1. ## pH logs

I am lost...

The pH of a solution ranges from 0 to 14. An acid has a pH less than 7. Pure water is neutral and has a pH of 7. The pH of a solution is given by pH= -log(H^+) where H^+ represents the concentration of the hydrogen ions in the slution in moles per liter. Find the pH if the hydrogen ion concentration is 1x10^-4

2. Originally Posted by getnaphd
I am lost...

The pH of a solution ranges from 0 to 14. An acid has a pH less than 7. Pure water is neutral and has a pH of 7. The pH of a solution is given by pH= -log(H^+) where H^+ represents the concentration of the hydrogen ions in the slution in moles per liter. Find the pH if the hydrogen ion concentration is 1x10^-4
This question is pretty straight forward. What was your problem?

$pH = - \log \left( H^{+} \right)$

when $H^+ = 1 \times 10^{-4}$

$pH = - \log \left( 10^{-4} \right)$

$\Rightarrow pH = 4 \log 10$

$\Rightarrow \boxed { pH = 4 }$

3. So all I had to do was to input 1x10^-4 where (H+) is at?

My stump is this: How do I know, when given an equation, when to use log? We are working on so many different equations that I do not know what cue is for log, what cue is for exponential equations. etc,

4. Originally Posted by getnaphd
So all I had to do was to input 1x10^-4 where (H+) is at?

My stump is this: How do I know, when given an equation, when to use log? We are working on so many different equations that I do not know what cue is for log, what cue is for exponential equations. etc,
first of all, this is the definition of pH, it includes the logarithm.

otherwise, we know to use logs if we have an unknown as a power and we can't solve it regularly with the techniques for general exponential equations

5. ok thanks