Question

With work shown.

7. Calculate the number of sodium atoms in 4.66 moles of sodium.

8. What is the molar mass fo a substance if 0.6502 moles of the substance has a mass of 19.27 grams?

9. How many grams are present in 7.5 moles of Cu (NO3)2?

10. How many atoms are present in a Mg sample with a mass of 14.6 grams?

11. How many atoms of H are present in 37.6 g of NH3?

12. How many atoms are present in 0.45 moles of P4O10?

13. The empirical formula of a compound is CH2O and it's formula weight is 120.12 amu. What is the molecular formula?

14. Analysis of an unknown sample indicated the sample contained 0.140g of N and 0.320 g of O. The molar mass of the compound was determined to be 92.02 amu. What is the molecular formula of the compound?

Answer 1

7. no of sodium atoms = no of moles * 6.023*10²³

                                      = 4.66*6.023*10²³

                                      = 2.806*10²⁴ atoms

8. molar mass = mass of substance/no of moles

                        = 19.27/0.6502   = 29.64 g/mole

9. mass of Cu(NO3)2   = no of moles* gram molar mass

                                      = 7.5*187.56 = 1406.7g

10. no of magnesium atoms = W*6.023*10²³/G.A.Wt

                                               = 14.6*6.023*10²³ /24

                                               = 3.7*10²³ atoms

11. no of hydrogen atoms = W*6.023*10²³ * atomicity of hydrogen/G.M.Wt

                                            = 14.6*6.023*10²³*3 /17

                                            =1.55*10²⁴ hydrogen atoms

12. no of atoms                = no of moles * 6.023*10²³ * atomicity

                                         = 0.45*6.023*10²³ *14

                                         = 3.794*10²⁴ atoms

13. molecular formula   = (empirical formula)n

                      n             = M.F.wt/E.F.Wt

                                    = 120.12/30 = 4

molecular formula = (CH2O)4 = C4H8O4