Required practical 4 Tests for cations and anions Flashcards
What is one way you can test for metal halides with sodium hydroxide
. Add 10 drops of your 0.1mol/dm group 2 metal halide solution
. Add 10 drops of 0.6mol/dm sodium hydroxide solution, mix, then add it until it’s in excess
. Gently shake the solution
What happens when excess sodium hydroxide is added to barium chloride
. Initially colourless solution
. After 10 drops it is still colourless
. In excess, it’s still colourless
What happens when excess sodium hydroxide is added to strontium chloride and calcium bromide
. Initially colourless
. After 10 drops a slight white precipitate forms
. In excess, there is still a slight white precipitate
The slight white precipitate is calcium hydroxide
What happens when excess sodium hydroxide is added to magnesium chloride
. Initially colourless
. After 10 drops a slight white precipitate forms
. In excess, white precipitate forms
Describe the overall pattern of group 2 metal halides in a reaction with sodium hydroxide
. Barium chloride: solution stays colourless
Going down the group, they react less with it.
So Magnesium chloride forms white precipitate but barium chloride stays colourless with it
What is a way you can test for group 2 metal cations with sulfuric acid?
How does it change down the group
. Add 10 drops of 0.1mol/dm barium chloride to a test tube
. Add 10 drops of 1.0mol/dm sulfuric acid. and mix
. Then add it in excess and gently shake
Repeat test with calcium bromide, magnesium chloride and strontium chloride
At the top of the group it forms a slight precipitate and goes colourless, down the group there is more of a white precipitate
How does barium chloride react with dilute sulfuric acid?
. It’s initially colourless before H2SO4 is added
And it forms a white precipitate after it is added, and also when it is in excess
You may add HCl also, to remove any carbonate ions which can form calcium carbonate with calcium when they react together
How does strontium chloride react with dilute sulfuric acid?
. Initially it is colourless
. After 10 drops a white precipitate forms
. In excess, It stays a white precipitate
How does calcium bromide react with dilute sulfuric acid?
. It is initially colourless
. A slight white precipitate forms after 10 drops
. And a slight white precipitate forms in excess acid
How does magnesium chloride react with dilute sulfuric acid?
. It is initially colourless
. A slight white precipitate forms after 10 drops
. It goes colourless again in excess
Describe the test for ammonium ions (NH4+) with sodium hydroxide
. Add 10 drops of 0.1mol/dm of ammonium chloride to a test tube
. Add 10 drops of 0.6moldm sodium hydroxide solution to it
. Warm solution in water bath because ammonia gas is very soluble
. Hold damp red litmus paper over the test tube with forceps as fumes are released
. The fumes should turn it blue
How do you test for carbonate ions in aqueous solution
. Add an equal volume of dilute HCl to sodium carbonate solution in a test tube
. Use a test tube to bubble it through calcium hydroxide (limewater) which will form calcium carbonate
. Put a stopper into the test tube containing limewater and shake
Positive test turns it from colourless to cloudy
What is the equation for sodium carbonate solution and hydrochloric acid
And for carbon dioxide with calcium hydroxide
Na2C03 + 2HCl —>
2NaCl + H20 + CO2
CO2 + Ca(OH)2 —>
CaCO3 + H20
Test for sulfate ions
. Add an equal volume of dilute HCl and Barium chloride to the solution containing sulfate ions
. If there are sulfate ions present, barium sulfate forms which is a white precipitate
What is the equation for magnesium sulfate with barium chloride
MgSO4 + BaCl2 —> BaSO4(s) + MgCl2(aq)
Describe the test for halide ions in aqueous solution before adding ammonia
You have potassium chloride, bromide and iodide
. Add 10 drops of potassium chloride to a test tube and add 5 drops nitric acid
. Then add 10 drops silver nitrate to the solution
. Swirl the test tube so the precipitate can evenly distribute
What colour precipitate do potassium chloride, bromide, and iodide form with nitric acid and silver nitrate solution
Chloride ions: White precipitate
Bromide ions: Cream precipitate
Iodide ions: Yellow precipitate
When an excess of ammonia solution is added to the silver halides, what occurs with chloride, bromide, and iodide ions
What are the reactions
. With concentrated and dilute ammonia solution, chloride ions dissolve
AgCl(s) + 2NH3 —> [Ag(NH3)2]+ + Cl-
. With concentrated ammonia solution, bromide ions dissolve
AgBr(s) + 2NH3(aq) → Ag [(NH3)2]+(aq) + Br-
. Iodide ions don’t dissolve in either so stays a yellow precipitate
No reaction
How do you test for group 7 solid salts
.Place a small spatula of solid potassium chloride in a dry test tube in a test tube rack
. Working in a fume cupboard, add a few drops of concentrated sulfuric acid
. Record observations
. Test gas evolved with blue litmus paper
. Repeat experiment with potassium bromide and potassium iodide
What can you see when solid potassium chloride reacts with concentrated sulfuric acid
. White steamy fumes
. Blue litmus paper turns red
What can you see when solid potassium bromide reacts with concentrated sulfuric acid
. Orange fumes
. It turns blue litmus paper red
What can you see when solid potassium iodide reacts with concentrated sulfuric acid
. Purple fumes and a purple/black solid
. Blue litmus paper turns red
What would the halide be if you added silver nitrate solution and nitric acid to a sodium halide, and there was no precipitate
Flouride ion
