Community College of Baltimore CountyCHEMIC 131

1) A sample of pure copper has a mass of 16.35 g. How many moles does this mass correspond to?

(A)3.887 mol

(B)1.549 x 10²³ mol

(C.)0.2573 mol

(D.)2.715 x 10^-23 mol

2. Which sample contains the greatest number of atoms?

(A)25g Cu

(B)25g F₂

(C)25g Ne

(D)25g Ba

Answer:

1. (C.)0.2573 mol 
2. (C)25g Ne

Explanation:

1.

Calculate the number of moles of 16.35 g pure copper (Cu) from its molar mass from the periodic table which is 63.546 g/mol using the formula below.

number of moles = mass / molar mass = (16.35 g) / (63.546 g/mol) = 0.2573 mol (C)

2.

From the formula below, the number of moles is inversely proportional to the molar mass.

number of moles = mass / molar mass

Now, from the molar masses of the choices which were searched from the internet/database, Ne (20.18 g/mol) has the lowest molar mass compared to Cu (63.55 g/mol), F₂(38.00 g/mol), and Ba (137.33 g/mol), hence, 25 g Ne will have the highest number of moles.

Note, that the number of moles is directly proportional to the number of atoms,

hence, 25 g Ne (C) will also have the greatest number of atoms.