Chem Flashcards
(42 cards)
Testing for gases
Hydrogen-place a burning splint into a tube containing gas . Pop sound will occur if hydrogen is present
Oxygen-place glowing splint into gas. If it is oxygen the splint will relight
Carbon dioxide-lime water turns cloudy
Chlorine gas-red litmus paper goes white
Flame colours
Lithium-crimson Potassium-lilac Copper-green Calcium-orange Sodium-yellow
Problems with flame test
If chemical is low in concentration then the flame is hard to distinguish
Sample could contain a mix which would mask the colour
Flame emission spectroscopy
Place metal solution into flame
Light emitted is passed into a spectroscope
This machine converts light into a line on a spectrum
Position of line allows us to identify the metal
Pros of instrumental methods
Much quicker
Much more sensitive
These methods are more accurate
Metal hydroxide percipatates
If you react magnesium or aluminum or calcium with sodium hydroxide then the precipitate is white.
Copper2 forms a blue precipitate
Iron 2 forms a green precipitate
Iron3 forms a brown precipitate
Identifying non metal ions
Carbonate - add dilute acid . If present fizzing will occur and a gas is formed . Funnel gas into lime water . If it goes cloudy then the gas was carbon dioxide
Sulfate-add dilute HCL to sample , add barium chloride to sample .white precipitate forms .
Halide-add dilute nitric acid , add dilute silver nitrate , each halide will form a different colour
Chloride-white
Bromide-cream
Iodide-yellow
Modern atmosphere composition
78 percent nitrogen
21 percent oxygen
Early atmosphere
During the first billion years it is is believe that there were intense waves of volcanic activity which released lots of water vapour. This water formed the oceans
Volcanoes also released lots of carbon dioxide . The atmosphere at this point was primarily all carbon dioxide, little to no oxygen was present
How did atmosphere change ?
Carbon dissolved into water slowly forming carbonate rock on sea beds. This absorbed lots from the atmosphere
Photosynthetic algae developed the ability to photosynthesise replacing huge amounts of carbon dioxide with oxygen
Formation of fossil fuels
Coal-formed by the remains of plant life . If the die in wet marshlands decomposition will not occur due to a lack oxygen. Over time these remains are compacted and compressed under high pressure and temp forming coal
Crude oil-formed from plankton. When the do not decompose they are compressed and subjected to high temperatures forming oil
Natural gas-found near pockets of oil
What is the general formula of alkanes
CnH2n+2
Properties of hydrocarbons
Viscosity-As the size of the hydrocarbons increase so does their viscosity
Flammability-short chain hydrocarbons are much more flammable
Boiling point-short chain hydrocarbons have a lower boiling point
Fractional distillation process
Crude oil is heated to a very high temperature
The oil boils and vapour is fed into the column
The vapours rise , the different hydrocarbons condense at different temperatures in the fractionating column.
Very long hydrocarbons condense at the bottom
Cracking
Long chained hydrocarbons are not as useful as smaller chained hydrocarbons
So they are separated into smaller hydrocarbons this is done through breaking the bonds between the atoms using high temperatures
However by separating the hydrocarbons alkenes are formed
What is an alkene ?
Unlike alkanes , alkenes are unsaturated hydrocarbons. They have double bonds between 2 carbon atoms and have 2 less hydrocarbons than the alkanes of the same name
To test for alkenes use bromine water,it will turn from orange to colourless
General formula for alkenes
CnH2n
What the is the functional group of alkenes
The double bond between 2 carbon atoms
Members of a homologous series all have the same functional group
Hydrogenation
When an alkenes reacts with hydrogen to form the alkane of the same name
A nickel catalyst is needed
Double bond converts into 2 single bonds
Hydration
Reacting alkenes with water forms an alcohol The double bond is broken Pressure 70 atm Temp at 300 Phosphoric acid as a catalyst
Reacting with halogens
Reacting halogens with alkenes causes the alkene to break it’s double bond . The 2 bonds connect to the 2 halogen atoms
What produces ethanol
Hydration with ethene
Fermentation of sugar in anaerobic conditions causes ethanol to form
Reacting alcohol with oxidising agent
Forms a carboxylic acid with a functional group of cooh
What happens when you place a carboxylic acid in water
Does not fully dissociate
CH3COO-
H2+
Both ions
