Reaction (18.10), described in the Integrative Example, is called a carbonate transposition. In such a reaction, anions of a slightly soluble compound (for example, hydroxides and sulfates) are obtained in a sufficient concentration in aqueous solution that they can be identified by qualitative analysis tests. Suppose that 3 M Na₂CO₃ is used and that an anion concentration of 0.050 M is sufficient for its detection. Predict whether carbonate transposition will be effective for detecting 

(a) SO₄^2- from BaSO₄(s); 

(b) Cl^- from AgCl(s); 

(c) F^- from MgF₂(s).

Integrative Example

Lime (quicklime), CaO, is obtained from the high-temperature decomposition of limestone (CaCO₃). Quicklime is the cheapest source of basic substances, but it is water insoluble. It does react with water, however, producing Ca(OH)₂ (slaked lime). Unfortunately, Ca(OH)₂(s) has limited solubility in water.

When Ca(OH)₂(s) reacts with a soluble carbonate, such as Na₂CO₃(aq), however, a greater amount of Ca(OH)₂(s) dissolves and the solution produced has a much higher pH. Equilibrium is displaced to the right in reaction (18.10) because CaCO₃ is much less soluble than Ca(OH)₂.

Transcribed Image Text:

Ca(OH)2(s) Ca²+ (aq) + 2 OH¯(aq) Ksp = 5.5 × 10-6