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
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 testube. 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 KMno4added to both, pink color of KMno4disappear in cooking oil but remain in pink in butter.
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.
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
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
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 isR-CO-R’ where R and R’ are alkyl groups and – C=O – is the functional group
The general formula of acid is R-COOHwhere ‘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.