Which of the following is a weak electrolyte in aqueous solution? A) HF B) NaF C) HCl D) KCl Could someone please explain why the answer is HF, thank you so much!

1 Answer
Jan 21, 2018

See the explanation below...


First, recognize both NaF and KCl as compounds consisting of a metal and a nonmetal. This means they are ionic solids (salts) and they are composed of ions in the solid phase. When dissolved, all these ions are freed from the crystal pattern they had been locked into in that solid. The large quantity of ions the results make both of them strong electrolytes.

Next, HCl. This is a strong acid. Although it is a molecular compound (not made of ions), when dissolved in water, the bonds in 100 % of the molecules come apart in such a manner that ions of #H^+# and #Cl^-# result. Therefore, it is also a strong electrolyte.

HF, on the other hand will ionize in water (becoming #H^+# and #F^-#), but only to a small extent, because it is a weak acid. Therefore, the solution consists of few ions, and conducts very slightly. HF is the weak electrolyte.

I have not attempted here to explain why HCl is strong while HF is weak. If that is part of the answer you are looking for, repost that question, and I'm sure someone will respond with an answer.