Calculating Hydrogen Ion Concentration & PH by Yonderboy98

[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? Yonderboy98

 

[Borek]

[H⁺] = 10^-pH
pH = -log([H⁺])

That's all.