Identifying Positive Ions

Question 1

What colours do sodium, potassium, calcium, and copper burn?

Answer 1

Sodium - orange. (Na+)
Potassium - lilac (K+)
Calcium - Brick-red (Ca2+)
Copper - blue-green - Cu2+

Question 2

What happens in precipate reactions?

Answer 2

Two solutions are reacted to form an insoluble solid compound - a precipitate. This happens when an alkali is added, such as a few drops of sodium hydroxide💧
The colour of the precipitate determines the ion in the compound.

Question 3

What precipitate does calcium form? Give the equation.

Answer 3

Ca2+ - White - Ca2+ + 2OH- -> Ca(OH)2 (s)

Question 4

What colour precipitate does copper(II) form?

Answer 4

Blue - Cu2+ + OH- -> Cu(OH)2

Question 5

What colour precipitates do iron(II) and iron(III) produce ?

Answer 5

Iron II - Sludgy green

Iron III - reddish brown.

Question 6

What happens when zinc (Zn2+ ) is added?

Answer 6

It forms a white precipitate at first but redissolves in excess sodium hydroxide to form a colourless solution.
Zn(OH)2 + OH2 -> Zn(OH)4 2-

Question 7

What is the purpose of an ionic equation?

Answer 7

To show the useful bits of reactions.

Question 8

How are flame tests used?

Answer 8

Compounds of some metals give characteristic colours when burned. These can identify ions in compounds.