CO₂ gets converted directly to a gaseous state on decrease of pressure to 1 atmosphere without changing into a liquid state. Due to this fact solid CO₂ is also known as DRY ICE.

4. Plasma: It is the fourth state of matter consisting of super energetic and super excited particles. These particles are in the form of ionised gases.

Examples:

• The plasma in stars is formed due to high temperature. 
• Glowing plasma formed in fluorescent tubes and neon sign bulbs.

These devices contain inert gases which get ionised due to the passage of electric current. The colour of the glowing plasma depends upon the nature of the gas.

5. Sublimation: The process in which a solid state directly changes into a gaseous state on heating or vice-versa on cooling.

6. Melting or Fusion: The process of changing a solid into a liquid state by absorbing heat at a constant temperature is known as Melting or Fusion. 

7. Freezing or Solidification: The process of changing a liquid into solid state by losing heat at a constant temperature is known as Freezing or Solidification.

8. Condensation: The process of changing a gas into a liquid state by giving out heat at constant temperature is known as Condensation .

Boiling or Vaporisation : The process of changing a liquid into a gaseous state by absorbing heat at constant temperature  is known as Boiling or Vaporisation .

Boiling is a bulk phenomenon. Particles from the bulk (whole) of the liquid change into a vapour state.

Evaporation: The phenomenon of changing the physical state from liquid to vapour, at any temperature is called evaporation.

Evaporation is a surface phenomenon. Particles from the surface gain required energy to overcome the forces of attraction present in the liquid and change into the vapour state.

The rate of evaporation depends upon the surface area exposed to the atmosphere, the temperature, the humidity and the wind speed.

Evaporation causes cooling.

Evaporation takes place at all temperatures, below the boiling point of a liquid

Factors affecting evaporation:

• Rate of evaporation increases with increase in surface area.

• Rate of evaporation increases with increase in temperature.

• Rate of evaporation increases with decrease in Humidity.

• Rate of evaporation increases with increase in wind speed.

Latent heat of boiling or Latent heat of Vaporisation: Latent heat of boiling or Latent heat of Vaporisation is the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point.

Kelvin is the SI unit of temperature. 

0°C = 273.16 K. 

For convenience, we take 0°C = 273 K after rounding off the decimal. 

To change a temperature on the Kelvin scale to the Celsius scale you have to subtract 273 from the given temperature, and to convert a temperature on the Celsius scale to the Kelvin scale you have to add 273 to the given temperature.

Conversion Formula: t°C = (t+273) K

Boiling point or Vaporisation point: Boiling point or Vaporisation point is the fixed temperature at which a liquid converts into a gaseous state at atmospheric pressure.

Melting point or Fusion point: Melting point or Fusion point is the temperature at which a solid starts converting into a liquid state at atmospheric pressure.

Evaporation Causes cooling: During evaporation the particles at the surface of the liquid gain energy from the surroundings and change into vapour.. Therefore Evaporation Causes cooling effect.

Sponge can be compressed although it is solid: Sponge contains minute holes in which air is trapped.So when it is pressed, the air gets expelled and the sponge gets compressed. Also,the material of the sponge is not rigid. 

Temperature does not change during change of state: The temperature remains constant at its melting and boiling points (during change of state) until all the substance melts or boils.

Because the heat supplied is continuously used up in changing the state of the substance by overcoming the force of attraction between the particles.

There is no increase in the kinetic energy of the particles and thus, temperature does not change. 

This heat energy absorbed without showing any rise in temperature is given the name latent heat of fusion/latent heat of vaporisation.

Effect of pressure on physical state of a substance: 

If pressure is applied, melting point decreases and boiling point increases

When pressure is increased, the particles come closer and the force of attraction increases between them and this results in a change of state. 

Example: When high pressure is applied to a gas by reducing its temperature, the particles of gas come close and get converted to a liquid. This is also known as liquefaction.

The amount of heat energy required in changing a 1 kg of solid into liquid at atmospheric pressure and its melting point is known as the latent heat of fusion.

[ Lice = 80 cal/g = 3.34 × 105 J/kg].

• The amount of heat which is required to convert 1 kg of the liquid (at its boiling point) to vapours of gas without any change in temperature is known as latent heat of vaporisation.

 [Lwater =540 cal/g= 22.5 × 105 J/kg].

• The amount of heat absorbed or liberated , Q = mL.

 • The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius.

• Q = m.s. t, where m = mass of the body, s = specific heat of the body and t is temperature difference and m.s is called thermal capacity.

• Change of liquid into vapours at any temperature below the boiling point.

Takes the latent heat from the body. Thus, the body cools when evaporation takes place.

Evaporation:

(1) Evaporation is a slow process.

(ii) Evaporation takes place at the surface mass of the liquid.

(iii) Evaporation takes place at all temperatures.

(iv) The substance becomes cool due to evapora- tion process.

(v) Heat is absorbed from the surroundings due to Evaporation. Absorption of heat from the surroundings causes cooling effect.

Boiling:

(1) Boiling is a rapid process.

(ii) Boiling takes place throughout the mass of a liquid.

(iii) Boiling takes place at a definite temperature called the boil- ing point.

(iv) The substance remains hot during the boiling process.

(v) Heat is required from an external source such as a burner for boiling to take place. 

Scales of temperature

• Three scales are commonly used for measuring temperature, namely, the Celsius scale, the Fahrenheit scale and the Kelvin scale.

• The relation between the Celsius and the Kelvin scale can be expressed as:

C + 273 = K

• The relation between the Celsius and the Fahrenheit scale can be expressed as follows.

Specific Heat

11.8 NATURAL PHENOMENA AND CONSEQUENCES OF HIGH SPECIFIC HEAT CAPACITY OF WATER

Some consequences of high specific heat capacity of water are given below.

(i) The climate near the seashore is moderate :

The specific heat capacity of water is very high (= 1000 cal kg-1 °C-1 or 4200 J kg-1 K-¹). It is about five times as high as that of sand. Hence the heat energy required for the same rise in temperature by a certain mass of water will be nearly five times that required by the same mass of sand. 

Similarly, a certain mass of water will give out nearly five times more heat energy than that given by sand of the same mass for the same fall in temperature. 

As such, sand (or earth) gets heated or cooled more rapidly as compared to water under similar conditions. 

Thus, a large difference in temperature is developed between the land and the sea due to which land and sea breezes are formed”. These breezes make the climate near the seashore moderate.

(ii) Hot water bottles are used for fomentation: The reason is that water does not cool quickly due to its large specific heat capacity, so a hot water bottle provides heat energy for fomentation for a long time.

(iii) Water is used as an effective coolant: By allowing water to flow in pipes around the heated parts of a machine, heat energy from such parts is removed (e.g. radiators in car and generator are filled with water). Water in pipes extracts more heat from surroundings without much rise in its temperature because of its large specific heat capacity.

(iv) In cold countries, water is used as a heat reservoir for wine and juice bottles to avoid their freezing: The reason is that water due to its high specific heat capacity can impart a large amount of heat before reaching up to the freezing temperature. Hence bottles kept in water remain warm and they do not freeze even when the surrounding temperature falls considerably.

(v) Farmers fill their fields with water to protect the crops from frost: In the absence of water, if on a cold winter night, the atmospheric temperature falls below 0°C, the water in the fine capillaries of plants will freeze, so the veins will burst due to the increase in volume of water on freezing. As a result, plants will die and the crop will be destroyed. In order to save crop on such cold nights, farmers fill their fields with water because water has a high specific heat capacity, so it does not allow the temperature in the surrounding area of plants to fall up to 0°C.

(vi) All plants and animals have a high content of water in their bodies: All plants and animals have nearly 80% to 90% of water in their bodies so it helps in maintaining the body temperature nearly same in all seasons due to high specific heat capacity of water.

SOME EXAMPLES OF HIGH AND LOW THERMAL CAPACITY

(1) The base of a cooking pan is made thick : By making the base of the cooking pan thick, its thermal capacity becomes large and it imparts sufficient heat energy at a low temperature to the food for its proper cooking. Further it keeps the food warm for a long time, after cooking.

(2) The base of an electric iron is made thick and heavy: By doing so, the thermal capacity of the base becomes large and it remains hot for a long duration even after switching off the current.

(3) The vessel used for measurement of heat (i.e., calorimeter) is made of thin sheet of copper:

The reason is that the specific heat capacity of copper is low and by making the vessel thin, its thermal capacity becomes low so that it takes a negligible amount of heat from its contents to attain the temperature of the contents.