Question 767683
logarithm is defined as
y = log to base b of x
if b is not stated then we are to assume base 10, in our case we have
8.1 = -log[c}
(-1) * (-1) = +, implies that 8.1 = -(-8.1) = 8.1
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from definition of logarithm
if y = log(x) then
x = b^y
therefore
c = 10^(-1)8.1
c = 7.9 X 10^-9 or 7.9 X e^-9
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check value
pH = -log(7.9 X 10^-9)
pH = -(-8.1)
pH = 8.1