[T]

Hello,

The question is:

Elements Q and R form both oxides and chlorides. Under laboratory conditions, QCl2 is a cherry- red liquid while RCl2 is a white solid. Which one of the following statements is most likely to describe the oxides of these elements?

A) Q forms a basic oxide QO while R forms an acidic oxide RO.
B) Q forms a basic oxide QO2 while R forms two acidic oxides RO and RO2.
C) Q forms two acidic oxides QO2 and QO3 while R forms a basic oxide RO.
D) Q forms an acidic oxide QO while R forms a basic oxide RO.
E) Q forms two acidic oxides QO and QO2 while R forms a basic oxide RO2.

From the information given Q would be a non-metal as it forms a liquid with chlorine and R is a metal as it forms a solid with chlorine. The charge of Q and R is +2. Q will produce a non-metal oxide and R will produce a metal oxide. As I gather metal oxides form a basic oxide while non-metal oxide will produce a acidic oxide. So therefore my answer is D. However, the answer is C. I know that non-metals can have different oxidation numbers but I don't understand why. Could someone explain this? I can't find anything good on the internet.

Thanks

[Borek]

Nothing wrong with your logic leading to D, but I suppose they expect you to know the identity of the red liquid.

[T]

I see, it was on a past olympiad exam. Don't know how they expected us to know it then.

Thanks Borek

[Dan]

It sounds like there is some context missing from the question. It sounds like one part of a multipart question, the sort that involve a large chemical scheme with many unknowns, which provides more clues as to what Q and R might be.

Your logic that oxides of Q will be acidic because Q must me a non-metal is fine, but this only narrows it down to C, D, or E.

Without more information, answering this question relies on you recognizing what the cherry red QCl₂ is. If you don't know, you can probably have a good guess: If Q is a non-metal and forms QCl₂ (i.e. oxidation state of Q is +2), then which group of the periodic table is it likely to come from?

[T]

If Q is a non-metal and forms QCl₂ (i.e. oxidation state of Q is +2), then which group of the periodic table is it likely to come from?

I would guess group 16, this is because they need to form 2 bonds to get a full shell, and the chlorine will pull the electron away from them so they will have oxidation state of +2.

I googled group 16 dichlorides, and sulfur dichloride is a red liquid. So Q is sulfur. However, without googling, I would not have been able to tell which group 16 non-metal is Q, could someone give me a hint to be able to find Q without googling.

Thanks