Organic Chem Flashcards
Describe the combustion of hydrocarbons
- exothermic reaction when reacted with o2
- complete combustion- c02 + water
- incomplete - co/ c + water
Decribe combustion of alkanes
- Exothermic reaction occurring when hydrocarbons are reacted with oxygen.
- Complete combustion produces carbon dioxide and water (carbon and hydrogen atoms are completely oxidised).
- Incomplete combustion produces carbon or carbon monoxide and water.
Alkane properties
- 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.
Fractional distillation
- 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.
Cracking
When large hydrocarbons are thermally broken down into smaller and useful molecules
What type of reaction is cracking
Thermal decomposition
Catalytic cracking
Reactant heated to vapor, passed over a hot catalyst (catalytic cracking) (450 degrees)
Steam cracking
heated to vapor, mixed with steam and heated to high temperatures (steam cracking) (>800 degrees)
Uses for products of cracking
The products are alkanes and alkenes - used as polymers and starting materials for synthesis.
Alkene
Unsaturated hydrocarbon. Contains a C=C bond.
General formula for alkenes is: CnH2n
Test for alkenes
Add bromine water. Colour change occurs from orange to colourless.
Combustion of alkenes
- incomplete - smokey yellow flame carbon monoxide, carbon dioxide and water vapour
- complete - carbon dioxide and water
Reaction of alkene with hydrogen
- cc double bond opens to make single cc bond
- hydrogenation; requires a higher temperature and a nickel catalyst
Reaction of alkenes with steam
- hydration; requires high temperature, pressure, and a catalyst
- cc double bond opens
- forms alcohol
Reaction of alkenes with halogens
Becomes saturated cc double bond opens
Alcohol
An organic compound that contains an -OH functional group
Characteristics of first 4 alcohols
- Dissolve in water to form a neutral solution.
- React with sodium to form hydrogen.
- Burn in oxygen.
- React with carboxylic acids in presence of acid catalyst to form esters.
What happens when alcohoks are oxidised
Carboxylic acids
3 uses of alcohols
- Fuels
- Solvents
- Drinks
Conditions for fermentation of glucose
37 degrees Celsius, aqueous solution of the glucose, absence of air, yeast added;
Carboxylic acid
Organic compounds that contain a COOH functional group
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 off hydrogen gas
What type of acid is carboxylic acid
It is a weak acid.
Why are carboxylic acids weak
They partially dissociated in water, thus the pH of a carboxylic acid in solution is not as low as a solution of a strong acid of the same concentration.
