logs and powers questions

Hi I'm new here. Unfortunately I dont have the time to make an official introduction, since I've been scratching my head over some assignments for the past three days and now I only have two hours left to do them.

I'd be really grateful if someone could help me with the following (listed from easiest to most difficult):

1) 2,2= -log(c), 2,2= pH value and c= molar concentration.

What is c in the above equation?

If the molar concentration in a liquid is multiplied by 100, the pH will be reduced by 2. Explain why (something to do with logarithmic rules).

2) f(x)= 225.027* x^ -0.5

- What is x when f(x) is 10.000?

- By which percent-rate will x increase if y decreases with 5 %

Now they're not that difficult, but I think the reason I can't seem to solve them is because I'm not sure if the reverse function of a negative power in this case x^-0.5, is 1/sqr(-0.5). When I try to isolate x, it certainly doesn't work to use 1/sqr(-0.5) in the process. Nor does it help when I try to use it to calculate the percent rate increase in x, for which the formula is: 1+ry= (1+rx)^a, rx= percent rate for x, ry= percent rate for y.

Please help ASAP!

Thank you in advance.