Which combination will produce a precipitate? a) NH4OH(aq) and HCl(aq) b) AgNO3(aq) and CaCl2(aq) c) NaOH(aq) and HCl(aq) d) NaCl(aq) and H2SO4(aq)
The Correct Answer and Explanation is :
Correct Answer: b) AgNO₃(aq) and CaCl₂(aq)
Explanation:
When solutions of ionic compounds are mixed, a precipitate forms if an insoluble product results from a double displacement reaction. Let’s analyze each combination:
a) NH₄OH(aq) and HCl(aq):
This is an acid-base reaction where NH₄OH (ammonium hydroxide) reacts with HCl (hydrochloric acid) to form NH₄Cl (ammonium chloride, a soluble salt) and water:
[
\text{NH₄OH} + \text{HCl} \rightarrow \text{NH₄Cl} + \text{H₂O}
]
No precipitate forms, as all products are soluble.
b) AgNO₃(aq) and CaCl₂(aq):
This reaction involves the mixing of AgNO₃ (silver nitrate) and CaCl₂ (calcium chloride). A double displacement reaction occurs:
[
\text{2AgNO₃} + \text{CaCl₂} \rightarrow \text{2AgCl} \downarrow + \text{Ca(NO₃)₂}
]
AgCl (silver chloride) is insoluble and forms a white precipitate, while Ca(NO₃)₂ (calcium nitrate) remains in solution. Hence, a precipitate forms in this reaction.
c) NaOH(aq) and HCl(aq):
This is a neutralization reaction between a strong acid (HCl) and a strong base (NaOH) to form water and NaCl (sodium chloride, a soluble salt):
[
\text{NaOH} + \text{HCl} \rightarrow \text{NaCl} + \text{H₂O}
]
No precipitate forms, as all products are soluble.
d) NaCl(aq) and H₂SO₄(aq):
When NaCl (sodium chloride) reacts with H₂SO₄ (sulfuric acid), no precipitate forms. Instead, this reaction produces gaseous HCl (hydrogen chloride) under certain conditions:
[
\text{NaCl} + \text{H₂SO₄} \rightarrow \text{HCl(g)} + \text{NaHSO₄}
]
This is not a precipitation reaction.
Conclusion:
Only b) AgNO₃ and CaCl₂ produces a precipitate, AgCl, based on the solubility rules for ionic compounds.