SHORT ANSWER TYPE QUESTIONS
Q.1. Draw the electron dot structure of ethyne and also draw its structural formula.
It is electron dot structure of ethyne (C2H2)
is its structural formula.
Q.2. Write the names of the following compounds.
(a) Pentanoic acid
Q.3. Identify and name the functional groups present in the following compounds.
Q.4. A compound X is formed by the reaction of a carboxylic acid C2H4O2 and an alcohol in presence of a few drops of H2SO4. The alcohol on oxidation with alkaline KMnO4 followed by acidification gives the same carboxylic acid as used in this reaction. Give the names and structures of
(a) Carboxylic acid
(b) Alcohol and
(c) The compound X.
Also write the reaction.
(a) Carboxylic acid is ethanoic acid (CH3COOH)
(b) Alcohol is ethanol (C2H5OH).
(c) ‘X’ is ethyl ethanoate (CH3COOC2H5)
Q.5. Why are detergents better cleansing agents than soaps? Explain.
Ans. It is because detergents form a lot of lather even with hard water. Hard water contains Ca2+ and Mg2+ ions which react with soap to form insoluble salts of calcium and magnesium called scum and soap goes waste. Detergents do not form insoluble compounds with Ca2+ and Mg2+ ions, therefore these are more effective.
Q.6. Name the functional groups present in the following compounds.
(c) CH3 CH2 CH2 CH2CHO
(b) Carboxylic acid
Q.7. Intake of small quantity of methanol can be lethal. Comment.
Ans. Methanol is oxidised to methanal in liver. Methanal is highly reactive and good reducing agent. It causes protoplasm to coagulate. It also affects the optic nerve and leads to blindness.
Q.8. Carbon, Group (14) element in the Periodic Table is known to form compounds with many elements. Write an example of a compound formed with:
(a) Chlorine (Group 17 of Periodic Table)
(b) Oxygen (Group 16 of Periodic Table)
(a) CCl4 (Carbon tetrachloride)
(b) CO2 (Carbon dioxide)
Q.9. In electron dot structure, the valence shell electrons are represented by crosses or dots.
(a) The atomic number of chlorine is 17.
Write its electronic configuration.
(b) Draw the electron dot structure of chlorine molecule.
Q.10. Catenation is the ability of an atom to form bonds with other atoms of the same element. It is exhibited by both carbon and silicon. Compare the ability of catenation of the two elements. Give reasons.
Ans. Carbon shows catenation to a large extent as compared to silicon as well as any other element due to smaller size of carbon. C—C bond is stronger than Si-Si bond because Si is larger in size, so it forms a weaker bond.
Q.11. Unsaturated hydrocarbons contain multiple bonds between the two C-atoms and show addition reactions. Give the test to distinguish ethane from ethene.
Ans. Add bromine water. Ethane will not react. Ethene will decolourise bromine water.
Ethane, a saturated hydrocarbon, will bum with blue flame which is non-smoky, whereas ethene, an unsaturated hydrocarbon, will bum with yellow flame which is smoky due to the presence of unburnt carbon particles.
Q.12. Match the reactions given in Column (A) with the names given in Column (B).
(a) - (iv) Esterification reaction because ester is being formed from carboxylic acid and alcohol.
(b) - (i) Addition reaction as hydrogen is being added.
(c) - (ii) Substitution reaction because hydrogen of methane is being substituted by chlorine atom.
(d) - (iii) Neutralisation reaction because acetic acid reacts with sodium hydroxide to form salt and water.
Q.13. Write the structural formulae of all the isomers of hexane.
Q.14. What is the role of metal or reagents written on arrows in the given chemical reactions?
(a) Ni is used as a catalyst
(b) Cone. H2SO4 acts as a dehydrating agent.
(c) Alkaline KMnO4 is an oxidising agent.
LONG ANSWER TYPE QUESTIONS
Q.15. A salt ‘X’ is formed and a gas is evolved when ethanoic acid reacts with sodium hydrogen carbonate. Name the salt ‘X’ and the gas evolved.
Describe an activity and draw the diagram of the apparatus to prove that the evolved gas is the one which you have named. Also write the chemical equation of the reaction involved.
The salt ‘X’ is sodium ethanoate. The gas evolved is CO2.
Pass the gas through lime water. It will turn milky. It shows that gas evolved is CO2.
Ca(OH)2 + CO2→ CaCO3 + H2O
Aim: To demonstrate the reaction of carboxylic acid with sodium carbonate and sodium hydrogencarbonate.
Materials Required: Ethanoic acid , sodium carbonate, sodium hydrogen-carbonate, lime water.
1. Set the apparatus as shown in diagram.
2. Take 1g of Na2CO3 and add 2 ml of ethanoic acid into it.
3. Pass the gas formed through lime water and note down the observations.
4. Repeat the same procedure with sodium hydrogen-carbonate and record your observations.
Fig: Evolution of carbon dioxide gas by reaction of ethanoic acid with sodium carbons
Observation: Brisk effervescence due to carbon dioxide formed which turns lime water milky.
2CH3COOH(l) + Na2CO3(s) → 2CH3COONa(aq) + H2O(l) + CO2(g)
CH3COOH(l) + NaHCO3 → CH3COONa(aq) + H2O(l) + CO2(g)
Conclusion: Carboxylic acid reacts with sodium carbonate and sodium hydrogencarbonate to liberate CO2 gas which turns lime water milky.
(a) What are hydrocarbons? Give examples.
(b) Give the structural differences between saturated and unsaturated hydrocarbons with two examples each.
(c) What is a functional group? Give examples of four different functional groups.
(a) Hydrocarbons are the compounds made up of carbon and hydrogen atoms only, e.g. CH4 (methane), C2H6 (ethane), CH2= CH2 (ethene), etc.
(b) Saturated hydrocarbons contain single covalent bonds only, and (ethane) are saturated hydrocarbons.
Unsaturated hydrocarbons contain double or triple covalent bonds, e.g.
(c) Functional group is an atom or group of atoms or reactive part of the compound which determines chemical properties of the those compounds, e.g.
(i) —OH (Alcohol)
Q.17. Esters are sweet smelling substances and are used in making perfumes. Suggest one activity and the reaction involved for the preparation of ester with a well labelled diagram.
Materials Required : Beaker, water, test tube, ethanol, acetic acid, conc. H2SO4, tripod stand, burner, wire gauze, etc.
1. Take 2 ml of ethanol in a test tube.
2. Add 2 ml of ethanoic acid (acetic acid) into it.
3. Add few drops of cone. H2SO4.
4. Warm it in a beaker containing water.
5. Observe the smell of the products formed.
Fig: Reaction of dil. CH3COOH and Ethonal in the presence of conc. H2SO4 - formation of ester
Observations: Pleasant fruity smelling compound (called ester) is formed.
Chemical Reaction Involved:
Conclusion: Carboxylic acid reacts with alcohol in presence of conc. H2SO4, which acts as a dehydrating agent to form esters.
Q.18. A compound ‘C’ (molecular formula, C2H4O2) reacts with Na-metal to form a compound ‘R’ and evolves a gas which burns with a pop sound.
Compound ‘C' on treatment with an alcohol ‘A’ in presence of an acid forms a sweet smelling compound ‘S’ (molecular formula C3H6O2). On addition of NaOH to ‘C’, it also gives R’ and water. ‘S’ on treatment with NaOH solution gives back ‘R’ and 'A'. Identify ‘C’, ‘R' ‘A’, ‘S ’ and write down the reactions involved.
H2 gas burns with ‘pop’ sound
‘C’ is ethanoic acid, ‘R’ is sodium ethanoate, ‘A’ is methanol and ‘S’ is methyl ethanoate.
Q.19. Look at figure and answer the following questions:
(a) What change would you observe in the calcium hydroxide solution taken in tube ‘B' ?
(b) Write the reaction involved in test tubes ‘A’ and ‘B’ respectively.
(c) If ethanol is given instead of ethanoic acid, would you expect the same change?
(d) How can a solution of lime water be prepared in the laboratory?
(a) Lime water will turn milky.
(b) Test tube A:
2CH3COOH(l) + Na2CO3(s) → 2CH3COONa(aq) + H2O(l) + CO2(g)
Test tube B:
Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)
(c) Ethanol will not react with Na2CO3.
(d) Add Ca(OH)2 in water, shake it well. Filter the solution. The filtrate is lime water.
Q.20. 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
The reaction is called dehydration.
The reaction is called oxidation.
Q.21. Draw the possible isomers of compound with molecular formula C3H6O and also give their electron dot structures. [CBSE Sample Paper 2018]
Ans: C3H6O represents aldehyde as well as ketone.
Q.22. Explain the given reactions with the examples
(a) Hydrogenation reaction
(b) Oxidation reaction
(c) Substitution reaction
(d) Saponification reaction
(e) Combustion reaction
(a) Hydrogenation reaction: When hydrogen is added to unsaturated hydrocarbons having double or triple bond in presence of Ni as catalyst, the reaction is called hydrogenation, e.g.
(b) Those reactions in which oxygen is added or hydrogen is removed are called oxidation reactions, e.g.
(c) Substitution reaction: The reaction in which one or more atoms of compound is replaced by another atom or group of atoms, it is called substitution reaction, e.g.
(d) Saponification reaction: When an ester reacts with sodium hydroxide to form sodium salt of carboxylic acid and alcohol, it is called saponification, e.g.
(e) Combustion reaction : When an organic compound burns in presence of air to form CO2 and H2O along with heat and light is called combustion reaction, e.g.
Q.23. An organic compound ‘A’ on heating with conc. H2SO4 forms a compound B, which on addition with 1 mole of hydrogen in presence of Ni forms a compound ‘C' One mole of compound ‘C’ on combustion forms two moles of CO2 and 3 moles of H2O. Identify the compounds A, B and C and write the chemical equation of the reactions involved. [HOTS]
Ans. The compounds are as follows:
A—Ethanol, B—Ethene, C—Ethane