Organic chemistry Flashcards
(35 cards)
What is crude oil?
Crude oil is a mixture of hydrocarbon compounds; a fossil fuel is the remains of ancient biomass.
Finite resource - cannot be replaced as it is used up.
What is a hydrocarbon?
A compound made exclusively of hydrogen and carbon atoms.
What are alkanes?
Saturated hydrocarbons of a general formula of CₙH₂ₙ₊₂
What is a homologous series?
Series of compounds with same general formula, same functional groups and similar chemical properties.
Describe the combustion of hydrocarbons
- Exothermic reactions occurring when hydrocarbons are reacted with oxygen.
- Complete combustion produce carbon dioxide and water (carbon and hydrogen atoms are completely oxidised).
- Incomplete combustion produces carbon monoxide and water (due to lack of oxygen).
Describe the physical properties of alkanes
- First few in series are gases, then change to liquids, then to solids.
- In general, boiling points and viscosity increase as molecules get bigger.
- Volatility and flammability decrease as molecules get bigger.
- Poor reactivity.
Explain how fractional distillation of crude oil takes place
- Crude oil is heated and vaporised.
- Vapor rises up the fractionating column (tower).
- The column is hotter at the bottom and cooler at the top.
- Hydrocarbons cool as they go up the column and condense at different heights, as they have different boiling points.
- Large molecules, high boiling points - collected at the bottom.
- Small molecules, low boiling points - collected at the top.
- This gives fractions, which can be used in various ways.
What is cracking?
When large hydrocarbons are thermally broken down into smaller and useful molecules.
What type of reaction is cracking?
Thermal decomposition.
What are the conditions for cracking?
Catalytic cracking - reactant heated to vapour, passed over a hot catalyst.
Steam cracking - mixed with steam and heated to high temperatures.
What are the conditions for cracking?
Reactant heated to vapour, passed over a hot catalyst (catalytic cracking), mixed with steam and heated to high temperatures (steam cracking).
How are the products of cracking used?
The products are alkanes and alkenes - alkenes are used as polymers and starting materials for synthesis of chemicals.
What is an alkene?
Unsaturated hydrocarbon. Contains a C=C bond.
General formula is CₙH₂ₙ
What is the test for alkenes?
Add bromine water. Colour change occurs from orange to colourless.
Describe the combustion of alkenes
They burn with smoky flames due to incomplete combustion.
Describe addition reaction of alkenes
Addition atoms cross the C=C so that the double bond becomes a single C-C bond.
a) With hydrogen - hydrogenation; requires a higher temperature and a nickel catalyst.
b) With steam - hydration; requires high temperature, pressure and concentrated phosphoric acid (H₃PO₄) as a catalyst.
c) With Br₂/Cl₂/I₂ - addition of halogens.
What is an alcohol?
An organic compound that contains an -OH functional group.
State characteristic of methanol, ethanol, propanol and butanol
- Dissolve in water to form a neutral solution.
- React with sodium to form hydrogen.
- Burn in air.
- React with carboxylic acids in presence of acid catalyst to form esters.
Oxidation/Oxidising agent added of the alcohols lead to..?
Carboxylic acids.
What are some uses of alcohol?
- Fuels.
- Drinks.
- Solvents.
State the conditions required for fermentation of glucose and state the equation of the reaction
30°C, aqueous solution of the glucose, absence of oxygen yeast, added.
C₆H₁₂O₆ → 2CH₃CH₂OH + 2CO₂
What are carboxylic acids?
Organic compounds that contain a COOH functional group.
State characteristics of carboxylic acids
- Dissolve in water to form an acidic solution (contains H⁺ ions).
- React with metal carbonates to form carbon dioxide.
- React with alcohols with an acid catalyst to produce esters.
- React with metals to give hydrogen gas.
What type of acid is carboxylic acid?
It is a weak acid.
