I'm learning Acid and Base at school, and I have a confusion in that topic.

The $\mathrm{pH}$ scale is measure of the $\ce{[H+]}$ in a solution. So why is its formula $-\log(\ce{[H+]})$? I don't understand why the formula is not just $\ce{[H+]}$ since the definition of the $\mathrm{pH}$ is that it is the measure of $\ce{[H+]}$ in a solution.

I think that we should write it like the latter since it gives us a easier number to work with. Example: $\mathrm{pH}=2$ instead of $\pu{0.02 mol/L}$.


closed as unclear what you're asking by hBy2Py, Pritt Balagopal, aventurin, pentavalentcarbon, Tyberius Apr 16 '18 at 19:25

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  • $\begingroup$ Please refer to the link: khanacademy.org/science/chemistry/acids-and-bases-topic Hope it helps!! $\endgroup$ – AbhigyanC Apr 4 '18 at 7:10
  • $\begingroup$ @Mérébé you have completely changed your question and now my answer does not seem much relevant. I don't think that one is should reword his questions to such an extent that the answer(s) received no longer look relevant. Also, you are arguing as to why is this scale used for measure of H+ ions which is completely nonsense. Did you ask your teacher why do we use meter (or other units) as a measure of length and why not something that is, say 0.8 of a meter? So your question is not appropriate. $\endgroup$ – Piyush Maheshwari Apr 9 '18 at 4:14

1) Yes, the pH scale indicates the concentration of $\ce{H+ }$ ion in a solution. But you probably don't know that pH is defined as the negative log(base 10) of $\ce{ H+}$ ion concentration $$\mathrm{pH = -log_{10}[H+]}$$

So, as the $\ce{[H+]}$ increases, its logarithm increases and the pH decreases.

2) No, the concentration and strength of an acid are different. Strength is its property, like $\ce{HCl}$ is strong and $\ce{CH_3COOH}$ is weak. These are related to their extent of dissociation in the solvent. However concentration is basically the amount of acid dissolved in a certain amount of the solvent.

But if the molarity of the acid is same, the higher concentration of $\ce{H^+}$ ions then indicate more dissociation of the acid and hence is a stronger acid.

Don't confuse with the word strength used in titration to denote the concentration of solute in $\pu{g/L}$.

3) This part of your question is not quite clearly stated.

But this might help you: titration of weak acid against a strong or weak base involves the formation of buffer, about which you probably don't know right now.


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