Question

1)How many moles of Sr are there in 93.2 grams of Sr?

2)How many grams of Ag are there in 0.692 moles of Ag?

3)How many grams of Ga are there in a sample of Ga that contains the same number of moles as a 39.1 gram sample of Mg? grams of Ga

Answer 1

1)How many moles of Sr are there in 93.2 grams of Sr?

Given mass of Sr , m = 93.2 g

At.mass of Sr = 87.6 g/mol

Number of moles of Sr , n = mass/molarmass

                                          = 93.2 g / 87.6 (g/mol)

                                         = 1.06 moles

Therefore the number of moles of Sr is 1.06 mol

2)How many grams of Ag are there in 0.692 moles of Ag?

At.mass of Ag is 108 g/mol

Given number of moles of Ag is 0.692 mol

We know that number of moles , n = mass / molar mass

                 mass = number of moles x molar mass

                          = 0.692 mol x 108 g/mol

                          = 74.7 g

Therefore the mass of Ag is 74.7 g

3)How many grams of Ga are there in a sample of Ga that contains the same number of moles as a 39.1 gram sample of Mg? grams of Ga

Given mass of Mg is 39.1 g

At.mass of Mg is 24.3 g/mol

So number of moles of Mg , n = mass/molar mass

                                               = 39.1 g / 24.3 (g/mol)

                                              = 1.61 mol

So the number of moles of Mg = number of moles of Ga = 1.61 mol

We know that 1 mole of of any compound contains avagadro number(=6.023x10 ²³) of molecules

       1 mole of Ga contains 6.023x10 ²³ molecules

    1.61 mole of Ga contains M molecules

M = (1.61 x 6.023x10 ²³) = 9.69 x10 ²³ molecules