Final answer:
Neither CSI(aq) + NaOH(aq) nor HCl(aq) + Ca(OH)2 will result in a precipitation reaction directly. For a precipitation reaction to take place, the products of the reactant pair should form an insoluble compound.
Step-by-step explanation:
The student is asking which pair of reactants will result in a precipitation reaction when mixed. The two given options are CSI(aq) + NaOH(aq) and HCl(aq) + Ca(OH)2. When mixed, NaOH (a strong base) and HCl (a strong acid) will undergo a neutralization reaction to produce water and an aqueous solution of NaCl, as shown in the equation HCl(aq) + NaOH(aq) → H2O + NaCl(aq). There is no precipitation reaction in this case as NaCl is highly soluble in water.
However, in the case of Ca(OH)2 mixing with HCl, the reaction forms a soluble solution of CaCl2 and water, without any precipitate. But based on general solubility rules, if one were to mix HCl with a sulfate or carbonate, a precipitate might form. This is because sulfates and carbonates can form insoluble compounds with certain cations like Ba2+ or Ca2+, respectively. Hence, neither of the provided reactant pairs will directly result in a precipitation reaction. To predict a precipitation reaction, we should look for products of the reactant pairs that form an insoluble compound.