Organic Chemistry Flashcards
What is a hydrocarbon?
A hydrocarbon is carbon and hydrogen atoms only
What are alkanes?
Simplest organic compounds formed. Only contain single bonds, and are hydrocarbons
What is the simplest alkane:
Methane (CH4)
What is the homologous series?
A homologous series contains compounds:
• With the same general formula
• Have similar chemical properties i.e react the same way
• Show a gradual variation in their physical properties e.g bp increases as the carbon chain gets longer
What is the general formula of an alkane
CnH2n+2
Reaction of alkanes: Combustion:
Like all hydrocarbons, alkanes burn to give CO2 and H2O
e.g Pentane: C5H12 + 8O2 -> 5CO2 + 6H2O
If there is a poor supply of oxygen, CO and sometimes C are also formed (incomplete combustion)
What is the simplest alkene?
Ethene (C2H4)
How many covalent bonds does Carbon form?
4
What is a double bond?
Where double carbon atoms share four electrons
What does saturated mean?
All alkanes are saturated hydrocarbons. This is because it has no double bonds - it contains carbon and hydrogen only.
What does unsaturated mean?
All alkenes are unsaturated hydrocarbons. This means that they have double bonds.
Describe the reaction of alkenes with bromine, Br2:
Alkenes react with pure liquid bromine Br2 (l) or a solution of bromine water Br2 (aq). In both cases, the orange bromine water is immediately discolourised. Alkanes do not react with bromine water, unlike in alkenes, for which the bromine becomes colourless.
What is the symbol equation for reaction of an alkene and bromine?
C2H4 + Br2 -> C2H4Br2
What type of reaction is bromine water and an alkene?
Addition reaction
Describe the reaction of alkenes with hydrogenation
- Requires a catalyst of finely divided nickel
- Vegetable oils are organic compounds which contain C=C double bonds (they are usually polyunsaturated, but some are monosaturated)
- Removing some of the double bonds helps the molecules to pack together better and the liquid becomes a solid fat.
- It is used to make margarine or as an alternative to animal fats in the food industry
- If all the double bonds are removed, a saturated fat has been made which is less healthy
Symbol reaction of hydrogenation:
C2H4 + H2 -> C2H6
Why is the nickel catalyst finely divided?
To give maximum surface area
Describe the reaction of alkenes with steam:
- Requires a catalyst of phosphoric acid, 300°c, 70 atmos pressure
- Ethanol is produced (alcohol)
Symbol equation for alkene reaction with steam
C2H4 + H2O -> C2H5OH (ethanol)
What is ethanol used for?
As a solvent and a fuel
What is addition polymerisation with alkenes?
Alkenes can be polymerised to form polymers
Describe the reaction with acidified potassium manganate (KMnO4)
Used as a test for alkenes:
- KMnO4 turns from pink/purple to colourless if shaken with an alkene
- KMnO4 is an oxidising agent. The colour changes when it oxidises an alkene
A good fuel is one which:
- Burns easily
- Produces little ash or smoke
- Produces a large amount per energy per gram when burnt
- Is easy to store and transport
How is coal formed, and how does it produce acid rain?
- Formed from decayed remans of trees and plants which grew millions of years ago.
- Has a high carbon content.
- Causes acid rain as it contains impurities such as sulphur and nitrogen atoms.
- These atoms such as carbon, sulphur and nitrogen are released with smoke as gases.
- Acid rain happens when sulphur oxide reacts with water molecules in the atmosphere, creating sulphuric acid
- Can be removed from fuels when burnt or SO2 can be removed by reacting with CaCo3/Limestone
Name two uses of natural gases:
- Heating, cooking and generating electricity
* To make hydrogen fuel
What is crude oil?
It is a complex mixture of hydrocarbons
Where does crude oil form and what happens with it?
It collects in porous rock underneath non porous rock. It is pumped up from under the ground and taken by pipe or tankers to oil refineries.
How is crude oil separated?
Fractional Distillation
List the order of hydrocarbons from top to bottom on diagram for crude oil:
- Gases (100°c) (at the top)
- Gasoline
- Naphtha
- Kerosene
- Diesel Oil
- Fuel oil
- Residue (Bitumen) (360°c coming from the bottom)
Uses of refinery gas:
Domestic heating and cooking
Use of gasoline
Fuel for cars
Use of kerosene
Aircraft fuel
Use of diesel
Fuel for cars, lorries and buses
Use of fuel oil
Fuel for ships
Bitumen
Surfacing of roads and roofs
As the chains get longer:
- They have a higher boiling point
- Not very volatile (evaporate less easily)
- Become more viscous/thick
- Does not flow easily
- Does not ignite easily
Why is hydrogen a good fuel?
- There are zero emissions, only waste products is oxygen meaning there is no co2 or global warming
- It is renewable as it is made from water
- Its combustion is exothermic
Problems with hydrogen:
- It is explosive
- Hard to transfer and store as it is gas
- Does not occur naturally, must be made from electrolysis of water
Equation for hydrogen:
2H2 + O2 -> 2H2O
What are biofuels
Made from living plants or animal waste, for example, sugar beet for ethanol. CO2 is absorbed from the atmosphere by photosynthesis. When burnt the same amount of Co2 is put back into the atmosphere, so is supposedly carbon neutral
Advantages of biofuels
- Produce less green house gases
- Carbon neutral (in theory)
- Alternative to fossil fuels
Problems with biofuels
- Expensive
- Energy is required to harvest, process and transport which produces co2
- Large amounts of land are needed
What is cracking?
Where any hydrocarbon is heated strongly over a catalyst in the absence of oxygen (anaerobic). It is the break down of larger molecules into smaller, more useful molecules. Has conditions of 500°c, aluminium oxide catalyst and no oxygen. Some contain double carbon bonds
