Masses and mole number - 1 | The Periodic Table and Atoms

  1. What is the molar mass M of CrBr3?
  2. Calculate number of moles n in 26.0 g of CrBr3?
  3. How many molecules N do you have in 26.0 g of CrBr3?
  4. How many atoms of bromine NBr do you have in 26.0 g of CrBr3?
  1. M = MCrBr3 = MCr + 3 x MBr = 51.9961 + 3 x 79.904 = 291.71 g.mol-1
     
  2. n = nCrBr3 = mCrBr3MCrBr3 = 26.0291.71 = 8.91 x 10-2 mol
     
  3. nCrBr3 NNA  ⇒ N = nCrBr3 x NA = 5.37 x 1022 molecules of CrBr3
     
  4. 3 atoms of Br in CrBr3:
    NBr = 3 x N = 1.61 x 1023 atoms of Br