M8 anion test flow charts

Question 1

what anions are being tested (8)

Answer 1

CH₃COO⁻
OH⁻
CO₃²⁻
SO₄²⁻
PO₄³⁻
Cl⁻
I⁻
Br⁻

Question 2

How many tests are there

Answer 2

5

Question 3

• What is the first test
• What are the results of each (1)
• What are the validations for the results

Answer 3

Use universal indicator paper or red litmus paper: hydrolyse to form OH⁻,

Results (OH⁻):
pH > 7 (colour (dark green - purple)or red litmus goes blue

eg (CH₃COO⁻ + H₂O ⇄ CH₃COOH + OH⁻)

Validation
FeCl₃₍ₐᵩ₎ + 3CH₃COOH₍ₐᵩ₎ → (CH₃COO)₃Fe₍ₛ₎ + 3HCl₍ₐᵩ₎ (red Ptte) (Iron chloride test)

Question 4

• What is the second test
• What are the results of each
• What are the validations for each of the results

Answer 4

1. Add dilute nitric acid (HNO₃) (in excess to remove CO₃²⁻)

Results(CO₃²⁻):
1. CO₃²⁻₍ₐᵩ₎ + 2H⁺₍ₐᵩ₎➝ CO₂₍𝓰₎ + H₂O₍ₗ₎ (Evanescence (vapour created))

Validations
1. Ca(OH)2₍ₐᵩ₎ + CO2₍𝓰₎ → CaCO3₍ₛ₎ + H2O₍ₗ₎ (white Ptte) (Lime water test)

Question 5

• What is the third test/s

- What are the results of each

Answer 5

Add excess barium nitrate solution

Result (SO₄²⁻)
Ba²⁺ + SO₄²⁻ → BaSO₄(s) (white Ptte)

Question 6

• What is the fourth test/s
• What are the results of each
• What are the validations for each of the result

Answer 6

Adding Ammonia (NH₃) (to make an alkaline solution + Barium nitrate (BaNO₃⁻)

Results (PO₄³⁻)
Ba²⁺ + PO₄³⁻ → Ba₃(PO₄)₂ (White Ptte)

Validation
The phosphomolybdate test
(acid catalyst)
PO₄³⁻ + (NH₄)₂MoO₄ → (NH₄)₃PMo₁₂O₄₀ (yellow Ptte)

Question 7

• What is the fifth tests
• What are the results of each (3)
• What are the validations for each of the results(3)

Answer 7

Test 1:
1. Add nitric acid (acidify the solution) + add excess silver nitrate solution

Results (Cl⁻, Br⁻, I⁻)
Ag⁺ + Cl⁻ → AgCl (white ptte)
Ag⁺ + Br⁻ → AgBr (cream ptte)
Ag⁺ + I⁻ → AgI (pale-yellow ptte)

Confirmatory test : (Cl)
Common step :2. Add dilute ammonia (NH3) solution. Stir to mix, and heat. (extract the filtrate (dissolved AgCl) and residue)

1. Acidify the filtrate with nitric acid and white silver chloride will form confirming the presence of chloride ions

Confirmatory test 2: (I)
1. Add concentrated ammonia solution to the residue. The AgBr will dissolve leaving a pale yellow AGI solid thus confirming the presence of iodide

Confirmatory test 3 (Br)
1.Acidify the ammoniated solution (confirm test2) with excess nitric acid (H(NO)3) a creamy AgBr will form thus detecting bromide ions