C9&10 Crude oil and fuels/Organic reactions Flashcards
What is meant by ‘homologous series’?
A group of organic compounds that have similar chemical properties, due to them having the same functional group.
What is a ‘functional group’?
An atom or group of atoms that give organic compounds their characteristic reactions
What is the functional group in alkenes?
The carbon-carbon double bond.
What is the relative formula mass of butene?
C4H4 = 56
What type of compound is produced when an alkene is reacted with steam in the presence of a catalyst?
Alcohol
What is the functional group of alcohols?
-OH
What is the general formula for alcohols?
C(n)H(2n+1)OH
Uses of alcohols
- Fuels, release energy when burnt
- Solvents, dissolve most things that water can, plus more e.g. hydrocarbons and oils
- Antibacterial gels, the alcohol makes it evaporate quickly
- Drinks
What is a hydrocarbon?
A compound containing only hydrogen and carbon
What are alkanes?
Saturated hydrocarbons
What is the general formula of alkanes?
C(n)H(2n+2)
Describe the two types of combustion of hydrocarbons.
COMPLETE COMBUSTION - produces carbon dioxide and water, carbon and hydrogen atoms are completely oxidised
INCOMPLETE COMBUSTION - produces carbon or carbon monoxide and water
Name the first four alcohols
Methanol, Ethanol, Propanol and Butanol
Describe the two ways to produce ethanol
- Hydration - Ethene (from cracking) + steam (high temperatures + catalyst) —> Ethanol
- Fermentation - Sugar (from sugar cane) + yeast (room temperature, in a slightly acidic solution + a few days) —> Ethanol (+carbon dioxide)
Evaluate the two different ways to produce ethanol
- Hydration requires high temperatures, which requires energy and money. Whereas, fermentation can be carried out at room temperature.
- Hydration has 100% atom economy because the only product is ethanol. Whereas, fermentation produces carbon dioxide.
- Ethene for hydration is coming from crude oil, which is a non-renewable resource. Whereas, fermentation uses sugar cane which is renewable.
- Ethanol from sugar cane is a batch process, meaning that it is moved from one place to another. Whereas, ethanol from hydration is a continuous process.
Properties of alcohols
- Soluble in water
- Neutral pH
- Highly flammable; burn with a clean flame
- React with sodium metal to produce hydrogen gas and a metal salt
What does the oxidation of alcohols produce?
Carboxylic acids
How are alcohols oxidised?
- When exposed to oxygen
- Or done chemically using an oxidising agent
What are carboxylic acids?
- A homologous series of compounds with the relative formula C(n)H(2n+1)COOH
- They have the functional group COOH
Properties of carboxylic acids
- Soluble in water
- Acidic pH (weak acid), turns orange in universal indicator
- React with carbonates to produce carbon dioxide, water and a metal salt
General equation for a reaction between carboxylic acid and carbonate
carboxylic acid + metal carbonate –> salt + carbon dioxide + water
Carboxylic acids are weak acids - what does that mean?
- They do not fully ionise in water - only some of the acid molecules dissociate, to release H+ ions, when dissolved in water.
- They have a lower concentration of H+ than a strong acid
General equation for the reaction between carboxylic acids and alcohols
carboxylic acid + alcohol —-> (acid catalyst) Ester + water
What is produced when carboxylic acids react with alcohols?
Ester and water
What are esters?
A homologous series of compounds with the functional group COO.
What type of reaction undergoes to form esters?
A condensation reaction (between a carboxylic acid and an alcohol)
Uses of esters
- Food flavourings
- Perfumes
Properties of esters
- Volatile, this means they have low boiling points and vaporise easily
- Have distinctive smells and tastes
Explain what happens when carboxylic acids dissolve in water
- When they dissolve, they ionise and release H+ ions resulting in an acidic solution
- They don’t ionise completely (not all acid molecules release their H+ ions)
- They form weak acidic solutions
- This means that they have a higher pH than aqueous solutions of strong acids with the same concentration
Properties of hydrocarbons
As the chain length (number of carbon atoms) increases
- the boiling and melting point increases
- the volatility decreases
- the viscosity increases
- the flammability decreases
What is the volatility of a substance?
The tendency to turn into a gas
What is the viscosity of a substance?
How easily it flows
What is the flammability of a substance?
How easily it burns
How is the volatility of a hydrocarbon affected by its size?
Volatility decreases as chain length increases: short chains have a higher volatility than long chains
How is the viscosity of a hydrocarbon affected by its size?
Viscosity increases as chain length increases: short chains are less viscous (very runny) than long chains (thick)
How is the flammability of a hydrocarbon affected by its size?
Flammability decreases as chain length increases: short chains have a higher flammability than long chains
How is the boiling point of hydrocarbons affected by its size?
Boiling point increases as chain length increases: short chains have a lower boiling point than long chains
Explain the process of fractional distillation
- Crude oil is heated and fed in near the bottom of a tall fractionating column as hot vapour
- Temperature decreases going up the column, so as the gases move up the column the hydrocarbons condense when they reach the temperature of their boiling points
- The different fractions are collected as liquids at different levels
- Short-chained hydrocarbons are piped out the top of the column as gases
Why do short-chained hydrocarbons make better fuels?
They ignite more easily and burn well, with cleaner flames
What type of process/reaction is the cracking of hydrocarbons?
Thermal decomposition
