To determine which of the given compounds would form precipitates in an aqueous solution, we need to apply the solubility rules for common ionic compounds.
1. Soluble Compounds:
- Sodium compounds ([tex]$Na^+$[/tex]) are generally soluble.
- Compounds containing the nitrate ion ([tex]$NO_3^-$[/tex]), ammonium ion ([tex]$NH_4^+$[/tex]), and alkali metal cations (such as [tex]$Na^+$[/tex]) are typically soluble.
2. Analyze Each Compound:
- NaCN (Sodium Cyanide): Sodium compounds are generally soluble in water. Therefore, [tex]$NaCN$[/tex] is soluble and does not form a precipitate.
- Na_2CO_3 (Sodium Carbonate): Sodium compounds are soluble in water. Thus, [tex]$Na_2CO_3$[/tex] is soluble and does not form a precipitate.
- FeSO_4 (Iron(II) Sulfate): Most sulfate compounds are soluble, but there are exceptions like [tex]$BaSO_4$[/tex], [tex]$PbSO_4$[/tex], and [tex]$CaSO_4$[/tex]. However, [tex]$FeSO_4$[/tex] is soluble under normal conditions but can form a precipitate under certain conditions (e.g., in the presence of another chemical that reacts with it).
- ZnS (Zinc Sulfide): Sulfides ([tex]$S^{2-}$[/tex]) tend to be insoluble except for those of alkali metals and ammonium. Therefore, [tex]$ZnS$[/tex] is generally insoluble and forms a precipitate.
- Ca(OH)_2 (Calcium Hydroxide): Calcium hydroxide is partially soluble in water. It is soluble to some extent, but it is not highly soluble, and it can form a precipitate, especially when the concentration exceeds its solubility.
- CuCO_3 (Copper(II) Carbonate): Carbonates ([tex]$CO_3^{2-}$[/tex]) are generally insoluble except for those of alkali metals and ammonium. Therefore, [tex]$CuCO_3$[/tex] is insoluble and forms a precipitate.
3. Summary Based on Solubility Rules:
- Soluble (do not form precipitates): [tex]$NaCN$[/tex], [tex]$Na_2CO_3$[/tex].
- Insoluble (form precipitates): [tex]$FeSO_4$[/tex], [tex]$ZnS$[/tex], [tex]$Ca(OH)_2$[/tex], [tex]$CuCO_3$[/tex].
Based on the analysis above, the compounds that form precipitates in an aqueous solution are:
[tex]\[ FeSO_4, ZnS, Ca(OH)_2, CuCO_3 \][/tex]
