The molecular formula of a compound used for bleaching hair is h2o2. calculate (a) mass of this compound that would contain 2.5 moles (b) no of moles of this compound that would exactly weight 30 get.

The RFM (Relative Formula Mass) of the substance H2O2 is:
H2 = 1 x 2
= 2
O2 = 16 x 2
= 32

32 + 2 = 34

USE THIS FORMULA:

*Mass = Moles x RFM*

Part A:

Mass = Moles x RFM
     = 2.5 x 34
     = 85 g

(You can always rearrange this formula to suit the question)

Part B:

Moles = Mass/RFM
          = 30/34
           =0.8823529 (Need a calculator haha)
           =0.88 (Rounded up to 2 decimal places)

I hope I helped, ask if you have any questions.