Organic Chemistry Flashcards
General formula for alkanes
CₙH₂ₙ₊₂
Which one is saturated and why?
Alkanes because the carbon atoms are fully bonded to hydrogen atoms
What is crude oil?
Mixture of molecules called hydrocarbons
What are hydrocarbons?
Molecules made up of hydrogen and carbon atoms only
1st 4 alkanes
Methane, Ethane, propane, butane
What is viscosity? What does a high viscosity mean?
Thickness of a fluid
They flow slowly
What happens as the size of the hydrocarbon molecules increases?
- More viscous
- Flammability decreases
- Boiling point increases
What happens when HC fuels are combusted?
- They release energy
- During combustion, the C and H atoms in the fuel react with oxygen. C AND H are oxidised - if O is unlimited, this reaction produces CO2 and H20 - AKA complete combustion
Fractional Distillation of Crude Oil
- Crude oil heated up (boiled) to high temp outside fractionating column
- HC vapours rise up the column
- HC condense when they reach their boiling point - turn to a liquid, liquid fractions are removed
- Remaining HC move up the column where its cooler and condense when they reach their BP
What kind of HC do not condense? Why?
Very short HC because they have low BP, they’re removed at the top of the column as gases
What do fractions contain?
HC with a similar number of C atoms
What is feedstock?
Chemical that is used to make other chemicals - polymers, solvents, lubricants, detergents
What are organic compounds?
All the products you get from crude oil
Reason for why we get such a large variety of products from crude oil
C atoms can bond together to form diff groups called homologous series (similar compounds with many properties in common)
What is cracking?
- Thermal decomposition reaction
- Breaking molcules down by heating them
2 types of cracking
- Catalytic c
- Steam c
What is catalytic cracking?
- Heat long chain HC to vaporise them (gas them)
- Then vapour is passed over a (hot powdered aluminium oxide) catalyst
- Long chain alkanes form into a shorter chain alkane and an alkene
What is steam c?
- Vaporise HC (gas)
- Mix them with steam
- Heat then to a v high temp
How do you test for alkenes?
- Bromine water (orange)
- Shake alkene with Br water –> colourless if alkene is present
General formula for alkenes?
CₙH₂ₙ
What is the displayed formula?
Shows you all the atoms and the covalent bonds
Whats a key fact about alkenes and their bonds?
They have at least 1 double covalent bond between the carbon atoms
Are alkenes unsaturated or not? Why?
Unsaturated because they have 2 few hydrogen atoms than the alkane with the same number of carbon atoms, double bond
What does “functional group” mean?
Part of a molecule that determines how it reacts
What is produced when combusting an alkene?
water, carbon monoxide and carbon because of incomplete combustion - causes them to burn in air with a smoky flame
What is hydrogenation? What conditions are needed?
Alkene + hydrogen -> alkane
* 150C
* Nickel catalyst to speed up reaction
What is hydration? What conditions are needed
Alkene + Water (steam) -> alcohol
* Water must be in the form of steam
* 300C
* Pressure = 70 atmospheres
* Phosphuric acid as a catalyst
* Reversible, to increase yield unreacted ethene + steam are passed back through the catalyst
What is the alcohol functional group?
OH
Advantage of making ethanol by hydration
- Produces a high yield of ethanol
Disadvantage of making ethanol by hydration
- High temp - lots of energy which is expensive
- Ethene comes from crude oil which is non-renewable
Ways to make ethanol
- Hydration with ethene
- Fermentation
How does fermentation work + conditions?
- Start with a sugar solution (glucose)
- Mix with yeast
- Yeast converts sugar solution to a solution of ethanol, CO2 is also produced
* 37C
* Conditions should be anaerobic
* Slightly acidic solution
Advantage of fermentation
- Low temp, not lots of energy needed
- Sugar from plants, thus renewable
Disadvantage of fermentation
- Product is an aqueous solution of ethanol - purify ethanol by distillation which needs energy
Are alcohols soluble or not in water? What solutions to they form?
Soluble, forms neutral solutions ph
How is the number of carbon atoms related to solubility?
As number of C atoms increase, solubility decreases
What happens when alcohols react with oxidising agents/ oxygen from the air?
They produce a carboxylic acid and water
What happens when alcohols are combusted? What is produced when its combusted in air?
Releases energy
C02 and H20
What is produced when ethanol reacts with sodium?
Sodium ethoxide + Hydrogen
Methanoic acid
HCOOH
Ethanoic acid
CH₃COOH
Propanoic acid
CH₃CH₂COOH
Butanoic acid
CH₃CH₂CH₂COOH
In water, are carboxylic acids weak or strong?Why?
weak, they only partially ionise in aqueous solutions, so they have a higher pH than a strong acid