- The more soluble the sample, the further it will travel
- Base line must be drawn with pencil otherwise the ink will interfere with
results or mix up with sample
- Water must be below base line otherwise ink will dissolve in water
- If sample does not move along the filter paper, the sample is not soluble. To solve, change the solvent.
2.41 describe tests for the gases:
i hydrogen
ii oxygen
iii carbon dioxide
iv ammonia
v chlorine
Hydrogen
- Hydrogen is less dense than air. It is odourless and colourless. Hydrogen reacts explosively with oxygen with air (i.e. during combustion). The reaction produces lots of heat (it is exothermic).
- Hydrogen + Oxygen -> Water
- 2H2(g) + O2(g) -> 2H2O(l)
- It is tested with a lit splint producing a squeaky pop.
- Oxygen is a colourless gas that is odourless. It has the same dense as air.
- It is tested with a glowing splint that re-light
- Carbon Dioxide
- Carbon dioxide is a colourless, odourless gas. It is more dense than air therefore it will stay in the test tube when you take the stopper off. It is a slightly acidic gas and produces carbonic acid when dissolved in water.
- It can be tested with a glowing splint that extinguishes or limewater than goes milky.
- Carbon dioxide is a colourless, odourless gas. It is more dense than air therefore it will stay in the test tube when you take the stopper off. It is a slightly acidic gas and produces carbonic acid when dissolved in water.
- It can be tested with a glowing splint that extinguishes or limewater than goes milky.
- Ammonia has the formula NH3. It is the only alkaline gas. It has a pungent odour and is highly soluble in water producing a solution called ammonium hydroxide (NH4OH), hence it cannot be collected by downwards displacement of water. It is used in fertiliser.
- NH3(g) + H2O(l) --> NH4OH(aq)
- OH- ion causes the alkalinity
- It can be tested by a damp red litmus paper. It turns damp red litmus paper blue.
- Chlorine is a highly toxic and acidic gas. It bleaches the colour out of things. It is a dense gas with a pale green colour and a pungent smell. It is used for bleaches and kills bacteria in swimming pool.
- Chlorine + Water -> Hydrochloric Acid (Red) + Hyperchlorous Acid (White)
- Cl2(g) + H2O(l) -> HCl(aq) + HOCl(aq)
- It can be tested with a damp blue litmus paper. It turns damp blue litmus paper red and very quickly white.
2.28 describe the use of anhydrous copper(II) sulphate in the chemical test for water
2.29 describe a physical test to show whether water is pure.
Purity of Water
Presence of Water
- Can be measured by testing for the boiling/freezing points
- Pure water freeze at 0 degrees C and boil at 100 degrees C
Presence of Water
- Put anhydrous copper sulphate in liquid/aqueous solution
- Positive test: Colour change of anhydrous copper sulphate from white to blue
2.39 describe tests for the cations:
i Li+, Na+, K+ , Ca2+ using flame tests
ii NH4+ using sodium hydroxide solution and identifying the ammonia evolved
iii Cu2+, Fe2+ and Fe3+ using sodium hydroxide solution
- Cations: Positive Ions. Usually metals except hydrogen.
- Anions: Negative Ions. Usually non-metals.
1. Put a squirt of metal solutions into a test tube.
2. Clean a piece of nichrome wire by dipping it into hydrochloric acid.
3. Hold it into a roaring Bunsen flame for a few seconds.
4. Dip the nichrome wire into the metal solution and quickly hold it into the roaring flame again.
5. Repeat several times and note the colour of flame produced.
6. Dip the nichrome wire into acid before testing with other metal solutions. Below are positive test results.
Positive Results
- Lithium: Scarlet Red
- Sodium: Yellow/Orange
- Potassium: Purple
- Calcium: Brick Red
- Copper: Green
1. Put 1 spatula of ammonium sulfate into a test tube.
2. Add a squirt of 1cm3 of sodium hydroxide solution.
3. Heat gently using a Bunsen Burner by giving it three quick tickles.
4. Damp a piece of red litmus paper and put it inside the test tube using a pair of tongs.
5. A positive result will turn the damp red litmus paper blue.
Sodium Hydroxide Solution Tests
- Put a squirt of metal solution in a test tube.
- Add a few drops of NaOH to the test tube.
- Note down any colour change. Below are positive test results.
Positive Results
- Copper 2+: Blue to light blue
- Iron 2+: Green to dark green
- Iron 3+: Yellow to rusty brown
- Cu 2+(aq) + 2OH-(aq) -> Cu(OH)2 (s)
- Fe 2+(aq) + 2OH-(aq) -> Fe(OH)2 (s)
- Fe 3+(aq) + 3OH-(aq) -> Fe(OH)3 (s)
2.40 describe tests for the anions:
i Cl-, Br- and I-, using dilute nitric acid and silver nitrate solution
ii SO4 2-, using dilute hydrochloric acid and barium chloride solution
iii CO3 2- using dilute hydrochloric acid and identifying the carbon dioxide evolved
Silver Nitrate Tests
1. Fill the test tube(s) with a squirt of salt solution.
2. Add some nitric acid (to acidify solution) then a few drops of silver nitrate solution.
3. Shake the test tube. Below are positive test results.
Positive Results
1. Fill the test tube(s) with a squirt of salt solution.
2. Add some hydrochloric acid (to acidify solution) and a few drops of barium chloride.
3. Shake the test tube.
Positive Result
1. Put a spatula of solid salt in a test tube.
2. Add a squirt of dilute hydrochloric acid.
3. Carbonate ion is present when there is fizzing.
4. Attach a a delivery tube to the test tube and pass the gas produced through 1cm3 of water.
5. Carbon dioxide is present if the lime water turns milky.
1. Fill the test tube(s) with a squirt of salt solution.
2. Add some nitric acid (to acidify solution) then a few drops of silver nitrate solution.
3. Shake the test tube. Below are positive test results.
Positive Results
- Yellow Precipitate: Iodide
- White Precipitate: Chloride
- Creamy Precipitate: Bromide
- Ag+(aq) + Cl-(aq) -> AgCl (s)
- Ag+(aq) + Br-(aq) -> AgBr (s)
- Ag+(aq) + l-(aq) -> Agl (s)
1. Fill the test tube(s) with a squirt of salt solution.
2. Add some hydrochloric acid (to acidify solution) and a few drops of barium chloride.
3. Shake the test tube.
Positive Result
- Sulphate Ion is present when a white precipitate is formed.
- Ba 2+(aq) + SO4 2-(aq) -> BaSO4(s)
1. Put a spatula of solid salt in a test tube.
2. Add a squirt of dilute hydrochloric acid.
3. Carbonate ion is present when there is fizzing.
4. Attach a a delivery tube to the test tube and pass the gas produced through 1cm3 of water.
5. Carbon dioxide is present if the lime water turns milky.