RBSE Class 9 Science Important Questions Chapter 2 Is Matter Around Us Pure?

Rajasthan Board RBSE Class 9 Science Important Questions Chapter 2 Is Matter Around Us Pure? Important Questions and Answers.

RBSE Class 9 Science Chapter 2 Important Questions Is Matter Around Us Pure?

Objective Type Questions

Question 1.
Which of the following is not a metalloid?
(a) Boron
(b) Bromine
(c) Silicon
(d) Germanium
Answer:
(b) Bromine

Question 2.
Which of the following metals is found in liquid state at room temperature?
(a) Mercury
(b) Gold
(c) Iron
(d) Copper
Answer:
(a) Mercury

Question 3.
How can we separate cream from milk?
(a) Centrifugation
(b) Chromatography
(c) Sublimation
(d) Distillation
Answer:
(a) Centrifugation

Question 4.
Tincture of iodine has antiseptic properties. This solution is made by dissolving:
(a) Iodine in potassium iodide.
(b) Iodine in vaseline.
(c) Iodine in water.
(d) Iodine in alcohol.
Answer:
(d) Iodine in alcohol.

Question 5.
Which of the following are homogeneous in nature?
(i) Ice
(ii) Wood
(iii) Soil
(iv) Air
(a) (i) and (iii)
(b) (ii) and (iv)
(c) (i) and (iv)
(d) (iii) and (iv)
Answer:
(c) (i) and (iv)

Question 6.
Which of the following are physical changes?
(i) Melting of iron metal
(ii) Rusting of iron
(iii) Bending of an iron rod
(iv) Drawing a wire of iron metal
(a) (i), (ii) and (iii)
(b) (i), (ii) and (iv)
(c) (i), (iii) and (iv)
(d) (ii), (iii) and (iv)
Answer:
(c) (i), (iii) and (iv)

Question 7.
Which of the following are chemical changes?
(i) Decaying of wood
(ii) Burning of wood
(iii) Sawing of wood
(iv) Hammering of a nail into a piece of wood
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)
Answer:
(a) (i) and (ii)

Question 8.
According to the definition of pure substance, which of the following is a pure substance?
(a) Ice
(b) Mercury
(c) Iron
(d) All of these
Answer:
(d) All of these

Question 9.
The main components of air are :
(a) nitrogen and carbon monoxide
(b) oxygen and nitrogen
(c) oxygen and carbon dioxide
(d) carbon monoxide and carbon dioxide
Answer:
(b) oxygen and nitrogen.

Question 10.
If we put camphor in an open container, its amount keeps on decreasing due to the phenomenon of:
(a) Evaporation
(b) Precipitation
(c) Condensation
(d) Sublimation
Answer:
(d) Sublimation

Question 11.
Which of the following can be separated by sublimation?
(a) Sand
(b) Ammonium chloride
(c) Sodium chloride
(d) Chalk powder
Answer:
(b) Ammonium chloride

Question 12.
Which of the following is not a non-metal?
(a) Iodine
(b) chlorine
(c) Carbon
(d) Silicon
Answer:
(d) Silicon

Question 13.
Fill in the blanks :
(i) A colloid is a mixture and its components can be separated by the technique known as ………………
(ii) Ice, water and water vapour look different and display different …………….. properties but they are ……………. the same.
(iii) A mixture of chloroform and water taken in a separating funnel is mixed and left undisturbed for some time. The upper layer in the separating funnel will be of ……………. and the lower layer will be that of …………….
(iv) A mixture of two or more miscible liquids, for which the difference in the boiling points is less than 25K can be separated by the process called …………….
(v) When light is passed through water containing a few drops of milk, it shows a bluish tinge. This is due to the …………… of light by milk and the phenomenon is called ………….. This indicates that milk is a solution.
Answer:
(i) heterogeneous, centrifugation.
(ii) physical, chemically.
(iii) water, chloroform.
(iv) fractional distillation,
(v) scattering, Tyndall effect, colloidal.

Question 14.
Match the items in column A with column B

Column A	Column B
(i) Number of gaseous elements.	(a) Hydrogen sulphide gas.
(ii) Colourless, odourless, flammable gas.	(b) 11
(iii) Rotten-egg like smell.	(c) Physical change
(iv) Heating ice	(d) Hydrogen

Answer:

Column A	Column B
(i) Number of gaseous elements.	(b) 11
(ii) Colourless, odourless, flammable gas.	(d) Hydrogen
(iii) Rotten-egg like smell.	(a) Hydrogen sulphide gas.
(iv) Heating ice	(c) Physical change

Question 15.
Match the items in column A with column B

Column A	Column B
(i) Silicon	(a) Gel
(ii) Cheese	(b) Chemical change
(iii) Making curd from milk	(c) Starch solution
(iv) Tyndall effect	(d) Metalloid

Answer:

Column A	Column B
(i) Silicon	(d) Metalloid
(ii) Cheese	(a) Gel
(iii) Making curd from milk	(b) Chemical change
(iv) Tyndall effect	(c) Starch solution

Question 16.
Read the statement carefully and identify whether they are True or False-
1. Carrosion of iron is a chemical change.
2. Both chemical and physical changes occur in the process of burning a candle.
3. Sugar is a heterogenous mixture in water.
4. Gallium and caesium exist in gaseous state at a temperature slightly above room temperature (303 K).
Answer:
1. True
2. True
3. False
4. False

Very Short Answer Type Questions

Question 1.
Name the process by which all dyes present in black ink be recovered.
Answer:
Chromatography.

Question 2.
Name the process by which pure copper sulphate can be obtained from its impure sample.
Answer:
Crystallisation.

Question 3.
Milk of Magnesia is called?
Answer:
True solution.

Question 4.
A colloid which have liquid as dispersed phase and solid as dispersion medium called?
Answer:
Gel.

Question 5.
Which component of solution is present in smaller proportion?
Answer:
Solute.

Question 6.
Name the process used to separate liquids which have difference in boiling points of less than 25°C.
Answer:
Fractional distillation.

Question 7.
What are two types of matter on the basis of composition?
Answer:
Pure substance and mixture.

Question 8.
Name two categories of pure substance.
Answer:
Element and compound.

Question 9.
Name the types of mixtures.
Answer:
Homogeneous mixture and heterogeneous mixture.

Question 10.
Write the name of any two compounds which sublime on heating.
Answer:
Ammonium chloride and iodine.

Question 11.
Give two examples of colloids from your daily life.
Answer:
Milk and fog.

Question 12.
Define the term Solvent.
Answer:
Component of solution that is present in the larger proportion and dissolves the other substance is called Solvent.

Question 13.
Classify the elements.
Answer:

1. Metals,
2. Non-metals,
3. Metalloids.

Question 14.
Name the constituents of German silver.
Answer:
Copper and zinc.

Question 15.
What is the meaning of ‘concentration of solution’?
Answer:
The relative amount of solute and solvent present in a given quantity of the solution is known as the concentration of a solution.

Question 16.
What is condenser?
Answer:
It is an apparatus which converts gas into liquid by cooling it.

Question 17.
Define dispersion medium.
Answer:
It is the component which is present in excess and acts as a medium in which colloidal particles are dispersed.

Question 18.
Define Chromatography.
Answer:
The process of separation of different dissolved constituents of a mixture by absorbing them over an appropriate absorber is called, Chromatography.

Question 19.
Give an example of a liquid and liquid type solution.
Answer:
Vinegar is a mixture of acetic add and water.

Question 20.
What is the principle of separation?
Answer:
The difference in physical or chemical properties of components of mixture is the basis of separation.

Question 21.
Give chemical name of chalk and quicklime.
Answer:
(i) Chalk : Calcium Carbonate
(ii) Quicklime : Calcium Oxide

Question 22.
Define the term heterogeneous.
Answer:
A substance that does not have the same properties throughout the mixture is called heterogeneous.

Question 23.
Name two metals which are highly malleable and ductile.
Answer:
Gold and silver.

Question 24.
Hydrogen is considered as element. Why?
Answer:
Hydrogen have one type of element and it cannot be broken by physical or chemical process, so it is considered as element.

Short Answer Type Questions

Question 1.
Give differences between mixture and compound.
Answer:

Compounds	Mixtures
1. Compounds are pure substances.	1. Mixtures are impure substances.
2. Compounds are made up of two or more elements combined chemically.	2. Mixtures are made up of two or more substances mixed physically.
3. The components of a compound are present in a fixed ratio.	3. The components of a mixture are present in different ratio.
4. Compounds have same properties throughout the compound part.	4. Mixtures do not have same properties throughout the mixture part.
5. A new substance is formed.	5. No new substance is formed.
6. The components of a compound can be separated only by chemical methods.	6. The components of a mixture can be separated by physical methods.

Question 2.
Write the properties of a solution.
Answer:

• It is a homogeneous mixture of solute and solvent.
• Solute partides cannot be separated by filtration.
• True solution is clear and transparent.
• True solution does not scatter light.
• Solute partides cannot settle out from solvent.

Question 3.
Write the properties of a colloidal solution.
Answer:

• The size of particles is too small of a colloid; vary from 1 nm to 10 nm.
• Colloid is too stable thus the particles do not settle down when left undisturbed.
• Particles cannot be separated from the mixture by the process of filtration.
• Colic dal solutions are translucent in nature.
• The particles of a colloidal solution scatter light.

Question 4.
What makes water as a universal solvent?
Answer:
Water acts as a universal solvent due to :

• The polar nature of its molecules.
• Its ability to produce soluble salt on interaction with a large number of substances.

Question 5.
(i) State the principle of the process of centrifugation.
(ii) List any three applications of centrifugation.
Answer:
(i) Centrifugation is the process of separating suspended particles from a liquid like colloids by churning the liquid at a high speed. The principle is that denser particles are forced to the bottom and lighter stay at the top when spun rapidly.

(ii) Applications of centrifugation :

• Used in dairies and homes to separate cream from milk or butter from cream.
• Used in washing machines to squeeze out water from clothes.
• Used in laboratories to separate colloidal particles from their solutions.
• Used in diagnostic labs for blood and urine test.

Question 6.
What is decantation? Explain.
Answer:
Decantation is the process of separating insoluble solids from liquids. A suspension of solid particles in a liquid is allowed to stand for sometime. Insoluble solid particles settle down at the bottom due to their weight. This is called sedimentation. The clear liquid is theri transferred into another container, without disturbing the settled particles. In other words, clear liquid is decanted and separated from solid.

Question 7.
How will you separate a mixture of common salt, camphor and iron filings? Describe the process.
Answer:
Mixture of common salt, camphor and iron filings :

• Magnet is passed over the mixture several times. Iron filings get attached to the magnet and are separated.
• Camphor is separated from the salt by sublimation. Camphor is collected as sublimate and common salt is separated as residue.

Question 8.
Differentiate between physical and chemical changes.
Or
Write any three differences between a physical change and a chemical change.
Answer:
There is a comparison of two types of changes which are as follows :

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

Question 9.
Melting of wax is a physical change but burning of wax is a chemical change. Explain.
Answer:

• Melting of wax changes the state of wax from solid to liquid. No new substance is formed. The chemical nature of solid wax and liquid wax is the same. Hence, melting of wax is a physical change.
• Burning of wax gives new gaseous products. Both the physical and chemical changes are taking place. Hence, burning of wax is a chemical change.

Question 10.
Why is water considered as compound?
Answer:
Water is considered as compound because :

• Water is composed of two elements : hydrogen and oxygen.
• The ratio of hydrogen and oxygen by mass in any sample of pure water is the same.
• The properties of water are different from its constituent elements : hydrogen and oxygen.
• Water can be decomposed by chemical means only {e g. electrolytically) into hydrogen and oxygen.

Question 11.
Give some examples where the property : malleability and ductility of metals are used in our life.
Answer:
Malleability means that metals can be hammered into sheets and foils. For example : Aluminium foils are used for wrapping food stuffs, silver foils are used for decorative purposes for sweets and fruits.

Ductility means that metals can be drawn into wires. Example : Gold and silver wires are used in ornaments, aluminium and copper wires are used for conduction of electric current.

Question 12.
Write characteristics of compounds.
Answer:
Characteristics of compounds :

• Compounds are the substances formed by chemical combination of two or more elements.
• The constituent elements are present in a fixed ratio.
• A chemical reaction takes place during the formation of a compound.
• Properties of a compound are different to those of its elements.
• Constituent elements cannot be separated by physical processes.

Question 13.
How can you test the purity of a given substance?
Answer:
A pure substance always has the same taste, colour or texture at particular temperature and pressure and fixed melting or boiling point. For example – Pure water boils at 100°C but if it has some impurities then water boils at a temperature above 100°C.

Question 14.
What is chromatography? What is its advantage over other methods of separation?
Answer:
Chromatography is the process to separate different components of a mixture by absorbing over a suitable absorber. The main advantages of this technique is :

• It can be used for small amount of mixture.
• Component of mixture do not get wasted.
• Constituent of mixture can be identified apart from separation.

Question 15.
Explain why particles of a colloidal solution do not settle down when left undisturbed, while in the case of a suspension they do.
Answer:
Colloid particles resist settling rapidly to the bottom of a vessel due to Brownian motion. Brownian motion is the random movement of colloidal particles suspended in a liquid or gas, caused by collisions with molecules of the surrounding medium. The particles in colloids are in constant motion. It has strong intermolecular forces of attraction between the particles. But, in a suspension, the particles are – bigger than that of a colloid and also molecular interaction in a suspension is not strong enough to keep the particles suspended, and hence they settle down.

Question 16.
Smoke and fog both are aerosols. In what way are they different?
Answer:
Both smoke and fog are aerosols that has gas as its dispersion medium.
Smoke: Smoke is a mixture of gases. It is formed by the incomplete combustion of fossil fuels such as coal, oil, and natural gas and carried on the hot air from burning. Dispersed phase in smoke is solid.

Fog: Fog is a natural phenomenon when the humidity reaches 100%, in other words, the air is saturated with moisture and contains many tiny liquid water droplets collecting into the air at the surface of the Earth. The fog may rise to form a low layer of stratus. It is non-polluting. Dispersed phase in fog is liquid.

Question 17.
Draw a labelled diagram to show the water purification system in water works.
Answer:
The water purification system in water works can be shown as :

Question 18.
How can we obtain pure copper sulphate from an impure sample?
Answer:
To obtain pure copper sulphate from an impure sample, take approximately 5 gm of impure sample of copper sulphate in a china dish and dissolve it in minimum amount of water with filtering out the impurities. Now evaporate water from the CUSO₄ solution to get a saturated solution. Cover the solution with a filter papar and leave undisturbed at room temperature to cool slowly for a day. We . can see the crystals of copper sulphate in the china dish. This process is called crystallisation.

Question 19.
What is the principle of separating funnel technique. Write any two applications of it.
Answer:
Principle : According to this technique, immiscible liquids separate out in layers depending on their densities.

Applications :

• To separate the mixture of oil and water.
• In the extraction of the iron from its are. The lighter slag is removed from the top by this method to leave the molten iron at the bottom in the furnace.

Long Answer Type Questions

Question 1.
Give difference between true solutions and colloidal solutions.
Answer:

True solutions	Colloidal Solutions
1. The particle size is very small.	1. The particle size is bigger than true solution.
2. True solutions are clear and transparent.	2. Colloidal solutions are translucent.
3. The particles are not visible under microscope.	3. The particles are visible under microscope.
4. The particle of a true solution can be recovered.	4. The particles of a colloidal solution cannot be recovered.
5. The particles of a true solution do not scatter light.	5. The particles of a colloidal solution scatter light.

Question 2.
Which type of mixtures are separated using fractional distillation? Draw a labelled diagram of the apparatus and describe the process.
Answer:
To separate the mixture of two or more miscible liquids for which the difference in boiling points is less than 25 K, fractional distillation process is used. For example- For the separation of different gases from air, different fractions from petroleum products etc.

Apparatus : It is similar to that for simple distillation, except that a fractionating column is fitted in between the distillation flask and the condenses. A simple fractionating column is a tube packed with glass beads. The beads provide surface for the vapours to cool and condense repeatedly.

Question 3.
How can we separate a mixture of two immiscible liquid? Describe the process.
Answer:
The mixture of two immiscible liquids can be separated using separating funnel. For example- Mixture of kerosene oil and water and mixture of groundnut oil and water are immiscible hquids. These can be separated using separating funnel.

Method: Pour the mixture of oil and water in a separating funnel. Let it undisturbed for sometime to form separate layers to oil and water. Now open the stopcock of the funnel and pour out the lower layer of water carefully. After that close the stopcock of the separating funnel as the oil reaches the stopcock.

Question 4.
What are colloids? Give their characteristics.
Answer:
Colloidal solution is a heterogeneous mixture whose particles are bigger than size of particle in solution but cannot be visible through naked eye. When the beam of light passes through a colloid, then the path of light becomes visible. For example : Milk, smoke, etc.
(i) Brownian movement: The particles of a colloid show Brownian movement. The particles in it never fully settle down even leaving for a long time to remain undisturbed. They show constant zigzag movement. The type of movement is caused by the constant collisions between the particles of the dispersing medium and dispersed phase.

(ii) Tyndall effect: If the beam of light passes through a colloid then the path of light becomes visible. This is called Tyndall effect. The colloidal particles shine because they scatter the light falling on them in all directions.

Question 5.
(i) Under which category of mixtures will you classify alloys and why?
Answer:
When constituent particles of a combination of two or more element or compound retains their properties, then it is called mixture. In an alloy, the constituent particles lose, hence alloys are classified as homogeneous mixture. For example : Steel is an alloy of carbon and iron.

(ii) A solution is always a liquid. Comment.
Answer:
Since, a solution is the homogeneous mixture of two or more substances, thus it is not necessary that a solution would always be a liquid.

A solution can be in all the three states of matter. A solution is a homogeneous mixture and can be in all the three states of matter.

For example – Solution of alcohol in water is a liquid.
Air is a solution of different gases.
Alloy is a solution which is in the form of solids.

(iii) Can a solution be heterogeneous?
Answer:
Solution is defined as the homogeneous mixture, hence a solution cannot be heterogeneous. But, when a mixture becomes heterogeneous, it cannot be fall under the definition of solution.

Question 6.
Iron filings and sulphur were mixed together and divided into two parts, ‘A’ and ‘B’. Part ‘A’ was heated strongly, while part ‘B’ was not heated. Dilute hydrochloric acid was added to both the parts and evolution of gas was seen in both the cases. How will you identify the gases evolved?
Answer:

Hydrogen gas is released, when dilute hydrochloric acid is added to part ‘B’. Hydrogen gas can be tested by bringing a burning matchstick or candle near it. When a burning matchstick is placed near the hydrogen gas, it burns with a pop sound, which is a test for hydrogen gas.
\(\mathrm{Fe}_{(s)}+\mathrm{S}_{(s)} \stackrel{\text { Heat }}{\longrightarrow} \mathrm{FeS}_{(s)}\)
FeS + 2HCl_(aq) → FeCl₂ + H₂S
Hydrogen sulphide gas released when dilute hydrochloric acid was added to part ‘A’. Hydrogen sulphide gas smells like a rotten egg, hence it could be confirmed by its smell.

Question 7.
A child wanted to separate the mixture of dyes constituting a sample of ink. He marked a line by the ink on the filter paper and placed the filter paper in a glass containing water as shown in fig. The filter paper was removed when the water moved near the top of the filter paper.

(i) What would you expect to see, if the ink contains three different coloured components?
Answer:
Streaks of different colours can be seen on the filter paper.

(ii) Name the technique used by the child.
Answer:
Chromatography.

(iii) Suggest one more application of this technique.
Answer:
Chromatography is used for separating pigments present in chlorophyll.

Question 8.
A group of students took an old shoe box and covered it with a black paper from all sides. They fixed a source of light (a torch) at one end of the box by making a hole in it and made another hole on the other side to view the light. They placed a milk sample contained in a beaker/ tumbler in the box as shown in the fig. They were amazed to see that milk taken in the tumbler was illuminated. They tried the same activity by taking a salt solution but found that light simply passed through it.

(a) Explain why the milk sample was illuminated. Name the phenomenon involved.
Answer:
Since, milk is a colloid and when light scattered from the particles of colloids, it was illuminated, thus fight was illuminated when passed through the milk. This is known as Tyndall effect.

(b) Same results were not observed with a salt solution. Explain.
Answer:
For scattering of fight the size of particles should be large enough. Since the particles of solution were not enough to scatter the beam of fight, hence same results were not observed.

(c) Can you suggest two more solutions which would show the same effect as shown by the milk solution?
Answer:
Soap bubbles and fog are the colloids, hence show same effect, i.e. scattering of fight. This is known as Tyndall effect.

Question 9.
You are provided with a mixture containing sand, iron filings, ammonium chloride and sodium chloride. Describe the procedures you would use to separate these constituents from the mixture.
Answer:
The given mixture can be separated using the following process :
(i) Magnetic Separation: Using magnetic separation the iron filings can be separated from the given mixture.
In this, a magnet is moved just above the mixture, since iron is a magnetic substance, it is attracted by magnet and stuck with it. By this, first of all iron filings are separated.

(ii) Sublimation: After the separation of iron filings, ammonium chloride is separated by the process of sublimation.
Since, ammonium chloride is a sublimate and it turns into vapour directly without changing into liquid, thus when the mixture is sublimated, the ammonium chloride is deposited over the inner wall of funnel leaving the sodium chloride and sand in the watch glass. Ammonium chloride is separated by scratching from the inner wall of the funnel.

(iii) Filtration: Now the left mixture of sand and sodium chloride is put in water, after stirring the sodium chloride is dissolved in water. The solution is separated by the process of filtration. The sand leftover is separated out by using the filter paper.

(iv) Vaporisation: By the process of vaporisation, the liquid so obtained is vaporised and crystals of ammonium chloride can be obtained.
Hence, by using the methods of magnetic separation, sublimation, Alteration, vaporisation and crystallisation the component of given mixture of sand, iron filings, ammonium chloride and sodium chloride can be separated.

Question 10.
Draw a flow chart showing the separation of components of Air.
Answer:
Air is a homogeneous mixture and its components can be separated by fractional distillation.
Steps :

Gases	Oxygen	Argon	Nitrogen
Boiling point	-183	-186	-196
% air by volume	20.9	0.9	78.1

Question 11.
The ‘sea water’ can be classified as a homogeneous as well as heterogeneous mixture. Comment.
Answer:
A mixture which has a uniform composition throughout is called a homogeneous mixture or solution. A mixture which does not have a uniform composition throughout is called a heterogenous mixture.

(i) Sea water looks like a single substance, i.e. salt, water and the gases are mixed together so completely that they cannot be differentiated as individual substances. The particles of a solution are smaller than 1 nm (10^-9 metre) in diameter. So, they cannot be seen by naked eyes. Therefore, we can classify seawater as homogeneous mixture.

(ii) Sea water can be classified as a heterogeneous mixture because when we view it under the microscope we can find bits of dirt, and other impurities like mud, decayed plant, etc. floating in it. It is mixture of many salts, water and other many impurities. Apart from these, many gases (air) are also dissolved in sea water. Because of salt and some other bigger size of impurities, sea water is classified as heterogeneous mixture.

Numerical Questions

Question 1.
Calculate the grams of NaCl (5.25% by mass) in 245 grams of a commercial bleach solution.
Answer:

Question 2.
110 g solution of salt is concentration of solution.
Answer:
Mass of solute = 110 g
Mass of solution = 550 g
% composition = \(\frac{110 \times 100}{550}\)
Concentration = 20% by mass

Question 3.
How much water should be mixed with 12 mL of alcohol to obtain 12% of alcohol? Calculate.
Answer:
Volume of solute = 12 mL
Concentration of solution = 12%
Volume of water = x
We know that