Topic 10 Flashcards
What formed the early earths atmosphere?
Gases produced by volcanic activity
What do scientists believe about the earths eskryxatomsphere billions of years ago contained:
Little or no oxygen
A large amount of carbon dioxide
Water vapour
Small amounts of other gases
EVIDENCE
mixture of gases released by volcanoes
Atmosphere of other planets in our solar system today which have not been changed by living organisms
Today’s atmosphere
Nitrogen and oxygen are the main gases in the modern atsmisohere
Ntrogen 78%
Oxygen 21%!
Other gases including argon water vapour sndncarbon dioxide 1%
The earth was very hot to start with as it cooled,
Water vapour condensed and fellnas rain to form the oceans
Earth cools and oceans forms …
Forms of life evolve in the oceans and photosynthesis begins
Oxygen builds up in the oceans
Oxygen builds up in the atmosphere
Carbon dioxide dissolved in the oceans …
Marine organisms used the dissolved carbon dioxide to make calcium carbonate for shells
The shells of dead Marin organisms fall to the sea bed and become part of the sediment
Over millions of years the layers is sediment become squashed and form sedimentary rocks
Some rocks contain iron
Very old rocks do not contain iron oxides but later ones do
Explain how these rocks provide evidence for changes o the earths atmosphere
The very old rocks are evidence that the early atmosphere contained little or no oxygen because they do not contain iron oxides
Later rocks do contain iron oxides which is evidence rhatxoxygen was released into the atmosphere and reacted with iron in the rocks
When oxygen was first produced it reacted with iron in rocks to produce
Iron oxides
This meant that even though primitive plants were photosynthesising oxygen levels in the atmosphere did not begin to rise straight away
State how the formation of oceans was a cause of decreasing carbon dioxide levels
Carbon dioxide dissolved in the oceans
Describe why the levels of oxygen in the atmosphere increased
Plants produced oxygen by photosynthesis
Suggest a reason that explains why scientists cannot be certain about the earths early atmosphere
No measurements were made then/no humans were on earth then
What does the greenhouse effect do
Helps to keep the earth warm enough for living organisms to exist
What happens in the greenhouse effect
Greenhouse gases in the atmosphere absorb heat radiated from the earth
The greenhouse gases then release energy in all directions
This reduces the amount of heat radiated into space keeping the earth warm
What types of greenhouse gases are particularly good at absorbing and emitting energy by radiation
Carbon dioxide -> burning fossil fuels
Methane -> livestock farming
Water vapour -> evaporation form oceans
The accumulation of greenhouse gases in the atmosphere :
Increased the greenhouse effect which then
Increases the warming effect in the atmosphere - global warming
Global warming is associated with
Long term changes to weather patterns - climate change
Rising sea levels due to melting ice and expanding ocean water
Describe how the greenhouse effect keeps the earth warm
Greenhouse gases absorb heat radiated from the earth thebgases then release the heat into the atmosphere
Explain how the increased use of fossil fuels which contain carbon and carbon compounds may lead to global warming
Fossil fuels give off carbon dioxide during combustion
Increased consumption releases more carbon dioxide
Which is a greenhouse gas
Socyhe greenhousebeffect increases
Flame test for lithium
Red
Sodium
Yellow
Potassium
Lilac
Calcium
Orange red
Copper
Blue green
How do you carry out a flame test
Clean flame test loop in acid each time rinse with water and check it is clean in the Bunsen burner flames
To test a substance dip the clean loop in a solution of the ions and hold at the edge of a blue flame
Some metal ions form
Coloured hydroxide precipitates
The sample solution is placed in a test tube and a few drops of dilute sodium hydroxide solution are added
Cooper metal ion colour of precipitate
Blue
Iron colour of precipitate
Iron (II)
Green
Iron (III) colour of precipitate
Brown
Describe how to distinguish between hydroxide precipitate formed by aluminium ions and that formed by calcium ions
Add excess sodium hydroxide solution
The aluminium hydroxide precipitate dissolved but the calcium hydroxide precipitate does not
Tests for sukfate and carbonate ions
Add dilute hudrochloricnacid then barium chloride solution
- sukfate ions white precipitate of barium sukfate
Add acid
- carbonate ions bubbles of carbon dioxide
Tests for halide ions
Add dilute nitric acid then silver nitrate solution
Chloride ions - white precipitate
Bromide ions - cream precipitate
Iodide ions - yellow precipitate
“Milk, cream, butter”
Test for ammonium ions
Add sodium hydroxide solution
Ammonium ions
Heat
Ammonia produces
Test for ammonia gas
Reaction produces water and ammonia
NH4+ (aq) + OH-(aq) -> H2O (l) + NH3 (g)
Detect ammonia gas produced:
- damp red litmus paper turns blue
- hydrogen chloride gas (from concentrated hydrochloride acid) reacts with ammonia to form a white smoke of ammonium chloride:
NH3 (g) + HCL (g) -> NH4CL (s)
Sharp smell
What do instrumental methods of analysis do
Use machines to detect and analyse substances
Compared with simple chemical tests and analysis, instrumental methods offer improved :
Sensitivity
• they can detect and analyse very small amounts of different substances
Accuracy
• they measure amounts of different substances very accurately
Speed of tests
• they carry out each analysis quickly and the machine can run all the time
What’s flame photometry
An instrumental method based on flame tests
The sample is vaporised in a hot flame
A spectrum of light emitted by metal ions is produced
The brightness of a particular wavelength is measure
The data from a flame photometer can
Identify the metal ions present in the sakolenhy comparing the spectrum with a reference spectrum form a known substance
Determine the concentration ofnions in a solution using a calibration curve
What are alkanes again?
A homologous series of saturated hydrocarbons
How to draw structures of alkanes
Write correct number of C
Draw lines between them
And 4 lines to each C
Write H at end of lines
First 4 alkanes
Methane
Ethane
Propane
Butane
Write a balanced equation for the complet combustion of butane
c4H10 + 61/2O2 -> 4CO2 + 5H2O
Explains why hexane is saturated
Had single carbon bonds not double
What are alkanes?
A homologous series of unsaturated hydrocarbons
General formula for Alkene
CnH2n
How to draw structures of alkenes
Write correct number of C
Draw a line between each C and add an extra two Between two C
Add lines so each C has 4 lines
Write H at end of each line
What happens in the complete combustion of alkenes?
Carbon is oxidised to carbon dioxide
Hydrogen is oxidised roxwater bapour
Alkenes react with bromine to produce
Colourless compound
Test for alkenes
Alkenes reacts with bromine because they are unsaturated
This is the basis of a test to distinguish between alkanes and alkenes :
Add a few drops of bromine water
It stays orange in an alkane
It decokourised in an alkene
Formula for butene
C4H8
