Sunday 15 January 2012

CBSE Class 10th Science | Chapter 4. Carbon and its Compounds | Solved Exercises

Points to Remember - What you have learnt

  1. Carbon is a versatile element that forms the basis for all living organisms and many
    of the things we use.
  2. This large variety of compounds is formed by carbon because of its tetravalency
    and the property of catenation that it exhibits.
  3. Covalent bonds are formed by the sharing of electrons between two atoms so that
    both can achieve a completely filled outermost shell.
  4. Carbon forms covalent bonds with itself and other elements such as hydrogen,
    oxygen, sulphur, nitrogen and chlorine.
  5. Carbon also forms compounds containing double and triple bonds between carbon
    atoms. These carbon chains may be in the form of straight chains, branched chains
    or rings.
  6. The ability of carbon to form chains gives rise to a homologous series of compounds
    in which the same functional group is attached to carbon chains of different lengths.
  7. The functional groups such as alcohols, aldehydes, ketones and carboxylic acids
    bestow characteristic properties to the carbon compounds that contain them.
  8. Carbon and its compounds are some of our major sources of fuels.
  9. Ethanol and ethanoic acid are carbon compounds of importance in our daily lives.
  10. The action of soaps and detergents is based on the presence of both hydrophobic and hydrophilic groups in the molecule and this helps to emulsify the oily dirt and hence its removal.

Activity 4.1 Page No. 58

  • Make a list of ten things you have used or consumed since the morning.
  • Compile this list with the lists made by your classmates and then sort the
    items into the following Table.
  • If there are items which are made up of more than one material, put them into both the relevant columns.
Things Which we have used or consumed since morningThings made of metalThings made of glass/clayOthers
  1. Water
  2. Washbasin
  3. Toilet Pot
  4. Toothpaste
  5. Tooth Brush
  6. Soap
  7. Towel
  8. Dress/Cloths
  9. Almirah
  10. Mirror
  11. Comb
  12. Shoes
  13. Steel Glass
  14. Glass
  15. Steel Plates
  16. China Clay Plates
  17. Cup
  18. Spoon
  19. Gas Stove
  20. Bread
  21. Butter
  22. Milk
  23. Sugar
  24. Knife
  25. School Bag
  26. Bicycle
  27. Notebook
  28. Books
  29. Pen
  30. Cold Drinks Bottle
  1. Almirah
  2. Steel Glass
  3. Knife
  4. Spoon
  5. Gas Stove
  6. Bicycle

  1. Washbasin
  2. Toilet Pot
  3. Glass
  4. China Clay Plates
  5. Cup
  6. Cold Drinks Bottle
  7. Mirror

  1. Water
  2. Tooth Paste
  3. Soap
  4. Towel
  5. Dress/Cloths
  6. Bread
  7. Butter
  8. Milk
  9. Sugar
  10. School Bag
  11. Notebook
  12. Books
  13. Pen

Activity 4.2 Page No. 67

  • Question 1. Calculate the difference in the formulae and molecular masses for:
    1. CH3OH and C2H5OH
    2. C2 H5 OH and C3 H7OH
    3. C3 H7OH and C4 H9OH
  • Answer:
    Molecular formulaMolecular massDifference of molecular massDifference in molecular formula
    (a)CH3OH and C2H5OH32 amu and 46 amu14UCH2
    (b)C2H5OH and C3H7OH46 amu and
    60 amu
    (c)C3H7OH and C4H7OH60 amu and
    74 amu
  • Question 2. Is there any similarity in these three?
  • Anser:All these three have alcoholic (-OH) function group.
  • Question 3. Arrange these alcohols in the order of increasing carbon atoms to get a family. Can we call this family a homologous series?
  • Answer: CH3OH, C2H5OH, C3H7OH, C4H9OH.
    Yes, It is a homologous series of alkane alcohols as each successive member of the series differs by - CH2 unit from proceeding member
  • Generate the homologous series for compounds containing up to
    four carbons for the other functional groups given in Table 4.3.

    Hetero atom Functional groupFormula of functional group
    CL/BrHalo - (Chloro/Bromo)- Cl, - Br
    (substitutes for hydrogen atom)
    1. Alcohol
    2. Aldehyde
    3. Ketone
    4. Carboxylic acid
    1. -OH

    2. H
    3. -C-
    4. O
  • Answer:
  • Chloro (-CI) --> CH3CI, C2H5CI,C3H7CI,C4H9CI. Aldehydes --> CH3CHO,C2H5CHO,C3H7CHO,C4H9CHO. Ketone -->CH2CO,C2H4CO,C3H6CO,C4H8CO. Carboxylic acids--> CH2COOH, C2H4COOH, C3H6COOH, C4H9COOH. 
    (i) Homologus series having Choloro (-Cl) functional group: CH3Cl, C2H5Cl, C3H7Cl, C4H9Cl. 
    (ii) Homologus series having Aldehydes functional group: CH3CHO, C2H5CHO, C3H7CHO, C4H9CHO.
    (iii)Homologus series having Ketone functional group: CH2CO, C2H4CO, C3H6CO, C4H8CO. 
    (iv) Homologus series having Carboxylic acids functional group:CH2COOH, C2H4COOH, C3H6COOH, C4H9COOH.

    Activity 4.3 Page No. 69

      CAUTION: This Activity needs the teacher’s assistance.
    • Take some carbon compounds (naphthalene,camphor, alcohol) one by one on a spatula and burn
    • Question 1.Observe the nature of the flame and note whether smoke is produced.
    • Answer: Saturated hydrocarbons burn generally with clear blue flame in sufficient supply of air with no visible smoke
    • Question 2.Place a metal plate above the flame. Is there a deposition on the plate in case of any of the compounds?
    • Answer: There is deposition in case of naphthalene and camphor on the plate.

    Activity 4.4 Page No. 69

    • Light a Bunsen burner and adjust the air hole at the base to get different types of flames/presence of smoke.
    • Question 1. When do you get a yellow,sooty flame?
    • Answer: When there is insufficient supply of O2 and the carbon particles do not burn completely.
    • Question 2. When do you get a blue flame?
    • Answer: When there is sufficient supply of O 2 to burn carbon particles do not burn completely burnt.

    Activity 4.5 Page No. 70

    • Take about 3 mL of ethanol in a test tube and warm it gently in a water bath.
    • Add a 5% solution of alkaline potassium permanganate drop by drop to this solution.
    • Question 1. Does the colour of potassium permanganate persist when it is added initially?
    • Answer: The purple colour due to permanganate get decolourised during the reaction
    • Question 2. Why does the colour of potassium permanganate not disappear when excess is added?
    • Answer: When all the alcohol gets consumed the reaction stops and the purple colour persists.

    Activity 4.6 Page No. 72

    • Teacher’s demonstration – Drop a small piece of sodium,about the size of a couple of grains of rice, into ethanol
      (absolute alcohol).
    • Question 1. What do you observe?
    • Answer: Sodium (Na) metal, being highly reactive, reacts with ethanol leading to the evolution of hydrogen and formation of other product, Sodium Ethoxide..
      2C2H5OH + 2Na ===> 2C2H5ONa + H2
    • Question 2. How will you test the gas evolved?
    • Answer:A burning spitter is bought near to the gas and the gas burns with pop sound. Also we can observe a layer of moisture inside the glass tube, showing presence of water formation out of this activity,therefore the gas evolved is H2 (gas).
      2H2 + O2 ===> 2h2O.

    Activity 4.7 Page No. 73

    • Compare the pH of dilute acetic acid and dilute hydrochloric acid using both litmus paper and universal indicator.
    • Are both acids indicated by the litmus test?
    • Answer: Yes.
    • Does the universal indicator show them as equally strong acids?
    • Answer: No.

    Activity 4.8 Page No. 73

    • Take 1 mL ethanol (absolute alcohol) and 1 ml glacial acetic acid along with a few drops of concentrated sulphuric acid in a test tube.
    • Warm in a water-bath for at least five minutes as shown in Fig. 4.11.
    • Pour into a beaker containing 20-50 ml of water and smell the resulting mixture.
    • Observation: The resulting mixture is a sweet-smelling substance.
    • Question 1.Which one is stronger acid, HCI or ethanoic acid?
    • Answer: Ethanoic acid is weaker acid then HCI as pH of HCI is less than the pH of ethanoic acid.
    • Question 2. What is glacial acetic acid?
    • Answer: 100% pure acetic acid is called glacial acetic acid.
    • Question 3. Name the raction which takes place between glacial acetic acid and absolute alcohol.
    • Answer: It is called esterification
      CH3 CH2OH+CH3 COOH===>CH3OOCC2H5+H2O
      EnthanolEhanoic acidEthyl ethanoate

    Activity 4.9 Page No. 74

    • Set up the apparatus as shown in Chapter 2, Activity 2.5.
    • Take a spatula full of sodium carbonate in a test tube and add 2 mL of dilute ethanoic acid.

    • Question 1. What do you observe?
    • Answer: Following reaction take place:
      Na2Co3 + 2CH3COOH =====> 2CH3 COONA + CO2 + H2O
      (Sodiums acetate)
    • Question 2. Pass the gas produced through freshly prepared lime-water. What do you observe?
    • Answer: The lime-wter turns milky.
    • Can the gas produced by the reaction between ethanoic acid and sodium carbonate be identified by this test?
    • Answer:Yes, the gas turns the lime-water milky. That means the gas produced is CO2.
    • Repeat this Activity with sodium hydrogencarbonate instead of sodium carbonate.
    • Answer:On repeating this activity with sodium hydrogencarbonate instead of sodium carbonate we get Sodium ethanoate along with Carbondioxide and water as follows :-
      NaHCO3 + CH3COOH -> CH3COONa + CO2 + H2O

    Activity 4.10 Page No. 74

    • Take about 10 ml of water each in two test tubes.
    • Add a drop of oil (cooking oil) to both the test tubes and label them as A and B.
    • To test tube B, add a few drops of soap solution.
    • Now shake both the test tubes vigorously for the same period of time.
    • Can you see the oil and water layers separately in both the test tubes immediately after you stop shaking them?
    • Answer:No, it is not clear.
    • Leave the test tubes undisturbed for some time and observe. Does the oil layer separate out?
    • In which test tube does this happen first?
    • Answer: In test tube A the oil layer separate out. In test tube A, it happens first.

    Activity 4.11 Page No. 76

    • Take about 10 ml of distilled water (or rain water) and 10 ml of hard water (from a tube well or hand-pump) in separate test tubes.
    • Add a couple of drops of soap solution to both.
    • Shake the test tubes vigorously for an equal period of time and observe the amount of foam formed.
    • Question 1. In which test tube do you get more foam?
    • Answer: The test tube containing distilled water has more foam.
    • Question 2. In which test tube do you observe a white curdy precipitate?
      Note for the teacher : If hard water is not available in your locality, prepare some hard water by dissolving hydrogencarbonates/sulphates/chlorides of calcium or magnesium in water.
    • Answer: In the test tube containing hard water.

    Activity 4.12 Page No. 76

    • Take two test tubes with about 10 mL of hard water in each.
    • Add five drops of soap solution to one and five drops of detergent solution to the other.
    • Shake both test tubes for the same period.
    • Question 1.Do both test tubes have the same amount of foam?
    • Answer: No, the test tube to which detergent was added has more foam.
    • Question 2. In which test tube is a curdy solid formed?
    • Answer: In the test tube in which soap was added.

    Intext Question : Page 61

    Question 1. What would be the electron dot structure of carbon dioxide which has the formula CO2?  
    Answer:The structure of CO2.  
    Question 2. What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur? (Hint – The eight atoms of sulphur are joined together in the form of a ring.)  
    Answer. Eight atoms (-S8)of sulphur molecule. Intext Question : Page 68 Question 1.How many structural isomers can you draw for pentane? Answer: We can draw three structural isomers of pentane. (a)
    HHHH H
    |||| |
    H-C-C-C-C-C- H
    |||| |
    HHHH H
    Normal Pentane (b)
    HH   H- C-HH
    Neo pentane 
    Question 2. What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?  
    Answer: The two Propertties of carbon are - (a) Catenation and (b) Tetra Covalency of crbon atom. Catenation is the unique property of carbon due to which carbon atoms can linkb among themxselves to form a straight, banched or clse chain. due to travelency, the carbon atoms can form sngle, double r triple covalent bond. This is why carbon leads to the large number of compounds. 
    3. What will be the formula and electron dot structure of cyclopentane? 
    Answer:The formula of Cyclopentane is C5H10
Dot structure of cyclopentane

    Question 4. Draw the structures for the following compounds. 
    (i) Ethanoic acid (ii) Bromopentane
    (iii) Butanone (iv) Hexanal. 
    Are structural isomers possible for bromopentane? 
    Answer: (a)
    HHHH H
    |||| |
    H-C-C-C-C-C- Br
    |||| |
    HHHH H
    |||| |//
    |||| |\
    Question 5. How would you name the following compounds?
    H-C-C-C-C-C= C-H
    Answer: (i) Bromo-ethane, (ii) Menthanol, (iii) Hex l-yne.  
    Intext Question : Page 71  
    Question 1. Why is the conversion of ethanol to ethanoic acid an oxidation reaction? Answer:
    Here, inm this reaction, there is a decrease in the number of hydrogen atoms in compound. Therefore, it is an oxidation reaction. Also number of oxygen atoms has increased.  
    Question 2. A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?  
    Answer: Air contains nitrogen and other inactve gaseous contents which resist the sufficient supply of oygen for burnng of ethny. So, air is not used for combustion ethny.
    Intext Question : Page 74 
      Question 1. How would you distinguish experimentally between an alcohol and a carboxylic acid? 
    Answer:We can distinguish these two compounds by using loborotry reagent Na2 CO3(solution)
    (i) When Na2CO3is added to the test tube containing CH3COOH, CO2 gas is envolved which turn lim water miklky.
    (ii) When Na2CO3 is add to the test tube containing CH3CH2OH then no gas is envolved.  
    Question 2. What are oxidising agents? Answer:Oxidizing agents are the chemical substances which themselves undergo reduction and can oxidise the other species. Example - KMNOCH4, and K2Cr2O7 are oxidising agents.
    Intext Question : Page 76  
    Question 1. Would you be able to check if water is hard by using a detergent? Answer: No, it is impossible because detergent is effective in both hard water and soft water. 
    Question 2.People use a variety of methods to wash clothes. Usually after adding the soap, they ‘beat’ the clothes on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes? 
    Answer:By the reaction of soap with the calcium and magnesium salts, foam is formed. This foam captures dust particles but also sticks to cloth. To remove them from cloth, agitation is neccessar. 

    SOLVED EXERCISES : Chapter 4. Carbon and its Compounds | CBSE: Class 10th ( Xth ) SCIENCE

    Question 1. Ethane, with the molecular formula C2H6 has :
    (a) 6 covalent bonds. (b) 7 covalent bonds. (c) 8 covalent bonds. (d) 9 covalent bonds. 
    Answer: (b) 7 covalent bonds.  
    Question 2. Butanone is a four-carbon compound with the functional group 
    (a) carboxylic acid. (b) aldehyde. (c) ketone. (d) alcohol.  
    Answer: (c) ketone. 
    Question 3. While cooking, if the bottom of the vessel is getting blackened on the outside, it means that (a) the food is not cooked completely. (b) the fuel is not burning completely. (c) the fuel is wet. (d) the fuel is burning completely. Answer:(b) the fuel is not burning completely.
    Question 4. Explain the nature of the covalent bond using the bond formation in CH3CI.  
    Answer: The bond line structure of Ch3Cl is given as
    Here 3-hudrogen atoms are linked with C-atom by single covalent bond. The bond between C and Cl atomsis covalent but due to higher value of electronegativity of Cl, the C-Cl bond is polar in nature. 
    Question 5. Draw the electron dot structures for (a) ethanoic acid. (b) H2S. (c) propanone. (d) F2 .  
    Answer: (a) Ethanoic acid: (B) H2S: (c) Propanone: (d) F2: Question 6. What is an homologous series? Explain with an example. Answer: A group of compounds of carbon having same general formula and same functional group is called homologous series. The members of homolugous series are called homologous. For, exampal, alcohol. (1) Menthanol _ CH3OH (2) Enthanl _ C2H5OH. (3) Propanol _ C3H7OH. (4) Butanol _ C4H9OH. Homologous series compounds have following characteristics: (a) They have same general formula for all compounds. (b) They have same functional group. (c) They have same chemical but different physical property. (d) They have difference of _ CH2 between two successive members. (e) Difference between masses of two successive member is 14 amu. 
    Question 7. How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties
     Answer: Difference between enthanol and enthanoic acid: Physical properties:
    EthanolEthanoic acid
    1.It has a Characteristic smell.1.It has typical vinegar smell.
    2.Pure alcohol (95% orabove) is called rectified alcohol.2.Pure ethanoic acid is called glacial acetic acid.
    Chemical properties:
    EthanolEthanoic acid
    1.Ethanol does not react with NaOH.C2H5OH. ==> No reaction.1.Enthonic acid reacts with NaOH to form sodium ethanoate. CH3COOH + Naoh ==> CH3COONa + H2O
    2. Ethanol does no react with Na2CO3Solution. C2H5 + Na2CO3 ===> No reaction.2. Enthanoic acid reacts with Na2CO3and gives Co2 gas. 2CH3COOH + Na2CO3 ===> 2CH3COONa + Co2 + H2O
    3.Enthanol on oxidation gives the enthanoic acid in presence of acidified KMNO4

                KMNO4 + H2SO4

    C2H5OH =========> CH3COOH
    3. No reaction with acidified KMNO4
    Question 8. Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also? 
    Answer: Soap molecule consists of two parts - one part is hydrophobic and other part is hysdrophilic. Hydrophobic part of soap is dissolvbed with dirt and hydrophilic part rem,ains suspend in water. Thus, many more molecules of soap are attached to dirt having their one end suspended in water. So, micelle is formed. Since ethanol is not polar as soaps, so, micelles will not be formed in othert slvent such asd enthonal also.  
    Question 9. Why are carbon and its compounds used as fuels for most applications?  
    Answer: Carbon and its compounds give large amount of heat on combustion due to high percentage of carbon and hydrogen. The compounds have optimum ignition temperature and are easy to handle. Their combustion can be controlled. Therfore carbon and its compounds are used as a fuel.  
    Question 10. Explain the formation of scum when hard water is treated with soap. Answer: Hard wter contains soluble salts of Ca and Mg. When soap is dissolved in hard water, insoluble salts of Ca +2 are formed which are called scum. Ca+2 ==> (RCOO)2CA + 2Na + Salt of calcium. scum. Mg+2 + RCOONa ==> (RCOO)2Mg + 2Na+ salt of magnesium. soap. scum 
    Question 11. What change will you observe if you test soap with litmus paper (red and blue)? 
    Answer: The litmus paper will turn red due to the basic nature of soap. 
    Question 12. What is hydrogenation? What is its industrial application?  
    Answer: The addition of hydrogen to unsaturar hydrocarbon in the presense of a catalyst is called hydrogenation. Ni/HCH2 H - C = C - H + 2H2 ===================> CH3CH3 Ethyne 473K Enthane Thye reaction is extermely useful in the hydrogenation of oils. The edible oils which are used for cooking are mostly groundnut oil, cotton oil etc. These are unsaturated compounds. These are hydrogenated to preper solid fat which is known as vanaspati ghee in the industries. Ni/ Edible oils + H2 ========> Fats.
    Question 13. Which of the following hydrocarbons undergo addition reactions:C2H6, C3H8, CH6, C2H2 and CH4 
    Answer: Among the said hydrocarbons only C3H6 and C2H2undergo addition reaction because they are unsaturated hydrocarbons having double and triple bond between two carbon atoms respectively.
    H-C=C-C-H====> C3H6(Propyne)
    H - C = C - H ==> C2H2(Ethyne)
    Question 14. Give a test that can be used to differentiate chemically between butter and cooking oil. 
    Answer:Butter is a saturated fat so it is does undergo catalytic hydrogenation but oil being unsaturated hydrocarbon can be hydrogenated in the presense of catalyst. Thus, the following reactions can be used to differnetiate between butter and cooking oil. H2/Catalyst Ni Butter ===================> No reaction. Ni/Pd Oil + H2 ==========> Butter. Catalyst 15. Explain the mechanism of the cleaning action of soaps. Answer:Soap or detergent molecules are made up of two parts. One end is long hydrocarbon chain which is water repelling (hydrophobic). The other end is anion of carbolxylic or sulphonic acid group which is water attracting (hydrophilic). So, when soap is dissolved in water, it forms group of many molecules known as milecules as shown below. the tail stick inwards and the headas outwards. In the case of soap, negative end is -COO-and in the case of detergent is -SO3- These micelles dissolve oily droplets or dirt by the hydrophobic ends. When water is agitated, the oily dirt tends to lift of form the dirty surface and dissociates into fragments.This gives an opportunity to other tails tostick to oil.The solution now contains small globules of oil surrounded by soap or detergent molecules. The negatively charged heads present in water pervent the small globules from comming togeher and form clusters. Thus, the oily dirt is removed from the object.

    Additional Questions

    Question 1.Name thwe alcohol which constitutes glycerides.
    . Question 2.Describe the process of making soap in the laboratory.
    Question 3.How is it that we can use deetergents for washing clothes even when the water is hard, but not soaps? What change has been made in the comp-sition of detergents to make them biodegradable?
    Answer:Take about 50ml of cotton seed oil in 400ml beaker. Add to it 100 ml of 20% solution of sodium hydroxide. Heat it for about 45minutes with constant stirring. The mixture becomes thick and the oil and water layers merge into each other . Then add about 20g of common salt and stir the mixture. A pale yellow solid float on the surface. It is separated and cooled. It forms a cake which is soap. (i) Detergents are sodium salts of sulphonic acid They can be used for washing clothes even when the water is hard because their calcium and magnesium salts are soluble in water. Soaps are sodium salts of fatty acids. They react with Ca2+ and Mg2+ ions to form salts which are insoluble in water and form scum. (ii) Nowadays, the detergents are made up of molecules in which the branching is kept minimum. Hence, they become easily degradable.


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