Kids took 5 ml samples of tap and bottled water and poured them in test tubes. They added three drops of a 10 % BaCl₂ aqueous dissolution to each sample and some white turbidity was noticed, more visible in tap water. When heated to boiling for around one minute at the flame of a Bunsen burner the white solid was observed at the bottom of the test tubes, even more noticeable in tap water. The white precipitate could be either barium sulfate or carbonate. While barium carbonate is soluble in 0,1 M HCl (aq) sulfate is not. Adding 10 drops of hydrochloric acid dissolution to each sample white solid and turbidity disappeared, so we concluded there were no sulfates in our water samples.

This test is based on the lower solubility in water of the barium carbonate and sulfate than that of chloride. Chemical reactions can be written as:

 

 

 

Carbonate and bicarbonate are in equillibrium in aqueous dissolutions. At pH = 7 the equilibrium is largely shifted in favor of bicarbonate.