Long Answers - Is Matter Around Us Pure, Science, Class 9 PDF Download

Q1. Give the difference between true solution, colloidal solution and suspension.
 Ans. The difference between true solution, colloidal solution and suspension

Q2. State the different types of colloids with examples.
 Ans. Different colloids are formed due to different dispersed phase and dispersing medium.

Q3. (a) Define solution. (b) Give different types of solutions with one example each.
 Ans. (a) solution: It is a homogeneous mixture of two or more substances. It consists of solute and solvent.
(b) Different types of solution:
(i) Based on solvent—Aqueous and non-aqueous Aqueous solution has water as solvent (sugar + water) Non-aqueous solution has some other solvent but not water. Example, (sulphur + carbon disulphide)
(ii) Depending on the amount of solute dissolved in solvent—Dilute solution and concentrated solution Dilute solution—Less amount of solute particles are present in a solvent.
Concentrated solution—Amount of solute present in its maximum capacity in a solvent.
(iii) Amount of solute present in its maximum capacity at a given temperature— Saturated and unsaturated solution. Saturated solution—It is a solution in which no more solute can further dissolve in a given solvent at a given temperature.
Unsaturated solution—It is a solution in which some more solute can dissolve in a solvent at a given temperature.
(iv) Depending on the size of solute particles

Q4. How can you separate the following mixtures?
 (a) Sand + iron (b) Cream from milk (c) Salt + water (d) Ammonium chloride + NaCl (e) Copper sulphate + water (f) Rice and dal (uncooked) (g) Gases from air (h) Petrol and diesel from crude oil (i) Drugs from blood (j) Acetone from water
 Ans.

Q5.

The Rf value of the mixture used in chromatogram is: A = 0.4, B = 0.5, C = 0.7, D = 0.9
 (a) Calculate the Rf value of the two chromatograms shown in the figure.
 (b) Name one solvent used in chromatography.
 (c) Why is the line used for spotting drawn with pencil?
 (d) If the chromatograms are colorless how can you locate them on the paper?
 Ans. (a) Use scale to find the solvent front and find the Rf value by using the above formula.
(b) Water and alcohol.
(c) The pencil will not interfere in the chromatography.
(d) By using the locating agent like ninhydrin the colorless spots can be detected.
 

Q6. A metal coin is dissolved in acid. Chromatography is used to test the solution formed. The diagram given shows the chromatogram obtained.
 (a) Describe how the chromatogram would be set up in the laboratory.
 (b) What can you say about the composition of the coin?
 (c) Which of the spots (A, B or C ) is more soluble in the 

solvent that was used in the chromatography?
 Ans. (a) To set up the chromatogram use the solvent, take chromatography paper and draw the base line with pencil, place the spot of the chromatogram on this line and dip it in the solvent such that the base line of the paper stays above the solvent line.
(b) The coin consists of three different materials as the chromatogram shows three spots.
(c) The spot B is more soluble in the solvent as it travelled the maximum distance.
 

Q7. Compare the simple distillation and fractional distillation.
 Ans. simple distillation: The distillation flask is used to separate two substances having the difference in their boiling point more than 23 degrees. fractional distillation: The fractionating column in the set up helps in the separation of the fractions which may have very low difference in their boiling point. The fractionating column is a long chamber which controls the separation of one fraction at a time starting from the one with the lowest boiling point.

Activity-Based Questions 

1. Let us divide the class into groups A, B, C and D.

•  Group A takes a beaker containing 50 ml of water and one spatula full of copper sulphate powder. Group B takes 50 ml of water and two spatula full of copper sulphate powder in a beaker.
• Groups C and D can take different amounts of copper sulphate and potassium permanganate or common salt (sodium chloride) and mix the given components to form a mixture.
• Report the observations on the uniformity in colour and texture.

Observations:

• Groups A and B have obtained a uniform composition throughout. Such mixtures are called homogeneous mixtures or solutions.

Some other examples of mixtures are:
(i) salt dissolved in water.
(ii) sugar dissolved in water.

• Comparing the colour of the solutions of the two groups. Though both the groups have obtained copper sulphate solution but the intensity of colour of the solutions is different. This shows that a homogeneous mixtures can have a variable composition. l Groups C and D have obtained mixtures, which contain physically distinct parts and have non-uniform compositions. Such mixtures are called heterogeneous mixtures.

Example: Mixture of sodium chloride and iron fillings, salt and sulphur; and oil and water are examples of heterogeneous mixtures.

2.

• Take approximately 50 ml of water each in two separate beakers.
• Add salt in one beaker and barium chloride in the second beaker with continuous stirring.
• When no more solute can be dissolved, heat the contents of the beaker to raise the temperature by about 5ºC.
• Start adding the solute again. 
• Is the amount of salt and sugar or barium chloride, that can be dissolved in water at a given temperature, the same?

Answers:

• Beakers (A) and (B) are saturated solutions. On heating the beakers, the solution becomes unsaturated. Some more solute can be dissolved in it.
• No, different substances in a given solvent have different solubilities at the same temperature.

3. 

• Let us again divide the class into four groups—A, B, C and D. l Distribute the following samples to each groups:
  – Few crystals of copper sulphate to group (A).
  – One spatula full of copper sulphate to group (B).
  – Chalk powder or wheat flour to group (C).
  – Few drops of milk or ink to group (D).
• Each group should add the given sample in water and stir properly using a glass rod. Are the particles in the mixtures visible?
• Direct a beam of light from a torch through the beaker containing the mixture and observe from the front. Was the path of the beam of light visible?
• Leave the mixtures undisturbed for a few minutes (and set up the filtration apparatus in the meantime).

Is the mixture stable or do the particles begin to settle after sometime?

• Filter the mixture. Is there any residue on the filter paper?
• Discuss the results and form an opinion.

observations:

4.

• Fill half a beaker with water.
• Put a watch glass on the mouth of the beaker, as shown in the figure given on next page.
• Put few drops of ink on the watch glass.
• Now start heating the beaker. We do not want to heat the ink directly. You will see that evaporation is taking place from the watch glass.
• Continue heating as the evaporation goes on and stop heating when you do not see any further change on the watch glass.
• Observe carefully and record your observations.

Questions: 

• What do you think has got evaporated from the watch glass?
• Is there a residue on the watch glass? 
• What is your interpretation? Is ink a single substance (pure) or is it a mixture?

Answers:

• Water and volatile substances get evaporated from the watch glass.
• Yes, residue is obtained on the watch glass.
• Ink is a mixture of a dye in water.

5.

• Take some full-cream milk in a test tube.
• Centrifuge it by using centrifuging machine for two minutes. If a centrifuging machine is not available in the school, you can do this activity at home by using a milk churner, used in the kitchen.
• If you have a milk dairy nearby, visit it and ask
  (i) how they separate cream from milk.
  (ii) how they make cheese (paneer) from milk.

Questions:

• What do you observe on churning the milk?
• Explain how the separation of cream from milk takes place.

Answers:

• On churning of the milk, denser solid particles in the test tube remain at the bottom and the lighter particles stay at the top.
• Separation of cream from milk takes place by centrifugation due to the differences in the densities of the particles present in a mixture.

6.

• Let us try 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 sometime 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 stopcock.

Question: Why a separating funnel is used?
 Answer: Separating funnel is used to separate two immiscible liquids, because the two layers are formed depending on their densities and the liquids can be separated.

 7.

• Take a thin strip of filter paper.
• Draw a line on it using a pencil, approximately 3 cm above the lower edge (as shown in figure given below).

• Put a small drop of ink (water soluble, that is, from a sketch pen or fountain pen) at the centre of the line. Let it dry.
• Lower the filter paper into a jar/glass/beaker/ test-tube containing water so that the drop of ink on the paper is just above the water level, as shown in the figure above and leave it undisturbed.
• Watch carefully, as the water rises up on the filter paper. Record your observations.
   

Questions: 

• What do you observe on the filter paper as the water rises on it?
• Do you obtain different colours on the filter paper strip? 
• What according to you, can be the reason for the rise of the coloured spot on the paper strip?

Answers:

• As the water rises up, the ink particles (dye) also rises along with it.
• Different colours are obtained on the filter paper strip as ink contains dye–mixture of two or more colour.
• The rise of the coloured spot on the paper strip shows the solubility of coloured components of ink in water. Those which rise faster are more soluble and get separated from the mixture.

8. 

• Let us try to separate acetone and water from their mixture.
• Take the mixture in a distillation flask. Fit it with a thermometer.
• Arrange the apparatus as shown in the figure below.
• Heat the mixture slowly keeping a close watch at the thermometer.
• The acetone vaporises, condenses in the condenser and can be collected from the condenser outlet.

• Water is left behind in the distillation flask.
   

Questions: 

• What do you observe as you start heating the mixture? 
• At what temperature does the thermometer reading become constant for some time?
• What is the boiling point of acetone? 
• Why do the two components separate?

Answers:

• On heating the mixture, the vapours of more volatile liquid i.e., acetone start rising in the flask.
• Thermometer reading became constant at 56.6°C.
• Boiling point of acetone is 56.6°C.
• The two components separate due to difference in their boiling point and these substances do not decompose on heating. The difference in the boiling point of acetone and water is large.

9.

• Take some (approximately 5 g) impure sample of copper sulphate in a china dish.
• Dissolve it in minimum amount of water.
• Filter the impurities out.
• Evaporate water from the copper sulphate solution so as to get a saturated solution.
• Cover the solution with a filter paper and leave it undisturbed at room temperature to cool slowly for a day.
• You will obtain the crystals of copper sulphate in the china dish.
• This process is called crystallisation.
   

Questions:

• What do you observe in the china dish? 
• Do the crystals look alike? 
• How will you separate the crystals from the liquid in the china dish?

Answers:

• The crystals of copper sulphate are obtained in the china dish.
• The crystals look alike to some extent.
• To separate crystals from the liquid in the china dish, we will use filter paper. The crystals will be spread on the filter paper so that water is absorbed by the paper and crystals are dried.

10. 

• Divide the class into two groups. Give 50 g of iron filings and 3 g of sulphur powder in a china dish to both the groups. 

Group I: Mix and crush iron filings and sulphur powder.

• Group II: Mix and crush iron filings and sulphur powder. Heat this mixture strongly till red hot. Remove from flame and let the mixture cool.
• Group I and II: l Check for magnetism in the material obtained. Bring a magnet near the material and check if the material is attracted towards the magnet.
• Compare the texture and colour of the material obtained by the groups.
• Add carbon disulphide to one part of the material obtained. Stir well and filter.
• Add dilute sulphuric acid or dilute hydrochloric acid to the other part of the material obtained. (Note: Teacher supervision is necessary for this activity.)
• Perform all the above steps with both the elements. (iron and sulphur separately).
   

Questions:

• Did the material obtained by the two groups look the same?
• Which group has obtained a material with magnetic properties? 
• Can we separate the components of the material obtained?
• On adding dilute sulphuric acid or dilute hydrochloric acid, did both the groups obtain a gas? Did the gas in both the cases smell the same or different?

Answers:

• The material obtained after the activity by the two groups looked different.
• Group I obtained a material with magnetic properties.
• The components of the material can be separated only in the case of Group I.
• Yes, both the groups obtained a gas, on adding dilute sulphuric acid or dilute hydrochloric acid.
  The smell of the gas in both the cases is different.
  The gas obtained by group I is hydrogen. It is colourless and odourless. The gas obtained by group II is hydrogen sulphide. It is a colourless gas but smells like rotten egg.

Value-Based Questions

Q1. Anil’s sister accidentally added some water into the bottle containing olive oil and she was afraid of the scolding. Anil helped his sister and separated the water from olive oil using bottle as separating funnel.
 (a) What is the principle of using and working of separating funnel?
 (b) Suggest two separation techniques used to separate liquid mixtures.
 (c) What value of Anil is seen in the above case?
 Ans. (a) The principle of separating funnel is difference in the densities of two liquids.
(b) Liquid mixtures can be separated by distillation and fractional distillation. (c) Anil showed the value of helping, caring and responsible behaviour.
 

Q2. Preeti saw a labour entering into the sewage manhole immediately after removing the lid. She promptly stopped the labour from entering into the manhole and told him to wait for some time before he enters into it.
 (a) What will happen if the labour immediately enters into the manhole (for cleaning) after removing the lid?
 (b) Name main gases that are released from the manhole.
 (c) What value of Preeti is seen in the above act?
 Ans. (a) If the labour immediately enters the manhole on removing its lid he would die due to suffocation and inhalation of poisonous gases which are compressed and released by sewage.
(b) Gases released from the sewage manhole are methane, carbon dioxide and hydrogen sulphide.
(c) Preeti shows the value of moral responsible behaviour and aware citizen.
 

Q3. Prasanna wanted to buy a deodorant from the shop. While buying a bottle he felt that it was slightly heavier than usual deodorant bottle that he purchased everytime. He read the weight mentioned on the bottle and told the shopkeeper to weigh the same. He found the bottle was heavy and on opening the deodorant bottle he found it half-filled with water. He complained the matter to the consumer authority.
 (a) Define density.
 (b) Apart from water what is the other substance that some shopkeepers add into the deodorant.
 (c) What value of Prasanna is reflected in this act?
 Ans. (a) Density of any substance is defined to be the mass of the substance per unit volume.
(b) One can add some cheap gases or compressed air in the deodorant bottles.
(c) Prasanna showed the value of being having leadership quality, rightful, aware and responsible citizen.

Q4. Rita’s father always got his vehicle checked for pollution control. He got it tested for the aerosol if released by his car. He also uses unleaded petrol and makes use of public transport wherever possible. He sparingly use his car.
 (a) What is aerosol?
 (b) What happens when smoke released from vehicle mixes with fog?
 (c) What are the values of Rita’s father is reflected here?
 Ans. (a) When the solid or liquid is dispersed in a gas it is called aerosol e.g. smoke.
(b) When smoke mixes with fog it forms smog.
(c) Rita’s father is an aware citizen, environmentally concerned and dutiful.

Practical Based Questions (Solved)

Q1. A student was given a mixture containing copper oxide (insoluble) and copper sulfate (soluble) and asked to separate them. Firstly, she stirred the mixture into water, then filtered it. Next, she evaporated the filtrate.
 (a) What substance was the residue in the filtration?
 (b) Describe what the filtrate was.
 (c) What difference in properties allows substances to be separated by filtration?
 (d) What substance was collected by evaporation?
 Ans. (a) copper oxide
(b) A solution of copper sulphate
(c) Particle size
(d) Solid copper sulphate

Q2. Sandy is learning to cook. He accidentally mixed the icing sugar with the corn flour and spilled some raw rice grains into it as well. (Icing sugar and cornflour are both fine powders. Icing sugar is soluble, cornflour is not.) To separate this mess, he firstly sieved it. What went through the sieve he stirred into water, and let it stand overnight? In the morning a sediment had formed. He carefully poured the clear liquid into a tray and put it into the warm oven to evaporate.
 (a) What was caught by the sieve?
 (b) What difference in properties allows substances to be separated by sieving?
 (c) What was the sediment? 
 (d) What solid will be in the oven tray when dry?
 (e) What other method might Sandy have used to collect the substance which was a sediment?
 Ans. (a) Rice
(b) Particle size
(c) Corn flour
(d) Icing sugar (or just sugar)
(e) Filtration

Q3. Name the technique(s) which are suitable for separating the following mixtures:

Ans.

Q4. The following diagram shows a set-up of a simple distillation.

Identify the distillate collected in the receiver. How would you determine that the distillate collected is a pure substance?
 Ans. On boiling sea water the water boils and turns into gas and then condensed as the distillate. A pure substance boils at a fixed temperature and the same can be noted on the thermometer in the apparatus.
 

Q5. A mixture of pebbles, fine sand and salt was sieved. What passed through the sieve was mixed with water and allowed to stand? A sediment formed. The clear liquid was poured off and evaporated. The sediment was also dried. Use a flowchart to show the procedure and what was collected.
 Ans.

Q6. A mixture of salt, water and chalk dust (insoluble) was filtered. The residue was dried. The filtrate was divided into two parts. One part was evaporated, the other part was distilled. Construct a flowchart and show what was collected at each step.
 Ans.