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NaCl, KBr, MgCl₂ and Na₂CO₃ are all ionic compounds, but not molecular compounds. It is better to use "formula units" instead of "molecules"

Avogadro constant = 6.02 × 10²³ /mol


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- Calculate the grams of NaCl in 12.04 × 10²³ molecules of NaCl?

No. of moles of NaCl = (12.04 × 10²³) / (6.02 × 10²³ /mol) = 2 mol
Molar mass of NaCl = (23.0 + 35.5) g/mol = 58.5 g/mol
Mass of NaCl = (2 mol) × (58.5 g/mol) = 117 g


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- Calculate the grams of KBr in 4.01 × 10²³ molecules of KBr?

No. of moles of KBr = (4.01 × 10²³) / (6.02 × 10²³ /mol) = 0.666 mol
Molar mass of KBr = (39.0 + 79.9) g/mol = 118.9 g/mol
Mass of KBr = (0.666 mol) × (118.9 g/mol) = 79.2 g


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- Calculate the grams of MgCl₂ in 8.4 ×10²⁴ molecules of MgCl₂?

No. of moles of MgCl₂ = (8.4 ×10²⁴) / (6.02 × 10²³ /mol) = 13.95 mol
Molar mass of MgCl₂ = (24.3 + 35.5×2) g/mol = 95.3 g/mol
Mass of MgCl₂ = (13.95 mol) × (95.3 g/mol) = 1330 g


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- Calculate the grams of Na₂CO₃ in 8.4 × 10²³ molecules of Na₂CO₃?

No. of moles of Na₂CO₃ = (8.4 ×10²³) / (6.02 × 10²³ /mol) = 1.395 mol
Molar mass of Na₂CO₃ = (23.0×2 + 12 + 16.0×3) g/mol = 106.0 g/mol
Mass of Na₂CO₃ = (1.395 mol) × (106.0 g/mol) = 148 g