C10 - Organic Reactions Flashcards
what are alkenes
Hydrocarbons which have a double bond between two of the carbon atoms in their chain
Why are alkenes called unsaturated
the C=C double bond means that alkenes have fewer hydrogens compared with alkanes with the same number of carbon atoms
Why are alkenes more reactive than alkanes
the double bond can open up to make a single bond, allowing the two carbon atoms to bond with other atoms
What is the general formula for alkenes
CnH2n
What are the first 4 alkenes and their number of carbon atoms
Ethene (2Cs) Propene (3Cs) Butene (4Cs) Pentene (5Cs)
What do alkenes combust completely to produce
Water and carbon dioxide
what is the equation for incomplete combustion of alkenes and the weaknesses
alkene + oxygen —> carbon + carbon monoxide + water (+energy)
Incomplete combustion results in a smoky yellow flame, less energy released and carbon monoxide is a poisonous gas
What is a functional group
an atom or group of atoms that give organic compounds their characteristic reactions (e.g. -OH functional group)
How do alkenes usually react
most of the time alkenes react via addition reactions where the carbon-carbon double bond opens up and leaves a single bond and a new atom is added to each carbon
What is the alkene reaction with hydrogen (Hydrogenation)
Hydrogen reacts with alkenes to open up the double bond and form the equivalent, saturated alkane. The alkene is reacted with hydrogen in the presence of a nickel catalyst at 60-150C
What is alkenes reaction with halogens
The double carbon non hind opens up and each carbon atom is bonded to a halogen atom and the result are saturated molecules.
(E.G. bromine and ethene react to form dibromoethane)
How to test for alkenes
When orange bromine water is added to an alkene, the bromine will add across the double bond, making a colourless dibromo-compound so the bromine water gets decolourised
What is alkenes reaction with steam
Water is added across the double bond and an alcohol is formed. This must happen using a catalyst, high pressure and a temperature over 100C
What is the general formula for an functional group of alcohols
CnH2n+1OH
All alcohols have an -OH functional group and end in ‘ol’
What are the first 4 alcohols and their formulas
Methanol (CH3OH)
Ethanol (C2H5OH)
Propanol (C3H7OH)
Butanol (C4H9OH)
What is the functional group of carboxylic acids
-COOH and their names end in ‘anoic acid’
What are the first 4 carboxylic acids and their formulas
Methanoic Acid (HCOOH) Ethanoic Acid (CH3COOH) Propanoic Acid (C2H5COOH) Butanoic Acid (C3H7COOH)
How are esters formed
Esters are formed from an alcohol and carboxylic acid. An acid catalyst is usually used (eg concentrated sulfuric acid).
Alcohol + Carboxylic acid —> ester + water
Uses of alcohols
- Used as solvents in industry as they can dissolve things water can dissolve and things water can’t dissolve
- Used as fuels as they burn cleanly, are non-smelly and are flammable
- Used in perfume
- Antiseptics
- Drinks
Properties of alcohols
flammable, low boiling and condensing points, low viscosity
How to produce ethanol from fermentation
- Extract glucose from crops
- Add yeast to glucose
- Fermentation converts sugar to ethanol
- 30-40C (optimum temp is 37C)
- anaerobic conditions
- slightly acidic solution
- batch process (stop and start)
glucose —> ethanol + carbon dioxide
It uses cheap equipment, sugar is renewable and is more carbon neutral. However it’s very slow, product is impure, high labour costs as it’s a batch process
How to produce ethanol from the hydration of ethene
- Extract crude oil from the ground
- Use fractional distillation then cracking to get ethene
- Hydration (addition of steam):
- phosphoric acid catalyst
- high temperature and pressure (300C & 60-70 atmospheres pressure)
- continuous process
It’s a fast reaction with 95-100% yield and the product is pure.
ethene + water —> ethanol
Combustion of alcohols
ethanol + oxygen —> carbon dioxide + water
Alcohol reaction with sodium
With ethanol, the sodium effervesces, produces hydrogen gas and gets smaller as it forms a solution of sodium ethoxide.
Their reactions are similar to but not as vigorous as the reaction between sodium and water
Oxidation of Alcohols
An alcohol is oxidised to a carboxylic acid when boiled with acidified potassium dichromate. The same reaction takes place is ethanol is left exposed to air as microbes from air produce ethanoic acid
Alcohols and water
Methanol, Ethanol, Propanol and Butanol are all soluble in water and their solutions have a neutral pH
Carboxylic acids and (metal) carbonates
Carboxylic acids react with carbonates to produce a salt, water and carbon dioxide. The salts formed end in -anoate)
Carboxylic acids and water
Carboxylic acids dissolve in water and when they dissolve in water they ionise and release H+ ions resulting in a acidic solution. However, they don’t completely ionise so they just form weak acidic solutions
How to make esters
Esters are formed when alcohols react with a carboxylic acid. An acid, usually concentrated sulphuric acid, is used as a catalyst.
alcohol + carboxylic acid —> ester + water
Testing for alcohols
Add a few drops of the alcohol to a test tube containing potassium dichromate solution acidified with sulphuric acid. The tube is warmed in a hot water bath and if alcohol is present the orange solution turns green
Testing for carboxylic acids
Carboxylic acids react with sodium hydrogen carbonate to produce carbon dioxide gas which will turn limewater cloudy when bubbled through it.
Carboxylic acid will also turn blue litmus paper red
Identifying esters
Esters can be identified by their sweet, fragrant odours
A what is a homologous series
a group of related organic compounds which have the same functional group (e.g. carboxylic acids)
