Is there a log button? if not is there another way

Calculate the log (base 10) of the number, then divide the result by the log (base 10) of the base.
For example, to calculate the base-3 log of 9, calculate the log of 9 to get 0.954 . Divide that by the log of 3 (about 0.477) to get 2.0 .
Since 9 is 3 squared, the log base 3 of 9 is 2, as we just calculated.

The antilog functions are the 2nd functions of the log functions on the top row of the keyboard.

To calculate the natural antilog of 3.1, press 3 . 1 2nd LN
To calculate the common antilog of 3.1, press 3 . 1 2nd LOG

The LOG command on a TI-83 calculator is located just to the left of the 7 button. In other words, starting from the bottom left key of the calculator (the ON button), as you move up, you will see the STO-> button, then the LN button, and then the LOG button.
To use the LOG command, you will press the LOG button. log( will appear. You will then enter the value of which you wish to take the logarithm and add the closing parenthesis ) and press ENTER.

You can calculate the log of x to any base b by calculating log(x)/log(b) or ln(x)/ln(b). So, to calculate log 5 to the base 3, press
LOG 5 ) / LOG 3 ENTER
or
LN 5 ) / LN 3 ENTER

For the inverse natural log, press 2nd LN. For the inverse common log, press 2nd LOG.

For example, to calculate the inverse natural log of 2, press 2nd LN 2 ENTER and you'll get about 7.389 .

The natural log is the LN key, located just to the left of the 7 key.

To calculate the common log, use the relationship log(x) = ln(x)/ln(10).

To calculate the natural log of 3, press 3 LN

To calculate the common log of 3, press 3 LN / 1 0 LN =

On the very top row, the 4th button over says "log." You would key that in and then key in what you are taking the log of. Something to note, calculators can only key in a log of base 10.

My way is really slow b/c I don't know the right way, but I always clear my memory (SHIFT, CLR on the 9 button), then type it in as an equation, for example: log(X)=-15.3, then press SHIFT, and SOLVE (on the calc button), then press =. It freezes up the calculator for several seconds though =/

The problem is simple. You're trying to get an [H+] concentration which is obviously going to have a value of some number times ten raised to a negative power. Therefore, you have to insert the negative value of the pH into the 10^(x). When you insert said negative number you will come out with the right answer.
i.e.
The pH of a sample of human blood was calculated to be 7.41. What is the [H+] concentration of the blood?
10^(-7.41) = [H+]
[H+] = 3.9 E-8  
(the answer should only have two sig. figs because the pH has two digits after the decimal.

yes