SOME IMPORTANT QUESTIONS.(X).!!

                                                    MCQ's

1. When ethanoic acid is added to a solution of substance X, a colourless and odourless gas Y is liberated. The gas Y turns lime water milky. The substance X is:
   (a) Sodium carbonate                       (b) Sodium hydroxide
   (c) Sodium acetate                            (d) Lime water
   
   
     
   2) A student added acetic acid to test tubes I, II, III , IV and then introduced a burning candle near the mouth of each test tube.
   
    
   The candle would be extinguished near the mouth of test tubes
   (a) I and II                        (b) II and III                  (c) III and IV                    (d) I and IV
   
   
   3)Which of the following is not observed when Al is added to the solution of copper sulphate?
   (a) Solution is blue in the beginning
   (b) Final solution is colourless
   (c) Final solution is light green
   (d) Brown mass is deposited an Al.
   
   
   4) Zinc granules were added to zinc sulphate, copper sulphate, aluminium sulphate and iron sulphate solutions as shown below. You would observe the deposition of metal on zinc in beakers
   
   

(b) is the correct option

        5) Four students A,B,C,D noted the initial colour of the solutions in beaker I, II, III and IV , After  

            inserting zinc rods in each solution and leaving it undisturbed for about two hour he noted the colour 

            of each solution again

               

They recorded their observations in the form of a table given below:



























Which student noted the colour change in all four beakers correctly?
(a) A                   (b) B                   (c) C                    (d) D

         QUESTION / ANSWERS :

Ques1: Write the next higher homologue of the following:

            (i) C₃H₆                     (ii)C₅H₈

_Ans:   (i) C₄H8                        (ii)C₆H₁₀

Ques2: An element has electronic configuration 2,8,3. What is the atomic number of this element? To which (i) group and (ii) period this element belong?

Ans:  Atomic Number : 13
         Group number:13     Period number: 3rd 

Ques3: How does the atomic size vary in a group from top to bottom and in period left to right? Explain

Ans:  Atomic size increases from top to bottom , as one new shell is added at every  step.
         Atomic size decreases along the period, as electrons are added in the same shell,  effective 
         nuclear  charge increases and size decreases.

Ques4: Give reasons for the following:

            (a) Unsaturated hydrocarbons show addition reactions but not saturated hydrocarbons.

            (b) Carbon only forms covalent compounds.

Ans: (a) Unsaturated hydrocarbons either have double/triple bond, one/two of which easily  

          breaks, being weak to form single covalent bonds, While saturated hydrocarbons have only 

         single bond which are strong.  

 

        (b) Carbon can neither lose 4 electrons as it requires too much energy , nor gain 4 electrons 

        as 6protons can't hold 10 electrons , therefore it only shares.

Ques5: State modern periodic law. Mention the position of (I) hydrogen and (ii) isotopes of the same element in the modern periodic table.

Ans: Modern Periodic Law: It states that the physical and the chemical properties of elements are the periodic function of their atomic number.
        (i) Write the position of H
        (ii) Position of isotopes same group and period.
         Group: Increases 1 group down the group.
         Period: Decreases from moving left to right along a period.

Ques6:. Complete the following reactions:

1. CH₃CH₂OH conc. H₂SO₄
                                        heat
2. CH₃COOH + NaHCO₃ ----->
3. CH₄ +Cl₂ sunlight
4. CH2 == CH2 + H2 --^Ni---->
5. C₂H₅OH + 0₂ ---^Alk.KMno4---------->
   
   
   
   

Ans: (i) CH₂==CH₂

        (ii) CH₃COONa + H₂O +CO₂

           _(iii) CH₃Cl + HCl

           _(iv) CH₃---- CH₃

           _(v) CH₃COOH + H₂O 

 

Ques7: (a) List two reasons for carbon forming a large number of compounds.

(b) An organic acid 'X' is a liquid which often freezes during winter time in cold countries. It has molecular formula C2H402. On warming with ethanol in the presence of a few drops of conc.H2SO4 a compound Y with sweet smell is formed.

   (i)Identify X and Y

   (ii)Write the chemical equation for the reaction involved.

Ans: (a) Carbon forms a large number of compounds due to its unique combination of small size and tetra valency, it form long chains (catenation) with strong bonds.

        (b) X =  CH₃COOH 

             Y = CH₃COO CH₂CH₃ 

            CH₃COOH + C₂H₅OH ----------> CH₃COOC₂H₅ + H₂O