Question

number of F- ions in 2.1g of AlF3 (use Na = 6

Answer 1

1 mole of AlF3 contain 1 mole of Al3+ ions and 3 moles F- ions


AlF3 = Al3+   + 3F-


Molar mass of AlF3 = 27 + 3x19 = 84g/mol


⇒ 84g of AlF3 has 3 moles of F-


2.1g of AlF3 will contain = (2.1x3)/84


                                       = 0.075 moles of F-



The Avogadro's number = 6.022 x 10^23



1 mole of F- has 6.022 x 10^23 ion


What about 0.075 moles = 0.075 x 6.022x10^23

                                        
                                        = 4.5165 x 10^22




2.1g of AlF3 contains 4.5165 x 10^22 F- ions