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The p-Block Elements — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryThe p-Block Elements5 Marks
Question
  1. Complete the equations for:
  1. $\text{BF}_3+\text{LiH}\rightarrow$
  2. $\text{B}_2\text{H}_6+\text{H}_2\text{O}\rightarrow$
  1. Give reasons:
  1. Conc $HNO_3$ is transported in aluminium container.
  2. Graphite is used as lubricant.
  3. Lead (IV) chloride is highly unstable towards heat.
✓

Answer

  1.  
  1. $2\text{BF}_3+6\text{LiH}\xrightarrow{\ \ \ \ \ \ }\text{B}_2\text{H}_6+6\text{LiF}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Diborane}$
  2. $\text{B}_2\text{H}_6+6\text{H}_2\text{O}\xrightarrow{\ \ \ \ \ \ }2\text{H}_3\text{BO}_3+6\text{H}_2\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Boric acid}$
  1.  
  1. Aluminium metal reacts with concentrated $HNO_3$ to form protective layer of aluminium oxide on its surface that prevents the lower layers to react with $HNO_3$​​​​​​​, i.e., rendering (making) lower layers passive for further reaction. Hence $HNO_3$​​​​​​​ can be stored and transported in Al vessels.
$2\text{Al}+6\text{HNO}_3(\text{conc.})\xrightarrow{\ \ \ \ \ \ \ }\text{Al}_2\text{O}_3\\+6\text{NO}_2+3\text{H}_2\text{O}$
  1. Graphite has hexagonal layer structure where layers can slide over one another due to weak van der Waals' forces between them ($\text{p}\pi-\text{p}\pi$ bonds). Therefore graphite can be used as lubricant.
  2. Lead can exit in +2 and +4 oxidation states. Down the group stability of lower oxidation state increases and that of higher oxidation state decreases due to inert pair effect. Hence lead (IV) chloride is unstable towards heat and readily decomposes to lead (II) chloride.
$\text{PbCl}_4\xrightarrow{\ \ \ \Delta\ \ \ }\text{PbCl}_2+\text{Cl}_2$

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