Case study ( 4 Marks )

Question 14 Marks

The given mixture contains three constituents A, B and C. The constituent A is a yellow coloured, solid element which dissolves in a liquid D. The constituents B is a blue coloured salt which is insoluble in liquid D but dissolves easily in another liquid E. The constitudent C is a liquid wlich is used in coolking food and forms a solid fat on hydrogenation.

What do you think could (i) constituent A, and (ii) liquid D be?
What could (i) constituent B, and (ii) liquid E be?
What could liquid C be?
How will you separate the mixture containing A, B and C.

Answer

Constituent A is yellow coloured solid element. It could be sulphur.
Sulphur dissolves in liquid D. So, liquid D could be carbon disulphide.

Constituent B is a blue coloured salt, which is insoluble in carbon disulphide but dissolves in water. So, it could be copper sulphate.
Liquid E could be water as it dissolves copper sulphate.

Liquid C could be vegetable oil as it turns into a solid fat on hydrogenation.
We will separate the mixture containing A, B, and C by following process:

At first, we filter the mixture of A, B, and C.
Vegetable oil C, being liquid, will be obtained as a filtrate.
Residue consists of A(sulphur) and B(copper sulphate).
We add water to the residue and shake it before filtering. A(sulphur) is obtained as residue.
Now, we evaporate filtrate to obtain B(copper sulphate).

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Question 24 Marks

100ml of water at room temperature of 25°C is taken in a beaker and a little of solid S is dissolved in it by stirring to obtain a solution X. More and more of solid S is added to the solution with constant stirring, while keeping the temperature of solution constant at 30°C. After some time it is observed that no more solid dissolves in water and at the same time some solid is also left undissolved at the bottom of the beaker. The contents of beaker are filtered through a filter paper to obtain solution Y in the form of a filtrate.

What name is given to solutions like X?
What name is given to solution like Y?
What will you observe if the solution Y at 30°C is cooled down to 10°C by keeping the beaker in crushed ice? Why?
What term is used to denote the amount of solid dissolved in 100 grams of water in a solution like Y?

Answer

X type of solutions is known as unsaturated solution.
Y type of solutions is known as saturated solution.
If solution Y at 30°C is cooled down to 10°C by keeping the beaker in crushed ice, some of the dissolved parts of the solid will separate from the solution and will settle at the bottom of the beaker as crystals. This occurs because of the decrease in the solubility of solids and reduction in temperature.
Solubility refers to the amount of a solid dissolved in 100 grams of water.

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Question 34 Marks

When the solid A is added to water, it dissolves with the evolution of a lot of heat and making little explosions to form two products B and C. The properties of products B and C are entirely different from those of solid A as well as water. Moreover, products B and C cannot be reconverted into solid A and water. When another solid D is added to water, it dissolves with the absorption of a little heat to form a product E which cools down. The product E shows the properties of both, solid D as well as water. Moreover, product E can be converted into solid D and water.

What type of change occurs when solid A is dissolved in water? Why?
What type of change occurs when sold D is dissolved in water? Why?
Name a metal which you think could behave like solid A. Also name the products B and C.
Name the solid D if it is the one which is used in making ordinary dry cells.
Name the process by which D can be recovered from E.

Answer

When solid A is dissolved in water, chemical change takes place. This is because the properties of products B and C are entirely different from those of solid A and water.
Physical change occurs when solid D is dissolved in water. This is because product E shows the properties of both, solid D and water.
Sodium metal could behave like solid A.

Product B is sodium hydroxide.
Product C is hydrogen.

Solid D is ammonium chloride.
D can be recovered from E by evaporation.

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Question 44 Marks

Tincture of iodine is a mixture of two materials X and Y. The material Y has a property that its solid form can be converted directly into vapours on heating by a process called Z.

What could X be?
What could Y be?
Name the process Z.
Which process would you use to recover both the components X and Y from tincture of iodine?
Which process can be used to recover only component Y from tincture of iodine?

Answer

Tincture iodine is a mixture of two materials X and Y. So, X is alcohol.
The material Y has a property and its solid form can be converted directly into vapours on heating by the process called Z. So, Y is iodine.
Process Z is called sublimation.
Process used to recover both the components, i.e., alcohol and iodine, from the tincture of iodine is distillation.
The process used to recover component Y only from the tincture of iodine is evaporation.

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Question 54 Marks

The liquid air has three components X, Y and Z whose boiling points are: -186°C, -183°C and -196°C, respectively. When liquid air is fed into a tall fractional distillation column from near its bottom and warmed up slowly:

Which component will be collected from near the bottom of the fraction distillation column? Why?
Which component will be collected from the top part of the fractional distillation column? Why?
Which component will be collected from the middle part of the fractional distillation column? Why?
What could the component X, Y and Z be?

Answer

Y will be collected from the area near the bottom of the fractional distillation column because it has highest boiling point (-183°C).
Z will be collected from the top part of the fractional distillation column because it has lowest boiling point (-196°C).
X will be collected from the middle part of the fractional distillation column because it has a boiling point -186°C, which is lower than that of Y but higher than that of Z.
X is liquid argon, Y is liquid oxygen, and Z is liquid nitrogen.

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Question 64 Marks

Three mixtures A, B and C are obtained by stirring three different solids in water taken in separate beakers. When mixture A is allowed to stand for some time, then its particles settle at the bottom of the beaker. When a beam of light is passed through mixture A in a dark room, the path of light becomes visible when observed from the side of the beaker. When mixture B is allowed to stand for a considerable time, even then its particles do not settle down. Mixture B, however, scatters the beam of light just like mixture A. The particles of mixture C do not settle down on keeping and it also does not scatter a beam of light passing through it.

What are the mixtures like A known as?
What are the mixtures like B known as?
What are the mixtures like C known as?
Name the phenomenon exhibited by A and B which occurs on passing a beam of light through them.
Name one mixture each which is like (i) A (ii) B, and (iii) C.

Answer

Mixtures like A are known as suspensions.
Mixtures like B are known as colloids.
Mixtures like C are known as true solutions.
The phenomenon exhibited by A and B, which occur on passing a beam of light through them, is called Tyndall effect.

Mud water mixture is like A.
Soap solution is a mixture like B.
Sugar solution is a mixture like C.

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Question 74 Marks

A solid mixture contains four constituents P, Q, R and S. P consists of tiny grains and it is mixed with cement for plastering the walls. Q is a white solid which is recovered on a large scale from sea water by the process of evaporation. R is in the form of tiny particles of a material whose corrosion is called rusting. And S is a white solid which is used in making ordinary dry cells.

What could P, Q, R and S be?
How would you separate a mixture containing P, Q, R and S?

Answer

P consists of tiny grains and it is mixed with cement for plastering the walls. So, P is sand. Q is a white solid, which is recovered on a large scale from sea water by the process of evaporation. It is common salt. R is in the form of tiny particles of materials, whose corrosion is called rusting. It is, iron filings. S is ammonium chloride.
At first, let us take the mixture of P, Q, R, and S.

We first separate R(iron filings) by using a magnet to attract them. Then separate S(ammonium chloride) by sublimation.
Now, we shake P(sand) and Q(common salt) with water. The mixture is then filtered.
Sand is obtained as residue.
Now, we will evaporate the filtrate to dryness to obtain Q(common salt).

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Question 84 Marks

There are three liquids A, B and C, all having different densities and different boiling points. Liquids A and C are organic in nature whereas liquid B is considered to be inorganic. When liquids A and B are put together in a container, they form a single layer. On the other hand, when liquids B and C are mixed, they form two separate layers:

Which process will you use to separate a mixture of A and B?
Which method will you use to separate a mixture of B and C?
Name the liquids which would behave like (i) a (ii) B and (iii) C.

Answer

Liquid A is organic and liquid B is inorganic. When mixed, they form a single layer, i.e., they are miscible liquids. So, we will use fractional distillation to separate the mixture of liquid A and liquid B.
Liquid B is inorganic and liquid C is organic. We will use a separating funnel to separate the mixture of liquid B and liquid C as they form two different layers.

Liquid A is organic. When liquid A and liquid B are put together in a container, they form a single layer. So, alcohol would behave like liquid A.
Liquid B is inorganic. So, water would behave like liquid B.
Liquid C is organic. When liquid B and liquid C are mixed together, they form two separate layers. Oil would behave like liquid C.

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Question 94 Marks

Many indigestion mixtures are suspensions. What do the instructions written on the bottle of an indigestion mixture tell us before taking the mixture, and why?

Answer

The instruction written on the bottles of indigestion mixtures is “shake well before use”. This is because indigestion mixtures are suspensions. If they are left undisturbed, the particles of suspensions settle down. Therefore, it is instructed to shake the bottle before using it.

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Question 104 Marks

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 figure. The filter paper was removed when the water moved near the top of the filter paper.

(i) Identify the technique used by the child.

(a) Sedimentation

(b) Filtration

(d) Distillation

(ii) What would you expect to see, if the ink contains three different coloured components?
(a) We will not see any band on the filter paper.
(b) We would see three bands on the filter paper at various lengths.
(c) We would see infinite bands on the filter paper.
(d) We would see single band on the filter paper.

iii) Give one application where you can use this technique.
(a) To separate salt from sand
(b) To separate wheat from husk
(c) To separate oil from water
(d) To separate drugs from blood.

(iv) For the separation of what kind of substances is the above process used ?
(a) For the separation of insoluble substances
(b) For the separation of single solute that dissolves in single solvent.
(c) For the separation of those solutes that dissolve in the same solvent.
(d) For the separation of those solutes that dissolve in the different solvents.

(v) What is chromatography ?
(a) It is an agricultural method to separate grains
(b) A method to separate magnetic impurities from non-magnetic impurities
(c) The process of separating the suspended particles of an insoluble substance
(d) Method of separating and identifying various components in a mixture, which are present in small trace quantities.

Answer

(d) Method of separating and identifying various components in a mixture, which are present in small trace quantities.

(d) To separate drugs from blood.

(b) The components of the ink will travel with water and we would see three bands on the filter paper at various lengths.

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Question 114 Marks

A Chemistry teacher explained the different types of separation of mixtures with the help of given adjoined chart. Now, in a practical test, students were provided with give samples and they were asked to separate the samples applying suitable separation methods. Now the students have to select the correct methods of separation.
(i) Fine mud particles suspended in water.

(a) Winnowing	(b) Sedimentation and Decantation
(c) Using a magnet	(d) Chlorination

(ii) Oil from water.

(a) Sedimentation and Decantation	(b) Filtration
(c) Separating funnel	(d) Winnowing

(iii) Sodium chloride from its solution in water.

(a) Filtration	(b) Separating funnel
(c) Sedimentation and Decantation	(d) Evaporation

(iv) Camphor from salt.

(a) Filtration

(b) Separating funnel

(d) Sedimentation

(v) Cream from milk

(a) Separating funnel

(b) Sedimentation

(d) Centrifugation

Answer

Based on the principles of separation of mixtures illustrated in the chart and the samples provided, here are the correct methods of separation:
(i) Fine mud particles suspended in water. The correct method is (b) Sedimentation and Decantation. The mud particles will settle at the bottom (sedimentation), and the clear water can then be poured off (decantation).
(ii) Oil from water. The correct method is (c) Separating funnel. Oil and water are immiscible liquids, so a separating funnel can be used to separate them based on their different densities.
(iii) Sodium chloride from its solution in water. The correct method is (d) Evaporation. When the solution is heated, the water evaporates, leaving the solid sodium chloride behind.
(iv) Camphor from salt. The correct method is (c) Sublimation. Camphor is a substance that can change directly from a solid to a gas upon heating, while salt does not. This property allows them to be separated.
(v) Cream from milk. The correct method is (d) Centrifugation. This process is used to separate a mixture by spinning it rapidly, which causes the denser components (skimmed milk) to move to the outside and the lighter components (cream) to stay in the center.

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Question 124 Marks

We take some ammonium chloride in a china dish and place the china dish on a tripod stand (see Figure). The china dish is covered with an inverted glass funnel. A loose cotton plug is put in the upper, open end of the funnel to prevent the ammonium chloride vapours from escaping into the atmosphere. The china dish is heated by using a burner. On heating, ammonium chloride changes into white vapours. These vapours rise up and get converted into solid ammonium chloride on coming in contact with the cold, inner walls of the funnel (see Figure). In this way, ammonium chloride collects on the inner sides of the funnel in the form of a sublimate and can be removed

(i) What name is given to the phenomenon which takes place?
(a) condensation (b) evaporation (c) sublimation (d) vaporisation

(ii) One of the following does not undergo sublimation. This one is :
(a) iodine (b) sodium chloride (c) ammonium chloride (d) camphor

(iii) The conversion of a solid into vapours without passing through the liquid state is called :
(a) vaporisation (b) fusion (c) sublimation (d) freezing

(iv) When heat is constantly supplied by a burner to boiling water, then the temperature of water during vaporisation :
(a) rises very slowly (b) rises rapidly until steam is produced
(c) first rises and then becomes constant (d) does not rise at all

(v) During summer days, water kept in an earthen pot (pitcher) becomes cool because of the phenomenon of :
(a) diffusion (b) transpiration (c) osmosis (d) evaporation

Answer

(i) What name is given to the phenomenon which takes place? The process where a substance changes from a solid directly to a gas, and then back to a solid, is called sublimation. The diagram explicitly shows ammonium chloride changing into vapours and then solidifying on the funnel. Correct Answer: (c) sublimation
(ii) One of the following does not undergo sublimation. This one is: Sublimation is a property of certain substances that go directly from a solid to a gas. Sodium chloride (common table salt) melts and boils, but it does not sublime under normal conditions. Iodine, ammonium chloride, and camphor are all known to sublime. Correct Answer: (b) sodium chloride
(iii) The conversion of a solid into vapours without passing through the liquid state is called: This is the scientific definition of sublimation. Correct Answer: (c) sublimation
(iv) When heat is constantly supplied by a burner to boiling water, then the temperature of water during vaporisation: During a phase change, such as boiling (vaporisation), the energy supplied is used to break the intermolecular forces holding the molecules together, not to increase the kinetic energy of the molecules. Therefore, the temperature remains constant until all the liquid has converted to gas. Correct Answer: (d) does not rise at all
(v) During summer days, water kept in an earthen pot (pitcher) becomes cool because of the phenomenon of: Earthen pots have tiny pores. Water seeps through these pores and evaporates from the outer surface. Evaporation is a cooling process because the molecules with the highest kinetic energy escape, taking energy away from the remaining water. Correct Answer: (d) evaporation

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Question 134 Marks

In the given below activity, on heating the solution, water evaporates, and we get back the ink dye in the watch glass. The different substance has a different boiling point. We use this property to separate the components of the mixture. Here, the boiling point of ink is much higher than that of water. On heating the ink solution, water evaporates while ink dye remains in the china dish.

(i) Name the process shown in the diagram.

(a) Boiling

(b) Filtration

(d) Distillation

(ii) Which type of substance can be separated by this method ?
(a) Any solvent from its non-volatile solute.
(b) The volatile solvent from its non-volatile solute.
(c) The non-volatile solvent from its non-volatile solute.
(d) The volatile solvent from its volatile solute.
(iii) What can we interpret about the nature of ink ?

(a) We cannot separate components of ink	(b) Ink is not a mixture
(c) Ink is pure substance	(d) Ink is a mixture of dyes in water.

(iv) Name the component which gets evaporated.
(a) Heating leads to the evaporation of water.
(b) Heating leads to the evaporation of dyes.
(c) Heating leads to the filtration of water.
(d) Heating leads to the distillation of dyes.

(v) Define the process shown in the diagram
(a) It is the process of conversion of a liquid into its vapours.
(b) It is a process of separating insoluble component by filtering the solution
(c) It is a process that separates a pure solid in the form of its crystals
(d) It is a technique to separate two miscible liquids

Answer

(i) Name the process shown in the diagram. The process of heating a solution to evaporate a solvent and leave a solute behind is a form of (a) Evaporation, though it's often used in a broader context to demonstrate separation. Given the options, (a) Boiling is the most direct action shown in the beaker, which leads to evaporation. However, the overall process of separating the components of the ink is through evaporation. Let's re-evaluate the options. The process of heating a liquid to get a non-volatile solid back is evaporation. The process of heating a liquid until it boils is boiling. The diagram shows the water boiling, which causes evaporation. So, "Boiling" is a more fundamental process shown. But let's assume the question is about the separation technique. The process of separating a volatile liquid from a non-volatile substance by heating is evaporation. Option (a) Boiling is the most accurate description of the physical process happening to the water.
(ii) Which type of substance can be separated by this method? The method separates a volatile component (water) from a non-volatile component (the dye in the ink). Therefore, the correct answer is (b) The volatile solvent from its non-volatile solute.
(iii) What can we interpret about the nature of ink? The activity shows that by heating the ink solution, one component (water) evaporates, leaving another component (the dye) behind. This demonstrates that ink is composed of at least two different substances. Therefore, the correct interpretation is (d) Ink is a mixture of dyes in water.
(iv) Name the component which gets evaporated. The description states that "water evaporates, and we get back the ink dye." Therefore, the component that gets evaporated is water. The correct option is (a) Heating leads to the evaporation of water.
(v) Define the process shown in the diagram. The diagram shows the conversion of a liquid (water) into its vapours by heating. This is the definition of evaporation (or boiling, which is a type of evaporation). The most fitting definition among the options is (a) It is the process of conversion of a liquid into its vapours.

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Science Case study ( 4 Marks )

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