Group 7, the Halogens: Required Practical 4 (includes Group 2) Flashcards
Which positive ions do you need to know the tests of?
- Group 2 ions
- Ammonium ions, NH4+
How can you identify group 2 ions?
- Adding sodium hydroxide
Outline the steps of the sodium hydroxide method of testing for group 2 ions
- 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
Describe the observation made when magnesium ions, Mg^2+, are added to NaOH and excess NaOH
• With OH-
- Slight white precipitate
• With excess OH-
- White precipitate
Describe the observation made when calcium ions, Ca^2+, are added to NaOH and excess NaOH
• With OH-
- Slight white precipitate
• With excess OH-
- Slight white precipitate
Describe the observation made when strontium ions, Sr^2+, are added to NaOH and excess NaOH
• With OH-
- Slight white precipitate
• With excess OH-
- Slight white precipitate
Describe the observation made when barium ions, Ba^2+, are added to NaOH and excess NaOH
• With OH-
- No change
• With excess OH-
- No change
What ions are needed to test for ammonium ions?
- Hydroxide ions, OH-
Outline the steps of the test for ammonium ions
- Add sodium hydroxide solution to solution containing unknown ions
- Gently heat
- Hold damp red litmus paper above solution
- Damp red litmus paper turns blue
What is the positive test result for the test for ammonium ions?
- Damp red litmus paper turns blue
What reaction, including state symbols, occurs between ammonium ions and hydroxide ions during the test for ammonium ions?
- NH4+ (aq) + OH- (aq) → NH3 (g) + H2O (l)
Which negative ions do you need to know the tests of?
- Sulfate ions, SO42-
- Hydroxide ions, OH-
- Carbonate ions, CO3^2-
- Halide ions
Outline the steps of the test for sulfate ions
- Add a little dilute hydrochloric acid
- Add barium chloride solution, BaCl2
- White precipitate of barium sulfate forms
What is the positive test result for sulfate ions?
- White precipitate of barium sulfate forms
Why do you need to add hydrochloric acid during the test for sulfate ions?
- To remove any carbonate and sulfite ions
- These would also produce a precipitate