Is Matter Around Us Pure

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Questions:

Generic 4

10 x 4 = 40

Write three main difference between a mixture and a compound.

Distinguish between metals and non-metals.

Write any three difference between a physical change and a chemical change.

State the principle used in separating different components of a mixture by the method of centrifugation.List any two application of this method.

How are colloidal, solution and suspension different from each other?

Give below is the list of some colloids. Make a list selecting them on the basis of type, dispersing medium. Also give the nature of dispersed phase in each.
Fog, cloud, shaving cream, milk, face cream, milk of magnesia, foam rubber, sponge, jelly, cheese, butter, paint, writing ink, smoke, blood, coloured gemstone.

(a)Compare true solution, suspension and colloidal in terms of:
(i) filterability
(ii) stability
(b) List two factors which bring about a change in the state of matters say, gas to liquid.

(a)State the difference between a pure substance and a mixture.Give one example of each.
(b) Identify homogeneous mixture from the following:
(i) smoke
(ii) brass
(iii) tincture of iodine
(iv) milk

Give the distinguishing feature of a pure substance or a compound and a mixture.

10.

List the various types of homogeneous and heterogeneous mixtures with examples.

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Answers Key:

Generic 4

10 x 4 = 40

Mixture	Compounds
1. elements or compounds just mix retaining the properties of a constituent substance	1. Element reacts to form a new substance that has totally different properties.
2. A mixture has a variable composition	2. The composition of the new substance or compound is fixed.
3. The constituent can be separated fairly easily by physical methods.	3. The constituents can be separated only by chemical methods.

metal	Non-metal
1. metals are solids at room temperature.	1. Non-metals may be a gas, a liquid or a solid at room temperature.
2. metals have a shiny metallic lustre. Their shining can be intensified by polishing.	2. Non-metals have a dull non-metallic lustre.
3. metals are hard substances.	3. Non-metals have a hardness of varying category
4. Metals are malleable.	4. non-metals are non-malleable
5. metals are ductile and can be drawn into wires.	5. Non-metals are not ductile and cannot be drawn into wires.
6. metals have high specific gravity.	6. non-metals have low specific gravity.
7. metals are good conductors of heat and electricity.	7. non-metals are bad conductors of electricity, except graphite which is a good conductor of electricity.
8. metals form alloys with other metals.	8. non-metals do not form alloys with other non-metals.

Given below is a comparison of two types of changes:

Physical changes	Chemical Changes
1. Changes take place only in properties such as colour, physical state, density, etc.	1. Change result in the formation of new chemical substance(S)
2. Change in temporary	2. Change in permanent
3. original Substance(s) can be obtained back easily	3. original substance(s) cannot be obtained back easily.
4. Chemical properties of the substance remain unchanged even after the change	4. New substances with different properties are formed.

1. Centrifugation is the process of separating suspended particles from a liquid-like colloid by churning the liquid at high speed. The principle is that denser particles are forced to the bottom and lighter stay at the top when spun rapidly.
2. The mixture is taken in a closed bottle and rotated at a high speed. The heavy particles settle at the bottom while light particles remain behind. For example, to separate cream from milk, milk is churned for 2-3 minutes. Cream being lighter than milk floats at the top of the mixture.
3. Applications of centrifugation:
(a) Used in washing machines to squeeze out water from clothes.
(b) Used in laboratories to separate colloidal particles from their solutions.
(c) Used in Diagnostic labs for blood and urine test.

Comparison of properties of true solution, colloidal solution, and suspension

Property	True solution	Colloidal solution	Suspension
(1) Appearance	homogeneous and transparent	Heterogeneous and translucent	heterogeneous and opaque
(2) particle size	< 1 nm (10^-7 cm)	1 nm - 100 nm	> 100 nm (10^-5 cm)
(3) Visibility	particles are not visible even with a powerful microscope	Particles can be seen with a high power microscope	particles can be seen with naked eyes
(4) Stability	Stable	Stable	Unstable
(5) Diffusion	Diffuse rapidly	Diffuse slowly	Do not diffuse
(6) Filterability	Pass through filter paper	passes through filter paper	can be separated by filter paper
Example	NaCI dissolved in water	Blood	Mud water.

Test of a colloidal solution or a suspension.
(i) A colloidal solution is turbid and particle settles down on adding a salt. In a suspension, particles settle down on keeping under the influences of gravity.
(ii) If the particles in a heterogeneous and opaque solution can be seen with naked eyes and get settl on keeping, then it is a suspension.

Select of colloids on the basis of type, dispersed phase and dispersion medium:

Colloids	Dispersing medium	Dispersed phase	Type
fog, clouds, mist, clouds smoke, automobile exhaust	Gas	Liquid solid	aerosol aerosol
shaving cream, milk, face cream, writing ink, blood, paint milk of magnesia, mud	Liquid	gas liquid solid	foam emulsion sol
foam, rubber, sponge, pumice jelly, cheese, butter, colored gemstone	Solid	gas liquid slid	Foam gel solid sol

Comparison of properties of a true solution, colloidal solution, and suspension

Property	True solution	Colloidal solution	Suspension
(1) Appearance	homogeneous and transparent	Hetrogeneous and transluscent	hetrogeneous and opaque
(2) particle size	< 1 nm (10^-7 cm)	1 nm - 100 nm	> 100 nm (10^-5 cm)
(3) Visibility	particles are not visible even with a powerful microscope	Particles can be seen with a high power microscope	particles can be seen with naked eyes
(4) Stablity	Stable	Stable	Unstable
(5) Diffusion	Diffuse rapidly	Difuse slowly	Do not diffuse
(6) Filtrability	Pass-through filter paper	passes through filter paper	can be separated by filter paper
Example	NaCI dissolved in watre	Blood	Mud water.

(a) Various points of distinction between a chemical compound and a mixture are summarised below:

Characteristics	Pure substance or compound	Mixture
1. Composition	The elements in a compound are present in definite proportion by weight.	The ingredients of a mixture may be present in varying ratios.
2. Homogeneity	A compound is always homogeneous	A mixture may be homogeneous (solution) or heterogeneous.
3. Properties	A compound has entirely different properties from those of its constituents.	Properties of a mixture are an average of the properties of its constituents.
4. Separation	The constituents of a compound cannot be separated by simple separation techniques.	The constituents of a mixture can be separated by simple methods.
5. Energy changs	Energy in the form of heat, light or electricity is either evolved or absorbed when a compound is formed	There is generally no energy change when a mixture is formed from its constituents.
6. volume change	At constant temperature and pressure, the formation of a compound may involve either no change or a large change in volume.	At constant temperature and pressure, the formation of a mixture involves either very little or no change in volume.

(b) Homogeneous mixture is brass, tincture of iodine.

Various point of distinction between a chemical compound and a mixture are summarised below:

Characteristics	Pure substance or compound	Mixture
1. Composition	The elements in a compound are present in definite proportion by weight.	The ingredients of a mixture may be present in varying ratios.
2.Homogeneity	A compound is always homogeneous	A mixture may be homogeneous (solution) or heterogeneous.
3. Properties	A compound has entirely different properties from those of its constituents.	Properties of a mixture are an average of the properties of its constituents.
4. Separation	The constituents of a compound cannot be separated by simple separation techniques.	The constituents of a mixture can be separated by simple methods.
5. Energy changs	Energy in the form of heat, light, or electricity is either evolved or absorbed when a compound is formed	There is generally no energy change when a mixture is formed from its constituents.
6. volume change	At constant temperature and pressure, the formation of a compound may involve either no change or a large change in volume.	At constant temperature and pressure, the formation of a mixture involves either very little or no change in volume.

10.

Homogeneous mixtures
(a) Solid solution. Alloys, e.g., brass, steel, bronze.
(b) liquid solution. Sugar solution in water, seawater, alcohol in water.
(c) Gaseous solution. Air, natural gas.
Heterogeneous mixtures
(a) Solid + Solid Sugar and sand, iron filings and sulphur, copper sulphate and potassium permanganate
(b) Solid + Liquid Pastes, suspensions, etc.
(c) Solid + gas Smok
(d) Liquid + Liquid Milk, emulsions.
(e) liquid + Gas Soap bubbles.

9th Standard CBSE Science - Is Matter Around Us Pure Four Marks Questions

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