Acidified misconception

pH is defined as :

$pH=-\log([H^+])$

Now for very highly concentrated acid $([H^+]>1M)$ $pH=-log([H^+])<0$

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Note:

• It is a very common misconception about pH that it lies between $0$ and $14$ , it don't have any defined limits (as you can see from the definition itself). For some highly concentrated acids $pH<0$ .

• $[H^+]$ denotes the concentration of $H^+$ ions