#1**0 **

7.2 = - log (H).....multiply both sides by -1

-7.2 = log (H) and we can write

10^{-7.2} = H ≈ 6.3 x 10^{-8}

CPhill
Mar 15, 2017

#2**0 **

log, or logarithm, is an operation. It is in the same category as a multiplication or addition. Logistically, the question you asked doesn't really make sense as it would be in the same line as asking, "what is 7.2 divided by a multiplication sign?"

What we're looking for here is the concentration of protons (H^{+}) or more accurately hydronium ions (H_{3}O^{+}). A pH of **7.2** says that your solution is 10^(-**7.2**) molar H_{3}O^{+}. A pH of **13.1** would mean your solution is 10^(-**13.1**) molar H_{3}O^{+}.

Logarithms are operators saying "to what number must your base be raised to achieve a number?" For instance, another way of writing 10^x = 1000 is writing log_{10}(1000) = x, where x = 3. Exponentials and logarithms are like additiion/subtraction or multiplication/division. They are inverse operators.

So, that means in order to know the concentration of H^{+} or H_{3}O^{+}, we can multiply both sides by negative one and exponentiate 10^(-7.2) to learn the molarity.

If anything I said was unclear, please let me know.

Cheers.

Guest Mar 15, 2017