CBSE Class 9 Science Is Matter around Us Pure assignment

CONCEPT DETAILS

SURVEY ANALYSIS

Conceptual levels of comprehension on the basis of feedback taken from the students

1. Pure Substance & mixture

Elements are made up of one kind of atoms only. Compounds are made up of one kind of molecules only.

Difference between Compound &Mixture

2. Types of Mixtures

Mixtures can also be grouped

i) on the basis of their physical states:

ii) on the basis of miscibility :

4. Separating the components of a mixture

The components of a heterogeneous mixture can be separated by

⇒ simple methods like -

hand picking , sieving , & Winnowing

⇒ special techniques like -

i) Evaporation : a mixture of salt and water or sugar and water.
ii) Centrifugation : Butter from curd, Fine mud particles suspended in water.
iii) Decantation : (Using separating funnel) : Oil from water.
iv) Sublimation : Camphor from salt,
v) Chromatography : Different pigments from an extract of flower petals.
vi) Distillation and fractional distillation : Separating components of Petroleum
viii) Magnetic separation: Iron pins from sand.

5. Concentration of Solution

The amount of solute present in a given amount (mass or volume) of solution.

Concentration of a solution = Amount of solute / Amount of solvent

OR

Amount of solute / Amount of solution

The concentration of a solution can be expressed as mass by mass percentage or as mass by volume percentage.

Mass by mass percentage of a solution = (Mass of solute / Mass of solution ) x 100

Mass by volume percentage of a solution = (Mass of solute / Volume of solution ) x 100

Types of Solutions

a) on the basis of size of solute particles:

types of colloids :

Colloidal solution is a heterogeneous mixture. It consists of two phases:-

(i) Dispersed phase : component present in small proportion
(ii) Dispersion medium : component present in large proportion

The particles of colloid are large enough to scatter a beam of light passing through it and make its path visible. Thus, they show Tyndall effect.

The colloidal particles are moving at random in a zigzag motion in all directions.

This type of zig-zag motion of colloidal particles is called Brownian movement.

b) on the basis of amount of solute:

c) on the basis of nature of solvent

6. Physical & Chemical Changes

Physical changes - Changes that do not result in the production of a new substance.

• If you melt a block of ice, you still have H2O at the end of the change.
• If you break a bottle, you still have glass.

Examples : melting, freezing, condensing, breaking, crushing, cutting, and bending.

Chemical changes - Changes that result in the production of another substance.

• As in the case of autumn leaves, a change in color is a clue to indicate a chemical change.
• a half eaten apple that turns brown.

7. Alloys

A material that has metallic properties and is composed of two or more chemical elements of which at least one is a metal.

• These cannot be separated into their components by physical methods.
• However, these are considered as mixture because these show the properties of its constituents and can have variable composition.
  The benefit of alloys is that you can combine metals that have varying characteristics to create an end product that is stronger, more flexible, or otherwise desirable to manufacturers.
• Aluminium alloys are extensively used in the production of automotive engine parts.
  Copper alloys have excellent electrical and thermal performance, good corrosion resistance, high ductility and relatively low cost.
• Stainless steel alloys are used for many commercial applications such as watch straps, cutlery etc.
• Titanium alloys have high strength, toughness and stiffness & are used in aerospace structures .

Exam Questions NCERT Class 9 Science Chapter 2 Is Matter Around Us Pure

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

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

Question : A colloid which have liquid as dispersed phase and solid as dispersion medium called-
Ans : Gel.

Question : The component of solution that is present in smaller proportion
Ans : Solute.

Question : (i) State the principle of the process of centrifugation.
(ii) List any three applications of centrifugation.
Ans : (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 :
(a) Used in dairies and homes to separate cream from milk or butter from cream.
(b) Used in washing machines to squeeze out water from clothes.
(c) Used in laboratories to separate colloidal particles from their solutions.
(d) Used in diagnostic labs for blood and urine test.

Question : Why is water considered as compound?
Ans : Water is considered as compound because :
(i) Water is composed of two elements : hydrogen and oxygen.
(ii) The ratio of hydrogen and oxygen by mass in any sample of pure water is the same.
(iii) The properties of water are different from its constituent elements : hydrogen and oxygen.
(iv) Water can be decomposed by chemical means only

Question : Write characteristics of compounds.
Ans : Characteristics of compounds :
(i) Compounds are the substances formed by chemical combination of two or more elements.
(ii) The constituent elements are present in a fixed ratio.
(iii) A chemical reaction takes place during the  formation of a compound.
(iv) Properties of a compound are different to those of its elements.
(v) Constituent elements cannot be separated by physical processes.

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

Question : Give natural example of mixture.
Ans : Sea water, minerals, soil.

Mark (1)

Q 1 Name the process which can be used to recover sugar from an aqueous sugar solution.

Q 2 What happens when a saturated solution is heated ?

Q 3 Name the process you would use to separate a mixture of water and alcohol.

Q 4 Give an example of an aqueous solution in which gas is dissolved.

Q 5 What is the cause of Tyndall effect as shown by colloid?

Q 6 How would you confirm that a colourless liquid given to you is pure water?

Q 7 Give two examples of colloidal solution.

Q 8 Name the technique to separate -
(a) Salt from sea water
(b) Butter from curd

Q 9 What is crystallization ?

Q 10 What is a saturated solution ?

Q 11 What is solution?

Marks (2)

Q 12 Which process would you use to separate colours in a dye ? Define the process.

Q 13 Fog and cloud are both colloidal in nature . How do they differ ?

Q 14 A compound is regarded as a pure substance but a mixture is not. Give reasons.

Q 15 What is sublimation ? Write two examples of sublimating substances.

Q 16 What do you understand by filtration ? Give one example also.

Q 17 Define colloid. Give one example also.

Q 18 What is meant by a suspension ? Write one example also.

Q 19 Define solution. Name its constituents also.

Q 20 What is meant by a mixture ? Write an example also.

Q 21 What do you understand by a pure substance? Give one exmaple also.

Q 22 What are suspensions?

Q 23 Define Alloys. Give one exmaple also.

Marks (3)

Q 24 (i) A solution has been prepared by dissolving 5 g of urea in 95 g of water. What is the mass percent of urea in the solution ?
(ii) Will blood show Tyndall effect?

Q 25 Classify the following into elements , compounds and mixtures-
(a) Soil (b) Magnesium (c) Salt solution (d) carbon dioxide (e) Gold (f) Methane

Q 26 How will you separate iron filings and ammonium chloride from the mixture of both with sand?

Q 27 How will you separate a mixture of mercury, water and benzene ?

Q 28 Write three differences between physical changes and chemical changes.

Q 29 Differentiate between homogeneous and heterogeneous mixtures.

Q 30 What are the two types of pure substances ? Explain.

Q 31 Write three properties of a colloid.

Q 32 (i) A solution contains 20 g of common salt in 160 g of water. Calculate the concentration in terms of mass percentage of the solution.
(ii) Can we separate a mixture of ammonium chloride and napthalene by sublimation? Give reasons also.

Q 33 Give three examples of solutions and mention th e solute and solvent present in them.

Q 34 (i) A solution contains 40 g of sugar dissolved in 360 g of water. Calculate the concentration of this solution.
(ii) Name the technique used to separate cream from milk.

Marks (5)

Q 35 Write 5 differences between compound and mixture.

Q 36 Write 5 properties of a true solution.

Q 37 (i) To make a saturated solution, 42g of sodium chloride is dissolved in100 g of water at 293K. Find its concentration at this temperature.
(ii) Name a domestic fuel which is (a) homogeneous (b) heterogeneous.

Q 38 Write 5 differences between a mixture and a compound.

Q 39 (a) Classify silver as metal or non-metal and write its four properties.
(b) If you have an iron rod and a plastic rod, which of them will produce sound when hit with an object?
(c) Differentiate copper and oxygen on the basis of their volume.
(d) Name the metal which is liquid at room temperature.

Q 40 (a) Classify sulphur as metal or non-metal and write four of its properties.
(b) Name –
(i) a non-metal which is a good conductor of electricity
(ii) a non-metal which is liquid at room temperature.
(iii) Name a non-metal that has lustre.

Q 41 (a) Classify a mixture of sugar in water as solution, colloid or suspension and write its six properties.
(b) Give one example each of solid solution and gas solution.
(c) Write the physical state of solute and solvent present in amalgam.

Q 42 (a) Is milk a pure substance? Give reasons also.
(b) Classify 24 carat gold as pure or impure substance. Give reasons also.
(c) Name two metalloids.
(d) Why carbon dioxide is classified as compound not as mixture?
(e) Write one example each of homogeneous mixture and heterogeneous mixture.

Q 43 (a) Give two reasons for why it is necessary to separate components of mixture of rice and small stones.
(b) Name the techniques used for:
(i) squeezing out water from clothes in washing machine.
(ii) separating components of ink.
(c) Kerosene oil and water do not mix with each other. What is the special name used to describe such liquids?
(d) You have a mixture of ammonium chloride and sodium chloride. Name the method you will use to separate them and why?

Q 44 (a) How will you separate the components of ink using chromatography? Explain with the help of a labelled diagram.
(b) What is the function of glass beads present in fractionating column?
(c) Which method out of evaporation and crystallisation is a better technique to separate sugar from sugar solution? Give reasons also.

Most Important Questions

Q 1 Gold can be drawn in wire. Name the property.

Q 2 Between sulphur and copper which one you will use for making wire.

Q 3 Silver is best conductor of electricity still the electrical wires are made of copper and aluminium. Why?

Q 4 (i) Name a soft metal.
(ii) Name the element present in diamond.
(iii) Name a non-metal having shining surface.
(iv) Name an element used as semi conductor

Q 5 Why metalloids are used as semiconductors?

Q 6 Why metals are used in making instruments like bells, tanpura and violin?

Q 7 Non-metals are bad conductors of electricity. Name a non metal which is conductor of electricity and is used in making electrodes.

Q 8 Is diamond element or compound? Write its composition.

Q 9 Non- metals are usually soft. Do you know any hard non-metal? If yes ,name it.

Q 10 From the following list make two separate lists one for physical changes and other for chemical changes.
baking of bread, switching of electric bulb, curdling of milk, dissolving sodium chloride in water, photosynthesis, rusting of iron, evaporation of water, formation of dew, sublimation of camphor, burning of charcoal or LPG, clotting of blood, crystallization of sugar, ripening of fruit, cooking of vegetables, melting of wax,

Q 11 Why water is a compound not a mixture?

Q 12 Which of the following will show properties of its constituents?
Methane or soil

Q 13 Name solute in brass

Q 14 Particle size of a substance was 50 nm. Is it solution or colloid or suspension

Q 15 A solution is prepared by dissolving 12g of sodium chloride in 150 g of solution. Calculate the mass percentage of solution.

Q 16 The properties of Solution, colloid and suspension are different from each other. Why?

Q 17 Name the solvent present on tincture of iodine.

Q 18 sample of vinegar has 40 gram of acetic acid in 140 ml of water. Calculate mass by volume percentage of the solution.

Q 19 Air is mixture of many gases. Is there any gas I it which acts as solvent? If yes name it and give reasons to support your answer.

Q 20 Write one example each of the following
(i) Aerosol
(ii) Emulsion
(iii) Foam
(iv) Sol
(v) Gel

Q 21 What is toned milk? Name the process and apparatus used to prepare toned milk in dairy.

Q 22 How will you separate the mixture of pebbles and bits of papers.

Q 23 Describe how will you separate the mixture of sand and sugar.

Q 24 Which of the following mixtures cannot be separated by sublimation?
(a) Mixture of ammonium chloride and sodium chloride
(b) Mixture of sugar and iodine
(c) Mixture of sodium chloride and anthracene
(d) Mixture of ammonium chloride and benzoic acid.

Q 25 Write the name of technique used to separate the mixture of engine oil and small pieces of metal.

Q 26 What is the principle of centrifugation?

Q 27 Name the process used to prepare the crystals of pure copper sulphate. Give reasons also.

Q 28 Name the process used to separate different gases from air.

Q 29 Mud is separated from muddy water by adding a chemical. Name it.

Q 30 There are many methods of separation of components of mixture. How will you decide which is the best method for separating constituents of given mixture?

Q 31 How will you separate the constituents of mixture of water, edible oil, and common salt

Q 32 Separate the constituents of mixture comprising of chalk powder, ammonium chloride and iron pieces.

Q 33 A liquid mixture has two liquids A and B. The boiling point of liquid A is 560C and that of liquid B is 700 C. Name the process by which these liquids can be separated.

Q 34 Why crystallization is better technique than evaporation

Q 35 Name the processes used to make river water fit for drinking

Question. What is the meaning of ‘Kroma’?

Answer:  ‘Kroma’ means colour in Greek.

Question. Naphthalene and sand can be separated by the process of-

Answer: Sublimation.

Question. Define the term Solvent.

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

Question. Name the constituents of German silver.

Answer: Copper and zinc.

Question. Identify the following as physical or chemical changes :
(a) Formation of cloud
(b) Magnetizing a iron nail
(c) Water boils to form steam
(d) An almirah gets rusted

Answer: (a) Formation of cloud Physical change
(b) Magnetizing a iron nail Physical change
(c) Water boils to form steam Physical change
(d) An almirah gets rusted Chemical change

Question. A homogeneous mixture of two or more substances called-

Answer: Solution.

Question. A colloid which have liquid as dispersed phase and solid as dispersion medium called-

Answer: Gel.

Question. Name two metals which are highly malleable and ductile.

Answer: Gold and silver.

Question. The component of solution that is present in smaller proportion

Answer: Solute.

Question. What are two types of matter on the basis of composition?

Answer: Pure substance and mixture.

Question. Give natural example of mixture.

Answer: Sea water, minerals, soil.

Question. Name two categories of pure substance.

Answer: Element and compound.

Question. Write the name of any two compounds which sublime on heating.

Answer: Ammonium chloride and iodine.

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

Answer: Crystallization.

Question. Give two examples of colloids from your daily life.

Answer: Milk and fog.

Question. Name the process by which all dyes present in black ink be recovered.

Answer: Chromatography.

Question36. 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 : Flow chart :

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

Question. Write the properties of a Solution.
Answer.
(i) It is a homogenous mixture of solute and solvent.
(ii) Solute particles cannot be separated by filtration.
(iii) True solution is clear and transparent.
(iv) True solution does not scatter light.
(v) Solute particles cannot settle out from solvent.

Question. Why is water considered as compound?
Answer. Water is considered as compound because :
(i) Water is composed of two elements : hydrogen and oxygen.
(ii) The ratio of hydrogen and oxygen by mass in any sample of pure water is the same.
(iii) The properties of water are different from its constituent elements : hydrogen and oxygen.
(iv) Water can be decomposed by chemical means only (e.g. electrolytically) into hydrogen and oxygen.

Question. What makes water as a universal solvent?
Answer. Water acts as a universal solution due to :
(i) The polar nature of its molecules.
(ii) Its ability to produce soluble salt on interaction with a large number of substances.

Question. Melting of wax is a physical change but burning of wax is a chemical change. Explain.
Answer.
(i) 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.
(ii) 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. (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 :
(a) Used in dairies and homes to separate cream from milk or butter from cream.
(b) Used in washing machines to squeeze out water from clothes.
(c) Used in laboratories to separate colloidal particles from their solutions.
(d) Used in diagnostic labs for blood and urine test.

Question. 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 by 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.