Paradox in pH calculation

[silverice]

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I can't wrap my head around this one. When the pH increases, the solution becomes more basic. But since pH =-log[H+], the proton concentration increases? Please help

 

[MedPR]

I can't wrap my head around this one. When the pH increases, the solution becomes more basic. But since pH =-log[H+], the proton concentration increases? Please help

It's easiest if you plug in numbers.

Let's start with a pH of 1. You know this is a very acidic solution. You also know that a solution with a pH of 1 has an [H+] of 10^-1. -log10^-1 = 1.

Now let's move up to a pH of 9. This is a pretty basic solution. pH of 9 = -log10^-9.

So, as you moved from an [H+] of 10^-1 to 10^-9, what happened? The pH went up, and therefore became more basic. Which number is bigger, 10^-1? Or 10^-9?

10^-1 = .1
10^-9 = .000000001

 

[ljc]

I can't wrap my head around this one. When the pH increases, the solution becomes more basic. But since pH =-log[H+], the proton concentration increases? Please help

The "pH" is the exponent in 10^(-pH), where 10^(-pH) is equal to the H+ concentration. So if pH is 1, you have 10^-1. pH of 5 = 10^-5. pH of 10 = 10^-10. As you can see, as pH goes up, H concentration goes down. You can't forget the negative.

If it helps, compare some SUPER low pH's like -1 and -2, plug them in:

10^-(-1) = 10^1 = 10 molar H+
10^-(-2) = 10^2 = 100 molar H+

So you should realize that at any pH above 0, you have an H+ concentration less than 1 molar. Any pH below zero, and your H+ concentration is above 1 molar. This is getting seriously acidic.

 

[silverice]

It's easiest if you plug in numbers.

Let's start with a pH of 1. You know this is a very acidic solution. You also know that a solution with a pH of 1 has an [H+] of 10^-1. -log10^-1 = 1.

Now let's move up to a pH of 9. This is a pretty basic solution. pH of 9 = -log10^-9.

So, as you moved from an [H+] of 10^-1 to 10^-9, what happened? The pH went up, and therefore became more basic. Which number is bigger, 10^-1? Or 10^-9?

10^-1 = .1
10^-9 = .000000001

Lol my brain short circuited. Your explanation is great thx!