1- Where are isotopes of the same element having different atomic masses placed in the periodic

table?

2-Iit is desired to obtain an erect image of an object, using an concave mirror of focal length 20cm.

(i) What should be the range of the distance of object from the mirror?

(ii) Will the image be bigger or smaller than the object?

(iii) Draw a ray diagram to show the image formation in this case.

3-(a) What are the main reasons why human beings are over-exploiting the forests?

(b)What are the effects of damages?

(c)Names the different measures taken up for the conservation of forests?

4- a) Define homologous series of organic compounds. Mention any two characteristics of

homologous series.

b) Name the compound formed on heating ethanol at 443k with excess of conc.H2SO4.

c) Describe a chemical test to distinguish between ethanol and ethanoic acid.

5-:a)Why do we classify elements ?

b) What were the two criteria used by Mendeleev in creating his periodic table?

c) In Mendeleev‘s periodic table, why was there no mention of noble gasses like helium, neon

and argon?

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

e) Would you place the two isotopes of chlorine, Cl-35 in different slot because of their different

atomic masses or in the same slot because their chemical properties are the same ? Justify your

answer.

6-Pollination may occur without fertilization but fertilization will not take place without

pollination. Give reason .

Due to paucity of time it would not be possible for us to provide the answers to all your queries. We are providing solutions to some your good queries. Try solving rest of the questions yourself and if you face any difficulty then do get back to us.

A-1) As the modern periodic table classifies the elements according to their atomic numbers, therefore the question of position of isotopes does not arise. Isotopes are the atoms of an element having the same atomic number but different atomic masses. Thus, all the isotopes will have the number of electrons (and therefore protons), and hence the problem of position of isotopes does not occur. 

A-4) (a) A homologous series is a series of organic compounds which belong to the same family (i.e. possess same functional group) and show similar chemical properties. The members of this series are called homologue and differ from each other by the number of CH₂ units in the main carbon chain. Following are the characteristics of a homologous series

• All homologues of a series have the same general formula e.g., all alkanes have the general formula C_n H_{2n + 2}, alkyl halides have the general formula C_nH_(2n+1)X
• Each consecutive member differs from the next by one carbon atom and two hydrogen atoms (-CH₂ group).
• The difference in the molecular mass between two consecutive homologues is 14 amu.
• The physical properties of homologues show a regular gradation.
• Homologues of a series have similar chemical properties.

(b) When ethanol is heated with concentrated H₂SO₄ at 443 K, we get ethene. Following is the chemical equation for the reaction

(c) Ethanol is an alcohol which has the OH functional group. Its chemical formula is C₂H₅OH. Ethanoic acid on the other hand is a carboxylic acid which has the chemical formula CH₃COOH. A chemical test to distinguish between ethanol and ethanoic acid is sodium bicarbonate (NaHCO₃) test. Ethanoic acid reacts with NaHCO₃ to form sodium ethanoate and carbon dioxide according to the following reaction

CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂

that is brisk effervescence will be observed in the above reaction.

On the other hand, ethanol will not react with sodium bicarbonate and so no effervescence will be observed in the reaction.