QUESTION BANK

                               CH-4    CARBON AND ITS COMPOUND

               VERY SHORT ANSWER QUESTIONS                              1 MARK   EACH

1.      On the basis of electronic configuration, how will you identify the first and the last element of a period?

Ans: (i) First element has 1 valence electron and last element has 8 valence electrons. 

        (ii) Number of valence shells remain same

2.      .Identify functional group of following-
(a).C ₂H ₅OH (b).CH ₃COOH

Ans: Alcohol and Carboxylic acid

3.      A non metal X exists in two different forms Y and Z. Y is hardest natural substance whereas Z is good conductor of electricity. Identify X, Y and Z

Ans : X= Carbon ,Y= Diamond, Z= Graphite

4.      Why is ethanol used as antifreeze?

Ans: Ethanol does not freeze easily. So in cold countries ethanol is mixed with petrol to avoid freezing of fuel.

5.      What are hydrophilic and hydrophobic parts in soap

Ans: The alkyl group consisting of long chains of carbon atoms is hydrophobic part while COO^-Na⁺ grp is hydrophilic in nature.

6.      

What is the role of Ni in given reaction?

7.      Vapours of a hydrocarbon were passed through bromine dissolved in carbon tetra chloride .The yellow colour of bromine got discharged? Predict the nature of the hydrocarbon.

Ans : Unsaturated ( alkene or alkyne)

SHORT ANSWER QUESTION TYPE I                                                          2 MARKS EACH

8.      Differentiate between addition reactions and substitution reactions shown by hydrocarbon.

        Ans: Addition reaction is a reaction in which, any group(s) is added to the substrate; whereas, Substitution

               reactions include reactions in which a group is replaced/substituted by another group

              Addition reaction always takes place at multiple bonds, whereas, substitution reactions has no such hard and 

              fast rule.

9.      (a) Why do alkanols not turn blue litmus red?

(b) Why is high temperature not favourable for alcoholic fermentation?

Ans: (a) Because alcohols are not in position to release H⁺ ions in solution.

         (b) The high temperature destroys the enzymes which required for fermentation

10.  (a) Why it is not easy for carbon to take part in the formation of ionic compounds?

         (b) The molecular formula C₃H₆O can represent an aldehyde and a ketone. Write their structure and their name.

        Ans (a) Because carbon atom needs a large energy to lose 4 electron and to gain 4 electron to form ionic  

               compound.

                (b). Propanal and propanone       

11.  Give a chemical test to distinguish between Ethane and Ethene .

Ans Bromine water test: ethene decolourise the yellow colour of bromine water and ethane does not

12.  Distinguish between esterification and saponification reactions of organic compounds.

Ans:Esterification is the reaction of a carboxylic acid with an alcohol to form an esterand water. Saponification is the reaction of an ester with a base to form a carboxylate salt and water.

13.   (a)Why are soaps not so effective in case of hard water?

(b) Give the of the following: (i) An aldehyde derived from methane (ii) The compound obtained from oxidation of ethanol by chromic anhydride.

 Ans: Hard water contains salts of calcium and magnesium. Thus soap have to react with Ca and Mg to form insoluble ppt called scum .So soap form less lather with water.

(b) Methanal and Ethanal.

SHORT ANSWER TYPE II                                                              3 MARKS EACH

14.  (a) Draw electronic structure of the following: (i) Formic acid (ii) Propanone

(b)Why is the conversion of propanol into propanoic acid is called an oxidation reaction?

Ans : (a)  (ii)

          (b)Due to loss of hydrogen  and gain of oxygen.

15.  Give reason for the following:-

(a)    Use of synthetic detergents causes pollution problems.

(b)   The element carbon forms a large number of compounds.

(c)    Air holes of the gas burners have to adjusted when heated vessels get blackened by the flame

Ans: (a) Due to their non biodegradable nature.

          (b) Due to catenation and tetravalency

          (c) To increase the supply of air or oxygen.

16.  (a) State the principle on which the cleansing action of soap is based

(b) Write isomers of pentane.

Ans The basic principle involved in the cleansing action of soap is the formation of micelle due to the presence of hydrophillic and hydrophobic part in the soap molecule.

(b)

 

17.  Draw the structures of the following: Benzene, Cyclo hexane, 3Bromobutene, 3 Methyl pentanoic acid, Methanal, Formic acid

Ans :   , (b)  (c)(d)

  (f)

18.  (a) Differentiate between soap and detergent.

         (b) An organic compound ‘A’ with molecular formula C₂H₆O reacts  with an acids’B’ which is used for 

    making synthetic vinegar and form a sweet smelling compound  ‘C’ having molecular formula C₄H₈O₂.

                (i)Identify A and C compounds

       

   Ans (a)

          

 (b)  A= Ethanol and C = Ester

19.  Write the following chemical reactions:

(i)                 Sodium metal reacts with ethanoic acid

(ii)               Sodium carbonate is added ethanoic acid

(iii)             Ethanoic acid reacts with dilute solution sodium hydroxide

Ans: (a) 2Na +2 CH₃COOH→ 2CH₃COONa+H₂

         (b)Na₂CO₃ +2 CH₃COOH→ 2CH₃COONa+H₂O+ CO₂

         (c) NaOH + CH₃COOH→ CH₃COONa+H₂O

 LONG ANSWER TYPE                                                                            5 MARKS EACH

18. (a) . Why does melting and boiling points of the member of Homologous Series increase gradually ?

(b)  What is observed on adding 5% solution of alkaline potassium permanganate solution drop by drop to some warm ethanol taken in testube.  Write the name of the compound formed during chemical reaction.

(c) How can you check which one is saturated butter or vegetable oil?

Ans: The number of carbon atoms in the molecule of the member of Homologous Series increases gradually .Van der Waals dispersion forces will be very small for a molecule like methane but will increase as the molecules get bigger. Therefore, the boiling points of the alkanes increase with molecular size(increase in no. of c atom)
(b) When a 5% solution of alkaline potassium permanganate solution is added drop  by drop to some warm ethanol taken in a test tube, magenta colour of alkaline  potassium permanganate disappears and ethanol has been changed to carboxylic acid. 

(c) Butter contain saturated compound where as cooking oil contain unsaturated compound. If Alkaline KMno4 added to both, pink color of KMno4 disappear in cooking oil but remain in pink in butter

19.

.

20 . (a) What are homologous series? List any two characteristics of homologous series.

       (b)Explain in brief cleansing action of soap.

Ans: (a) A homologous series is a family of compounds with the same general formula and similar chemical 

     properties.

         Features include a general formula and neighbouring members differing by CH₂, with similar chemical properties and with a gradation in physical properties. They all contain the same functional group.

(b) A soap molecule is a sodium or potassium salt of long chain carboxylic acid. It consists of two parts, i.e., a long hydrocarbon tail and a negatively charged head. The hydrocarbon tail is hydrophobic, i.e., insoluble in water and repelled by water while the polar end is soluble in water and hydrophilic in nature. When soap is applied on a wet dirty surface, the polar end of the soap molecule dissolves in water while the non-polar end attaches it to dirt molecule, as dirt is non-polar in nature. This results in the formation of spherical clusters called asMicelles. In micelle the hydrophobic tails are in the interior of the cluster while the ionic ends are on the surface of the cluster. Due to ion-ion repulsion the micelle stay in the solution as a colloid and do not come together to form precipitate. Thus, an emulsion is formed which helps to dissolve dirt in water and it is finally washed with running water.

21. (a)  A mixture of ethyne and oxygen is burnt for welding. Can you tell why a mixture of ethyne and air is not  

       Used?

(b)  why sodium chloride added during preparation of soap?

(c) Why are soap not effective as a cleaning agent in hard water?

(d) Why is soap not used in acidic solution?

Answer: (a) Ethyne is un saturated carbon compound  and burns in air with a sooty flame, because the oxygen from air is insufficient to burn the carbon completely. Thus, pure oxygen is used which completely burns carbon and hydrogen and produces a very hot flame.

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

(c) Hard water contains sodium and magnesium ions. Soap form precipitate with these ions and thus thrown out of the solution.

(d) This is because free fatty acid of soap get precipitated

22.   How can Ethanol and Ethanoic acid be differentiated on the basis of physical and chemical properties? 
Ans. Physical properties :
(a). Ethanol has a sharp bitter burning taste, whereas ethanoic acid has a sour taste.
(b) On cooling ethanol does not freeze, but ethanoic acid freezes.                   
Chemical Properties :
(a) Ethanol gets dehydrated by conc. sulphuric acid, but ethanoic acid does not get dehydrated by conc. sulphuric acid.
(b) Ethanol does not displace hydrogen with zinc or magnesium, but ethanoic acid displaces hydrogen with zinc or magnesium

23.  (a) Why is graphite a good conductor of electricity?

(b)  Explain why, soaps form scum with hard water whereas detergents do not                

(c) Why does Ethanoic acid called glacial acetic acid?

(d)  Alkanes (both alkanes and cycloalkanes) are virtually insoluble in water, but dissolve in organic solvents. However, liquid alkanes are good solvents for many other non-ionic organic compounds. Give reason.

Answer: (a) Graphite is a good conductor of electricity. Its structure is the main reason for this property. Each carbon atom in graphite is directly linked to only three carbon atoms through covalent bonds. Therefore, out of the four valence electrons in a carbon atom, only three are used for bonding and the fourth is relatively free and can move from one carbon atom to the other. These free electrons make graphite a good conductor of electricity.

(b) In hard water, due to the presence of Ca +2 and Mg +2 ions, soaps form insoluble salt. This Precipitate is called scum.  Detergent does not show this property as its charged end does not react with Ca+2 and Mg+2 ions

(c) . On cooling, pure Ethanoic acid is frozen to form ice like flakes. They look like glaciers, so it is called glacial acetic acid.
(d) Van der Waals forces do not release a sufficient amount of energy to compensate for the energy required to break the hydrogen bonds in water. The alkane does not dissolve.
In most organic solvents, the primary forces of attraction between the solvent molecules are Van der Waals - either dispersion forces or dipole-dipole attractions. Therefore, when an alkane dissolves in an organic solvent, the Van der Waals forces are broken and are replaced by new Van der Waals forces. The two processes more or less cancel each other out energetically; thus, there is no barrier to solubility.      

    

        CHAPTER: 5                          PERIODIC CLASSIFICATIONS OF ELEMENTS

          VERY SHORT ANSWERS                                                                          1 MARK EACH

1.      State one reason for placing Mg and Ca in the same group of  the periodic table.

Ans: Due to 2 valence electrons in valence shell

Element	A	B	C	D	E
Atomic.no	7	10	12	4	19

2.      (i) Which element belongs to third period of periodic table?

(ii) Which is inert gas?

Ans (i) C (ii) B

3.      Which has bigger size and why? Chlorine or Bromine

Ans Bromine because its atomic  no is 35 and it has more shells

4.      How would the tendency of lose electrons changes as you go across the periods?

Ans: Decreases                          

5.      Identify the group and period of element having atomic no 17

Ans: group- 17 and period -3

6.      An element having atomic no 20 is categorised as metal  or a non metal . why?

Ans: Metal because it loses electron

SHORT ANSWER TYPE I                                                                                   2 MARKS EACH

7.      Atomic number is considered to be a more appropriate parameter than atomic mass for classification of elements in a periodic table. Why?

Ans: We know that atomic number gives us the number of protons in the nucleus of an atom. Atomic number increases by one in going from one element to the next but atomic mass does not vary regularly from element to element. Atomic number of every element is fixed. That is why atomic number is considered to be a more appropriate parameter for the classification of elements than atomic mass.

8.      (a) An unknown element is given the name ‘eka- phosphorus’? What does it means?

(b)What is meant by periodicity in properties of elements?

Ans: It means element placed after Phosphorus in the same group.

(b) Periodicity refers to trends or recurring variations in element properties with increasing atomic number. Periodicity is caused by regular and predictable variations in element atomic structure.

9.      ‘Hydrogen is regarded as rouge element in the periodic table’. Elaborate

Ans: H exhibits properties of both, Alkali metals like, 1 valence electron, ability to form halides etc. and those of halogens like non-metal, diatomic molecule, gaseous state etc. Hence it position is not fixed in the periodic table and called as a rogue element. .

10.  Can the following group of elements be classified as Dobereiner’s triad? Na, Si, Cl  Explain with reason.

Ans: No, because the mean of atomic mass is not equal to mass of Si.

11.  Arrange the following elements in the increasing order of metallic character : Mg , Ca, K, Ge.

Ans  Ge <Mg<Ca<K

12.  Why do all the elements of the same group have similar properties?

Ans: The properties of the elements are linked with the valence shell electronic configuration of their atoms. The elements with the same configuration are expected to have similar properties.

13.   Lithium, sodium potassium belong to same group called alkali metals. Why?

Ans: Because they form oxides and hydroxides that dissolve in water to give alkaline solutions and the alkaline hydroxide is formed when the metals react with water.

SHORT ANSWER TYPE II                                                                    3 MARKS EACH

14.   The elements Li, Na and K, each having one valence electron, are in period 2, 3 and 4
respectively of modern periodic table. 3
(i) In which group of the periodic table should they be?
(ii) Which one of them is least reactive?
(iii) Which one of them has the largest atomic radius? Give reason to justify your
answer in each case.
Answer. Electronic configuration of Li, Na and K can be written as:
Li → 2, 1
Na → 2, 8, 1
K → 2, 8, 8, 1
(a) As all of them have only on electron in their valence shell they belong to Group 1.
(b) Li is the least reactive among them due to its smallest size as it has only 2 shells.
(c) K has the largest atomic radius among the three because it has maximum number
of shells.
Higher the number of shells, larger is the atomic radius

15.   Nitrogen(atomic number=7) and phosphorus(atomic number=15) belong to same group-15 of the periodic table. Write the electronic configuration of these two elements. Which of these two will be more electronegative? Why.

Answer. Electronic configuration of N (7) = 2, 5 Electronic configuration of P (15) = 2, 8,5 Nitrogen will be more electronegative due to electro negativity decreases from top to bottom because atomic size increases.

16.   An element 'M' has atomic number 11.  (a) Write its electronic configuration.

(b) State the group to which 'M' belongs. (c) Is 'M' a metal or a non-metal.

(d) Write the formula of its chloride.

Ans. Atomic number of „M‟ = 11

(i) Electronic configuration : 2, 8, 1

(ii) Since, the valence shell contains 1 electron, it belongs to group 1.

(iii) M is a metal.

(iv)  The formula of its chloride is M Cl.

17.  State reasons for the following:                                                                                                               

      (i)Both Mg and O have valency equal to 2 .Are they chemically similar also?

       (ii)Out of C,B and N elements , which has the maximum size? Why?

       (b)Find the period of the following elements having atomic number: 19and 9

        Ans: (a)(i) No, Mg losses 2 electron whereas O gains 2 electron

                     (ii) B has maximum size because atomic radius decreases in period.

(a)     19= 4 period , 9= 2 period.

18.  Account reason for the following:

(a)    Elements in a group of the periodic table have similar chemical properties                                  

(b)   Discuss any two drawbacks of Mendeleev’s periodic table.

      Ans:(a).  Due to same number of valence electrons

(c)    Position of hydrogen and  position of isotopes.

19.  (a) Explain how the tendency to gain electrons change on moving down a group. 

(b)   If an element A is a member of group 14, write the formulae of its chloride and oxide. Predict the nature of bonding in the compound formed. Give reason for your answers. 
Ans:  (a) On moving down the group, atomic size increases. As a result, effective nuclear charge decreases and hence the tendency to gain electrons(electronegativity) decreases

(b) A member of group 14 have valency = 4 So, there is Covalent bonding 
Chloride – ACl₄ Belong to Gr.14 valency is 4 Oxide – AO_2.    

LONG ANSWER TYPE                                                                                        5 MARKS

20.  (a) Discuss any two achievements of Modern Periodic Table. 

   (b) Discuss any two limitations of Mendeleev’s classification. 

   (c) How were these removed in the Modern Periodic Table (any one) 
Ans:
(a) (i) Prediction of properties of elements could be made with more precision.
      (ii) Elements were sequentially arranged in increasing order of atomic number. (no reversals were required)
      (iii) Number of elements between two elements was countable.
(b) (i) Position of Hydrogen     (ii) Positioning of Isotopes   (iii) Position exchange of Ni and Co.   (iv) Variable increase in mass from one element to other. 
​(c) When the elements are arranged according to their atomic numbers on the basis of modern periodic law, all the anomalies (defects) of Mendeleev’s classification disappear. For example, Position of isotopes: All the isotopes of an element have the same number of protons, so their atomic number is also the same. Since all the isotopes of an element have the same atomic number, they can be put at one place in the same group of the periodic table.

21.  A quiz contest was being held in the school for chemistry students. The quiz-master said :
An element has the electronic configuration 2, 8, 7.
(a) What is the atomic number of this element?
(b) Which of the elements N, F, P and Ar shows similarity with this element ?
(c) We daily use a compound of this element in our food. What is that ?
(d) A compound of this element causes hardness of water. What is that ?
Ans: (a) Atomic number=17  (b) F - as it belongs to the same group as the element(Cl)
(c)NaCl-Common Salt  (d) Ca(HCO₃)₂ causes temporary hardness of water.

22.  (a)  What happens to the metallic character of the elements as we move in a period from left to right in the periodic table? Give reason.

            (b)  What happens to the melting points and boiling points of elements while moving down in a group?

            (c) Why Chlorine (atomic number 17) is more electronegative than sulphur (atomic number 16)

            (d)  The two isotopes of chlorine have atomic masses 35 u and 37 u. Should they be placed in same slot in the  

             periodic table?

            (e)  Why did Mendeleev leave some gaps in his periodic table?

       Answer(a) Metallic character of the element decreases along a period . In period  atomic size decrease,As a result,  

                 effective nuclear charge increases and hence the tendency to loose electrons(electroposivity) decreases .

          (b) . The melting points and boiling points decrease while moving down in group of metals.   The melting points  

           and boiling  points increases while moving down in group of non-metals.

         (c) : The nucleus of chlorine has more tendency to attract an extra electron than the nucleus of sulphur because

           chlorine needs  only one 1 electron to complete its shell. Hence, chlorine is more electronegative than sulphur.

        (d)  )  Yes, they should be placed in the same slot because periodic table is based on the atomic numbers of the

          element and both the   isotopes of chlorine have the same atomic number (Z = 17).

         (e) Mendeleev left gaps in his periodic table to keep the elements with similar properties together if predicted.

            New elements  would be discovered later and they would occupy those gaps.

23.  The position of three elements A,B and C in the periodic table are shown below

Group-16	Group-17
-	-
-	A
-	-
B	C

     (a) State whether A is a metal or non-metals. 

    (b) State whether C is more reactive or less reactive than A.

    (c) Will C be larger or smaller in size then B.       

     (d) Which type of ion, cat ion or anion will be formed by element A

  Ans-(a)-Non-metal

   (b) A is more reactive due to small size, have more tendency to accept outside electron

   (c) C is smaller in size than B due to atomic size decreases from left to right in a period

    (d) Anion formed due to tendency to accept electron

24.  A part of the periodic table has been shown below :

Group →	1	2	13	14	15	16	17	18
Period ↓
1
2	A	C					E	G
3	B			D			F

                        Answer the following questions on the basis of position of elements in the above table.

(a) Which element is a noble gas? Give reason.

(b) Which element is most electronegative? Give reason.

(c) Write the electronic configuration of (i) B and (ii) E.

Ans: (a) G , element of 18 group.

          (b) E, bcoz electronegativity decreases down the group.

          (c). B= 2,8,1    E= 2,7.

25.  (a) Why did Mendeleev treated the hydrides and oxides of element as the basic properties  of elements for their classification?

             (b)  Why does silicon is classified as Metalloid?

             (c)  Element X forms a chloride with the formula XCl₂ which is solid with a high melting point. X would

               most likely be in the same group of periodic table as (a). Na (b). Mg (c). Al  (d). Si?

              (d) How could the modern periodic table remove various anomalies of Mendeleev’s periodic table?

    Ans: (a)  During the period when Mendeleev gave his periodic table atomic numbers and electronic configurations   

            were not known. Comparison of properties of elements could be best done by comparing their compounds.  

              He selected oxides and hydrides because oxygen and hydrogen form compounds with most of the elements

            due to their high reactivity.

        (b) Silicon is gray color solid at room temperature with very high melting point and boiling point that lose or     

         gain 4 electrons [ 3s², 3p²] having both metallic and non metallic properties so it is classified as Metalloid eg.  

          SiO₂

        (c)Mg

        (d) Various anomalies are removed in following ways-

             (i) The position for all isotopes of an element justified since they have same atomic number.

             (ii) The position of certain elements which are earlier misfit like Co-58.9 is placed before Ni-58.7 are now

            justified because Co                    

              has lower atomic number than Ni.

            (iii) Cause of periodicity explained due to same electronic configuration repeated after certain gap.