mole and mass conversion

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Explanation: 

Q       Calculate the mass in grams of ,

                        (i)7.75 moles of Al2O3

                        Molar mass of Al2O3 = 27x2 + 16x 3 = 54 + 48 = 102 g/ mole

                        Mass in grams = Mole X molar mass = 7.75 X 102 = 790.5 grams

 

                        (ii) 15 moles of H2SO4

                        Molecular weight of H2SO4= 2x1+ 1x 32 + 4 x 16 = 2+32+64

                        Mass in grams = Mole X molar mass = 15 X 98 = 1470 g

                        (iii)1.0 x 1025  molecules of H2O

                        Mole = number of particles    = 1.0 X 1025    = 0.166 X 1025-23= 0.166x102

                                     Avogadro,s number      6.02 x 1023

                        Or 16.6 moles of water

                        Mass in grams= Mole x M.wt= 16.6 x 18 =298.8 g

 

Q                   How many moles are present in each of the following samples?

(a)  30 grams of MgS

Molar mass of MgS = 24 + 32 = 56g/mol

Mole = mass in grams  = 30  0.5357 moles

       Molar mass           56           

(b)  75 g of ca

 

Moles = mass in grams  = 75  =  1.875

                  Molar mass        40

 

(c)  8.85 kg of CO2

Molar mass of CO2 = 44g/mol

Mass of CO2 in grams = 8.85 X 1000 = 8850  grams

Moles = mass in grams   = 8850  = 201.14 moles

                  Molar mass           44

(d)  40 dm3 of O2 at stp

Molar volume = 22.414 dm3 at stp

Mole = volume in dm3   =  40 dm3  = 1.785 moles

            Molar volume          22.414

(e)  7.5 X 1020 molecules of C6H6

                                    Moles = number of molecules   = 7.5 X 1020   = 1.246 x 10-3

                                                Avogadro,s number             6.02 X 1023

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