ph calculations

[Yonderboy98]

I know what the formal definition of ph is, and I am comfortable with logarithms, anti-logs, and the laws of exponents. Still, I get confused doing actual calculations and would greatly appreciate your input on the following:
Suppose something has a ph of 3.5-How do you calculate the hydrogen ion concentration?
Suppose something has a ph of 7.2- How do you calculate the hysdrogen ion concentration?
Suppose that something has a hydrogen ion concentration of 2.8 times ten to the minus 15-How do you calculate its ph?
Suppose that something has a hydrogen ion concentration of 3.6 times ten to the minus 9-How do you calculate its ph?:surprised Yonderboy98

[Borek]

[H+] = 10-pH
pH = -log([H+])

That's all.

Borek
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General Chemistry Software (http://www.chembuddy.com)
www.pH-meter.info (http://www.ph-meter.info)