There are three isotopes of silicon; they have mass numbers of 28, 29, and 30. The atomic mass of silicon is 28.086amu. Which isotope would you say is the most abundant?

A. 7,20x10⁻³mol NaF

B. 4,33x10²¹ F⁻ ions

C. 1,88x10⁻³g Na⁺

D. 3,1x10²² formula units

E. 132,08g/mol

F. 15,9g of CHCl₃; 0,293 mol of CHCl₃

Explanation:

A. 119g × (0,254% / 100) = 0,302g of NaF × (1mol / 41,99g) = 7,20x10⁻³mol NaF

B. 7,20x10⁻³mol NaF ≡ 7,20x10⁻³mol F⁻ × (6,022x10²³ ions / mol) = 4,33x10²¹ F⁻ ions

C. 1,35g × (0,254% / 100) = 0,00343g of NaF × (22,99g Na⁺ / 41,99g NaF) = 1,88x10⁻³g Na⁺

D. 119g × (4,4% / 100) = 5,236g of KNO₃ × (1mol / 101,1g) = 0,0518mol × (6,022x10²³ F.U / 1mol) = 3,1x10²² formula units

E. Formula of ammonium sulfate is (NH₄)₂SO₄. Molar mass is obtained thus:

N: 2N×(14g/mol) = 28g/mol

H: 8H×(1,01g/mol) = 8,08g/mol

S: 1S×(32g/mol) = 32g/mol

O: 4O×(16g/mol) = 64g/mol

Molar mass: 28 + 8,08 + 32 + 64 = 132,08g/mol

F. Molar mass of chloroform is 119,38g/mol, thus:

0,133 mol × (119,38g/mol) = 15,9g of CHCl₃

35,0g  × (1mol / 119,38g) = 0,293mol of CHCl₃

I hope it helps!