Science · X-Factor Notes

Physical and Chemical Changes, Solution

Physical and Chemical Changes, Solution revision notes for UPPCS Prelims.

13 revision facts

I. Physical and Chemical Changes

Concept	What to remember	Asked in UPPCS
Physical Change	Changes the physical traits (shape, size, color) of a substance without altering its internal chemical structure. It is generally a reversible process.
Example of Physical Change	Change of water into vapour is a physical change. Dissolving sugar in water is a physical change, as sugar can be recovered by evaporating the water.	UPPCS (Pre) 1992
Chemical Change	A process where atoms are rearranged to form a new substance with a different chemical composition. It is an irreversible process.
Example of Chemical Change	Souring of milk is an example of a chemical change. Softening of vegetables when cooked alters the molecular composition and is irreversible, thus it is a chemical change.	I.A.S. (Pre) 2014
Chemical Reaction Rate	A chemical reaction becomes faster at a higher temperature because molecular motion becomes more rapid.	UPPCS (Pre) 2017
Pasteurization	A process where milk is first heated up for a longer time and then cooled. This process is related to changes in properties like enzyme activity.	U.P. Lower Sub. (Pre) 1998
Exothermic Processes	Processes that release energy (heat). Examples include the dilution of an acid ($\text{H}_2\text{SO}_4$) and the reaction of water with quick lime.

II. Properties of Solutions

Concept	What to remember	Asked in UPPCS
Effect of Impurities on Boiling Point	When some impurities are mixed with a liquid, its boiling point increases.
Freezing Point Depression	Temperature below $0^\circ\text{C}$ can be achieved by a mixture of salt and ice because the salt decreases (or lowers) the freezing point of ice.	U.P. Lower Sub. (Pre) 1998; I.A.S. (Pre) 1993
Unsaturated Solution Volume	If an unsaturated sugar solution is prepared by mixing $100$ grams of sugar with half litre of water, the volume of the solution remains constant (or does not change).	UPPCS (Pre) 2017
Osmosis	The process where the solvent moves through a semi-permeable membrane from a region of lower solute concentration to a region of higher solute concentration to equalize concentration.	I.A.S. (Pre) 2005
Reverse Osmosis	External pressure is applied upon the concentrated solution to reverse the movement of the solvent (from concentrated to dilute solution). This technique is used to purify solutions.	I.A.S. (Pre) 2005

III. Separation and Purification

Concept	What to remember	Asked in UPPCS
Purification of Solids	Distillation is generally used for purifying liquid impurities. It is not useful for the purification of solid impurities; methods like sublimation and crystallization are used for solids.	U.P. R.O./A.R.O. (Pre) (Re. Exam) 2016

I. Physical and Chemical Changes

Concept	What to remember	Asked in UPPCS
Physical Change	Changes the physical traits (shape, size, color) of a substance without altering its internal chemical structure. It is generally a reversible process.
Example of Physical Change	Change of water into vapour is a physical change. Dissolving sugar in water is a physical change, as sugar can be recovered by evaporating the water.	UPPCS (Pre) 1992
Chemical Change	A process where atoms are rearranged to form a new substance with a different chemical composition. It is an irreversible process.
Example of Chemical Change	Souring of milk is an example of a chemical change. Softening of vegetables when cooked alters the molecular composition and is irreversible, thus it is a chemical change.	I.A.S. (Pre) 2014
Chemical Reaction Rate	A chemical reaction becomes faster at a higher temperature because molecular motion becomes more rapid.	UPPCS (Pre) 2017
Pasteurization	A process where milk is first heated up for a longer time and then cooled. This process is related to changes in properties like enzyme activity.	U.P. Lower Sub. (Pre) 1998
Exothermic Processes	Processes that release energy (heat). Examples include the dilution of an acid ($\text{H}_2\text{SO}_4$) and the reaction of water with quick lime.

II. Properties of Solutions

Concept	What to remember	Asked in UPPCS
Effect of Impurities on Boiling Point	When some impurities are mixed with a liquid, its boiling point increases.
Freezing Point Depression	Temperature below $0^\circ\text{C}$ can be achieved by a mixture of salt and ice because the salt decreases (or lowers) the freezing point of ice.	U.P. Lower Sub. (Pre) 1998; I.A.S. (Pre) 1993
Unsaturated Solution Volume	If an unsaturated sugar solution is prepared by mixing $100$ grams of sugar with half litre of water, the volume of the solution remains constant (or does not change).	UPPCS (Pre) 2017
Osmosis	The process where the solvent moves through a semi-permeable membrane from a region of lower solute concentration to a region of higher solute concentration to equalize concentration.	I.A.S. (Pre) 2005
Reverse Osmosis	External pressure is applied upon the concentrated solution to reverse the movement of the solvent (from concentrated to dilute solution). This technique is used to purify solutions.	I.A.S. (Pre) 2005

Concept

What to remember

Asked in UPPCS

Purification of Solids

Distillation is generally used for purifying liquid impurities. It is not useful for the purification of solid impurities; methods like sublimation and crystallization are used for solids.

U.P. R.O./A.R.O. (Pre) (Re. Exam) 2016