Required practical 4 Tests for cations and anions

Question 1

What is one way you can test for metal halides with sodium hydroxide

Answer 1

. 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

Question 2

What happens when excess sodium hydroxide is added to barium chloride

Answer 2

. Initially colourless solution
. After 10 drops it is still colourless
. In excess, it’s still colourless

Question 3

What happens when excess sodium hydroxide is added to calcium bromide and strontium chloride

Answer 3

. 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

Question 4

What happens when excess sodium hydroxide is added to magnesium chloride

Answer 4

. Initially colourless
. After 10 drops a slight white precipitate forms
. In excess, white precipitate forms

Question 5

Describe the overall pattern of group 2 metal halides in a reaction with sodium hydroxide

Answer 5

. Barium chloride: solution stays colourless

The others all form a slight white precipitate with it

Question 6

What is a way you can test for group 2 metal cations with sulfuric acid?

How does it change down the group

Answer 6

. 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

Question 7

How does barium chloride react with dilute sulfuric acid?

Answer 7

. 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

Question 8

How does strontium chloride react with dilute sulfuric acid?

Answer 8

. Initially it is colourless
. After 10 drops a white precipitate forms
. In excess, It stays a white precipitate

Question 9

How does calcium bromide react with dilute sulfuric acid?

Answer 9

. It is initially colourless
. A slight white precipitate forms after 10 drops
. And a slight white precipitate forms in excess acid

Question 10

How does magnesium chloride react with dilute sulfuric acid?

Answer 10

. It is initially colourless
. A slight white precipitate forms after 10 drops
. It goes colourless again in excess

Question 11

Describe the test for ammonium ions (NH4+) with sodium hydroxide

Answer 11

. 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

Question 12

How do you test for carbonate ions in aqueous solution

Answer 12

. Add an equal volume of dilute HCl to sodium carbonate solution in a test tube
. Use a test tube to bubble it through calcium carbonate (limewater)
. Put a stopper into the test tube containing limewater and shake

Positive test turns it from colourless to cloudy

Question 13

What is the equation for sodium carbonate solution and hydrochloric acid

And for carbon dioxide with calcium hydroxide

Answer 13

Na2C03 + 2HCl —>
2NaCl + H20 + CO2

CO2 + Ca(OH)2 —>
CaCO3 + H20

Question 14

Test for sulfate ions

Answer 14

. 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

Question 15

What is the equation for magnesium sulfate with barium chloride

Answer 15

MgSO4 + BaCl2 —> BaSO4(s) + MgCl2(aq)

Question 16

Describe the test for halide ions in aqueous solution before adding ammonia

Answer 16

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

Question 17

What colour precipitate do potassium chloride, bromide, and iodide form with nitric acid and silver nitrate solution

Answer 17

Chloride ions: White precipitate
Bromide ions: Cream precipitate
Iodide ions: Yellow precipitate

Question 18

When an excess of ammonia solution is added to the silver halides, what occurs with chloride, bromide, and iodide ions

What are the reactions

Answer 18

. 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

Question 19

How do you test for group 7 solid salts

Answer 19

.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

Question 20

What can you see when solid potassium chloride reacts with concentrated sulfuric acid

Answer 20

. White steamy fumes
. Blue litmus paper turns red

Question 21

What can you see when solid potassium bromide reacts with concentrated sulfuric acid

Answer 21

. Orange fumes
. It turns blue litmus paper red

Question 22

What can you see when solid potassium iodide reacts with concentrated sulfuric acid

Answer 22

. Purple fumes and a purple/black solid
. Blue litmus paper turns red

Question 23

What would the halide be if you added silver nitrate solution and nitric acid to a sodium halide, and there was no precipitate

Answer 23

Flouride ion