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# PH=-log(H) PH is 7.2 need help

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what is 7.2 divided by a negative log

Guest Mar 15, 2017
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#1
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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
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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 (H3O+).  A pH of 7.2 says that your solution is 10^(-7.2) molar H3O+.  A pH of 13.1 would mean your solution is 10^(-13.1) molar H3O+.

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 log10(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 H3O+, 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
#3
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My teacher confirmed the answer was 6.3*10^-8 Thanks

Guest Mar 15, 2017

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