Class 10 Chemistry
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Topics we learn:
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Solved Questions
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Class 10
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CLASS 10
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Questions from board paper(5 marks each)
1. A saturated organic compound 'A' belongs to the homologous series of alcohols. On heating 'A' with concentrated sulphuric acid at 443 K, it forms an unsaturated compound 'B' with molecular mass 28 u. The compound 'B' on addition of one mole of hydrogen in the presence of Nickel, changes to a saturated hydrocarbon 'C'.
(i) Identify A, B and C.
(ii) Write the chemical equations showing the conversion of A into B.
(iii) What happens when compound C undergoes combustion?
(iv) State one industrial application of hydrogenation reaction.
(v) Name the products formed when compound A reacts with sodium.
2. (i) With the help of diagram, show the formation of micelles, when soap is applied on oily dirt. (ii) Take two test tubes X and Y with 10 mL of hard water in each. In teat tube 'X', add few drops of soap solution and in test tube add a few drops of detergent solution. Shake both the test tubes for the same period.
(1) In which test tube the formation of foam will be more ? Why ?
(2) In which test tube is a curdy solid formed ? Why ?
3.(i) Name the simplest saturated hydrocarbon. Draw its electron dot structure. Which type of bonds exist in this compound ?
(ii) Name any two mixtures of the carbon compound used as a fuel in daily life, of which the above mentioned compound is an important component.
(iii) In which homologous series of carbon compounds can this compound be placed ? Write the general formula of the series. (iv) Which type of flame is produced on burning it ?
4.(a) An acid 'X' and an alcohol 'Y' react with each other in the presence of an acid catalyst to form a sweet-smelling substance 'Z'. Identify and 'Z'. Write the chemical equation for the reaction involved and name it. The substance 'Z' on treatment with sodium hydroxide produces back the alcohol and sodium ethanoate Write the chemical equation for the reaction involved and name it, giving justification for the name.
5. (i) What happens when a small piece of sodium is dropped in ethanol ? Write the equation for this reaction. (ii) Why is glacial acetic acid called so ? (iii) What happens when ethanol is heated at 443 K in the presence of conc. H2SO4 ? Write the role of conc. H2SO4 in this case. (iv) Write an equation showing saponification.
6. A neutral organic compound 'X' (Molecular formula C2H6O) on reacting with acidified K2Cr2O7 gives an organic compound which is acidic in nature. X' reacts with on warming in the presence of conc. H2SO4 to give a sweet smelling compound Z
(i) Identify X, Y and Z
(ii) Write the chemical equations for the reactions in the conversion of (1) X to Y and (2) `X' to 'Z'.
(iii) State the role of (1) acidified K2Cr2O7 in the conversion of 'X' to Y and (2) conc. H2SO4 in the reaction of X and Y
(iv) Name the reaction which occurs when 'Z' reacts with an alkali.
7.Carry out the following conversions, stating the condition(s) for each:
(i) Ethanol Ethene (ii) Ethene Ethane (iii) Ethane Chloroethane
(iv) Ethanol Ethanoic acid (v) Ethanoic acid Ethyl ethanoate
8. (i)A compound 'A' with a molecular formula of C2H402 reacts with a base to give salt and water. Identify 'A', state its nature and the name of the functional group it possesses. Write chemical equation for the reaction involved.
(ii) When the above stated compound 'A' reacts with another compound 'B' having molecular formula C2H6O in the presence of an acid, a sweet smelling compound 'C' is formed.
(1) Identify B and C. (2) State the role of acid in this reaction. (3) Write chemical equation for the reaction involved.
9. (i) Name the compound formed when ethanol is heated at 443 K in the presence of conc.H2SO4 and draw its electron dot structure. State the role of conc.H2SO4 in this reaction.
(ii) What is hydrogenation ? Explain it with the help of a chemical equation. State the role of this reaction in industry.
10. (i) What are isomers ? Write the structures of two compounds having molecular formula C3H60 and give their names. (ii) What are soaps ? How are they chemically different from detergents ? Why do soaps not work effectively in hard water ? {Hint: CH3COCH3 and CH3CH2CHO are propanone and Propanol}
OR (i) What is a homologous series of carbon compounds ? Write general formula for alkynes. Name and draw the electron dot structure of first homologue of this series. (ii) State the meaning of the functional group in an organic compound. Write the formula of the functional group present in alcohols and carboxylic acids.
(i) Identify A, B and C.
(ii) Write the chemical equations showing the conversion of A into B.
(iii) What happens when compound C undergoes combustion?
(iv) State one industrial application of hydrogenation reaction.
(v) Name the products formed when compound A reacts with sodium.
2. (i) With the help of diagram, show the formation of micelles, when soap is applied on oily dirt. (ii) Take two test tubes X and Y with 10 mL of hard water in each. In teat tube 'X', add few drops of soap solution and in test tube add a few drops of detergent solution. Shake both the test tubes for the same period.
(1) In which test tube the formation of foam will be more ? Why ?
(2) In which test tube is a curdy solid formed ? Why ?
3.(i) Name the simplest saturated hydrocarbon. Draw its electron dot structure. Which type of bonds exist in this compound ?
(ii) Name any two mixtures of the carbon compound used as a fuel in daily life, of which the above mentioned compound is an important component.
(iii) In which homologous series of carbon compounds can this compound be placed ? Write the general formula of the series. (iv) Which type of flame is produced on burning it ?
4.(a) An acid 'X' and an alcohol 'Y' react with each other in the presence of an acid catalyst to form a sweet-smelling substance 'Z'. Identify and 'Z'. Write the chemical equation for the reaction involved and name it. The substance 'Z' on treatment with sodium hydroxide produces back the alcohol and sodium ethanoate Write the chemical equation for the reaction involved and name it, giving justification for the name.
5. (i) What happens when a small piece of sodium is dropped in ethanol ? Write the equation for this reaction. (ii) Why is glacial acetic acid called so ? (iii) What happens when ethanol is heated at 443 K in the presence of conc. H2SO4 ? Write the role of conc. H2SO4 in this case. (iv) Write an equation showing saponification.
6. A neutral organic compound 'X' (Molecular formula C2H6O) on reacting with acidified K2Cr2O7 gives an organic compound which is acidic in nature. X' reacts with on warming in the presence of conc. H2SO4 to give a sweet smelling compound Z
(i) Identify X, Y and Z
(ii) Write the chemical equations for the reactions in the conversion of (1) X to Y and (2) `X' to 'Z'.
(iii) State the role of (1) acidified K2Cr2O7 in the conversion of 'X' to Y and (2) conc. H2SO4 in the reaction of X and Y
(iv) Name the reaction which occurs when 'Z' reacts with an alkali.
7.Carry out the following conversions, stating the condition(s) for each:
(i) Ethanol Ethene (ii) Ethene Ethane (iii) Ethane Chloroethane
(iv) Ethanol Ethanoic acid (v) Ethanoic acid Ethyl ethanoate
8. (i)A compound 'A' with a molecular formula of C2H402 reacts with a base to give salt and water. Identify 'A', state its nature and the name of the functional group it possesses. Write chemical equation for the reaction involved.
(ii) When the above stated compound 'A' reacts with another compound 'B' having molecular formula C2H6O in the presence of an acid, a sweet smelling compound 'C' is formed.
(1) Identify B and C. (2) State the role of acid in this reaction. (3) Write chemical equation for the reaction involved.
9. (i) Name the compound formed when ethanol is heated at 443 K in the presence of conc.H2SO4 and draw its electron dot structure. State the role of conc.H2SO4 in this reaction.
(ii) What is hydrogenation ? Explain it with the help of a chemical equation. State the role of this reaction in industry.
10. (i) What are isomers ? Write the structures of two compounds having molecular formula C3H60 and give their names. (ii) What are soaps ? How are they chemically different from detergents ? Why do soaps not work effectively in hard water ? {Hint: CH3COCH3 and CH3CH2CHO are propanone and Propanol}
OR (i) What is a homologous series of carbon compounds ? Write general formula for alkynes. Name and draw the electron dot structure of first homologue of this series. (ii) State the meaning of the functional group in an organic compound. Write the formula of the functional group present in alcohols and carboxylic acids.
Activity based Questions with answer: Class 10 Chapter: Carbon and Its Compounds
1. Q. What happen when few drops of alkaline KmNO4 added to Ethanol?
Ans: In the begging color of KmNO4 disappear. When excess KmNO4 is dissolved in solution colour cannot disappear because whole Ethanol gets oxidized into Ethanoic acid.
CH3CH2OH ---- KmNO4------Heat-------> CH3COOH
Hence, alkaline KmNO4 or Acidified K2Cr2O7 oxidized alcohol into ethanoic acid
Ethanol is highly inflammable and catches fire readily. This is why during oxidation it should never be heat directly on a burner. it should be heated on a water bath
2. Q. How can we convert unsaturated hydrocarbon into saturated hydrocarbon?
Ans: By the addition reaction of unsaturated hydrocarbon with halo atom in the presence of catalyst.
HC=CH +H2 -------------Ni--------5700 K------> Ch3-CH3
R2C=CR2 + H2 ------------Ni---------> R2HC-CHR2 (Vegetable Gee)
This reaction is known as Hydrogenation reaction.
3. Q. How can you test that given hydrocarbon is unsaturated?
Ans: When few drops of Bromine is added to unsaturated hydrocarbon its colour disappear due to addition reaction.
For example: If drops of bromine water added to ethyne, the reddish brown colour of Bromine disappear due to addition reaction . HC≡CH + Br2 -------------> HBr2 C – CHBr2 (Tetra Broomo ethane is formed)
4. Q. How can you prepare alkenes from Ethanol?
Ans: When Ethanol heated in presence of Conc.H2SO4 or Al2O3 at 623 degree C ,Ethanol loose water molecules and form alkenes. C2H5OH ---H2SO4------623C------>CH2=CH2 + H2O
5. Q. What happen when a piece of sodium metal added to Ethanol?
Ans: Sodium ethoxide is formed with evolution of H2 gas
C2H5OH + Na -------------> C2H5ONa + H2
6. Q. What happens when few drops of Conc.H2SO4 is added to Solution of Ethanoic acid and Ethanol?
Ans: A substance with fruity smell is formed called Ester.This reaction is known as Esterification
C2H5OH + CH3COOH ------H2SO4------> CH3COO C2H5 (Ester or, Ethyl Ethanoate)
7. Q. What types of flame produce by burning of Benzene, Nepthline and Camphor?
Ans: Smoky flame due presence of excess carbon content.
8. Q. What is Gasol?
Ans: The mixture of petrol with alcohol up to 20% is known gasol.
9.Q. Why Acetic acid is called glacier acid?
Ans: Acetic acid freezes at 290K in cold weather and form crystals.This is why acetic acid is called glacier acid.
10. Q. What is saponification?
Ans: When sodium hydroxide react with ester and form alcohol and sodium Ethanoate. This reaction is used to form soap So this reaction is known as saponification.
CH3COO C2H5 + NaOH ------------> CH3COONa + C2H5OH
11. Q. Why does melting and boiling points of the member of Homologous Series increase gradually ?
Ans: The number of carbon atoms in the molecule of the member of Homologous Series increases gradually .Van der Waals dispersion forces will be very small for a molecule like methane but will increase as the molecules get bigger. Therefore, the boiling points of the alkanes increase with molecular size(increase in no. of c atom)
12. Q. Why does the viscosity of the member of Homologous Series increase gradually?
Ans: The viscosity increases as relative molecular mass and size increases.
13. Q. Why alkanes cannot dissolve in water but is soluble in organic solvent?
Ans: This is because alkane does not release a sufficient amount of energy to break the hydrogen bonds in water. Therefore, the alkane does not dissolve.
14. Q. Why doesn’t soap form micelles in ethanol as they form in water?
Ans: In organic solvent like ethanol, soap is completely soluble, hence no micelle is not formed
15. Q. What is observed on adding 5% solution of alkaline potassium permanganate solution drop by drop to some warm ethanol taken in test tube. Write the name of the compound formed during chemical reaction.
Ans: When a 5% solution of alkaline potassium permanganate solution is added drop by drop to some warm ethanol taken in a test tube, magenta colour of alkaline potassium permanganate disappears and ethanol has been changed to carboxylic acid.
The reaction is as follows. CH3 - CH2OH --------------- > CH3COOH
16. Q. How would you distinguish experimentally between an alcohol and a carboxylic acid on the basis of a chemical property?
Ans: we take alcohol and a carboxylic acid in two separate test tubes. Add sodium hydrogen carbonate in both the test tubes. The test tube, from which the effectiveness evolves, contains carboxylic acid. The effervescence is due to the evolution of carbon dioxide gas. However, from test tube containing alcohol there is to effervescence, because no carbon dioxide gas is produced there.
17. Q. A straight-chain alkane will have a boiling point higher than a branched-chain alkane?
Ans: This is due to the greater surface area in contact.
18. Q. Why do Alkanes stable and less reactive than alkenes ?
Ans: This is because saturated hydrocarbons contain only single bonds which are very stable and difficult to break. On the other hand, unsaturated hydrocarbons contain pie bonds, which can be easily broken as they are more strained.
19. Q. How can you check which one is saturated butter or vegetable oil?
Ans: Butter contain saturated compound where as cooking oil contain unsaturated compound. If Alkaline KMno4 added to both, pink color of KMno4 disappear in cooking oil but remain in pink in butter.
Vegetable Oil + H2 ----Ni--------> CH3 - CH3
20. Q. What's the difference between cracking and pyrolysis?
Ans: Pyrolysis : The decomposition of a compound on heating in absence of air is known as pyrolysis. Pyrolysis is used on a massive scale to turn coal into coke for metallurgy, and fractional distillation
Cracking: The breakdown of large organic compounds by use of a catalyst and low temperature to form fewer different compounds is called Cracking.
C22H46 ---> C11H24 (an alkane) + C11H22 (an alkene)
21. Q. What do you mean by Intra and Inter molecular dehydration of Ethanol?
Ans:
(a) Intra molecular dehydration :
Ethanol, when heated with excess conc. H2SO4 at 443 K undergoes intra molecular dehydration (i.e. removal of water within a molecule of ethanol).
CH3CH2OH -------Conc.H2SO4/443K-----> CH2 = CH2 +H2O
(b) Inter molecular dehydration :
When excess of alcohol is heated with conc. H2SO4 at 413K two molecules condense by losing a molecule of water to form ether (i.e. removal of water from two molecules of ethanol).
C2H5- OH + C2H5HO -------Conc.H2SO4/413K----> C2H5-O-C2H5 (Diethyl ether)+H2O
22. Q. Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
Ans. When ethanol is oxidised, hydrogen is removed from its molecule and oxygen is added so as to form ethanoic acid. Thus, conversion of ethanol into acetic acid is an oxidation reaction.
23. Q. A mixture of ethyne and oxygen is burnt for welding. Can you tell why a mixture of ethyne and air is not used?
Ans: Ethyne is un saturated carbon compound and burns in air with a sooty flame, because the oxygen from air is insufficient to burn the carbon completely. Thus, pure oxygen is used which completely burns carbon and hydrogen and produces a very hot flame.
24. Q. How will you distinguish between alcohol and carboxylic acid experimentally? (V. Imp.)
Ans. Take two test tubes A and B and place about 1 g of sodium carbonate in them. Pour alcohol in test tube A and carboxylic acid in test tube B. Shake the contents of the test tubes.
The test tube in which a brisk effervescence takes place, with the liberation of a colourless gas (CO2) is carboxylic acid. The test tube in which no reaction takes place is alcohol.
25. Q. Unsaturated hydrocarbons show addition reactions but not saturated hydrocarbons?
Ans: In saturated hydrocarbons all the four bonds of carbon are fully utilised and no more hydrogen or other atoms can attach to it. Thus, they can undergo only substitution reactions not addition reactions.
26. Q. How can ethanol and ethanoic acid be differentiated on the basis of physical and chemical properties?
Ans. Physical properties :
(a). Ethanol has a sharp bitter burning taste, whereas ethanoic acid has a sour taste.
(b) On cooling ethanol does not freeze, but ethanoic acid freezes.
Chemical Properties :
(a) Ethanol gets dehydrated by conc. sulphuric acid, but ethanoic acid does not get dehydrated by conc. sulphuric acid.
(b) Ethanol does not displace hydrogen with zinc or magnesium, but ethanoic acid displaces hydrogen with zinc or magnesium
27. Q. ‘‘Saturated hydrocarbons burn with a blue flame while unsaturated hydrocarbons burn with a sooty flame’’. Why?
Ans. This is because saturated hydrocarbon has high percentage of hydrogen than that of unsaturated hydrocarbons
28. Q. Why is the reaction between methane and chlorine considered as a substitution reaction.?
Ans: reaction between methane and chlorine is considered as a substitution reaction since the hydrogen atoms of methane are replaced by chlorine atoms.
29. Q. How would you bring about the following conversions? Name the process and write the reaction involved.
(a) ethanol to ethene (b) propanol to propanoic acid.
Ans. (a) By the dehydration of ethanol in the presence of concentrated H2SO4
CH3 CH2 OH --------- Hot conc. H2SO4 → CH2 = CH2 + H2O
(b) By the oxidation of propanol using oxidising agent such as alkaline KMnO4.
CH3 CH2 CH2 OH ---Alk. KMnO4 + Heat -→ CH3 CH2 COOH
1. Q. What happen when few drops of alkaline KmNO4 added to Ethanol?
Ans: In the begging color of KmNO4 disappear. When excess KmNO4 is dissolved in solution colour cannot disappear because whole Ethanol gets oxidized into Ethanoic acid.
CH3CH2OH ---- KmNO4------Heat-------> CH3COOH
Hence, alkaline KmNO4 or Acidified K2Cr2O7 oxidized alcohol into ethanoic acid
Ethanol is highly inflammable and catches fire readily. This is why during oxidation it should never be heat directly on a burner. it should be heated on a water bath
2. Q. How can we convert unsaturated hydrocarbon into saturated hydrocarbon?
Ans: By the addition reaction of unsaturated hydrocarbon with halo atom in the presence of catalyst.
HC=CH +H2 -------------Ni--------5700 K------> Ch3-CH3
R2C=CR2 + H2 ------------Ni---------> R2HC-CHR2 (Vegetable Gee)
This reaction is known as Hydrogenation reaction.
3. Q. How can you test that given hydrocarbon is unsaturated?
Ans: When few drops of Bromine is added to unsaturated hydrocarbon its colour disappear due to addition reaction.
For example: If drops of bromine water added to ethyne, the reddish brown colour of Bromine disappear due to addition reaction . HC≡CH + Br2 -------------> HBr2 C – CHBr2 (Tetra Broomo ethane is formed)
4. Q. How can you prepare alkenes from Ethanol?
Ans: When Ethanol heated in presence of Conc.H2SO4 or Al2O3 at 623 degree C ,Ethanol loose water molecules and form alkenes. C2H5OH ---H2SO4------623C------>CH2=CH2 + H2O
5. Q. What happen when a piece of sodium metal added to Ethanol?
Ans: Sodium ethoxide is formed with evolution of H2 gas
C2H5OH + Na -------------> C2H5ONa + H2
6. Q. What happens when few drops of Conc.H2SO4 is added to Solution of Ethanoic acid and Ethanol?
Ans: A substance with fruity smell is formed called Ester.This reaction is known as Esterification
C2H5OH + CH3COOH ------H2SO4------> CH3COO C2H5 (Ester or, Ethyl Ethanoate)
7. Q. What types of flame produce by burning of Benzene, Nepthline and Camphor?
Ans: Smoky flame due presence of excess carbon content.
8. Q. What is Gasol?
Ans: The mixture of petrol with alcohol up to 20% is known gasol.
9.Q. Why Acetic acid is called glacier acid?
Ans: Acetic acid freezes at 290K in cold weather and form crystals.This is why acetic acid is called glacier acid.
10. Q. What is saponification?
Ans: When sodium hydroxide react with ester and form alcohol and sodium Ethanoate. This reaction is used to form soap So this reaction is known as saponification.
CH3COO C2H5 + NaOH ------------> CH3COONa + C2H5OH
11. Q. Why does melting and boiling points of the member of Homologous Series increase gradually ?
Ans: The number of carbon atoms in the molecule of the member of Homologous Series increases gradually .Van der Waals dispersion forces will be very small for a molecule like methane but will increase as the molecules get bigger. Therefore, the boiling points of the alkanes increase with molecular size(increase in no. of c atom)
12. Q. Why does the viscosity of the member of Homologous Series increase gradually?
Ans: The viscosity increases as relative molecular mass and size increases.
13. Q. Why alkanes cannot dissolve in water but is soluble in organic solvent?
Ans: This is because alkane does not release a sufficient amount of energy to break the hydrogen bonds in water. Therefore, the alkane does not dissolve.
14. Q. Why doesn’t soap form micelles in ethanol as they form in water?
Ans: In organic solvent like ethanol, soap is completely soluble, hence no micelle is not formed
15. Q. What is observed on adding 5% solution of alkaline potassium permanganate solution drop by drop to some warm ethanol taken in test tube. Write the name of the compound formed during chemical reaction.
Ans: When a 5% solution of alkaline potassium permanganate solution is added drop by drop to some warm ethanol taken in a test tube, magenta colour of alkaline potassium permanganate disappears and ethanol has been changed to carboxylic acid.
The reaction is as follows. CH3 - CH2OH --------------- > CH3COOH
16. Q. How would you distinguish experimentally between an alcohol and a carboxylic acid on the basis of a chemical property?
Ans: we take alcohol and a carboxylic acid in two separate test tubes. Add sodium hydrogen carbonate in both the test tubes. The test tube, from which the effectiveness evolves, contains carboxylic acid. The effervescence is due to the evolution of carbon dioxide gas. However, from test tube containing alcohol there is to effervescence, because no carbon dioxide gas is produced there.
17. Q. A straight-chain alkane will have a boiling point higher than a branched-chain alkane?
Ans: This is due to the greater surface area in contact.
18. Q. Why do Alkanes stable and less reactive than alkenes ?
Ans: This is because saturated hydrocarbons contain only single bonds which are very stable and difficult to break. On the other hand, unsaturated hydrocarbons contain pie bonds, which can be easily broken as they are more strained.
19. Q. How can you check which one is saturated butter or vegetable oil?
Ans: Butter contain saturated compound where as cooking oil contain unsaturated compound. If Alkaline KMno4 added to both, pink color of KMno4 disappear in cooking oil but remain in pink in butter.
Vegetable Oil + H2 ----Ni--------> CH3 - CH3
20. Q. What's the difference between cracking and pyrolysis?
Ans: Pyrolysis : The decomposition of a compound on heating in absence of air is known as pyrolysis. Pyrolysis is used on a massive scale to turn coal into coke for metallurgy, and fractional distillation
Cracking: The breakdown of large organic compounds by use of a catalyst and low temperature to form fewer different compounds is called Cracking.
C22H46 ---> C11H24 (an alkane) + C11H22 (an alkene)
21. Q. What do you mean by Intra and Inter molecular dehydration of Ethanol?
Ans:
(a) Intra molecular dehydration :
Ethanol, when heated with excess conc. H2SO4 at 443 K undergoes intra molecular dehydration (i.e. removal of water within a molecule of ethanol).
CH3CH2OH -------Conc.H2SO4/443K-----> CH2 = CH2 +H2O
(b) Inter molecular dehydration :
When excess of alcohol is heated with conc. H2SO4 at 413K two molecules condense by losing a molecule of water to form ether (i.e. removal of water from two molecules of ethanol).
C2H5- OH + C2H5HO -------Conc.H2SO4/413K----> C2H5-O-C2H5 (Diethyl ether)+H2O
22. Q. Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
Ans. When ethanol is oxidised, hydrogen is removed from its molecule and oxygen is added so as to form ethanoic acid. Thus, conversion of ethanol into acetic acid is an oxidation reaction.
23. Q. A mixture of ethyne and oxygen is burnt for welding. Can you tell why a mixture of ethyne and air is not used?
Ans: Ethyne is un saturated carbon compound and burns in air with a sooty flame, because the oxygen from air is insufficient to burn the carbon completely. Thus, pure oxygen is used which completely burns carbon and hydrogen and produces a very hot flame.
24. Q. How will you distinguish between alcohol and carboxylic acid experimentally? (V. Imp.)
Ans. Take two test tubes A and B and place about 1 g of sodium carbonate in them. Pour alcohol in test tube A and carboxylic acid in test tube B. Shake the contents of the test tubes.
The test tube in which a brisk effervescence takes place, with the liberation of a colourless gas (CO2) is carboxylic acid. The test tube in which no reaction takes place is alcohol.
25. Q. Unsaturated hydrocarbons show addition reactions but not saturated hydrocarbons?
Ans: In saturated hydrocarbons all the four bonds of carbon are fully utilised and no more hydrogen or other atoms can attach to it. Thus, they can undergo only substitution reactions not addition reactions.
26. Q. How can ethanol and ethanoic acid be differentiated on the basis of physical and chemical properties?
Ans. Physical properties :
(a). Ethanol has a sharp bitter burning taste, whereas ethanoic acid has a sour taste.
(b) On cooling ethanol does not freeze, but ethanoic acid freezes.
Chemical Properties :
(a) Ethanol gets dehydrated by conc. sulphuric acid, but ethanoic acid does not get dehydrated by conc. sulphuric acid.
(b) Ethanol does not displace hydrogen with zinc or magnesium, but ethanoic acid displaces hydrogen with zinc or magnesium
27. Q. ‘‘Saturated hydrocarbons burn with a blue flame while unsaturated hydrocarbons burn with a sooty flame’’. Why?
Ans. This is because saturated hydrocarbon has high percentage of hydrogen than that of unsaturated hydrocarbons
28. Q. Why is the reaction between methane and chlorine considered as a substitution reaction.?
Ans: reaction between methane and chlorine is considered as a substitution reaction since the hydrogen atoms of methane are replaced by chlorine atoms.
29. Q. How would you bring about the following conversions? Name the process and write the reaction involved.
(a) ethanol to ethene (b) propanol to propanoic acid.
Ans. (a) By the dehydration of ethanol in the presence of concentrated H2SO4
CH3 CH2 OH --------- Hot conc. H2SO4 → CH2 = CH2 + H2O
(b) By the oxidation of propanol using oxidising agent such as alkaline KMnO4.
CH3 CH2 CH2 OH ---Alk. KMnO4 + Heat -→ CH3 CH2 COOH
31. Q. why sodium chloride added during preparation of soap?
Ans: This help to decrease solubility of soap and help in precipitation of soap from aqueous solution. This preparation is known as salting out.
32. Q. Why is soap not used in acidic solution?
Ans: This is because free fatty acid of soap get precipitated
RCOO – Na+ + H+ ---------------> RCOOH + Na+
33. Q. Why are soap not effective as a cleaning agent in hard water?
Ans: Hard water contains sodium and magnesium ions. Soap form precipitate with these ions and thus thrown out of the solution.
2RCOO – Na+ + Mg2+ ---------------> (RCOO)2 Mg + 2Na+
34. Q. Alkanes (both alkanes and cycloalkanes) are virtually insoluble in water, but dissolve in organic solvents. However, liquid alkanes are good solvents for many other non-ionic organic compounds. Give reason.
Ans: Van der Waals forces do not release a sufficient amount of energy to compensate for the energy required to break the hydrogen bonds in water. The alkane does not dissolve.
In most organic solvents, the primary forces of attraction between the solvent molecules are Van der Waals - either dispersion forces or dipole-dipole attractions. Therefore, when an alkane dissolves in an organic solvent, the Van der Waals forces are broken and are replaced by new Van der Waals forces. The two processes more or less cancel each other out energetically; thus, there is no barrier to solubility.
35. Q. What is the difference between Oxidation and combustion?
Answer: Combustion is the complete oxidation of organic compound into carbon dioxide and water molecules in presence of oxygen gas while oxidation is the addition of oxygen in a organic compound or with an element the loss of electron from an atom or ion is also oxidation.
Hence, all Oxidation reactions are not combustion reaction but all combustion reactions are Oxidation. Oxidation reaction does not involve heat where as combustion reactions do.
36. Q. Why does Ethanoic acid called glacial acetic acid?
Ans. On cooling, pure Ethanoic acid is frozen to form ice like flakes. They look like glaciers, so it is called glacial acetic acid.
37. Q. A mixture of ethyne and oxygen is burnt for welding. Can you tell why a mixture of ethyne and air is not used?
Ans. Ethyne has only two hydrogen atoms and two carbon atoms in its molecule. It burns in air with a sooty flame, because the oxygen from air is insufficient to burn the carbon completely. Thus, pure oxygen is used which completely burns carbon and hydrogen and produces a very hot flame
38. Q. What is functional group ? need more to know
Ans: Functional group may be defined as an atom or group of atoms or reactive part which is responsible for the characteristic properties of the compounds.
The chemical properties of organic compounds are determined by the functional groups while their physical properties are determined by the remaining part of the molecule.
The general formula of alcohol is R-OH where ‘R’ is an alkyl group and –OH is the functional group.
The general formula of aldehydes is R – CHO where ‘R’ is an alkyl group or hydrogen atom and – CHO is the functional group
The general formula of ketone is R-CO-R’ where R and R’ are alkyl groups and – C=O – is the functional group
The general formula of acid is R-COOH where ‘R’ is a hydrogen atom or alkyl group and –COOH is the functional group.
The general formula of esters is R-C=O- OR’ where R and R’ are alkyl groups and – C=O - OR is the functional group
39. Q. Why is graphite a good conductor of electricity?
Ans: Graphite is a good conductor of electricity. Its structure is the main reason for this property. Each carbon atom in graphite is directly linked to only three carbon atoms through covalent bonds. Therefore, out of the four valence electrons in a carbon atom, only three are used for bonding and the fourth is relatively free and can move from one carbon atom to the other. These free electrons make graphite a good conductor of electricity.
40. Q. (a) Differentiate between soap and detergent.
(b) Explain why, soaps form scum with hard water whereas detergents do not
Ans:
(a)Difference between soap and detergent:
Soap
(i) sodium salt of long chain carboxylic acid.
(ii) Soaps are biodegradable
(iii) Not suitable with hard water
Detergent
(i) Ammonium or sulphate of long chain of carboxylic acid.
(ii) Not biodegradable
(iii) Working well in hard water
(b) In hard water, due to the presence of Ca +2 and Mg +2 ions, soaps form insoluble salt. This Precipitate is called scum.
Detergent does not show this property as its charged end does not react with Ca+2 and Mg+2 ions
41. Q. How does soap clean the clothes?
Ans: When dirty clothes are mixed with water and soap, the ionic part of the soap being water attractive, dissolves in water whereas the hydrocarbon part of the soap being water repellent unites with the oil or greese part. When dirty clothes are rinsed with water, the dirt particles attached with the soap molecules, dissolve in water and come out. In this way, clothes become clean.
Ans: This help to decrease solubility of soap and help in precipitation of soap from aqueous solution. This preparation is known as salting out.
32. Q. Why is soap not used in acidic solution?
Ans: This is because free fatty acid of soap get precipitated
RCOO – Na+ + H+ ---------------> RCOOH + Na+
33. Q. Why are soap not effective as a cleaning agent in hard water?
Ans: Hard water contains sodium and magnesium ions. Soap form precipitate with these ions and thus thrown out of the solution.
2RCOO – Na+ + Mg2+ ---------------> (RCOO)2 Mg + 2Na+
34. Q. Alkanes (both alkanes and cycloalkanes) are virtually insoluble in water, but dissolve in organic solvents. However, liquid alkanes are good solvents for many other non-ionic organic compounds. Give reason.
Ans: Van der Waals forces do not release a sufficient amount of energy to compensate for the energy required to break the hydrogen bonds in water. The alkane does not dissolve.
In most organic solvents, the primary forces of attraction between the solvent molecules are Van der Waals - either dispersion forces or dipole-dipole attractions. Therefore, when an alkane dissolves in an organic solvent, the Van der Waals forces are broken and are replaced by new Van der Waals forces. The two processes more or less cancel each other out energetically; thus, there is no barrier to solubility.
35. Q. What is the difference between Oxidation and combustion?
Answer: Combustion is the complete oxidation of organic compound into carbon dioxide and water molecules in presence of oxygen gas while oxidation is the addition of oxygen in a organic compound or with an element the loss of electron from an atom or ion is also oxidation.
Hence, all Oxidation reactions are not combustion reaction but all combustion reactions are Oxidation. Oxidation reaction does not involve heat where as combustion reactions do.
36. Q. Why does Ethanoic acid called glacial acetic acid?
Ans. On cooling, pure Ethanoic acid is frozen to form ice like flakes. They look like glaciers, so it is called glacial acetic acid.
37. Q. A mixture of ethyne and oxygen is burnt for welding. Can you tell why a mixture of ethyne and air is not used?
Ans. Ethyne has only two hydrogen atoms and two carbon atoms in its molecule. It burns in air with a sooty flame, because the oxygen from air is insufficient to burn the carbon completely. Thus, pure oxygen is used which completely burns carbon and hydrogen and produces a very hot flame
38. Q. What is functional group ? need more to know
Ans: Functional group may be defined as an atom or group of atoms or reactive part which is responsible for the characteristic properties of the compounds.
The chemical properties of organic compounds are determined by the functional groups while their physical properties are determined by the remaining part of the molecule.
The general formula of alcohol is R-OH where ‘R’ is an alkyl group and –OH is the functional group.
The general formula of aldehydes is R – CHO where ‘R’ is an alkyl group or hydrogen atom and – CHO is the functional group
The general formula of ketone is R-CO-R’ where R and R’ are alkyl groups and – C=O – is the functional group
The general formula of acid is R-COOH where ‘R’ is a hydrogen atom or alkyl group and –COOH is the functional group.
The general formula of esters is R-C=O- OR’ where R and R’ are alkyl groups and – C=O - OR is the functional group
39. Q. Why is graphite a good conductor of electricity?
Ans: Graphite is a good conductor of electricity. Its structure is the main reason for this property. Each carbon atom in graphite is directly linked to only three carbon atoms through covalent bonds. Therefore, out of the four valence electrons in a carbon atom, only three are used for bonding and the fourth is relatively free and can move from one carbon atom to the other. These free electrons make graphite a good conductor of electricity.
40. Q. (a) Differentiate between soap and detergent.
(b) Explain why, soaps form scum with hard water whereas detergents do not
Ans:
(a)Difference between soap and detergent:
Soap
(i) sodium salt of long chain carboxylic acid.
(ii) Soaps are biodegradable
(iii) Not suitable with hard water
Detergent
(i) Ammonium or sulphate of long chain of carboxylic acid.
(ii) Not biodegradable
(iii) Working well in hard water
(b) In hard water, due to the presence of Ca +2 and Mg +2 ions, soaps form insoluble salt. This Precipitate is called scum.
Detergent does not show this property as its charged end does not react with Ca+2 and Mg+2 ions
41. Q. How does soap clean the clothes?
Ans: When dirty clothes are mixed with water and soap, the ionic part of the soap being water attractive, dissolves in water whereas the hydrocarbon part of the soap being water repellent unites with the oil or greese part. When dirty clothes are rinsed with water, the dirt particles attached with the soap molecules, dissolve in water and come out. In this way, clothes become clean.
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