pH and pOH

[752779]

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Hi guys two things I'm confused about:
frist of all how do you calculate -log(.001) = 3 without using the calculator?

second, why is 3 is not the answer to, why do we have to use pH +pOH =14 and use 14-3 = 11?

 

[theonlytycrane]

Think of .001 as 1 * 10^-3. We know that [-OH] = .001 so we can't calculate the pH directly. But we can calculate the pOH which is equal to -log10([-OH]).

pOH = -log10(1 * 10 ^-3). log10 and 1 * 10 cancel -> pOH = - (-3) = 3.

Using pH + pOH = 14, we get pH = 11.

 

[752779]

Think of .001 as 1 * 10^-3. We know that [-OH] = .001 so we can't calculate the pH directly. But we can calculate the pOH which is equal to -log10([-OH]).

pOH = -log10(1 * 10 ^-3). log10 and 1 * 10 cancel -> pOH = - (-3) = 3.

Using pH + pOH = 14, we get pH = 11.

Please elaborate on " .001 as 1 * 10^-3"

 

[theonlytycrane]

It's scientific notation: .001 = 1 * 10^-3

 

[752779]

It's scientific notation: .001 = 1 * 10^-3

Thanks so much, i have not taken math in over 10 years, likewise with chemistry and physics... thanks, you're a life saver!