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Chemical tests (Gas tests (Hydrogen, H2 (Collect the gas in a boiling tube…
Chemical tests
Gas tests
Hydrogen, H2
Collect the gas in a boiling tube and insert a lit splint. If a 'pop' is heard, hydrogen is present.
Oxygen, O2
Take a glowing splint and insert it into the sample of gas. If it reignites, oxygen is present.
Carbon dioxide, CO2
Bubble the gas into limewater. If the limewater turns cloudy, carbon dioxide is present.
Chlorine, Cl2
Direct the gas to a piece of damp UI paper. If it turns red then bleaches, chlorine is present.
Ammonia, NH3
Direct the gas to a damp piece of red litmus paper. If the paper turns blue, ammonia is present.
Anions
Halides
Add a few drops of dilute nitric acid (to remove impurities) and then silver nitrate. Halides are present if a precipitate forms. Silver halides are insoluble.
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Sulphates
Add a few drops of dilute hydrochloric acid and then barium chloride. If sulphate ions are present a white precipitate will form. Barium sulphate is insoluble.
Carbonates
Add dilute hydrochloric acid and cover the test tube with a delivery tube. Put the other end in limewater. If the limewater turns cloudy carbonate ions are present as a metal carbonate reacted with hydrochloric acid produces carbon dioxide.
Cations
Flame Tests
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1.Use a clean flame test wire. 2. Heat the nichrome wire. 3. Dip it in the hydrochloric acid. 4. Dip the wire into the compound you are testing so a small blob is collected on the wire. 5. Put the tip of the wire into a flame and see what colour it turns.
Wet Test
Add a few drops of NaOH. If a precipitate is formed a cation is present. Identify it, if the precipitate is coloured. If not add more to see if it dissolves.
Aluminium, Al = White + Precipitate dissolves as more NaOH is added to the solution
Calcium, Ca = White + Precipitate will not dissolve in the NaOH solution
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Iron(II), Fe = Pale green
Iron(III), Fe = Red-brown
Ammonium
Add drops of NaOH. Heat the mixture with a piece of damp litmus paper in the top of the boiling tube. If the litmus paper turns blue ammonium is present as ammonium reacts with hydroxide ions to form ammonia and water.
Water
Chemical
Dehydrate the copper sulphate in a bunsen burner. It should turn from blue to white. Add the sample to the anhydrous copper sulphate and note a colour change. If it is back to it's original blue, the sample is, or contains water.
Physical
Boil the sample. If it boils at 100°C it is pure water as only pure water boils at that temperature. Then add 'impurities' such as sodium chloride, which raises the boiling point, and heat again to check.