To determine which of the given reactions does not occur, we need to analyze each reaction based on typical chemical reaction rules.
1. Reaction 1:
[tex]\[
HNO_3(aq) + NaOH(aq) \rightarrow
\][/tex]
This is an acid-base reaction where nitric acid (HNO_3) reacts with sodium hydroxide (NaOH) to form sodium nitrate (NaNO_3) and water (H_2O). This is a standard neutralization reaction, which occurs regularly:
[tex]\[
HNO_3(aq) + NaOH(aq) \rightarrow NaNO_3(aq) + H_2O(l)
\][/tex]
Therefore, this reaction occurs.
2. Reaction 2:
[tex]\[
Na_2SO_4(aq) + KOH(aq) \rightarrow
\][/tex]
Both sodium sulfate (Na_2SO_4) and potassium hydroxide (KOH) are strong electrolytes, dissociating completely in aqueous solution to give sodium ions (Na^+), sulfate ions (SO_4^{2-}), potassium ions (K^+), and hydroxide ions (OH^-). In this scenario, there are no ions that would react to form a precipitate, water, or gas. Hence, no reaction occurs:
[tex]\[
Na_2SO_4(aq) + KOH(aq) \rightarrow \text{no reaction}
\][/tex]
3. Reaction 3:
[tex]\[
K_2CO_3(aq) + Ca(NO_3)_2(aq) \rightarrow
\][/tex]
This reaction involves the mixing of potassium carbonate (K_2CO_3) and calcium nitrate (Ca(NO_3)_2) in aqueous solution. Calcium carbonate (CaCO_3) is insoluble in water and will precipitate out of solution:
[tex]\[
K_2CO_3(aq) + Ca(NO_3)_2(aq) \rightarrow CaCO_3(s) + 2KNO_3(aq)
\][/tex]
Therefore, this reaction occurs, forming a precipitate of calcium carbonate.
4. Reaction 4:
[tex]\[
Ni(s) + HCl(aq) \rightarrow
\][/tex]
Here, solid nickel (Ni) reacts with hydrochloric acid (HCl) to form nickel chloride (NiCl_2) and hydrogen gas (H_2). This is a standard reaction between a metal and an acid:
[tex]\[
Ni(s) + 2HCl(aq) \rightarrow NiCl_2(aq) + H_2(g)
\][/tex]
Therefore, this reaction occurs.
After analyzing all the reactions, we find that the second reaction,
[tex]\[
Na_2SO_4(aq)+ KOH(aq) \rightarrow \text{no reaction}
\][/tex]
does not proceed. Thus, the answer is:
The second reaction:
[tex]\[
Na_2SO_4(aq) + KOH(aq) \rightarrow \text{no reaction}
\][/tex]
### Conclusion:
In which of the following does no reaction occur?
Na_2SO_4(aq) + KOH(aq) \rightarrow
