Tests for Anions and Cations

Question 1

2 ways to test for Cations?

Answer 1

The flame test and sodium hydroxide solution

Question 2

How does the test for cations with sodium hydroxide solution work? And for which metals ions?

Answer 2

You take the metal ions and combine it with sodium hydroxide solution and if it forms a precipitate then you can identify the ion.

• A white precipate = aluminium (disappears with excess sodium hydroxide), calcium or magnesium
• A blue precipate = copper 2+
• A green precipate = iron 2+
• A brown precipate = iron 3+

Question 3

How does the flame test for Cations work? (method)

Answer 3

• A nichrome wire loop is dipped in concentrated hydrochloric acid and heated to clean
• re-dipped in hydrochloric acid and dipped in the metal compound
• hold loop in roaring blue Bundsen flame and the colour of the flame identifies which ion is present

(if more then one then some colours may mask others)

Question 4

What colour is the flame colour and the ion charge for:

• Lithium
• Sodium
• Potassium
• Calcium
• Copper

Answer 4

• Crimson, +1
• Yellow, +1
• Lilac, +1
• Orange red, +2
• Green, +2

Question 5

Test for (anion) carbonates?

Answer 5

add acid - carbon dioxide bubbles through limewater to form white cloudy

Question 6

Test for (anion) Halide?

Answer 6

add nitric acid - add silver nitrate - yellow precipitate = iodide -1, cream precipitate + bromide -1, white precipitate = chloride ions

Question 7

Test for (anion) Sulphates?

Answer 7

add HCl acid - add barium chloride - white precipitate formed