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1. 2.82<br />
2. 8.30<br />
3. 0.00<br />
4. 3.485<br />
5. 12.000<br />
6. 4.00<br />
Sörenson also just mentions the reverse direction. That is, suppose you know the pH and you want to<br />
get to the hydrogen ion concentration ([H + ])?<br />
Here is the equation for that:<br />
[H + ] = 10¯pH<br />
That's right, ten to the minus pH gets you back to the [H + ] (called the hydrogen ion concentration).<br />
This is actually pretty easy to do with the calculator. Here's the sample problem: calculate the [H + ]<br />
from a pH of 2.45.<br />
This problem can be done very easily using your calculator. However, be warned about putting<br />
numbers into the calculator.<br />
So you enter 2nd, 10 x , (-), 2.45, enter.<br />
The answer, to the proper number of significant digits is: .00355.<br />
The pH of an acidic pond is 5. What is the hydrogen ion concentration (moles per liter)?<br />
The answer is:<br />
pH = -log (hydrogen ion concentration)<br />
The answer was .00001. Thus, 5 = -log (.00001).<br />
We'll take the formula that you started with (pH = -log([H+])) and work to the answer (solve for [H+]).<br />
pH = - log ([H+]) Given.<br />
pH = log ([H+] (-1) ) Since logarithms are like exponents, when you multiply a log by<br />
something, you can just move it to the inside of log as an exponent.<br />
10 pH = 10 log ([H+] (-1)) Take each side to tenth power.<br />
10 pH = [H+] (-1) Since "log" is just another notation for "log base 10", when you<br />
raise a log to the tenth power, the log cancels out.<br />
[H+] = 10 (-pH)<br />
Take the reciprocal of both sides.<br />
That is the general form. To answer the specific question,<br />
5 = - log ([H+])<br />
5 = log ([H+] (-1) )<br />
10 5 = [H+] (-1)<br />
10 (-5) = [H+]<br />
[H+]<br />
= .00001 mol/L