10th Solved Extra Score Paper(Carbon and its Compounds)

1.Q. Why doesn’t soap form micelles in ethanol as they form in water?

Ans:  A molecule of soap is made up of two parts a hydrophilic polar end and a hydrophobic  hydrocarbon part. In a soap solution, the hydrocarbon portion of several soap molecules huddle together  whereas the polar ends project outward into the polar solvent, water. These spherical clusters of hundreds of molecules are called micelle.

In organic solvent like ethanol, soap is completely soluble, hence no micelle formation

2. Q. Organic compound 'x' of molecular formula C₂H₄O₂ gives brisk effervescence with sodium bi carbonate . Give name and molecular formula of x with balanced equation

Ans:  The compound X is ethanoic acid, commonly known as acetic acid. On reaction with sodium bicarbonate, it forms sodium acetate, water and carbon dioxide gas. Thus the brisk effervescence observed is due to carbon dioxide gas. Its molecular formula is C₂H₄O₂ . 

Following is the chemical equation for the reaction: CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂

3. Q. A compound X has molecular formula C₃H₄ one mole of X reacts with 2 moles of hydrogen to yield a compound Y deduce the structure of X and Y

Ans:  X is propyne.   Y is propane.                    

CH₃ C º CH + 2H₂ --------------> CH₃ - CH2- CH3  

4. Q. What is hydrolysis?

Ans:  Hydrolysis means addition of water to a molecule resulting in breaking of bonds that are present in the molecule.

Ethyl ethanoate is heated under reflux with a dilute acid such as dilute hydrochloric acid or dilute sulphuric acid. The ester reacts with the water present to produce ethanoic acid and ethanol.

CH₃COO CH₃ + H₂O CH₃COOH + CH₃OH

5. Q. What is Dehydrogenation?

Ans: Dehydrogenation is a chemical reaction that involves the removal of hydrogen from a molecule. It is the reverse process of hydrogenation.  When the vapour of ethanol is passed over red hot copper catalyst [ 573 K], it is dehydrogenated to acetaldehyde.  

CH₃CH₂OH   -------->      CH₃CHO (Methanol) +H₂

6. Q. What is Decarboxylation?

Ans: Decarboxylation is a chemical reaction that removes a carboxyl group and releases carbon dioxide (CO₂).

When sodium salt of ethanoic acid is heated with soda lime (Solid mixure of 3 parts of NaOH and 1 part of CaO) methane gas is formed.                    

CH₃COONa ---NaOH------> CH₄ ↑ + Na₂CO₃

7.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.

8. Q. why sodium chloride added during preparation of soap?

Ans: This help to decrease solubility of soap and help in precipitation of soap from aqueous solution. This preparation is known as salting out.

9. Q. Why is soap not used in acidic solution?

Ans: This is because free fatty acid of soap get precipitated in acid.  

RCOONa  +    H+    ------> RCOOH     +   Na+      

10 Q. What's the difference between cracking and Pyrolysis?

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.              

C₂₂H₄₆       ---> C₁₁H₂₄ (an alkane) + C₁₁H₂₂ (an alkene)

11 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.

12. 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 KMnO ₄ added to both, pink color of KMno4 disappear in cooking oil but remain in pink in butter           Vegetable Oil  + H₂           CH₃    -   CH₃  

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