Question

how many Ba^2+ ions and how many AsO4^3- ions are present in a 10.0g sample of Ba3(AsO4)3-

Answer 1

mass of Ba3(ASO4)2   = 10g

gram molar mass of Ba3(ASO4)2    = 689.8194g/mole

no of moles of Ba3(ASO4)2    = mass of Ba3(ASO4)2 /gram molar mass of Ba3(ASO4)2

                                                = 10/689.8194   = 0.0145moles

Ba3(ASO4)2 (aq) ---------------> 3Ba^2+ (aq) + 2AsO4^3- (aq)

0.0145 moles                              3*0.0145 moles   2*0.0145 moles

no of moles of Ba^2+ ions = 3*0.0145 moles   = 0.0435 moles

no of Ba^2+ ions               = 0.0435*6.023*10^23   = 2.62*10^22 Ba^2+ ions

no of AsO4^3-            = 2*0.0145 moles   =   0.029 moles of AsO4^3-

no of AsO4^3- ions   = no of moles * 6.023*10^23

                                  = 0.029*6.023*10^23   = 1.75*10^22 AsO4^3- ions

Please in this proble Ba3(AsO4)3   formula . But actual formula is Ba3(ASsO4)2