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

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryThe p-Block Elements5 Marks
Question
Explain the following:
  1. Silicones are used for making water proof fabrics.
  2. Boron does not form $B^{3+}$ ion.
  3. Boric acid is considered as a weak acid.
  4. Carbon forms covalent compounds while lead forms ionic compounds.
  5. Graphite is used as a lubricant.
✓

Answer

  1. Silicones are synthetic polymers containing repeated units of $R_2SiO$ where 'R' is alkyl group. Therefore are water repellants i.e. do not absorb water and are used for making water proof fabrics.
  2. Boron has small size and very high 3rd ionisation energy. Therefore $B^{3+}$ ion does not form.
  3. Boron is metalloid so $B_2O_3$ is weakly acidic, boric acid does not ionize completely in aqueous solution due to less ionic character. It accepts a pair of electrons from OH ion. Hence boric acid is weak acid.
$\text{H}-\text{OH}+\text{B(OH})_3\xrightarrow{\ \ \ \ \ \ \ \ }[\text{B(OH})_4]^-+\text{H}^+$
  1. 'C' has small size and high ionisation energy. Therefore forms covalent compound whereas 'Pb' has bigger size. Therefore has low ionisation energy, so it forms ionic compound.
  2. Graphite is soft and slippery and have high melting point. That's why it is used as lubricant in machine parts to reduce friction.

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