How to determine the strongest oxyacid of chlorine?


> 
> Which is the strongest acid here?
> 
> 
> * $\ce{HClO}$
> * $\ce{HClO2}$
> * $\ce{HClO3}$
> * $\ce{HClO4}$
> 
> 
> 


I found [this question](https://chemistry.stackexchange.com/questions/22056/which-of-the-following-is-the-strongest-base), didn't really get the first answer, but [this one](https://chemistry.stackexchange.com/a/22060/16632) in particular seemed interesting.


Apparently, you calculate a $\mathrm{p}K\_\mathrm{a}$ for each substance.


According to [this website](http://www.columbia.edu/%7Ecrg2133/Files/CambridgeIA/Chemistry/AcidityBasicitykPa.pdf).


$$\mathrm{p}K\_\mathrm{a} = -\log\_{10}K\_\mathrm{a}$$


I need to find out $K\_\mathrm{a}$ then. From what I understand $K\_\mathrm{a}$ is obtained from dividing the concentrations of products by the concentrations of reagents. However, how am I supposed to do so if I am not given any equilibrium reactions?




In such questions you're supposed to know certain rules of acidity. You can find some of them on [this page](http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch11/factors.php). In your case fourth rule, concerning oxoacids, is relevant and as you can see there, it's described on this very case. More precise formulation is so called Pauling's Rule described [here](http://chemistrytextbookcrawl.blogspot.com/2013/02/paulings-rules.html). In general the more oxo groups connected to central atom, the more acidic compound.


Related: [How are Pauling's rules applied to Nitric acid?](https://chemistry.stackexchange.com/q/29131)


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