4. CARBON & ITS COMPOUNDS
Questions:
1. Identify a property o f amorphous silicon in the following. [SSLC, April 2018]
(a) Does not bum in the air
(b) Has dark grey colour
(c) Oxidizes at the surface level when heated in the air
(d)Less reactive
Ans: (c) Oxidizes at the surface level when heated in the air.
2. An example of polyfunctional compound is [SSLC, April, 2017]
(a)Glycine
(b) Ethanol
(c) Ethanamine
(d) Methanal
Ans: (a) Glycine.
3. Match the Column: [SSLC, April, 2018]
Ans: A. (iii), B. (iv), C. (ii), D. (i)
4. What is a homologous series o f carbon compounds?
A ns : A homologous series is the family of organic c ompound having the s a me functiona l group, a nd the successive (adjacent) me mbe r s of w hic h differ by C H 2 unit or 14 ma s s unit.
5. Write the name and molecular formula of the first member of the homologous series o f alkynes.
Ans: Ethyne, C2H2.
6. Molecular formula o f a hydrocarbon is C3H 8. Draw its complete structure and write its name
. Ans:
The name o f the hydrocarbon is propane.
7. What is the difference between two consecutive members in a homologous series in alkanes in terms of: (i) Molecular mass, (ii) N umber of atoms of elements.
Ans: Difference in: (i) Molecular mass = 1 4 a.m.u. (ii) N umber of atoms of elements = C Hr
8. Write the number o f covalent bonds in the molecule o f Ethane
Ans: Seven covalent bonds.
9 . N ame the process b y which unsaturated fats are changed to saturated fats.
Ans: Hydrogenation.
10. The molecular formula of the first member of a certain group of organic compounds is C H2O (HC HO ). Determine the name and the molecular formula of the third member of this group if the members o f this group are in homologous series. What is the general name for this group o f organic compounds? [SSLC April, 2018]
Ans: Name → P ropanol/P ropanaldehyde. Molecular formula → C3H6O (C2H5CHO) Aldehydes
11. What is a covalent bond? What type of bond exists in (i) C Cl4, (ii) C aC l2?
Ans : The chemical bonds formed between two atoms b y the sharing of electrons between them is known as a covalent bond. The sharing of electrons between the two atoms takes place in such a way that both the atoms acquire stable electronic configuration of their nearest noble gas (i) C Cl4: Covalent bond (ii) CaCl2: Ionic bond
12. List two differences between saturated and unsaturated hydrocarbons.
13. What are covalent compounds ? Why are they different from ionic compounds ? List their three characteristics.
Ans : (a) C ova lent compounds are those compounds which are formed b y sharing of electrons between two atoms/which contain covalent bonds.
(b) C ovalent compounds are different from ionic compounds because the ionic compounds are formed b y the transfer o f electrons.
(c) Three characteristics o f covalent compounds are:
(i) Generally have low melting and b o iling points.
(ii) Generally insoluble or less soluble in water but soluble in organic solvents.
(iii) Do not conduct electricity.
14. Write the molecular formula of the following compounds and draw their electron- dot structures: (i) Ethane (ii) Ethene (iii) Ethyne Ans: (i) Ethane: C2H6 (ii) Ethene: C2H4 (iii) Ethyne: C2H2
15. State the meaning o f functional group in a carbon compound. Write the functional group present in (i) Ethanol, and (ii) Ethanoic acid and also draw their structures.
Ans : F unctional group is an atom o r a group o f atoms that is bonded to a carbon chain. It defines the chemical property of the organic compound:
16. List two tests for experimentally distinguishing between an alcohol and a carboxylic acid and describe how these tests are performed. OR How would you distinguish experimentally between an alcohol and a carboxylic acid?
Ans: (i) W e can distinguis h between an alcohol and a carboxylic acid o n the basis o f their reaction with sodium carbonate and sodium hydrogen carbonate. C arboxylic acids reacts with sodium carbonate and sodium hydrogen carbonate to evolve C O 2 gas that turns lime water milky. Alcohol, o n the other hand, d o not react with sodium carbonate and sodium hydrogen carbonate. (ii) Alcohol reacts with sodium metal to produce hydrogen gas with rapid effervescence. O n the other hand, carboxylic acid does not show this type o f chemica l reaction with sodium metal.
17. Give two examples o f covalent compounds which you have studied. State any four properties in which covalent compounds differ from ionic compounds.
Ans : Two examples o f covalent compounds are ethanol, and ethanoic acid. Difference between the properties o f Covalent and Ionic compounds:
18. List tw o reasons for carbon f or ming a large numbe r of c ompounds . N a me the type of bonding f ound in mos t of its c ompounds . W hy doe s carbon f or m c ompounds ma inly by this kind of bonding. Give reason w hy the carbon c ompounds : (i) Generally have low melting and boiling points. (ii) D o not conduct electricity in molte n state.
Ans: Two of the main reason because of which carbon forms a large number o f organic compounds are: 1. Tetravale nt nature o f carbon 2. Greater C — C bond strength C arbon compounds are formed b y covalent bonds. (i) C a r bon c ompounds , ha ve low melting a nd boiling point be c a us e these c ompounds are bonde d w ith covale nt bond a nd also forces of attraction be tw e e n these molec ules are not very strong. (ii) Because carbon compounds are covalent in nature, they are bad conductors o f electricity; they lack free electrons.
19. What is saponification? [SSLC June 2016]
Ans : Process o f neutra lizing the fatty acids present in the oils or fats b y adding sodium hydroxide or Votassium hydroxide is saponification.
20. N ame the products formed when ethanoic acid reacts with a sodium hydrogen carbo nate.
Ans : S odium ethanoate, carbon dioxide and water.
21. Draw the electron dot structure o f nitrogen molecule.
Ans:
22. What happens when methane is burnt in air?
Ans : Methane bums in air with the formation o f carbon dioxide and water. CH4 + 2O2 ⟶ CO2 + 2H2O + Heat energy
23. (i) Describe the mechanism of cleansing action o f soaps. [SSLC July, 2018]
(ii) Why d o soaps not work in hard water?
Ans: (i) Soap molecules form micelles where ionic end of soap dissolves in water while carbon chain dissolves in oil. The emulsion in water thus formed helps in dissolving the dirt in water and we can wash our clothes clean.
(ii) S oaps react with calcium or magnesium ions to form an insoluble substance which results in wastage o f soap.
24. What is hydrogenation of Oils? Write two advantage of its. [SSLC April, 2016]
Ans : It is the process o f converting liquid oils into solid fat b y passing hydrogen gas in presence o f suitable catalyst. A dv an tages: (i) Shelf life increases (ii) Easy to transport
25. List any four differences between soaps and detergents.
Ans : Difference between soaps and detergents:
26. The structural formula o f an ester is:
Write the structural formula of the acid and the alcohol from which it might b e prepared. N ame the process of formation o f ester.
Ans: CH3COOH + C4H9OH → Acid Alcohol CH3 COOC4H9 + H2O Es ter
Process is Esterification.
27. What are esters? How they are prepared? List two uses o f esters.
Ans : Esters are the derivatives of carboxylic acids which contain — C O O R group. The - O H group in an acid is replaced b y — O— alkyl or aryl group to form an ester. Esters are represented b y the formula R1C O O R2 where R1 and R2 represent an alkyl or aryl group. P rep aration of esters: When carboxylic acids are heated with alcohols in the presence o f an acid catalyst, esters are produced.
Us e s o f esters:
(i) Esters are used in food as flavours and fragrances.
(ii) In making of soaps
(iii) Esters are used as solvents
(iv) Ester are used in medicines.
(v) Esters are used as emulsifying agents.
28. (a) What is isomerism? N ame the isomers o f butane. [SSLC April, 2018]
(b) N ame the air pollutant liberated during incomplete combustion o f methane.
(c) N ame the importance of hydrogenation o f oils.
Ans : (a) P henomenon in which organic compounds have same molecular formula with different structural arrangement o f atoms in them is known as isomerism. n-butane and iso -butane.
(b) Carbon monoxide (C O )
(c) Hydrogenated oils.
(i) Have more shelf life, easy to transport.
(ii) Do not produce foul smell.
29. (a) The boxes given here with numbers 1, 2, 3 and 4 represent a class of hydrocarbons. Write the name of first member of that respective class acco rding to the numbers given.
Ans: (a)(1) Methane (2) Ethyne (3) Cyclopropane (4) Benzene (b) (i) Carboxylic group, Butanoic acid (ii) Aldehyde, Propanal
30. What would b e the electron dot structure o f a molecule o f sulphur which is made up of eight atoms o f sulphur?
Ans:
Te xtbook Exercises:
1. Ethane, with the molecular formula C 2H 6 has (a) 6 covalent bonds (b) 7 covalent bonds (c) 8 covalent bonds (d) 9 covalent bonds
Ans: (b) 7 covalent bonds
2. Butanone is a four-carbon compound with functional group (a) Carboxylic group (b) Aldehyde (c) Ketone (d) Alcohol
Ans: (c) Ketone
3. W hile c ooking, if the bottom of the vessel is getting bla c ke ne d on the outside , it me a n that
(a) Food is not cooked completely
(b) The fuel is not burning completely
(c) The fuel is wet
(d) The fuel is burning completely
Ans: (b) The fuel is not burning completely
4. Explain the nature o f covalent bond using the bond formation o f CH3Cl.
A ns :
The carbon a tom will share 4 electrons a nd hydr oge n or chlorine share one each to be c ome stable. I n this w a y, C f or ms three covale nt bonds w ith hydr oge n a toms a nd one covalent bond w ith chlor ine a tom.
5. Draw the electron dot structures for
(a) Ethanoic acid
(b) H 2S
(c) Propanone
(d) F2
Ans:
6. What is a homologous series? Explain with an example.
Ans : The family of organic compounds in which all the members can b e represented b y same general formula is known as homologous series. E.g. All the membe rs of alcohol homologous series can b e represented b y CnH2 n + 1 formula.
7. How can ethanol and ethanoic a cid b e differentiated o n the basis of their physical and chemical p roperties?
Ans : Ethanol has low boiling point (18℃) as compared to ethanoic acid (118℃) Ethanol can’t re act with sodium carbonate while ethanoic acids produces C O 2 gas.
8. Why does micelle formation take place when soap is added to water? Will the micelle b e formed in other solvents such as ethanol also?
Ans : Micelle formation takes place due to two opposite ends in soap molecules, the hydrophilic end, i.e. water soluble and the hydrophobic end, i.e. water repe lling end.
9. Why re carbon and its compounds used as fuels for most application?
Ans : Because these compounds have high calorific value and low ignition temperature.
10. Explain the formation o f scum when hard water is treated with soap?
Ans : When soap is added in hard water, the calcium and magnesium ions cause precipitation of soap and the precipitate formed is called scum.
11. What change will you observes if you test soap with litmus paper (red and blue)?
Ans : It will change red litmus into blue and no effect will b e there o n blue litmus.
12. What is hydrogenation? What is its industrial application?
Ans : The reaction in which unsaturated hydrocarbon combines with hydrogen in the presence o f nickel o r palladium is known as hydrogenation reaction. Application: Conversion of vegetable oil into vegetable ghee.
13. Which of the following hydrocarbon undergo addition reactions? C2H6 , C3H8 , C3H6 , C2H2 and CH4
Ans: C3H6 and C2H2
14. Give a test which is used to differentiate chemically between butter and cooking oil?
Ans: The cooking oil will fade the colour of Baeyer’s reagent (alkaline K MnO 4 sol. and bromine water). The butter will not have any effect o n these reagents.
15. Explain the mechanism o f the cleaning action of soap.
Ans :
W h e n s oa p is dis s olve d in w a te r , it f or ms a colloida l suspension. In this colloida l suspension, the soap molecule s cluster together to form micelles and remain radially suspended in water with the hydrocarbon end towards the centre and the ionic end directed outward. The dirt particles always adhere to the oily or greasy layer present on the skin or clothes. When a dirty cloth is dipped into a soap solution, its non-polar hydrocarbon end of micelles get attached to the grease or oil present in dirt and polar end remains in water layer. The mechanical action of rubbing subsequently, dislodges the oily layer from the dirty surface shaping it into small globules. A stable emulsion of oil in water is formed. The emulsified oil or grease globules bearing the dirt can now be readily washed with water.
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