Tips and Tricks of The Day

Ex: The degree of dissociation in a weak electrolyte increases:

 

Solution : In weak electrolyte the degree of dissociation is very small. So it increases with increasing dilution.

Ex: If a hollow pipe passes across the centre of gravity of the earth, then what changes would take place in the velocity and acceleration of a ball dropped in the pipe?

 

Solution: The ball will execute S.H.M. to and fro about the centre of the earth. At the centre, the velocity of the ball will be maximum (acceleration zero) and at the earth's surface the velocity will be zero (acceleration maximum).

Ex: Electrons cannot be a part of a nucleus but protons can be a constituent part of it. Why?

 

Solution: This is because of the fact that the de-Broglie wavelength of electrons is larger than the size of the nucleus while that of protons is smaller than the size of the nucleus.

Ex: In a mercury barometer, at sea level, the normal pressure of the air (one atmosphere) acting on the mercury in the dish supports a 76 cm column of mercury in a closed tube. If you go up in the air, until the density has fallen to half its sea level value, what height of mercury column would you expect?

 

Solution: Pressure exerted by a gas is directly proportional to its density. When we go high up in air at a point where the density of air falls to half its sea level value, the pressure also reduces to half its sea-level value. Hence the height of mercury column is also halved i.e., it becomes 38 cm.

Ex: If you set up the seventh harmonic on a string fixed at both ends, how many nodes and antinodes are set up in it:

 

Solution:

String will vibrate in 7 loops so it will have 8 nodes 7 antinodes. 

Number of harence number of nodes = Number of antinodes + 1

= 7+1 = 8

Ex: Heat equivalent to 50 joule is supplied to a thermodynamic system and 10 joule work is done on the system. What is the change in the internal energy of the system in the process?

 

Solution: Here ΔQ = +50J,ΔW = −10J 

∴   ΔU = ΔQ−ΔW = 50−(−10)=+60J Thus internal energy of the system increases by 60J

Ex: Equal masses of water and a liquid of density 2 are mixed together, then the mixture has a density of:

 

Explanation:

If two liquid of equal masses and different densities are mixed together then density of mixture            

ρ = 2ρ1ρ2 / ρ1+ρ2 = 2×1×2 / 1+2 = 4/3

Ex: The monomers used in the production of nylon-66 are:

 

Solution: Adipic acid (HOOC−(CH₂)₄−COOH) and Hexamethylene diamine  (NH₂−(CH₂)₆−NH₂)

Ex: The crystalline salts of alkaline earth metals contain more molecules of water of crystallisation than the corresponding salts of alkali metals.

 

Solution: This is due to smaller cationic size of the alkaline earth metals (e.g.,Mg²⁺) than the alkali metals (e.g.,Na⁺) present in their salts. As a result, the positive charge density on the former is more and can attract greater number ofH₂O molecules compared with latter. Therefore, crystalline salts of alkaline earth metals contain more water molecules as water of crystallisation as compared to salts of alkali metals.

Ex: If the binding energy of the deutrium is 2.23 MeV. The mass defect given in a.m.u. is:

 

Solution:

Mass defect Δm = 2.23 / 931 = 0.0024.