Analysis Flashcards
What are the three steps to identify positive ions in substances?
- flame test
- add sodium hydroxide
- to produce precipitate
- warm solution in hot water baths and test gas produced with damp litmus paper
Describe how to carry out a flame test
- clean a platinum wire by diffing it into concentrated acid to remove any impurities thta may change colour of flame
- then dip wire into solid being testes and hold it above à blue Bunsen flame until a recognisable colour change is visible
Why is platinum wire used?
- inert (unreactive) and so doesn’t colour the flame
- high melting point so can withstand heat from blue flame
Lithium flame test
Red
Sodium flame test
Yellow
Postassium flame test
Lilac
Calcium flame test
Orange-red
Copper(II) flame test
Blue-green
Name the four ways to collect gases
- gas syringe
- over water
- upward delivery
- downward delivery
What can we use gas syringe method for?
- any gas
- most accurate measuring
What can we use over water method for?
- only works for gasses that are not soluble in water as they’d bubble through it and collect at top
- works for gases in similar density to air
What can we use the upward delivery method for?
- gases thta are less dense than air so they would rise over it can collect at top
- solubility in water is irrelevant
What can we use downward delivery for?
- gasses that are more dense than air air as they would sink beneath it
- solubility is irrelevant
Hydrogen density compared to air and solubility in water
- less dense than air air as
- insoluble in water
Oxygen density compared to air and solubility in water
- equal density to air
- insoluble in water
CO2 density compared to air and solubility in water
- more dense than air
- insoluble in water
Chlorine density compared to air and solubility in water
- more dense than air
- soluble in water
Ammonia density compared to air and solubility in water
- less dense than air air as
- soluble in water
Test for chlorine gas
- damp red litmus paper
- positive result = litmus paper bleaches
Test for ammonia
- damp red litmus paper
- positive result = red litmus paper tunes blue (gas was alkaline)
Test for hydrogen
- lit splint in tube of hydrogen
- squeaky pop will be heard
CO2 test
- bubble through limewater
- positive result = limewater turns cloudy
Test for oxygen
- use a glowing splint into tube if oxygen
- positive result = splint will relight
Test for presence of water
- anhydrous white copper(II) sulfate
- turns from white to blue
Test for purity of water
- heat water and measure boiling point
- positive result = pure water boils at 100 degrees C
Test for copper(II) ions
- add sodium hydroxide to copper(II) sulfate
- positive result = clear blue solution becomes a cloudy blue one ( blue precipitate forms)
test for iron(II)
- add sodium hydroxide to iron(II) sulfate
- positive result = colourless solution. becomes green due to formation of green precipitate
Test for Iron(III)
- add sodium hydroxide to iron (III) sulfate
- positive result. = yellow solution to red-brown precipitate forms
Test for ammonia
- add sodium hydroxide to ammonium chloride
- positive result = turned red damp litmus paper blue
Why must litmus paper be damp when testing for ammonia?
acids and alkalis only react when dissolved in water
Test for sulfates using sodium sulfate
- add sodium sulfate to a test tube and then add some hydrochloric acid and barium chloride
- positive result = white precipitate forms
Why do we add acid to a sulfate solution?
To prevent the formation of other precipitates as the acid will react with any carbonates present
Test for sulfates using copper(II) sulfate
- take a test tube and add sopper(II) sulfate and add hydrochloric acid and barium chloride
- positive result = white precipitate forms
Test for carbonate ions using calcium carbonate
- add calcium cabr8nate to hydrochloric acid
- then collect gas using downward delivery
- bubble gas through limewater
Test for carbonate ions using sodium carbonate
- add hydrochloric to sodium carbonate
- collect gas produced using downward delivery
- bubble gas produced through limewater
Percentages of gasses in the air
- nitrogen = 78%
- oxygen = 21%
- carbon dioxide = 0.04%
- argon and other gasses = less than 1%
Describe using phosphorus to calculate percentage of oxygen in the air
- phosphorus on evaporating basin on water in bell jar and use hot glass rod to heat it
Why must the solution to test for halides be acidified?
prevent the formation of other precipitates
Test for chloride ions
- add potassium chloride to a test tube with water and then add a few drops of silver nitrate
- positive result = whiter precipitate forms
Test for bromide ions
- to a test tube containing water add potassium bromide and then silver nitrate contact prevent
- positive result = cream coloured precipitate forms
Test for iodide ions
- to a test tube containing water add potassium iodide and then add silver nitrate
- positive result = yellow precipitate formed
How to do the bell jar experiment
- heat à glass rod and light phosphorus in evaporating basin to set it alight to a yellow flame and white smoke is produced
- water level rises to replace oxygen as phosphorus oxide forms
Where does the water rise up to in the bell jar experiment?
Up to 20% air used up
Describe copper oxide syringe method to find oxygen percentage in air
- measure mass of empty syringe
- add copper into it and measure mass
- pass oxygen over copper until black copper oxide forms
- measure mass of empty
- change in volume of gas = percentage of oxygen in the air
How do we know when the gas syringe experiment finished?
Volume of gas is no longer changing
Core practical 5 - iron wool
- Force a piece of iron wool to the bottom of a burette.
Use enough iron wool so that it is approximately 3 cm
deep in the burette, ensuring the end of the burette
is sealed. - Fill a plastic trough to a few cm depth with water.
- Pour some water into the burette, then invert it, placing the end of the burette underwater in the plastic trough
so that the water does not fall out. The exact volume of water in the burette is not important, as long as the initial reading on the burette can be recorded. - Record the initial volume of the water in the burette.
- Leave this apparatus at the side/back of the lab for at least one week.
- After one week, record the final volume of the water in the burette.
How to increase accuracy of core practical 5
Use. Measuring cylinder with smaller scale divisions
