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An aqueous solution of an unknown solute is tested with litmus paper and found to be acidic. The solution is weakly conducting compared with a solution of NaCl of the same concentration. Part A Which of the following substances could the unknown be: KOH, NH3, HNO3, KClO2, H3PO3, CH3COCH3 (acetone)?

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laurahai

Answer:

H₃PO₃

Explanation:

KOH, NH₃, and KClO₂ are all basic so they must not be the unknown solute since the solution is acidic.

CH₃COCH₃ is a nonelectrolyte, which means it does not dissociate into ions when it dissolves in water. Acetone must not be the unknown since the solution is weakly conducting.

The two remaining candidate, HNO₃ and H₃PO₃ are both acids. The unknown solution does not conduct electricity as well as a solution of NaCl of the same concentration, which means that the unknown acid must not dissociate to the same extent as NaCl. Both NaCl and HNO₃ (a strong acid) dissociate 100%. Thus, the unknown solute must be H₃PO₃, which is known to be a weak acid (doesn't dissociate 100%).