1) Calculate the molecular weight of (NH₄)₂S

Step One: two atoms of nitrogen, eight of hydrogen and one of sulfur

Step Two: N = 14.0067 amu, H = 1.0079 amu, S = 32.06 amu

Step Three: (2 x 14.0067) + (8 x 1.0079) + (1 x 32.06)

Step Four: 28.0134 + 8.0632 + 32.06 = 68.14 amu (when rounded off to the correct number of significant figures)

2) Calculate the molecular weight of Fe₂O₃

Step One: two atoms of iron and three of oxygen

Step Two: Fe = 55.847 amu and O = 15.9994 amu

Step Three: (2 x 55.847) + (3 x 15.9994)

Step Four: 111.694 + 47.9982 = 159.692 amu (when rounded off to the correct number of significant figures)

3) Calculate the molecular weight of KClO₄

Step One: one atom of potassium, one of chlorine, and four of oxygen.

Step Two: K = 39.098 amu, Cl = 35.453 amu, O = 15.9994 amu

Step Three: (1 x 39.098) + (1 x 35.453) + (4 x 15.9994)

Step Four: 39.098 + 35.453 + 63.9976 = 138.549 amu (when rounded off to the correct number of significant figures)

4) Calculate the molecular weight of SF₆

Step One: one atom of sulfur and six of fluorine

Step Two: S = 32.06 amu and F = 18.998 amu

Step Three: (1 x 32.06) + (6 x 18.998)

Step Four: 32.06 + 113.990 = 146.05 amu (when rounded off to the correct number of significant figures)

5) Calculate the molecular weight of (NH₄)₂SO₄

Step One: two atoms of nitrogen, eight of hydrogen, one of sulfur, and four of oxygen

Step Two: N = 14.0067 amu, H = 1.0079 amu, S = 32.06 amu, O = 15.9994

Step Three: (2 x 14.0067) + (8 x 1.0079) + (1 x 32.06) + (4 x 15.9994)

Step Four: 28.0134 + 8.0632 + 32.06 + 63.9976 = 132.13 amu (when rounded off to the correct number of significant figures) Return