On the pH scale, each unit change in pH represents a tenfold increase in acidity or alkalinity.

Question

Trying to solve similar type equation to this.

On the pH scale, each unit change in pH represents a tenfold increase in acidity or alkalinity. According to the diagram, vinegar is how many times as acidic as pure water?

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Could you answer this if instead of $3.2$ it were $6$? $5$? $4$? — Jonas Meyer, May 19 '13 at 19:58

score 1 · Answer 1 · answered May 19 '13 at 20:19

1

Hint Each unit decrease in pH represents a tenfold increase in acidity. In other words the increase in acidity was:

$$10^{n-(n-1)}=10^{1}$$

Use some algebra to generalize this.

answered May 19 '13 at 20:19

rurouniwallace

6,266

score 1 · Answer 2 · answered May 19 '13 at 23:01

1

Simply put isn't it 10^(3.8) ?

answered May 19 '13 at 23:01

Stephen Nand-Lal

569

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Welcome to MSE! I think it would help if you could add more details as to why this is true and how you arrived at it. Just some friendly advice. Regards – Amzoti May 19 '13 at 23:35
I think that explaining where that $3.8$ came from would be sufficient in this case. New member or not :-) But also, Stephen, this is a serious concern among many members. Do try to make your answer useful to the original poster. The point in answering this kind of questions is usually not to show that you know how to solve it yourself, but to explain the thought process to the asker. I think you will quickly learn this kind of best practices! Welcome to MSE in spite of this mild criticism! – Jyrki Lahtonen May 20 '13 at 09:29
how di dyou get 3.8? – user73122 May 21 '13 at 15:56

score 0 · Answer 3 · answered Feb 20 '17 at 23:01

Correct. It would have 10^3.8 times more acidity. Or put another way, vinegar has 10^3.8 times as many free [H+] and [H3O+] ions in solution as pure water.

To get technical, it is actually -log(activity H+), where H+ per molecule of H20 is about 10^-7. Thus more strongly acidic solutions have a higher activity 10^-3.2 mol H+/mol H2O.

wendy.krieger · Answer 4 · 2013-05-20T09:18:52.123

pH represents the negative logrithm of H+ ions. So the number ic $ln(c)/ln(0.1)$.

Acidity could then be written as $7-pH$ as a logrithm, or $10^{7-pH}$ as a number.

If you are using a different number system, the units are gram-moles per litre, and the adjustment to water is to add 3 to the pH, eg $pH_{12}=(pH_{10}+3)/log_{10}(12)$. This would reference it to a 'water-mole', eg gram-mole / cc, where 'water' = 'gram/cc'.

On the pH scale, each unit change in pH represents a tenfold increase in acidity or alkalinity.

4 Answers4