Understanding pH: Solving Confusing Problems with Strong Acids and Bases

[nautica]

I know this is simple, but I am a bit confused

1) find the pH of 12.1 M HCl - the negative log gives me -1.8. What am I doing wrong

2) 50% NaOH (roughly 15 M) - I am not sure how to do this one either

thanks
nautica

 

[Pyrrhus]

Well, HCL is a strong acid, so it dissociates completely in ions. Of course aqueous solution.

$$HCl + H_{2}O \rightarrow H_{3}O^{+} + Cl^{-}$$

$$H_{3}O^+ \approx H^+$$

I get pH -log(12.1) = -1.08, are you sure is 12.1 M?

Well, i barely remember my freshman chemistry, wait for more help.

 

[gravenewworld]

What's wrong? You are allowed to have pH values that are negative and that are also above 14.

 

[chem_tr]

If the concentration is beyond the limits of Ostwald's dilution principle, then some weird results like this is likely to occur, as gravenenewworld said in a different way. Nautica, your findings of negative pH and pOH values are normal, as these are very concentrated and are not obeying the principle.

 

[nautica]

Thanks, I was aware that pH could be negative, but I did not realize they would get that negative. I was thinking around zero and negative 0.5 or so.

thanks
Nautica