Video: Identifying the Pair of Weak Electrolytes in a Set of Pairs of Chemicals

Which of the following are weak electrolytes in aqueous solutions? [A] NO and NO₂ [B] ¹⁴N and ¹⁵N [C] CH₃CO₂K and CH₃CO₂Na [D] CH₃CH₂OCH₃ and CH₃CH₂CH₂OH [E] S₂ and S₈


Video Transcript

Which of the following are weak electrolytes in aqueous solutions? A) NO and NO₂, B) ¹⁴N and ¹⁵N, C) CH₃CO₂K and CH₃CO₂Na, D) CH₃CH₂OCH₃ and CH₃CH₂CH₂OH, or E) S₂ and S₈.

Weak electrolytes are substances that do not completely disassociate or break up into ions when introduced into a liquid. This means that when you add a substance that’s a weak electrolyte to a liquid like water to form an aqueous solution. Some of the molecules will dissociate into ions. But some of them will remain intact. We can compare this to a strong electrolyte like hydrochloric acid, for example, which would completely dissociate into ions when introduced to a liquid. Examples of strong electrolytes include strong acids and bases as well as salts. And examples of weak electrolytes include weak acids and bases.

Now that we know about weak electrolytes, let’s take a look at our answer choices. Our first answer choice is nitrogen oxide and nitrogen dioxide. Nitrogen oxide does not react readily with water. And when nitrogen dioxide reacts with water, it forms a mixture of HNO₃ and HNO₂. HNO₃ is nitric acid, which is a strong acid. So it would behave as a strong electrolyte, not a weak electrolyte. HNO₂ is nitrous acid, which is a weak acid. So it would be a weak electrolyte. So nitrogen oxide has no reaction with water. So it can’t be a weak electrolyte. And nitrogen dioxide reacts with water to form a mixture of a strong electrolyte and a weak electrolyte. So this answer choice is probably not the one we’re looking for. But let’s save it for now.

Answer choice B is nitrogen-14 and nitrogen-15, which are both isotopes of nitrogen. Isotopes are simply atoms of the same element that have a different number of neutrons. Since these are just atoms of nitrogen, they won’t dissociate into ions when they’re introduced to water. So answer choice B is not correct.

Our next answer choice is potassium acetate and sodium acetate. In both potassium acetate and sodium acetate, there’s an ionic bond between the potassium or the sodium and the acetate. Since there’s an ionic bond, this seems like a good candidate for something that would break up into ions in water. Acetate is a weak base since it’s the conjugate base of acetic acid, which is a weak acid. Since acetate is a weak base and weak bases are weak electrolytes, answer choice C seems like the answer choice that we’re looking for. But let’s check out the other remaining answer choices.

Answer choice D are two organic compounds called methyl ethyl ether and propanol. Neither of these compounds have any reaction with water. So they can’t be weak electrolytes.

Our final answer choice is S₂ and S₈, which are both different forms of the element sulphur. Neither of these have any reaction with water. So again, we wouldn’t expect them to be weak electrolytes.

Of our answer choices, answer choice C, potassium acetate and sodium acetate are definitely weak electrolytes. So this is the answer that we’re looking for.

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