What would you observe when a saturated solution of potassium nitrate prepared at 353 K is allowed to cool to room temperature?

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As solution cools, potassium chloride gets crystallized or precipitated. Because at 353K, solubility of potassium chloride is 54 g per 100 g of water. Whereas at room. temperature (20°C) it is 35 g. So excess of potassium chloride dissolved gets precipitated.

Text Solution

Solution : (a) When a saturated solution of potassium chloride prepared at `60^(@)`C is allowed to cool at room temperature, crystals of potassium chloride will be formed. <br> (b) Initially, sugar will obtained as water wil get evaporated. But on dry heating sugar gets charred and it turns back. <br> `C_(12)H_(22)O_(11)overset(triangle)(to)underset((Black))(12C)+11H_(2)Ouarr.` <br> (c) The black coloured compound, iron sulphide is formed when a mixture of iron filings and sulphur powder is heated strongly. <br> `underset("Iron filings")(Fe)+underset("Sulphur powder")(S) overset(triangle)(to) underset("Iron sulphide")(FeS)`

• Answer:

    (a) When a saturated solution of potassium chloride prepared at 60'C is allowed to cool at room temperature, crystals of potassium chloride will be formed. (b) Initially, sugar will obtained as water will get evaporated. But on dry heating sugar gets charred and it turns black.

  
  (c) The black coloured compound, iron sulphide is formed when a mixture of iron filings and sulphur powder is heated strongly.
  
  
  

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• Answer:

    The colloidal particles are smaller and not heavy. They always remain in a state of zig-zag motion, called Brownian movement, which counters the force of gravity acting on colloidal particles and hence, helps in providing stability to colloidal sols by not allowing them to settle down. Apart from this, colloidal particles are charged and repel each other. This fact also do not the particles of colloidal solution to settle down. Whereas particles of suspension are larger, heavy and have less movement, thus settle down due to gravity.
  

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• Answer:

    In smoke and fog. dispersion medium is same, i.e., air but they differ in dispersed phase. In smoke, solid carbon particles are dispersed in air while in fog, liquid water particles are dispersed in air.
  

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• Answer:

    (a) It is a physical property as no new compound is formed because steel is an alloy and alloy is a homogeneous mixture of two or more metals or of metallic elements with non-metallic elements. (b) It is chemical property because chemical reaction takes place between zinc and hydrochloric acid with the evolution of hydrogen gas and a compound zinc chloride is formed.

  
  (c) It is physical property because cutting with knife does not form new substance. (d) It is chemical property as new compound is being formed by the reaction of metal oxide and water.
  
  
  

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Page 5

• Answer:

    In the given question, student 'C' has made it correctly because 50% (mass by volume) means 50 g of solute for every 100 mL of solution and not in 100 mL of solvent. Mass/volume per cent

  
  Student 'A' dissolved 50 g of NaOH in 100 mL  of water (solvent) which is incorrect. Student 'B' dissolved 50 g of NaOH in 100 g of water (solvent), which is incorrect.
  

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Page 6

• Answer:

    (a) The process is sublimation because when dry ice (solid CO2) is kept at room temperature at one atmospheric pressure, it sublimes leaving no residue. (b) This process is diffusion because in diffusion, mixing of one substance (ink) into another substance (water) goes on until a uniform mixture is formed. (c) This process is dissolution/diffusion as potassium permanganate crystal is dissolved in water. (d) This process is evaporation as acetone evaporates when kept open in the bottle. (e) This process is centrifugation. Milk is put in a closed container in big centrifuge machine. When machine is switched on, milk is rotated at a very high speed. Due to this, milk separates into 'cream' and 'skimmed milk'. The cream being lighter, floats over the skimmed milk and then can be removed. (f) This process is sedimentation as sand does not dissolve completely in water and forms suspension and settles down at the bottom when left undisturbed for some time. (g) This shows Tyndall effect, i.e., scattering of light by colloidal solution or by particles in a fine suspension. Dust particles are suspended in air which scatter the light coming from small hole.
  

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Page 7

• Answer:

    Sample 'B' will not freeze at

  
   as, it is impure water. It is because sample ?B' boils at 102°C while the boiling point of pure water is 100°C. It means this sample contains impurities. Only pure substance has sharp melting point.
  

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Page 8

• Answer:

    Gold is soft metal and can easily change its shape with a little force. Therefore, it is not suitable for making ornaments. But when it is alloyed with copper or silver, the gold becomes harder and stronger and its brittleness decreases. Thus, it becomes suitable for making ornaments.
  

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Page 9

• Answer:

    As the given element is sonorous and highly ductile, therefore, it is categorised as a metal. Some other e pected characteristics of are (i) It should possesses metallic lustre and can be polished. (ii) It should be good conductors of heat and electricity. (iii) It should be ductile. (iv) It should be malleable. (v) It should has high tensile strength. (vi) It should has high densities and melting  point/boiling point too. (vii) It should be hard (except sodium and potassium which are soft metals). (viii) It should be solid at room temperature (except mercury, which is liquid at room temperature). While the characteristics of non-metals are (i) Non-metals are neither malleable nor ductile and do not conduct electricity. (ii) Metalloids show some properties of metals and some other properties of non-metals.
  

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Page 10

• Answer:

    (a)  Example Mixture of acetone and water. Method   Simple distillation can be used to separate a mixture of volatile and non-volatile components. (b)   Example Mixture of kerosene and petrol. Method Simple distillation can be used to separate two volatile components with appreciable difference in boiling points. (c) Example Mixture of mustard oil and water. Method Separating runnel is used to separate a mixture of immiscible liquids. (d) Example Mixture of ammonium chloride and common salt. Method   Sublimation can be used to separate the mixture in which one component changes directly from solid to gas. (e)   Example A mixture of different pigments  from an extract of flower petals. Method Chromatography method can be used to separate two different substances present in the same solution.
  

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Page 11

• Answer:

    (a) A colloid is a heterogeneous mixture and its components can be separated by the technique known as centrifugation. (b) Ice, water and water vapour look different and display different physical properties but they are chemically the same. (c) 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 water and the lower layer will be that of chloroform (It is because water is lighter than chloroform). (d) A mixture of two or more miscible liquids, for which the difference in the boiling points is less than 25 K can be separated by the process called fractional distillation. (e) When light is passed through water containing a few drops of milk, it shows a bluish tinge. This is due to the scattering of light by milk and the phenomenon is called Tyndall effect. This indicates that milk is a colloidal solution.
  

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Page 12

• Answer:

    According to law of constant composition or definite proportions; irrespective of the source a chemical compound it is always found to be made of the same elements combined together in the same fixed proportion by mass. Thus, in the light of the above law, it will be a pure substance. It is because sugar obtained by different sources like sugarcane and beetroot will have the same composition.
  

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Page 13

• Answer:

    Examples of Tyndall effect (i) When sunlight passes through the canopy of a dense forest. (ii) When a fine beam of light enters a dark room through a small hole.
  

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Page 14

• Answer:

    No, alcohol cannot be separated from water by using a separating funnel because alcohol is completely miscible in water.
  

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Page 15

• Answer:

    (a) The phenomena given in question is a chemical change because the composition of product formed is different from the substance taken. The reaction involved is

  
  (b) Yes When CaO dissolves in water it forms calcium hydroxide which is basic solution.
  
   (ii) When
  
  (g) dissolves in water it forms carbonic acid which is acidic solution.
  
  
  

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Page 16

• Answer:

    (a) Iodine is a lustrous non-metal. (b) Bromine is a non-metal which exists as a liquid at room temperature. (c) Graphite is the allotropic form of carbon and it is a good conductor of electricity. (d) Carbon is a non-metal which is known to form the largest number of compounds. (e) Phosphorus is a non-metal other than carbon which shows allotropy. (f) Oxygen is a non-metal which is required for combustion.
  

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Page 17

• Answer:

    1.                    

  Elements	Compounds
  	Sand
  Hg Diamond (Carbon)

  Wood is neither an element nor compound. It is a mixture.
  

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• Answer:

    These are not compounds (a) Chlorine gas               (c) Iron                                   (e) Aluminium                 (f) Iodine (g) Carbon                           (i) Sulphur powder
  

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Page 19

• Answer:

    Fractionating column is the most important part of the fractional distillation apparatus. This column is provided with some glass beads in it.            

  
  Separation of miscible liquids by fractional distillation   It helps to obstruct the upward movement of the vapours of the two liquids. The vapours of high boiling liquid gets condensed earlier (at lower level). The energy (latent heat) released helps to take the vapours of low boiling liquid to a height in the fractionating column. The advantages are as given below (i) This method can separate the liquids with a boiling point difference about or less than 25 K, (ii) During the process, both evaporation and condensation take place simultaneously. (iii) A mixture (like petroleum) can also be separated by fractional distillation process which contains several components.
  

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Page 21

• Answer:

    As part 'A' is heated, a compound FeS is formed by the reaction between iron filings and sulphur. When dilute HCI is added to part A, FeS will react with dil HCI to form H2S gas which has smell of rotten eggs and will turn lead acetate paper black.

  
  
  
  
  As part 'B' is not heated, so B is a mixture of iron filings and sulphur powder. When dil, HCI is added to it, iron filings react with dill. HCl to form
  
  (g) which burns with a 'pop' sound if burning match stick is brought near it.
  
  
  

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Page 22

• Answer:

    (a) Three different coloured spots are obtained on the strip at different heights. (b) Chromatography (paper chromatography) technique is used. (c) The chromatography method is also employed to separate drugs from the blood.
  

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Page 23

• Answer:

    (a) The milk sample was illuminated because milk is a colloidal solution and its particles are big enough to scatter the light, hence, they scatter the light passing through it. The phenomenon observed is called "Tyndall effect". (b) As salt solution is a true solution i.e., solute particle size is too small to scatter the light, hence, it does not show "Tyndall effect". (c) Examples of colloid are gold sol, arsenius sulphide

  
  sol., Blood etc,
  

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Page 24

• Answer:

    (a) Physical change because evaporation of water takes place but no change occurs in the composition of the substance. (b) Physical change because it is also involving only movement of air, no change in composition of air. (c) First physical change, when kerosene vaporises. After that, burning of kerosene is a chemical change as new products are formed. (d) Physical change as there occurs only the dissolution. (e) Physical .change as there is no change in composition. Only the separation of components takes place by the physical phenomenon, centrifugation.
  

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Page 25

• Answer:

    (a) No, the two solutions do not have the same concentration. (b) Mass percentage of solution prepared by

  
  
  
  Mass percentage of solution prepared by Sarika
  
  The solution prepared by Ramesh has less percentage (9.09%) by mass than that of Sarika (10%).
  

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Page 26

• Answer:

    (i) Remove iron filings with the help of magnet Place the mixture on a paper of petridish, move a bar magnet many times over the mixture. Iron filings get attached to the magnet and get separated. (ii) Remove ammonium chloride from sand and sodium chloride by sublimation The remaining mixture is transferred to China dish and subjected to sublimation. Ammonium chloride will get vaporised and change into vapours and on condensation will form

  
   Sand and sodium chloride will be left in China dish. (iii) Remove sand from sodium chloride by filtration after dissolution Dissolve the sand and sodium chloride in water, Sodium chloride will dissolve. Filter the solution. Sand will be left as residue and is separated. (iv) Get sodium chloride by evaporation or crystallization. In the filtrate sodium chloride is present. So, evaporate the filtrate to dryness to get sodium chloride back or use crystallisation.
  

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