chapt 16 (hydrocarbons)

Question 1

what is homologous series? (1)

Answer 1

Homologous series - family of compounds that has the same general formula and same functional group.

Question 2

Alkanes (7)

Answer 2

• no funct. grp, only C-C and C-H single bonds. (saturated)
• general formula CnH2n+2
• simple molecular substances, weak FOA btwn molecules = low m.p & b.p (increases down the homologous series as FOA inc. due to size inc. )
• more viscous down the series as molecular size inc.
• insoluble in water but soluble in organic solvents.
• undergo combustion.
• undergo substitution (with halogens) in presence of UV light.

Question 3

Alkenes (9)

Answer 3

• funct. grp C=C
• CnH2n
• starts frm 2 carbons (ethene)
• simple molecular substances, weak FOA btwn molecules = low m.p & b.p (increases down the homologous series as FOA inc. due to size inc. )
• more viscous down the series as molecular size inc.
• insoluble in water but soluble in organic solvents.
• undergo combustion.
• undergo addition reactions.
  -> Hydrogenation (making of margarine frm veg oil) -> whr alkenes react with hydrogen to form alkanes. (temp. 150 degree celsius, catalyst nickel.
  ->Bromination(test of unsaturation) -> react with halogens (bromine). Bubbling aq bromine into alkene, decolourised = unsaturated.
  ->Polymerisation -> ethene reacting tgt to get long molecules (high temp. & pressure with catalyst)
• Cracking - brk large molecules (alkane) into small molecules (alkene). -> add catalyst to speed up cracking (catalytic cracking)