Group 7, the Halogens: Required Practical 4 (includes Group 2)

Question 1

Which positive ions do you need to know the tests of?

Answer 1

• Group 2 ions

- Ammonium ions, NH4+

Question 2

How can you identify group 2 ions?

Answer 2

• Adding sodium hydroxide

Question 3

Outline the steps of the sodium hydroxide method of testing for group 2 ions

Answer 3

• Add dilute NaOH dropwise to a test tube containing metal solution and observe the precipitate that forms
• Keep adding NaOH until it’s in excess and record changes

Question 4

Describe the observation made when magnesium ions, Mg^2+, are added to NaOH and excess NaOH

Answer 4

• With OH-
- Slight white precipitate

• With excess OH-
- White precipitate

Question 5

Describe the observation made when calcium ions, Ca^2+, are added to NaOH and excess NaOH

Answer 5

• With OH-
- Slight white precipitate

• With excess OH-
- Slight white precipitate

Question 6

Describe the observation made when strontium ions, Sr^2+, are added to NaOH and excess NaOH

Answer 6

• With OH-
- Slight white precipitate

• With excess OH-
- Slight white precipitate

Question 7

Describe the observation made when barium ions, Ba^2+, are added to NaOH and excess NaOH

Answer 7

• With OH-
- No change

• With excess OH-
- No change

Question 8

What ions are needed to test for ammonium ions?

Answer 8

• Hydroxide ions, OH-

Question 9

Outline the steps of the test for ammonium ions

Answer 9

• Add sodium hydroxide solution to solution containing unknown ions
• Gently heat
• Hold damp red litmus paper above solution
• Damp red litmus paper turns blue

Question 10

What is the positive test result for the test for ammonium ions?

Answer 10

• Damp red litmus paper turns blue

Question 11

What reaction, including state symbols, occurs between ammonium ions and hydroxide ions during the test for ammonium ions?

Answer 11

• NH4+ (aq) + OH- (aq) → NH3 (g) + H2O (l)

Question 12

Which negative ions do you need to know the tests of?

Answer 12

• Sulfate ions, SO42-
• Hydroxide ions, OH-
• Carbonate ions, CO3^2-
• Halide ions

Question 13

Outline the steps of the test for sulfate ions

Answer 13

• Add a little dilute hydrochloric acid
• Add barium chloride solution, BaCl2
• White precipitate of barium sulfate forms

Question 14

What is the positive test result for sulfate ions?

Answer 14

• White precipitate of barium sulfate forms

Question 15

Why do you need to add hydrochloric acid during the test for sulfate ions?

Answer 15

• To remove any carbonate and sulfite ions

- These would also produce a precipitate

Question 16

Give the reaction between sulfate ions and barium ions during the sulfate ions test, including state symbols

Answer 16

• Ba^2+ (aq) + SO4^2- (aq) → BaSO4 (s)

Question 17

Outline the steps of the hydroxide ions test

Answer 17

• Add universal indicator or red litmus paper to solution

- Solution or paper turns blue

Question 18

What is the positive result of the hydroxide ion test?

Answer 18

• Solution or paper turns blue

Question 19

Outline the steps of the test for carbonate ions

Answer 19

• Add dilute hydrochloric acid

- Results in effervescence

Question 20

What is the positive result for the carbonate ions test?

Answer 20

• Effervescence

Question 21

Give the reaction between carbonate ions and hydrogen ions during the test for carbonate ions, including state symbols

Answer 21

• CO3^2- (aq) + 2H+ (aq) → CO2 (g) + H2O (l)