A solution has a hydroxide-ion concentration of 1.5 x 10-5M. a. What is the concentration of the hydrogen ions in this solution?

b. What is the pH of this solution?

c. Is the solution acidic, basic, or neutral?

To determine the number of helium atoms present in a given mass of helium, we first convert the mass into number of moles by dividing the atomic mass of helium which is 4 grams per mole. Then, we multiply the Avogadro's number which represents the number of units in one mole of any substance. This has the value of 6.022 x 10^23 units / mole. We do as follows:

537 kg He ( 1000 g / 1 kg ) ( 1 mol / 4 g ) ( 6.022 x 10^23 atom / mol ) = 8.08x10^28 atoms He