chemistry - topic 7

• What is the main focus of section 4.7 in the study material?

  Organic Chemistry
• What physical properties of hydrocarbons are influenced by the size of their molecules?

  • Boiling points increase as molecules get bigger
  • Viscosity increases as molecules get bigger
  • Volatility decreases as molecules get bigger
  • Flammability decreases as molecules get bigger
• How do boiling points and viscosity of hydrocarbons change with molecular size?

  They increase as the molecules get bigger.
• What happens to volatility and flammability of hydrocarbons as their molecules increase in size?

  Both volatility and flammability decrease as the molecules get bigger.
• What is crude oil primarily composed of?

  Crude oil is mainly composed of hydrocarbons.
• What is the origin of crude oil?

  Crude oil is the remains of ancient biomass, mainly plankton, buried in mud.
• What type of hydrocarbons are most abundant in crude oil?

  Alkanes
• What type of bonds do alkanes contain?


  Alkanes contain only single covalent bonds.

  
• What is the general formula for alkanes?

  The general formula for alkanes is $C_nH_{2n+2}$.
• What are the first four alkanes and their molecular formulas?

  • Methane: CH4
  • Ethane: C2H6
  • Propane: C3H8
  • Butane: C4H10

  
• What is produced during the complete combustion of hydrocarbons?

  Carbon dioxide and water are produced.
• Write the general equation for the complete combustion of a hydrocarbon.

  Hydrocarbon + Oxygen → Carbon dioxide + Water
• What is the balanced equation for the combustion of methane?


  $CH_4 +$$2O_2 \rightarrow CO_2 +$$2H_2O$
• How does fractional distillation of crude oil work?

  1. Oil is pre-heated and passed into a column.

  2. Some of the oil evaporates.

  3. Vapours rise up the column and cool.

  4. Some vapours condense and flow out.

  5. Some vapours remain as gases and exit the top.

  6. Each fraction has a different boiling point.

  7. Temperature decreases upwards in the column.

  8. Small molecules condense at the top; larger ones at the bottom.
• What are some products derived from crude oil?

  Petrol, diesel oil, kerosene, heavy fuel oil, and liquefied petroleum gases.
• What are the uses of cracking products?

  • Fuels with small molecules
  • Alkenes for producing polymers
  • Starting materials for many chemicals
• What is the process of cracking in hydrocarbons?

  Cracking involves heating hydrocarbons to vaporize them and then breaking them down into smaller molecules.
• What type of reactions are cracking reactions?

  Cracking reactions are thermal decomposition reactions.
• Complete the balanced equation for the cracking of decane: Decane → ?

  Pentane + Pentene
• How do alkenes react in combustion reactions compared to alkanes?

  Alkenes tend to burn with smoky flames due to incomplete combustion.
• What happens to the double bond in alkenes during addition reactions?

  The double bond becomes a single carbon-carbon bond as atoms are added across it.

  
• What are the first four members of the homologous series of alkenes?

  • Ethene
  • Propene
  • Butene
  • Pentene

  
• What is the general formula for alkenes?

  The general formula for alkenes is $C_nH_{2n}$.
• Why are alkenes considered unsaturated hydrocarbons?

  Because they contain two fewer hydrogen atoms than the corresponding alkane.

  
• What are the properties of alcohols?


  • Contain the functional group –OH
  • Dissolve in water to form neutral solutions
  • React with sodium to produce hydrogen
  • Burn in air
• What are the first four members of the homologous series of alcohols?

  Methanol, ethanol, propanol, and butanol.
• How can alcohols be oxidized?

  Alcohols can be oxidized to carboxylic acids by oxidizing agents like potassium dichromate.
• Write the complete combustion equation for ethanol.

  $CH_3CH_2OH (l) +$$3 O_2(g) \rightarrow 2CO_2(g) +$$3 H_2O(l)$
• What are the conditions needed for fermentation to produce ethanol?

  • Yeast
  • No air
  • Temperatures between 30 – 40°C
• Why is fermentation done in the absence of air?

  To prevent the oxidation of ethanol to ethanoic acid.
• What are the properties of carboxylic acids?

  • Dissolve in water to produce acidic solutions
  • React with carbonates to produce carbon dioxide
  • React with alcohols to produce esters
  • Are weak acids

  
• What is the functional group of carboxylic acids?

  The functional group is –COOH.

  
• What are the first four members of the homologous series of carboxylic acids?

  • Methanoic acid
  • Ethanoic acid
  • Propanoic acid
  • Butanoic acid

  
• How are esters formed?


  • From the reaction of carboxylic acids with alcohols
  • In the presence of an acid catalyst (sulfuric acid)

  
• Write the equation for the formation of ethyl ethanoate.

  $CH_3COOH +$$CH_3CH_2OH \rightarrow CH_3COOCH_2CH_3 +$$H_2O$
• What is addition polymerization?

  • Involves the joining of small unsaturated molecules (monomers)
  • Double bonds open up to form large saturated molecules (polymers)
• What is condensation polymerization?


  • Involves monomers with two functional groups
  • Small molecules (like water) are lost during the reaction
• What are some naturally occurring polymers important for life?

  • DNA
  • Proteins
  • Starch
  • Cellulose
• What is the role of DNA in living organisms?

  DNA encodes genetic instructions for development and functioning.
• What are the monomers that make up DNA?

  Nucleotides