Question

How many oxygen atoms are in 1.00 g of the mineral

troegerite, (UO

2

)

3

(AsO

4

)

2

•12 H

2

O (

M

= 1304.0)?

(A)

6.47

×

10

21

(B)

8.31

×

10

21

(C)

1.20

×

10

22

(D)

1.39

×

10

22

Answer 1

Given: molecular mass of mineral = 1304g

Number of O atoms in 1g =?

SOLUTION

First of all, count the number of O atoms in the mineral (UO₂) ₃(AsO₄)₂.12H₂O . The mineral contains total 26 Oxygen atoms (6in( UO₂)_3, 8in (AsO4) ₂ and 12 oxygen in water of crystallization, total=26atoms)

1mole of any substance contains atoms =6.022×10²³  atoms

1mole of any substance =gram molecular mass

Thus, 1304g of mineral contains oxygen atoms=26×6.022×10²³ atoms

1g of mineral contains oxygen atoms = 26×6.022×10²³ atoms × 1g÷1304g =156.572 ×10²³ atoms ×1g ÷ 1304g

= 0.12007 ×10²³ atoms

After round off answer =1.201×10²²atoms

Thus, the correct option is (c)