Class 11th

Lower the electrode potential, better is the reducing agent. Since the electrode potentials increase in the order: K⁺/K (-2.93 V), Mg²⁺/Mg (-2.37 V), Cr³⁺/Cr (-0.74 V), Hg²⁺/Hg (0.79 V), Ag⁺/Ag (0.80 V), therefore, reducing power of metals decreases in the same order, i.e., K, Mg, Cr, Hg, Ag.

Based on the relative positions of these metals in the activity series, the correct order is Mg, Al, Zn, Fe, Cu.

(i) When emf is positive, the reaction is feasible.
E^o_{? cell} = E^o_{? Fe}? −E^o_{? I2}? =0.77−0.54=0.23V
Reaction is feasible.

(ii) E^o_? cell? =E^o_{? Ag}? −E^o_{? Cu}? =0.80−0.34=0.46V
Reaction is feasible.

(iii) E^o_? cell? =E^o_{? Fe}? −E^o_{? Cu}? =0.77−0.34 =0.43 V
Reaction is feasible.

(iv) E^o_? cell? =E^o_{? Fe}? −E^o_{? Ag}? =0.77−0.80=−0.03 V
Reaction is not feasible.

(v) E^o_? cell? =E^o_{? Br2?} ? −E_Fe? =1.09−0.77=0.32 V 
Reaction is feasible.

5.35. When density of liquid and vapours becomes the same; the clear boundary between liquid and vapours disappears. This temperature is called critical temperature.

The balanced equation for the reaction is:

4NH_3? (g)+5O₂? (g)→4NO (g)+6H₂? O (g)

The molar masses of ammonia and oxygen are 17 g/mol and 32 g/mol respectively.

68 g of NH₃ will react with O₂ = 160 g.

Therefore, 10 g of NH₃ will react with O₂ = 160/68 x 10 g = 23.6 g
But the amount of O₂ which is actually available is 20.0 g which is less than the amount which is needed. Therefore, O₂ is the limiting reagent and hence calculations must be based upon the amount of O₂ taken and not on the amount of NH₃ taken. From the equation,
160 g of O₂ produce NO = 120 g
Therefore, 20 g of O₂ will produce NO =120/160 x 20 = 15 g

5.34. The temperature at which the vapour pressure of a liquid is equal to external pressure is called boiling point of liquid.

5.33. Molecules of liquids are held together byattractive intermolecular forces. Liquids havedefinite volume because molecules do notseparate from each other. However, moleculesof liquids can move past one another freely, therefore, liquids can flow, can be poured andcan assume the shape of the container in whichthese are stored.

(a) Phosphorous, chlorine and sulphur are the non metals which can show disproportionation reaction. The reactions shown are:

P_4? + 3OH^? + 3H₂? O? PH₃? + 3H₂? PO₂^?

? Cl₂? + 2OH^? ? Cl^? + ClO^? + H₂? O

S₈? +12OH^? ?4S^2? +2S₂? O₃^2? ? +6H₂? O

(b) Copper, gallium and indium are the metals that show disproportionation reaction. 

The reactions are shown below.

2Cu⁺? Cu²⁺ + Cu

3Ga⁺? Ga³⁺ + 2Ga

3In⁺? In³⁺ + 2In