Harvey mixes two liquids. which observation of the new mixture most likely indicates a precipitate is forming?
a) a cloudy appearance
b) a bubble formation
c) a change in color
d) a change in odor

the answer is choice A

Answer is: A) a cloudy appearance.

B) Formation of bubble means gas is formed.

C) and D) means new substance is formed, but not necessarily precipitate.

For example, balanced chemical reaction: Ca²⁺(aq) + SO₄²⁻(aq) → CaSO₄(s) .

Calcium sulfate (CaSO₄) has very low solubility in water (Ksp for calcium sulfate is 2.36·10⁻⁴).

Calcium cation (Ca²⁺) will form a precipitate with other anions also:

1) with oxalate anion (C₂O₄²⁻) will form CaC₂O₄(s), calcium oxalate.

2) with phosphate anion (PO₄³⁻) will form Ca₃(PO₄)₂(s), calcium phosphate.

3) with hydroxide anion (OH⁻) will form Ca(OH)₂(s), calcium hydroxide.

4) with carbonate (CO₃²⁻) will form CaCO₃(s), calcium carbonate.