Test for Ions

Question 1

Name the 2 tests for Group 2 ions

Answer 1

• Dilute sodium hydroxide
• Dilute sulfuric acid

Question 2

Test for Group 2 Ions

Describe what you would do using dilute sodium hydroxide

Answer 2

1. Add 10 drops of barium chloride in test tube
2. Add 10 drops of sodium hydroxide in test tube & mix well
3. Add sodium hydroxide, dropwise, until in excess
   
   • Test tube shouldn’t be more than half-way full
4. Repeat this test with calcium bromide, magnesium chloride and strontium chloride

Question 3

Test for Group 2 Ions

Describe what you would do using dilute sulfuric acid

Answer 3

1. Place about 10 drops of barium chloride in test tube
2. Add 10 drops of sulfuric acid in test tube & mix well
3. Add sulfuric acid, dropwise, until in excess
   
   • Test tube shouldn’t be more than half-way full
4. Repeat this test with calcium bromide, magnesium chloride and strontium chloride

Question 4

Test for Group 2 Ions

Results when using dilute sodium hydroxide: fill in the blanks

Answer 4

Question 5

Describe the test for ammonia gas

Answer 5

• Ammonia gas is alkaline
• Can test for it using damp piece of red litmus paper
• If ammonia present = paper turns blue

Question 6

Testing for Ammonia

Why does red litmus paper have to be damp?

Answer 6

So ammonia gas can dissolve

Question 7

If you add hydroxide ions to solution containing ammonium ions (NH₄⁺), what it produce?

Answer 7

ammonia gas and water

Question 8

Write an equation to show the reaction between hydroxide ions and ammonium ions

Answer 8

Question 9

Describe the test for ammonium ions

Answer 9

1. Add dilute sodium hydroxide solution to unknown substance in test tube & gently heat mixture
2. If ammonia given off = ammonium ions must be present

Question 10

Write the equation for the test for sulfate ions

Answer 10

Question 11

Hydroxide ions make solution ____

Answer 11

alkaline

Question 12

Describe the test for hydroxide ions

Answer 12

1. Dip piece of red litmus paper into solution
2. If hydroxide ions present = paper turns blue

Question 13

Describe the test for carbonate ions (CO₃^2-)

Answer 13

1. Add dilute hydrochloric acid = solution with carbonate ions will fizz
2. Bubble gas (CO₂) through test tube of limewater and watch what happens
3. Limewater = cloudy = carbonate ions in solution

Question 14

Why is that when you add dilute hydrochloric acid to a solution with carbonate ions, it will fizz?

Answer 14

∵ carbonate ions react with hydrogen ions in acid to give carbon dioxide

Question 15

Write the equation of carbonate ions reacting with hydrogen ions

Answer 15

Question 16

Test for Group 2 Ions

Results when using dilute sulfuric acid: fill in the blanks

Answer 16

Question 17

Describe the test for halide ions in solid salts using
concentrated sulfuric acid

Answer 17

1. Add small amount of solid potassium chloride in test tube
2. Add few (2 to 5) drops of concentrated sulfuric acid
3. Test gas produced with moist blue litmus paper
   
   • Make sure litmus paper doesn’t touch side of tube
4. Repeat experiment with solid potassium bromide
   
   • Test gas produced using strip of filter paper dipped in acidified potassium dichromate solution
5. Repeat experiment with solid potassium iodide
   
   • Test gas produced using strip of filter paper dipped in lead nitrate solution

Question 18

Name 2 safety procedures when testing for halide ions in solid salts using concentrated sulfuric acid

Answer 18

• Gloves must be worn
• Must be done in fume cupboard

Question 19

State the results of when potassium chloride reacts with concentrated sulfuric acid. Include the paper result.

Answer 19

Question 20

State the results of when potassium bromide reacts with concentrated sulfuric acid. Include the paper result.

Answer 20

Question 21

State the results of when potassium iodide reacts with concentrated sulfuric acid. Include the paper result.

Answer 21

Question 22

Describe the test for sulfate ions (SO₄^2-)

Answer 22

1. Add dilute hydrochloric acid and then barium chloride solution, BaCl_2(aq)
2. If white precipitate of barium sulfate forms = original compound contained sulfate

Question 23

Test for sulfate ions

Why should you acidify the solution?

Answer 23

To get rid of any lurking sulfites or carbonates which will also produce a white precipitate

Question 24

Describe the test for halides

Answer 24

1. Add dilute nitric acid (HNO₃) and then silver nitrate solution (AgNO₃)
2. Precipitate is formed (of silver halide)

Question 25

Test for Halides What is the result for fluoride?

Answer 25

No precipitate

Question 26

Test for Halides What is the result for chloride?

Answer 26

White precipitate of silver chloride

Question 27

Test for Halides What is the result for bromide?

Answer 27

Cream precipitate of silver bromide

Question 28

Test for Halides What is the result for iodide?

Answer 28

Yellow precipitate of silver iodide

Question 29

Test for Halides What can you do to be sure of your results & why does this work?

Answer 29

* You can test your results by adding ammonia solution * Each silver halide has a different solubility in ammonia

Question 30

Test for Halides Write the general equation

Answer 30

Question 31

Fill in the gaps (speed)

Answer 31

Question 32

Fill in the gaps

Answer 32

Question 33

Test for Halides Why do you add dilute nitric acid?

Answer 33

To remove ions which may interfere with test