Wednesday, December 12, 2012

X(10th) Carbon and its compounds: F.A-III Solved Questions Paper

Carbon and its compounds  F.A-III              Q. An organic compound burns with a sooty flame. Is it saturated or unsaturated compound? Justify

Answer: it is unsaturated compound. Unsaturated compound have low percentage of hydrogen o incomplete combustion takes palace and produce sooty flame  .

Q. Write next two members of the homologous series given below 
C2H6, C3H8

Answer: Since two adjacent member of the homologous series differ by CH2, the next two members of the homologous series will be C4H10, C4H12

Q. What is the difference between two consecutive members in a homologous series in alkanes in  terms of  (i) molecular mass  (ii) number of atoms of elements.

Answer:(i) two adjacent member of the homologous series differ by 14 a.m.u (ii) two adjacent member of the homologous series differ by one carbon atom and two hydrogen atom[CH2]

Q. Molecular formula of a hydrocarbon is C3 H8. Draw its complete structure and write its name.
 Answer : It is Propane     
        H    H     H
        I      I     I
H – C – C -  C- H
        I      I     I
       H    H     H

Q. (a) Write chemical names of CH3COCH3, C2H5COOH. 
(b) What happens when acetic acid and ethanol react in presence of concentrated H2SO4 ? Write the reaction there in.

Anss: chemical names of CH3COCH3, C2H5COOH are Propanone and Propenoic acid
 when acetic acid and ethanol react in presence of concentrated H2SO4 form sweat smelling compound Easter (Ethyl Ethanoate) .Here concentrated H2SO4 act as a catalyst. This reaction is called Esterification. 

Q. Name an element, other then carbon, which exhibits the property of catenation upto seven or eight atoms? Are these compounds stable?  

Answer: Silicon forms compounds with hydrogen which have chains of upto seven or eight atoms, but these compounds are very reactive. The Silicon - Silicon bond is not very strong and hence it is unstable.

Q. Two elements X and Y have atomic numbers 12 and 16 respectively. To which period of the modern periodic table do these two elements belong ? What type of bond will be formed between them and why ?

Answer:  Atomic number of X i.e., Z = 12
Electronic configuration of X = 2, 8, 2
Atomic number of Y i.e., Z = 16
Electronic configuration of Y = 2, 8, 6 1     
They belong to the third period.
They will form ionic bond because X is a metal and Y is a non – metal. X loses 2 electrons which will be gained by Y. 

Q. (a) Give a chemical test to distinguish between saturated and unsaturated hydrocarbons.
 (b) Name the products formed when ethanol burns in air. List two forms of energy that are librated on burning ethanol. 
(c) Why is the reaction between methane and chlorine considered a substitution reaction?

Answer: (a) Bromine water Test.: 

Bromine water is yellow-red-brown in color.  If unsaturated hydrocarbons are added to it then the solution turns colorless.  I.e. the unsaturated hydrocarbons decolorize bromine water. Whereas no change takes place to the solution when saturated hydrocarbons are added to bromine water.
Therefore this test is used to distinguish between saturated and unsaturated hydrocarbons chemically.

(b) When ethanol burns in air (in oxygen) gives carbon dioxide  and release  heat and light.

(c) The reaction between methane and chlorine is considered a substitution reaction because hydrogen attached to carbon is replaced by chlorine. This reaction takes place in presence of light and CCl4 is formed.

CH4 + Cl2 → CH3Cl + HCl (in the presence of sunlight)

Q. An organic compound ‘A’ of molecular formula C2H6O on oxidation with dilute alkaline KMnO4 solution gives an acid ‘B’ with the same number of carbon atoms. Compound ‘A’ is often used for sterilization of skin by doctors.
(i) Name the compounds ‘A” and ‘B’.  
(ii) Write the chemical equation involved in the formation of ‘B’ from ‘A’

Answer: (i) the compounds ‘A” and ‘B’ are  alcohols and carboxylic acids
(ii) The chemical equation involved in the formation of ‘B’ from ‘A’

Q. (a) Explain with the help of chemical equation the following properties of carbon compounds.
(i) Addition Reaction  
(ii) Substitution Reaction 
(b) Differentiate between vegetable oils and animal fats.  
(c) What is meant by hydrogenation ?

Answer:(a) (i) The reaction in which unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons is called addition reaction.

(ii) A kind of  reaction in which a chemical reagent (substituent) displaces the another atom or group (leaving group) in a compound, e.g., Substitution of Hydrogen of Methane by chlorine  in which hydrogen of saturated hydrocarbon is replaced by Cl one by one in the presence of sunlight is called Substitution Reaction  .
CH4 + Cl2 → CH3Cl + HCl (in the presence of sunlight)

(b) Oils : 
1. Oils are liquid at room temperature 
2. Oils containing unsaturated fatty acids.

Fats : 
1. Fats are solid at room temperature.    
 2. Fats containing saturated fatty acids. 

(c) Hydrogenation of vegetable oils means that molecular hydrogen in reacted with unsaturated vegetable oils to provide vegetable oils which are partially or fully saturated. It means to reduce or remove double bonds present in the oil. This process is carried out in the presence of a catalyst. Hydrogenation of vegetable oils produces vegetable oils which have higher melting point.
Example: R2 C=CR2 + H → R2 CH-CHR2
R= hydrogen atom or an alkyl group ;   
Catalysts used are generally platinum, palladium, nickel

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