LONG ANSWER -Class 10 – Science -Chemistry -Chapter 4 – Carbon and its Compounds

LONG ANSWER -Class 10 – Science -Chemistry -Chapter 4 – Carbon and its Compounds

Q1. You are given balls and stick model of six carbon atoms and fourteen hydrogen atoms and sufficient number of sticks. In how many ways one can join the models of six carbon atoms and fourteen hydrogen atoms to form different molecules of C6 H14 

Ans : There are five ways in which six carbons can be joined with 14 hydrogen atoms.

Q2. Soaps and detergents are both types of salts. State the difference between the two. Write the mechanism of the cleansing action of soaps. Why do soaps not form lather (foam) with hard water? Mention any two problems that arise due to the use of detergents instead of soaps.

Ans : a. Soaps are sodium or potassium salts of fatty acids e.g. —COONa. Detergents are sodium or potassium salts of sulphonic acids e.g. —SO3 Na or —SO4 Na

 b. Soaps are sodium or potassium salts of fatty acids. They contain —COONa group. Detergents are sodium or potassium salts of sulphonic acids. They contains —SO3 Na or —SO4 Na group. Soap has ionic end which is hydrophilic, interacts with water while carbon chain is hydrophobic interacts with oil, grease. The soap molecules orient themselves in a cluster in which hydrophobic tails are inside the cluster and ionic ends face outside. These cluster are called micelles. These attract oil which is washed away by water.

c. Soaps react with Ca2+ and Mg2+ ions in hard water to form calcium or magnesium salts of fatty acids which are insoluble in water and thus interfere in action of soap,

d. (i) Detergents are more expensive than soaps.

 (ii) Some detergents are not biodegradable i.e. will create pollution.

 Q3. a. Give a chemical test to distinguish between saturated and unsaturated hydrocarbons.

b. Name the products formed when ethane burns in air. Write the balanced chemical equation for the reactions showing two types of energies liberated.

c. Why is reaction between methane and chlorine in presence of sunlight is considered a substitution reaction.

Ans : a. Saturated hydrocarbons will not react with bromine water whereas unsaturated hydrocarbons will decolourise it

b. Carbon dioxide and water will be formed. 

 2C2 H6 + 7O2  –>  4CO2 (g) + 6H2 O(l) + Heat + Light

c. It is because hydrogen atom is substituted by halogen atom, that is why it is called substitution reaction.

Q4.  a. You have three unlabelled test tubes containing ethanol, ethanoic acid and soap solution. Explain the method you would use to identify the compounds in different test tubes by chemical tests using litmus paper and sodium metal.

 b. Give reason of formation of scum when soaps are used with hard water.

Ans: a. Red litmus paper will become blue in soap solution only. Ethanoic acid will turn blue litmus red only. Ethanol will react with Na metal to form sodium ethoxide and hydrogen gas will be liberated.

 b. Soaps are sodium or potassium salts of fatty acids which react with Ca2+ and Mg2+ ions in hard water to form calcium or magnesium salts of fatty acids which are insoluble in water called scum.

Q5. What are micelles? Why does it form when soap is added to water? Will a micelle be formed in other solvents such as ethanol also? State briefly how the formation of micelles help to clean the clothes having oily spots.

Ans :  Micelles are cluster of molecules in which hydrophobic tails are inside the cluster 3 and the ionic ends are at the surface of clusters. Soap molecules when dissolved in water they form a cluster due to hydrophobic part of molecules orient themselves away from water. So they arrange towards inside of the cluster while hydrophilic part remain outside of cluster. No, micelles will not be formed in alcohol. Soap in form of micelles is able to clean because the oily dirt will be collected in centre of micelle which is rinsed away by water.