Chromium(III) oxide reacts with hydrogen sulfide (H2S) gas to form chromium(III) sulfide and water: Cr2O3(s) + 3H2S(g) → Cr2S3(s) + 3H2O(l) To produce 156 g of Cr2S3, (a) how many moles of Cr2O3 are required? mol (b) how many grams of Cr2O3 are required? g

(a) 0.779 mol Cr₂O₃

(b) 118 g Cr₂O₃

Explanation:

Step 1: Convert 156 g Cr₂S₃ to moles

Cr Molar Mass - 52.00 g/mol × 2 = 104.00 g/mol

S Molar Mass - 32.07 g/mol × 3 = 96.21 g/mol

156 g Cr₂S₃ ÷ 200.21 g/mol = 0.779182 mol Cr₂S₃

Step 2: Find conversion from Cr₂S₃ to Cr₂O₃

1 mol Cr₂S₃ equals 1 mol Cr₂O₃

Step 3: Use Dimensional Analysis

0.779182 mol Cr₂S₃ · = 0.779182 mol Cr₂O₃

0.779182 mol Cr₂O₃ ≈ 0.779 mol Cr₂O₃ (3 significant figures)

Step 4: Convert moles to grams

Cr Molar Mass - 52.00 g/mol × 2 = 104.00 g/mol

O Molar Mass - 16.00 g/mol × 3 = 48.00 g/mol

0.779182 mol Cr₂O₃ · 152.00 g/mol = 118.436 g Cr₂O₃

118.436 g Cr₂O₃ ≈ 118 g Cr₂O₃ (3 significant figures)

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.