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Which of the following pairs of aqueous solutions will form a precipitate when mixed?

a) KNO₃ + HNO₃
b) NaNO₃ + HCl
c) MgCl₂ + Pb(NO₃)2
d) HCl + NaOH

1 Answer

5 votes

Final answer:

Out of the provided options, the combination of MgCl₂ and Pb(NO₃)₂ will form a precipitate. The resulting precipitate is lead(II) chloride (PbCl₂), which is insoluble in water.c) MgCl₂ + Pb(NO₃)2

Step-by-step explanation:

The question asked is about predicting whether a precipitate will form when two aqueous solutions are mixed. Specifically, we need to identify among the given pairs which will result in a precipitate. To determine this, we consider the solubility rules and check if any combination of cations and anions from the solutions form an insoluble compound.



Out of the given options, MgCl₂ + Pb(NO₃)₂ will form a precipitate when mixed, because lead(II) chloride (PbCl₂) is generally insoluble in water. The reaction is as follows:



MgCl₂ (aq) + Pb(NO₃)₂ (aq) → PbCl₂ (s) ↓ + Mg(NO₃)₂ (aq)

In this reaction, the ions Pb²⁺ and Cl⁻ combine to form the insoluble precipitate PbCl₂.

The other options, such as KNO₃ + HNO₃ and NaNO₃ + HCl, will not form a precipitate because all the products of their possible reactions are soluble in water. Additionally, HCl + NaOH will result in a neutralization reaction producing water and a soluble salt, so no precipitate will form there either.

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