I. Very short answer type questions:
1. What do you mean by pure substance?
Ans. A substance is called pure when all of its constituent particles are of one kind and exhibit the same and definite set of properties throughout its bulk.
2. What is an element?
Ans. Element is a pure substance that can not be broken down into a simpler substance by the physical and chemical processes. It is made up of one kind of atoms. Ex - Na, Ca, etc.
3. What are the four types of elements?
Ans. Four types of elements are :
(i) Metals- Na,Ca (ii) Non metal - C, N
(iii) Metalloids- B, Si and (iv) Noble gases - He, Ne.
4. What is a mixture? What are its various types?
Ans. A mixture is composed of two or more substances whose particles are in contact but not chemically combined and have not lost their individual properties.
Ex. A mixture of sugar and water, salt and water, etc.
5. Name two types of mixture.
Ans. Two types of the mixture are
(a) Homogeneous mixture and
(b) Heterogeneous mixture.
6. What is a compound?
Ans.- Compound is a pure substance composed of two or more elements combined chemically in a fixed proportion by mass. The properties of a compound are different from the properties of its constituent elements.
Ans. The substance of the solution that dissolves the other component in is called the solvent.
8. Define solute.
Ans. The substance of the solution that is dissolved in the solvent is called the solute.
9. Define true solutions.
Ans. A homogeneous transparent mixture of two or more substances in which the size of the particles is about 10-10 m is called a true solution.
10. What is a saturated solution?
Ans. A saturated solution is a solution that contains solute at a given temperature as much solute as it can hold in a given mass of solvent.
11. What is the unsaturated solution?
Ans. An unsaturated solution is a solution that contains less solute at a given temperature as much solute as it can hold in a given mass of solvent.
12. Define solubility.
Ans. The solubility of the substance is the mass of the substance in grams that dissolve in 100 gm of solvent or solution.
13. Write the name of two methods to separate different gases from the air.
Ans. Two methods of separation of gases are diffusion and liquefaction.
14. What are alloys?
15. Write the name of the elements of the brass.
Ans. Copper (70%) and zinc (30%) are the two elements of brass.
16. Define crystallization.
17. Write the name of two elements that are liquid at room temperature.
Ans. Two elements at room temperature are Hg (mercury) and Br( bromine).
18. What are metalloids?
Ans. Metalloids are monatomic elements that show the properties of both metals and nonmetals. Ex - Arsenic, antimony, germanium, etc.
II. Short answer type questions:
1. Define solution, solute, and solvent?
Ans. Solution - A homogeneous mixture of two or more substances chemically non-reacting whose composition can be varied within certain limits called a solution.
Solute - Solute is the substance to be dissolved in the solvent.
Solvent - Solvent is the substance in which solute to be dissolved.
2. Write the name of solute and solvent in the following mixture:
(i) A solution of sugar in water.
(ii) A solution of iodine and alcohol (Tincture iodine)
(iii) Aerated drinks like soda water(aerated drink).(iv) Tincture iodine
Ans. (i) A solution of sugar in water - Solute - Sugar, Solvent - water
(ii) A solution of iodine and alcohol- Solute - Iodine, Solvent - alcohol.
(iii) Aerated drinks like soda water - Solute - Carbon dioxide, Solvent - water.
3. Define homogeneous and heterogeneous mixture.
Ans(a) Homogeneous mixture - A mixture that has the same composition and properties throughout their mass is called a homogeneous mixture. Ex.- sugar solution.
(b) Heterogeneous mixture - A mixture that has different compositions and properties in different parts of their mass is called a heterogeneous mixture. Ex.- sand and salt.
4. What is a colloidal solution? What are its various properties?
Ans. A colloidal solution is a heterogeneous mixture in which the size of the particle lies between 1mm (10-9 m) and 1000mm (10-6 m).
properties - Colloidal solution is fairly stable. Particles of this solution cannot be separated by filtration.
5. What is the Tyndall effect? Which kinds of solutions show it?
Ans. When a beam of light is passed through a glass of milk in a dark, a path of the beam is observed. This phenomenon is called the Tyndall effect, it is due to the scattering of light by the particles of colloidal solution.
6. Write a method to separate a mixture of salt and ammonium chloride?
Ans. Sublimation: In the mixture of salt and ammonium chloride, ammonium chloride is a sublime substance. On heating the mixture, ammonium chloride sublime and separate from the mixture and sodium chloride left in the container.
7. Define solubility. Write the factors on which solubility depends.
Ans. Solubility - The amount of the solute present in the saturated solution at a given temperature is called its solubility. Therefore solubility of a solute in a particular solvent at a fixed temperature is the equivalent of the maximum number of grams of the solute necessary to saturate 100 g of that solvent at that temperature.Factors on which solubility depends -
(i) Temperature- The solubility of solids in water increases with the rise in temperature and solubility of gases in water decreases with rising temperatures.
(ii) Size of the solute particles - Smaller the size of the particles, greater the solubility of that solute. (smaller size of the particles, greater it's total surface area exposed to the solvent).
(iii) Stirring - This helps to increase the rate of formation of a solution.
8. How can we separate a mixture of salt and ammonium chloride?
Ans. A mixture of salt and ammonium chloride can be separated by a sublimation process. In this process mixture of a salt and ammonium chloride is heated in a dish covered with a funnel, sublime substance ammonium chloride changes into vapour and condenses into a solid in the neck of the funnel whereas common salt is left behind the dish.
9. Write two examples where the crystallization technique is better than evaporation.
Ans. Crystallization technique is better than
simple evaporation technique as –(i) Some solids decompose or some, like sugar, may get charred on heating to dryness.
(ii) some impurities may remain dissolved in the solution even after filtration. On evaporation, these contaminate the solid.
Ex- (i) Purification of salt that we get from seawater.
(ii) Separation of crystals of alum (phitkiri) from impure samples.
10. Write the differences between a physical and a chemical change.
Ans. Physical change - A physical change is the process, which changes the shape, size, physical state, but not it's chemical composition.
Ex- When ice is heated, it changes into water and then changes into water vapour, but there is no change in chemical properties.
Ex- When ice is heated, it changes into water and then changes into water vapour, but there is no change in chemical properties.
Chemical change - A chemical change is a permanent change in which a new substance is formed with different compositions and chemical properties.
Example - When iron is kept in moist air, it slowly changes into a brown substance called rust with different composition and chemical properties.
Example - When iron is kept in moist air, it slowly changes into a brown substance called rust with different composition and chemical properties.
11. The interconversion of states is a physical change, why?
Ans. The interconversion of states is a physical
change because these changes occur without
a change in the chemical properties of the substance and in the composition.
Although ice, water, and water vapour all are different in a state like solid, liquid, and gas, they are chemically the same.
III. Long answer type questions:
1. What is a suspension? What are the properties of suspension?
Ans. It is a heterogeneous mixture in which the solute particles do not dissolve and remain suspended throughout the liquid.
Properties -i. Suspensions are a heterogeneous mixture.
ii. The particles of its greater than 1000 mm.
iii. Suspension neither passes through animal membranes nor through filter paper.
iv. Suspension particles may scatter light passing through it.
2. A solution contains 60g of NaCl in 400g of water. Calculate the concentration in terms of mass by the mass percentage of the solution.
Ans . Given:
Mass of solute - 60 gm
Mass of solution = mass of solute + mass of solvent
= 60 + 400 = 460 gm.
Mass percentage = mass of solute x 100
Mass of solution
Mass percentage = 60 x 100 =13.04%
460
3. What is centrifugation? Where it is used?
Ans. Centrifugation is the method of separating solid particles from a solution according to their size, shape, and density.
It is used:
i. In washing machines to squeeze out water from the wet cloths.
ii. For separating cream from milk.
iii. In diagnostic laboratories for testing blood/urine.
4. What is chromatography? What are its various applications and underline the basic principle involved?
Ans. Chromatography a technique for the separation of a mixture by passing it in solution or suspension through a medium in which the components move at different rates.
Principle - It is based on the difference in the rate of adsorption of different substances on the surface of a solid medium. It occurs in two phases, one is the stationary phase and the other is the moving phase.
Applications - i. Chromatography is used in industrial processes to purify chemicals
ii. Forensic Testing: This can take the form of crime scene testing (the analysis of blood or cloth samples) and iii. Drug testing.
5. What is crystallization? Where is it used? Why is this better than a simple evaporation technique?
Ans. It is a Separation technique. The process of cooling a concentrated hot solution of a substance to obtain crystals is called crystallization. The process of crystallization is used for obtaining a pure substance from the impure substance.
Uses -
i. The salt we get from seawater has many impurities in it. The crystallization method is used to remove these impurities.
ii. To get sugar crystal from the sugar solution.
Reasons for being better than simple evaporation: The process of evaporation gives residue which may contain impurities. When there is a requirement to obtain solid without impurity, the crystallization method is preferred.
In some cases e.g. sugar crystal cannot be obtained by simple evaporation technique because sugar gets charred on heating to dryness. In such cases, the crystallisation technique is applied.
6. What is a distillation and fractional distillation? What is the basic property that separates the two methods?
Ans. Distillation is a process of heating a liquid into vapour and then cooling the vapour to get back liquid. Distillation is a widely used method for separating the component substances from a liquid mixture by selective evaporation and condensation.
Fractional distillation - Fractional distillation is the process of separating two miscible liquids into fractions differing in boiling point (and hence chemical composition) by means of distillation, the distillate is collected in fractions boiling at different temperature.
7. What are the properties of a solution?
Ans. Properties of a solution:
(i) The particles of a solution are smaller than 1 nm (10-9 meters) in diameter. They cannot be seen by naked eyes.
(ii) It is a homogeneous mixture.
(iii) They
do not scatter a beam of light passing
through the solution. So, the path of
light is not visible in a solution.
(iv) The solute particles cannot be
separated from the mixture by the
process of filtration. The solute particles
do not settle down when left undisturbed.
8. What are the differences between saturated and unsaturated solutions?
Ans. Saturated solution: (i)A saturated solution is a solution which contains solute at a particular temperature as much solute as it can hold in a given mass of solvent
(ii) No more solute can be dissolved in a saturated solution at this temperature.
Unsaturated solution :
(i) An unsaturated solution is a solution that contains less solute at a given temperature as much solute as it can hold in a given mass of solvent.
(i) An unsaturated solution is a solution that contains less solute at a given temperature as much solute as it can hold in a given mass of solvent.
9. What do you mean by the concentration of the solution? Write an expression of concentration of the solution.
Ans. The concentration of a solution is the
amount of solute present in a given amount of solution, or the amount
of solute dissolved in a given mass or volume
of solvent.
The concentration of solution = Amount of solute/
Amount of solution
Or
Amount of solute/Amount of solvent.
Or Mass by the mass percentage of a solution = (Mass of solute / Mass of solution) ×100
Or Mass by volume percentage of a solution = (Mass of solute/volume of solution) ×100
10. What are the dispersed phase and dispersed medium in the colloidal solution? Write some examples.
Ans. The components of a colloidal solution are
the dispersed phase and the dispersion
medium. The solute-like component of the
dispersed particles in a colloid form the
dispersed phase, and the component in which
the dispersed phase is suspended is known
as the dispersing medium.
A few common examples are :
Dispersed
phase
|
Dispersing Medium
|
Type
|
Example
|
Liquid
|
Gas
|
Aerosol
|
Fog, clouds, mist
|
Solid
|
Gas
|
Aerosol
|
Smoke, automobile
exhaust
|
Gas
|
Liquid
|
Foam
|
Shaving cream
|
Liquid
|
Liquid
|
Emulsion
|
Milk, face cream
|
Solid
|
Liquid
|
Sol
|
Milk of magnesia,
mud
|
Gas
|
Solid
|
Foam
|
Foam, rubber, sponge,
pumice
|
Liquid
|
Solid
|
Gel
|
Jelly, cheese, butter
|
Solid
|
Solid
|
Solid Sol
|
Coloured gemstone, milky
glass
|
11. How we can obtain coloured component (dye) from blue-black ink?
Ans. Evaporation can be used to
obtain coloured component which is volatile, from its solution. Keep a watch glass on the
mouth of the beaker which is half-filled with water. Put a few drops of ink on
the watch glass. Now start heating the beaker. We should not heat the ink
directly. we will see that evaporation is taking place from the watch glass.
Continue heating as the evaporation goes on and stop heating when we do not see
any further change on the watch glass.
Now we will observe that the water gets evaporated
from the watch glass and residue is left in the watch glass which is
the coloured component that is a dye. In this way, evaporation can be used to obtain volatile components from its solution.
12. How can we separate cream from milk? Write three applications of the centrifugation method?
Ans. Milk is a mixture that contains different amounts of fat. In this mixture, particles are very small and pass through a filter paper. So filtration technique cannot be used for separation. Such mixtures are separated by the centrifugation process. In this process, denser particles of milk are forced to the bottom and the lighter particle cream stays at the top when spun rapidly.
Three applications:
(i) Used in dairies and home to separate butter from cream.
(ii) Used in washing machines to squeeze out water from wet clothes.
(iii) Used in diagnostic laboratories for blood and urine tests.
Ans. Milk is a mixture that contains different amounts of fat. In this mixture, particles are very small and pass through a filter paper. So filtration technique cannot be used for separation. Such mixtures are separated by the centrifugation process. In this process, denser particles of milk are forced to the bottom and the lighter particle cream stays at the top when spun rapidly.
Three applications:
(i) Used in dairies and home to separate butter from cream.
(ii) Used in washing machines to squeeze out water from wet clothes.
(iii) Used in diagnostic laboratories for blood and urine tests.
13. What is the principle of separation of immiscible liquids?
How can we separate a mixture of two immiscible liquids?
Writes its applications.
Ans. The principle of separation of immiscible liquids separates out in different layers depending on their different densities.
To separate kerosene oil from water using a separating funnel.
Pour the mixture of kerosene oil and water in a separating funnel.
Let it stand undisturbed for some time so that separate layers of oil and water are formed.
Open the stopcock of the separating funnel and pour out the lower layer of water carefully.
Close the stopcock of the separating funnel as the oil reaches the stop-cock.
In this way, we can separate two immiscible liquids.
Applications:
(i)To separate a mixture of oil and water.
(ii)In the extraction of iron from its ore, the lighter slag is removed from the top
(iii)by this method to leave the molten iron at the bottom in the furnace.
How can we separate a mixture of two immiscible liquids?
Writes its applications.
Ans. The principle of separation of immiscible liquids separates out in different layers depending on their different densities.
To separate kerosene oil from water using a separating funnel.
Pour the mixture of kerosene oil and water in a separating funnel.
Let it stand undisturbed for some time so that separate layers of oil and water are formed.
Open the stopcock of the separating funnel and pour out the lower layer of water carefully.
Close the stopcock of the separating funnel as the oil reaches the stop-cock.
In this way, we can separate two immiscible liquids.
Applications:
(i)To separate a mixture of oil and water.
(ii)In the extraction of iron from its ore, the lighter slag is removed from the top
(iii)by this method to leave the molten iron at the bottom in the furnace.
14. Define chromatography. Write its applications.
Ans. Chromatography is a technique used for the separation of those solutes that dissolve in the same solvent. This technique was first used for the separation of colours, so this name was given.
Applications :
To separate:
(i) Colours in a dye
(ii) Pigments from natural colours
(iii) Drugs from the blood.
Ans. Chromatography is a technique used for the separation of those solutes that dissolve in the same solvent. This technique was first used for the separation of colours, so this name was given.
Applications :
To separate:
(i) Colours in a dye
(ii) Pigments from natural colours
(iii) Drugs from the blood.
15. How we can obtain different gases from the air?
Ans. Air is a homogeneous mixture and we can be obtained different gases by fractional distillation. The flow diagram shows the steps of the process.
Step 1: First we compress air and cool by increasing pressure and decreasing temperature. Air converted into liquid air.
Step 2: Now allow the liquid air to worm up slowly in a fractional distillation column.
Gases get separated at a different height.
In this way, we can obtain different gases from the air.
Ans. Air is a homogeneous mixture and we can be obtained different gases by fractional distillation. The flow diagram shows the steps of the process.
Step 1: First we compress air and cool by increasing pressure and decreasing temperature. Air converted into liquid air.
Step 2: Now allow the liquid air to worm up slowly in a fractional distillation column.
Gases get separated at a different height.
In this way, we can obtain different gases from the air.
16. Explain with an example where both physical and chemical changes take place.
Ans. A physical change is a process, which changes the shape, size, physical state, but not it's the chemical composition.
A chemical change is a permanent change in which a new substance is formed with different compositions and chemical properties.
When a candle burns both physical and chemical changes take place.
The melting of wax and vapourization of melted wax is a physical change. The burning of wax is a chemical change in which new substance carbon dioxide and water vapour formed.
17. Write five properties of metal and nonmetal.
Ans. Properties of metals:
(i) They have a luster
(ii) They conduct heat and electricity.
(iii) They are ductile and can be drawn into wires.
(iv) They are malleable and can be hammered into thin sheets.
(v) They are sonorous, make a ringing sound when hit.
Examples of metals are gold, silver, copper, iron, sodium, potassium, etc. Mercury is the only metal that is liquid at room temperature.
Properties of nonmetals:
(i) They are not lustrous.
(ii) They are poor conductors of heat and electricity.
(iii) They are not ductile.
(iv) They display a variety of colours.
(v) They are not sonorous or malleable.
Examples of non-metals are oxygen, hydrogen, nitrogen, bromine, iodine, chlorine, carbon, etc.
Ans. Properties of metals:
(i) They have a luster
(ii) They conduct heat and electricity.
(iii) They are ductile and can be drawn into wires.
(iv) They are malleable and can be hammered into thin sheets.
(v) They are sonorous, make a ringing sound when hit.
Examples of metals are gold, silver, copper, iron, sodium, potassium, etc. Mercury is the only metal that is liquid at room temperature.
Properties of nonmetals:
(i) They are not lustrous.
(ii) They are poor conductors of heat and electricity.
(iii) They are not ductile.
(iv) They display a variety of colours.
(v) They are not sonorous or malleable.
Examples of non-metals are oxygen, hydrogen, nitrogen, bromine, iodine, chlorine, carbon, etc.
18. Write five differences between compound and mixture.
Ans.
Mixtures
|
Compounds
|
1. Elements or compounds just mix together to form a mixture and no the new compound is formed.
|
1. Elements react to form new compounds.
|
2. A mixture has a variable composition.
|
.2. The composition of each new substance is always fixed.
|
3. A mixture shows the properties of the constituent substances.
|
3. The new substance has totally different properties.
|
4. The constituents can be separated by physical methods.
|
4. The constituents can be separated only by chemical methods.
|
5. The mixture may be homogenous or heterogeneous.
|
5. The compound is a
pure substance.
|
19. How we can obtain pure copper sulfate from an impure sample?
Ans. We can obtain pure copper sulfate from an impure sample by the crystallization process.
Take approximately 5 g some impure sample of copper sulfate in a china dish. Dissolve it in a minimum amount of water and filter the impurities out. Evaporate water from the copper sulfate solution so as to get a saturated solution then cover the solution with a filter paper and leave it undisturbed at room temperature to cool slowly for a day. After some days we will obtain the crystals of copper sulfate in the china dish. This process is called crystallization,
20. What do you mean by the concentration of the solution?
Ans. The concentration of a solution is the amount of solute present in a given amount (mass or volume) of the solution, or the amount of solute dissolved in a given mass or volume of solvent.
The concentration of solution = Amount of solute/ Amount of solution Or Amount of solute/Amount of solvent.
21. Write the two expressions of the concentration of a solution.
Ans. Two expressions of the concentration of a solution are
(i) Mass by the mass percentage of a solution
=( Mass of solute × 100)/Mass of solution
(ii) Mass by volume percentage of a solution
= (Mass of solute ×100 )/Volume of solution.
22. Write the differences between a physical and a chemical change.
Ans. Physical change - A physical change is a process that changes the shape, size, physical state, but not it's chemical composition.
Ex- When ice is heated, it changes into water and then changes into water vapour, but there is no change in chemical properties.
Chemical change - A chemical change is a permanent change in which a new substance is formed with different compositions and chemical properties.
Example - When iron is kept in moist air, it slowly changes into a brown substance called rust with different composition and chemical properties.
23. A solution contains 40 g of common salt in 320 g of water. Calculate the concentration in terms of mass by the mass percentage of the solution.
Ans. Given:
Mass of solute - 40 gm. Mass of solvent = 320 gm
Mass of solution = mass of solute + mass of solvent
= 40 + 320 = 360 gm.
Mass percentage = mass of solute x 100
Mass of solution
Mass percentage = 40 x 100 =11.11%
360
NCERT QUESTIONS:
- What is meant by a pure substance?
- List the points of differences between homogeneous and heterogeneous mixtures.
- Differentiate between homogeneous and heterogeneous mixtures with examples.
- How are sol, solution, and suspension different from each other?
- To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature.
- How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than 25ºC), which are miscible with each other?
- Name the technique to separate: (i) butter from curd, (ii) salt from sea-water, (iii) camphor from salt.
- What type of mixtures are separated by the technique of crystallization?
- Classify the following as chemical or physical changes:
• cutting of trees,
• melting of butter in a pan,
• rusting of almirah,
• boiling of water to form steam,
• passing of electric current, through water and the water breaking down into hydrogen and oxygen gases,
• dissolving common salt in water,
• making a fruit salad with raw fruits, and
• burning of paper and wood. - Try segregating the things around you as pure substances or mixtures.
- Which separation techniques will you apply for the separation of the following?
(a) Sodium chloride from its solution in water.
(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.
(c) Small pieces of metal in the engine oil of a car.
(d) Different pigments from an extract of flower petals.
(e) Butter from curd.
(f) Oil from water.
(g) Tea leaves from tea.
(h) Iron pins from sand.
(i) Wheat grains from husk.
(j) Fine mud particles suspended in water. - Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate, and residue.
- (a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313 K?
(b) Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to cool at room temperature. What would she observe as the solution cools? Explain.
(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?
(d) What is the effect of change of temperature on the solubility of a salt? - Explain the following giving examples.
(a) saturated solution
(b) pure substance
(c) colloid
(d) suspension - Classify each of the following as a homogeneous or heterogeneous mixture. soda water, wood, air, soil, vinegar, filtered tea.
- How would you confirm that a colourless liquid given to you is pure water?
- Which of the following materials fall into the category of a “pure substance”? (a) Ice (b) Milk (c) Iron
(d) Hydrochloric acid (e) Calcium oxide
(f) Mercury (g) Brick (h) Wood (i) Air. - Identify the solutions among the following mixtures.
(a) Soil (b) Sea water (c) Air (d) Coal (e) Soda water. - Which of the following will show the “Tyndall effect”?
(a) Salt solution (b) Milk (c) Copper sulfate solution (d) Starch solution. - Classify the following into elements, compounds and mixtures.
(a) Sodium (b) Soil (c) Sugar solution
(d) Silver (e) Calcium carbonate (f) Tin
(g) Silicon (h) Coal (i) Air (j) Soap (k) Methane
(l) Carbon dioxide (m) Blood. - Which of the following are chemical changes?
(a) Growth of a plant (b) Rusting of iron (c) Mixing of iron filings and sand
(d) Cooking of food (e) Digestion of food (f) Freezing of water (g) Burning of a candle.
