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Practice each question, then open the answer or worked solution.
In the ring test of NO3– ion, Fe2+ ion reduces nitrate ion to nitric oxide, which combines with Fe2+ (aq) ion to form the brown complex. Write the reactions involved in the formation of a brown ring.
NO3– + 3Fe2+ + 4H+ → NO + 3Fe2+ 2H2O
Thus the complex formed is brown.
Explain why the stability of oxoacids of chlorine increases in the order given below:
HClO< HClO2< HClO3< HClO4
As the electronegativity of halogen decreases, the tendency of XO3 group ( X = halogens) to withdraw electrons of the O-H bond towards itself decreases and hence the acid strength of the perhalic acid decreases.
Explain why ozone is thermodynamically less stable than oxygen.
Ozone is thermodynamically less stable because it decomposes into oxygen and this decomposition leads result in the liberation of heat, so its entropy is positive and free energy is negative.
P4O6 reacts with water according to equation P4O6 + 6H2O → 4H3PO3.
Calculate the volume of 0.1 M NaOH solution required to neutralise the acid formed by dissolving 1.1 g of P4O6 in H2O.
P4O6 + 6H2O 4H3PO3
4H3PO3 + 8NaOH Na2HPO3 + 8H20
Overall reaction :
P4O6 + 8NaOH 4Na2HPO3 + 2H2O
Moles of P4O6 = 1.1/220 = 0.5
Acid formed by one mole of P4o6 requires = 8 mol
Acid formed by 0.005 mol of NaOH is present in 100mL solution
0.04 of NaOH is present in solution = 1000/0.1 *0.04 = 400mL
White phosphorus reacts with chlorine and the product hydrolyses in the presence of water. Calculate the mass of HCl obtained by the hydrolysis of the product formed by the reaction of 62 g of white phosphorus with chlorine in the presence of water.
When white phosphorous reacts with chlorine:
P4 + 6Cl2 4PCl3
PCl3 + 3H2O H3PO3 + 4HCl ]*4
P4 +6Cl2 +12H2O 4H3PO3 +12HCl
Moles of white P= 62/124 = 0.5mol
1mol of white P4 produces HCl = 12mol
0.5 mol of white P4 will produce HCl = 12*0.8 = 6mol
Mass of HCl = 6*36.5 = 219.0g
Name three oxoacids of nitrogen. Write the disproportionation reaction of that oxoacid of nitrogen in which nitrogen is in +3 oxidation state.
There are three oxoacids of nitrogen.
Nitric acid(HNO3), Nitrous acid (HNO2), Hyponitrous acid (H2N2O1)
+ 3 oxidation is shown by HNO2, Therefore it undergoes disproportion reaction,
To calculate the oxidation state, consider the oxidation state of N is x.
3HNO2 HNO3 + 2NO +H2O
The oxidation state of nitrogen in HNO2 is +3
X + (+1) +2*(-2) = 0, x= +3
The oxidation state of nitrogen in HNO3 is +5
X + (+1) + 3*(-2) = 0, x= 5
The oxidation state of nitrogen in NO is +2
X + (-2) = 0, x =2
Therefore +3 oxidation state changes to +5 and +2 oxidation states.
Nitric acid forms an oxide of nitrogen on reaction with P4O10. Write the reaction involved. Also, write the resonating structures of the oxide of nitrogen formed.
P4O10 + 4HNO3 4HPO3 + 2N2O5
White phosphorous is very reactive as compared to red phosphorous due to angular strain in white phosphorous.
Phosphorus has three allotropic forms — (i) white phosphorus (ii) red phosphorus and (iii) black phosphorus. Write the difference between white and red phosphorus on the basis of their structure and reactivity.
1. White phosphorus
(i) It is soft waxy solid having garlic order
(ii) It is poisonous
(iii) Has low melting point and boiling point because P4 molecules are held together by weak van der Waal forces of attraction
2. Red Phosphorus
(i) It is hard, crystalline, odourless solid
(ii) It is non-poisonous
(iii) It has a high melting point because of its polymeric structure.
Give an example to show the effect of concentration of nitric acid on the formation of oxidation product.
4Zn +10HNO3(dil) 4Zn(NO3)2 + NH4NO3 + 3H2O
4Zn +10HNO3(dil) 4Zn(NO3)2 + N2O + 5H2O
4Zn +4HNO3(conc.) Zn(NO3)2 + NO2 + 2H2O
PCl5 reacts with finely divided silver on heating and a white silver salt is obtained, which dissolves on adding excess aqueous NH3 solution. Write the reactions involved to explain what happens.
PCl5 reacts with silver to form white silver salt(AgCl). Which than dissolves on adding excess aqueous NH3 to form a soluble complex
PCl5 + 2Ag 2AgCl(white ppt.) + PCl3
AgCl + 2NH3(aq) [Ag(NH3)]+Cl-