(FINAL) Chemistry Notebook 2016-17

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