Question

final exam 2025
solutions

1. a substance dissolves in water to form a conducting solution that does not affect litmus. this evidence is explained as a/an

neutral molecular substance that has dissociated in solution
base substance that has dissociated in solution
neutral ionic substance that has dissociated in solution
acid substance that has dissociated in solution
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Explanation:

• For neutral molecular substance: Molecular substances (e.g., sugar, \(C_{12}H_{22}O_{11}\)) do not dissociate into ions in solution. Since they lack free - moving ions, their solutions do not conduct electricity. So this option is incorrect.
• For base substance: Bases (e.g., \(NaOH\)) dissociate in water to produce \(OH^-\) ions (\(NaOH=Na^{+}+OH^{-}\)). A solution with a significant amount of \(OH^-\) ions will turn red litmus paper blue. Since the solution in question does not affect litmus, this option is incorrect.
• For neutral ionic substance: Ionic substances (e.g., \(NaCl\)) dissociate into ions in solution (\(NaCl = Na^{+}+Cl^{-}\)). The presence of free - moving ions (\(Na^{+}\) and \(Cl^{-}\)) allows the solution to conduct electricity. Also, a neutral ionic substance (like \(NaCl\)) does not produce an excess of \(H^{+}\) or \(OH^-\) ions that would affect litmus paper.
• For acid substance: Acids (e.g., \(HCl\)) dissociate in water to produce \(H^{+}\) ions (\(HCl = H^{+}+Cl^{-}\)). A solution with a significant amount of \(H^{+}\) ions will turn blue litmus paper red. Since the solution in question does not affect litmus, this option is incorrect.

Answer:

neutral ionic substance that has dissociated in solution