Question

Calculate each of the following quantities. Remember Significant Figures.

(a) mass in kilograms of 4.3 x 10^20 molecules of NO2.

(b) moles of Cl atoms in 0.0460 g C2H4Cl2

(c) number of H- ions in 5,54 g SrH2

Answer 1

(a) mass in kilograms of 4.3 x 10^20 molecules of NO2.

mass = no of molecules / avagadros number*Mwt in kg

        = (4.3*10^20/(6.023*10^23))*46*10^-3
   
         = 3.3*10^-5 kg

(b) moles of Cl atoms in 0.0460 g C2H4Cl2

Mo of mole of Cl atoms = w of C2H4Cl2/mwt of C2H4Cl2 *2

                         = (0.046/98.96)*2

                         = 9.3*10^-4 mol

(c) number of H- ions in 5.54 g SrH2

number of H- ions = (w of SrH2/mwt of SrH2)*2* avagadros number(N0)

                    = (5.54/237.88)*2*6.023*10^23

                    = 2.8*10^22