Analysis Of Ions And Gases Flashcards
Describe how to do a flame test.
1) Clean the end of the Nichrome wire by dipping into HCL, place in a roaring Bunsen. Repeat until wire no longer produces a colour.
2) Dip end of wire into fresh HCL and then into solid sample.
3) Place wire into non roaring, non luminous flame.
4) Record colour of the flame
Flame test: Lithium
Li +
Pink/Red
Flame test: Sodium
Na+
Orangey-yellow
Flame test: Potassium
K+
Lilac
Flame test: Copper (II)
Cu2+
Greeney-blue
Flame test: Calcium
Ca2+
Brick red
Describe how to work out the analysis of metal cations.
- Add NaOH a drop at a time to a solution of you cation.
- The OH- ions in the solution react with some positive metal ions in precipitation reactions to produce coloured insoluble metal hydroxide precipitates.
Observation of Copper (II) and Sodium Hydroxide -
Blue precipitate formed
Observations of Iron (II) and Sodium Hydroxide-
Green precipitate formed (murkyish)
Observations of Iron (III) and Sodium Hydroxide -
Orangey-browny precipitate formed.
Describe the analysis of ammonium (NH4+).
- Add 2cm3 of sodium hydroxide to the solid/solution under test.
- Warm the mixture, in a water bath.
- If ammonium ions are present, then ammonia gas (NH3) will be produced.
- This is a pungent smelling gas, which turns damp red litmus paper blue.
Describe the analysis of positive ions.
- Add small amount of NaOH to a solution of you +be ions.
The OH- ions in the solution react with some positive metal ions in precipitation reactions to produce coloured insoluble metal hydroxide precipitates.
How do you identify a carbonate?
- Add dilute HCl (2cm depth) to the solid carbonate or its aqueous solution.
- Use delivery tube to bubble the gas through lime water.
Observations of Calcium Carbonate with dilute HCl
- Limewater turns cloudy
- Bubbles of gas
How do you identify sulphates?
- Add dilute HCl (2cm depth) and Barium Chloride solution (2cm depth) to a solution of a sulphate (2cm depth).
- HCl is added first to remove any carbonate ions that might be present - would also produce the same observation, giving false positive test.
Observations of Sodium Sulphate with dilute HCl and Barium Chloride -
Solution turns cloudy
How do you identify Chlorides, Bromides and Iodides?
- Add dilute nitric acid (1cm depth) and silver nitrate solution (2cm depth) of chloride or a bromide or an iodide (2cm depth).
- Nitric acid reacts with any other ions that might give a confusing precipitate (produces nitrates, and all nitrates are soluble)
Observation of chloride with dilute nitric acid and silver nitrate solution -
Forms a white precipitate.
Observation of bromide with dilute nitric acid and silver nitrate -
Forms a cream precipitate.
Observation of iodide with dilute nitric acid and silver nitrate -
Forms a yellow precipitate.
When is upwards delivery used?
- For gases less dense than air e.g H2, NH3
What happens in upwards delivery?
The gas produced pushes the air in the gas jar/test tube out the bottom
When is downwards delivery used?
For gases more dense then air e.g CO2 and Cl2.
What happens in downwards delivery?
The gas produced pushes the air in the gas jar/test tube out of the top.
What happens when the gas is “over water” (displacement occurs)?
The gas produced in the reaction is bubbled through a trough of water into a upside down jar filled with water. The gas displaces the water, pushing it out the bottom. A ‘beehive shelf’ directs the gas into the gas jar.
When is over water (displacement) used?
Only works for insoluble gases/slightly soluble gases.
H2 is insoluble, O2 and CO2 are only slightly soluble in water.
- Wouldn’t work for NH3 and Cl2 as they are soluble.
When is a gas syringe used?
Can be used to collect any gas. For testing the gas must be transferred to a test tube using one of the first 3 methods.
Test for chlorine and result
Damp blue litmus paper
- Will turn red
- Bleach it
Test for hydrogen and result
Put a lit splint in a test tube
- squeaky pop
Test for ammonia and result
Use damp red litmus paper
- Turns blue
Test for Carbon Dioxide and result
Bubble gas through lime water
- Limewater turns cloudy/milky
Test for oxygen and result
Put glowing splint in test tube
- Splint relighting
Where should the preparation and testing of chlorine and ammonia occur? Why?
Both are toxic, therefore going to be released in the atmosphere.
Should be done in a fume cupboard.
Chemical test for water
Water turns white anhydrous copper (II) sulphate BLUE.
- Only confirms water is present not pure.
How to test if water is pure?
It should melt at 0ºC and boil at 100ºC.
