Can anyone check my work/ me figure out how to do this?

determine the ph of the following solution.

a 4.5 x 10^-3 m hbr solution

my work:
all i did was -log(4.5x10^-3) and got 2.35 but i am not sure at all how to do this

In this chemical reaction, 325 grams of barium (ba) react completely. how many moles of lithium (li) are produced?

A5.000 g sample of niso4 h2o decomposed to give 2.755 g of anhydrous niso4. what is the formula of the hydrate? what is the full chemical name for the hydrate? what is the molar mass of the hydrate? niso4•_h2o what is the mass % of water in the hydrate?

How can the periodic table be used to predict the behavior of elements?