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The table below lists some acids and bases.

\begin{tabular}{|l|l|l|l|}
\hline Strong acids & Weak acids & Weak bases & Strong bases \\
\hline HBr & [tex]$CH _3 COOH$[/tex] & [tex]$NH _3$[/tex] & NaOH \\
\hline [tex]$HNO _3$[/tex] & HCOOH & [tex]$NH _4 OH$[/tex] & KOH \\
\hline [tex]$H _2 SO _4$[/tex] & & & [tex]$Ca ( OH )_2$[/tex] \\
\hline \hline
\end{tabular}

Which reaction yields a salt that has a [tex]$pH \ \textless \ 7$[/tex]?

A. [tex]$KOH + HBr$[/tex]
B. [tex]$HCOOH + KOH$[/tex]
C. [tex]$Ca ( OH )_2 + H _2 SO _4$[/tex]
D. [tex]$NH _3 + HNO _3$[/tex]



Answer :

GinnyAnswer
To determine which reaction yields a salt with a pH less than 7, we need to analyze the nature of the reactants involved. Specifically, we have to consider whether each reactant is a strong or weak acid or base, and then determine the resulting pH of the salt produced:

1. KOH + HBr:
- KOH is a strong base.
- HBr is a strong acid.
- A reaction between a strong base and a strong acid yields a neutral salt (pH = 7).

2. HCOOH + KOH:
- HCOOH (formic acid) is a weak acid.
- KOH is a strong base.
- A reaction between a weak acid and a strong base produces a salt with pH greater than 7 (basic).

3. Ca(OH)2 + H2SO4:
- Ca(OH)2 (calcium hydroxide) is a strong base.
- H2SO4 (sulfuric acid) is a strong acid.
- A reaction between a strong base and a strong acid yields a neutral salt (pH = 7).

4. NH3 + HNO3:
- NH3 (ammonia) is a weak base.
- HNO3 (nitric acid) is a strong acid.
- A reaction between a weak base and a strong acid produces a salt with pH less than 7 (acidic).

Thus, the reaction that yields a salt with a pH less than 7 is:

NH3 + HNO3

So, the correct answer is: [tex]\( NH_3 + HNO_3 \)[/tex].

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