Solutions of Carbon And Its Compounds (Page No - 264) - Chemistry Lakhmir Singh, Class 10 | Extra Documents, Videos & Tests for Class 10 PDF Download

Question 33:
(a) What happens when ethanol reacts with ethanoic acid in the presence of a little of concentrated sulphuric acid ? Write equation of the reaction involved.
 (b) What happens when ethanol is heated with concentrated sulphuric acid at 170°C ? Write the equation of the reaction which takes place.
 Solution :

(a) When ethanol reacts with ethanoic acid in the presence of a little of concentrated sulphuric acid, a sweet smelling ester called ethyl ethanoate is formed. 

 (b) When ethanol is heated with concentrated sulphuric acid at 1700-C, it gets dehydrated to form ethene. 

Question 34:
(a) What happens when ethanol is oxidised with alkaline potassium permanganate (or acidified potassium dichromate) ? Write the equation of the reaction involved.
 (b) Choose those compounds from the following which can turn blue litmus solution red :
 HCHO, CH₃COOH, CH₃OH, C₂H₅OH, HCOOH, CH₃CHO Give reasons for your choice.
 Solution :
(a) When ethanol is oxidised with alkaline potassium permanganate (or acidified potassium dichromate), it gets oxidised to form ethanoic acid.
(b) CH₃COOH and HCOOH can turn blue litmus solution red. These are organic acids.

Question 35:
(a) Explain the process of preparation of soap in laboratory.
 (b) Why is common salt (sodium chloride) added during the preparation of soap ?
 (c) Why is soap not suitable for washing clothes when the water is hard ?
 Solution :
(a) Soap can be prepared in the laboratory as follows:
1. Take about 20 ml of castor oil (cottonseed oil, linseed oil or soya bean oil) in a beaker.
2. Add 30 ml of 20% sodium hydroxide solution to it.
3. Heat the mixture with constant stirring till a paste of soap is formed.
4. Then add 5 to 10 grams of common salt (sodium chloride).
5. Stir the mixture well and allow it to cool. On cooling the solution, solid soap separates out.
6. When the soap sets, it can be cut into pieces called ‘soap bars’.
(b) Common salt is added to the mixture to make the soap come out of solution. Though most of the soap separates out on its own but some of it remains in solution. Common salt is added to precipitate out all the soap from the aqueous solution.
(c) When soap is used for washing clothes with hard water, a large amount of soap in water is reacting with the calcium and magnesium ions of hard water to form an insoluble precipitate called scum, before it can be used for the real purpose of washing.

Question 36:
(a) What happens when methane (natural gas) burns in air ? Write the chemical equation of the reaction involved.
 What happens when ethanoic acid reacts with sodium carbonate ? Write chemical equation of the reaction involved.
 Give a test that can be used to differentiate chemically between butter and cooking oil.
 Solution :

(a) Carbon dioxide and water vapour are formed when methane burns in air. 

(b) Ethanoic acid reacts with sodium carbonate to form sodium ethanoate and carbon dioxide.  

(c) Add bromine water to a little of cooking oil and butter taken in separate test tubes: 

(i) Cooking oil decolourises bromine water (showing that it is an unsaturated compound). (ii) gutter does not decolourise bromine water (showing that it is a saturated compound). 

Question 37:
(a) Describe, giving equation, a chemical reaction which is characteristic of saturated hydrocarbons (or alkanes).
 What is an oxidising agent ? Name two oxidising agents which can oxidise ethanol to ethanoic acid.
 Describe one reaction of a carboxylic acid.
 Solution :

(a) Substitution reaction of methane with chlorine: Methane reacts with chlorine in the presence of sunlight to form chloromethane and hydrogen chloride.

(b) An oxidising agent is one which oxidises other substances by providing oxygen or removing hydrogen. Alkaline potassium permanganate and acidified potassium dichromate can be used as oxidising agents. 

(c) Reaction with alcohols: Ethanoic acid reacts with alcohols in the presence of a little of conc. sulphuric acid to form esters. 

Question 38:
(a) Write names and formulae of hydrocarbons containing a single and a double bond (one example for each). Give one characteristic chemical property of each.
(b) What is a detergent ? Name one detergent.
(c) Why have detergents replaced soap as a washing agent ?
 Solution :
(a) (i) Single bond: Methane, CH₄. They are quite unreactive hence they undergo substitution reaction with chlorine in presence of sunlight.
(ii) Double bond: Ethene, CH₂=CH₂. They undergo addition reaction in the presence of a catalyst like nickel or palladium.
(b) A detergent is the sodium salt of long chain benzene sulphonic acid which has cleansing properties in water. Ex: Sodium n-dodecyl benzene sulphonate.
(c) Detergents are better cleansing agents than soaps because they do not form insoluble calcium and magnesium salts with hard water, and hence can be used for washing even with hard water.

Question 39:
(a) How does ethanoic acid react with sodium hydrogencarbonate ? Give equation of the reaction which takes place.
 (b) Why are carbon and its compounds used as fuels for most applications ?
 Which of the two is better for washing clothes when the water is hard : soap or detergent ? Give reason for your answer.
 Solution :

(a) Ethanoic acid reacts with sodium hydrogencarbonate to evolve brisk effervescence of carbon dioxide gas. 

CH₃COOH+ NaHCO₃ → CH₃COONa+ CO₂ + H₂O 

(b) Carbon and its compounds used as fuels because they burn in air releasing a lot of heat energy. 

(c) Detergent is better for washing clothes with hard water. They are better cleansing agents than soaps because they do not form insoluble calcium and magnesium salts with hard water, and hence can be used for washing even Wth hard water.

Question 40:
(a) What is meant by a substitution reaction ? Give an example (with equation) of the substitution reaction of, an alkane.
(b) How is soap made ? Write a word equation involved in soap making.
Solution :

(a) The reaction in which one (or more) hydrogen atoms of a hydrocarbon are replaced by some other atoms (like chlorine), is called a substitution reaction. 

Example: Substitution reaction of methane with chlorine:- Methane reacts Wth chlorine in the presence of sunlight to form chloromethane and hydrogen chloride. 

 (b) Soap is made by heating animal fat or vegetable oil with concentrated sodium hydroxide solution.  

Question 41:
(a) How is ethanoic acid obtained from ethanol ? Write down the chemical equation of the reaction involved.
 (b) How would you distinguish between ethanol and ethanoic acid by chemical test ?
 (c) Explain the formation of scum when hard water is treated with soap.
 Solution :

(a) Ethanoic acid is obtained from ethanol by the means of oxidation reaction. When ethanol is heated with alkaline potassium permanganate solution (or acidified potassium dichromate solution), it gets oxidised to ethanoic acid. It is called an oxidation reaction because oxygen is added to it during this conversion. 

(b) Litmus test: Some blue litmus solution is added to the organic compound (to be tested). If the blue litmus solution turns red, it shows that the organic compound is acidic in nature and hence it is a carboxylic acid (ethanoic acid). Ethanol has no effect on any litmus solution. 

(c) When soap is used for washing clothes with hard water, a large amount of soap in water reacts with the calcium and magnesium ions of hard water to form an insoluble precipitate called scum. This makes the cleaning of clothes difficult. 

Question 42:
(a) What happens when methane reacts with chlorine ? Give equation of the reaction which takes place.
(b) What is hydrogenation ? What is its industrial application ?
(c) Give any two differences between soaps and detergents.
Solution :

(a) Methane reacts with chlorine in the presence of sunlight to form chloromethane and hydrogen chloride. This reaction is called substitution reaction. 

 (b) The addition of hydrogen to an unsaturated hydrocarbon to obtain a saturated hydrocarbon is called hydrogenation. Application: Vegetable oils are hydrogenated to form vegetable ghee (or vanasapati ghee).

(c)

Question 43:
(a) What happens when ethanoic acid reacts with sodium hydroxide ? Write equation of the reaction involved.
 (b) What happens when vegetable oils are hydrogenated ? Name the catalyst used.
 (c) What is the advantage of detergents over soaps for washing clothes ? Also state one disadvantage.
 Solution :

(a) Ethanoic acid reacts with sodium hydroxide to form a salt called sodium ethanoate and water. 

CH₃COOH+NaOH → CH₃COONa+H₂O

(b) On hydrogenation, the liquid vegetable oils change into solid fat (vanasapati ghee). Nickel or palladium can be used as the catalyst. 

(c) Advantage: Detergents can be used even with hard water and have stronger cleaning action. 

Disadvantage: Detergents are not biodegradable and hence cause water pollution.

Question 44:
(a) An organic compound X of molecular formula C₂H₄O₂ gives brisk effervescence with sodium hydrogencarbonate. Give the name and formula of X.
 (b) A mixture of ethyne (acetylene) and oxygen is burnt for welding. Can you tell why a mixture of ethyne and air is not used ?
 (c) Name a chemical reaction which is characteristic of unsaturated hydrocarbons (like alkenes and alkynes).
 Solution :
(a) Ethanoic acid, CH₃COOH gives brisk effervescence with sodium hydrogencarbonate.
(b) A mixture of ethyne and air is not used for welding because burning of ethyne in air produces a sooty flame (due to incomplete combustion) which is not hot enough to melt metals for welding.
(c) Addition reactions are a characteristic of unsaturated hydrocarbons.

Question 45:
(a) What is meant by an addition reaction ? Give an example (with equation) of an addition reaction of an alkene.
 (b) What is added to groundnut oil when it is to be converted to vanaspati ghee ?
 (c) Which of the two is better for our health : butter or vegetable oil ? Why ?
 Solution :

(a) The reaction in which an unsaturated hydrocarbon combines with another substance to give a single product is called an addition reaction. 

Example: Ethene reacts with hydrogen when heated in the presence of nickel catalyst to form ethane:

(b) Hydrogen is added to groundnut oil when it is to be converted to vanaspati ghee.

 (c) Vegetable oil is better because it has unsaturated fatty acids v.hich are good for our health.