# Halogen question

• Jun 5th 2011, 10:30 AM
igcsestudent
Halogen question
Hello
This question really confused me.... here it is

The equation shows the reaction between a halogen and the aqueous ions of another halogen.

X2 + 2Y^- = 2X^- + Y2

What could X2 be? and that could the colour of Y^- be?

A) chlorine / brown
B) chlorine / colourless
C) iodine / brown
D) iodine / colourless

the answer should be B, but how, I reckon if X displaced Y (it did right?), then it must be more reactive, hence it has a lighter colour (as we go down group 7 elements, they get darker in colour) that made me choose A as an answer, which is incorrect :-(

Any explanation would be very much appreciated http://www.chemistryhelpforum.com/ch...lies/smile.gif
Thanks
• Jun 5th 2011, 03:32 PM
e^(i*pi)
Quote:

Originally Posted by igcsestudent
Hello
This question really confused me.... here it is

The equation shows the reaction between a halogen and the aqueous ions of another halogen.

X2 + 2Y^- = 2X^- + Y2

A) chlorine / brown
B) chlorine / colourless
C) iodine / brown
D) iodine / colourless

Quote:

the answer should be B, but how, I reckon if X displaced Y (it did right?), then it must be more reactive, hence it has a lighter colour (as we go down group 7 elements, they get darker in colour) that made me choose A as an answer, which is incorrect :-(
Yes, X displaced Y. It means that X is a stronger oxidising agent (X has gained an electron so it has been reduced) than Y. The oxidising power of the halogens decreases as we go down group 7 (your colour analogy is correct although it's better to talk about oxidation and reduction).

The question is very badly written because since Cl can displace both Br and I then A and B could apply. Is there another part to the question that would help here?
• Jun 5th 2011, 08:30 PM
igcsestudent
thanks :-)