Gen chem destroyer # 91

[deleted738762]

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I understand the # of particles concept affecting colligative properties. I initially thought HCl would give the higher freezing point because of 2 ions, and HClO has 3 ions. Since HClO is a weak acid it only partially dissociates to give how many ions? How would I compare between the two?

 

[Don Kim]

HClO has 2 ions. If I remember correctly, all of the choices dissociate to form 2 ions. So to discriminate amongst them, you would have to use acidity. The more it dissociates, the more it will lower the freezing point. (more ions = lower freezing point). So the one with the least dissociation ability will lead to a higher freezing point. So HClO4, and HCl are crossed out right off the bat because they are strong acids and will lead to the lowest freezing points. Then you would have to count how many oxygens the rest of the choices have since they are all oxy-acids. More oxygen atoms = more acidic. So HClO3 vs HClO2 vs HClO. HClO is least acidic, will dissociate the least, and therefore contribute the least to freezing point depression.

 

[deleted738762]

I see what you are saying. I was thinking in terms HClO4 would yeild 5 ions because H+ Cl- 5 oxygens.

Thanks