Convert between the mass and the amount of any substance: type its formula and either the mass in grams or the moles, and the other is calculated from the molar mass.
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From the article Mass ↔ Mole Conversion — The Central Skill of Stoichiometry.
Question: How many moles are there in 25.0 g of sodium hydroxide, NaOH?
Step 1 — molar mass. Na = 22.990, O = 15.999, H = 1.008
M(NaOH) = 22.990 + 15.999 + 1.008 = 39.997 g mol⁻¹
Step 2 — direction. Mass given, moles wanted → divide.
Step 3 — calculate. n = 25.0 / 39.997 = 0.62505
n = 0.625 mol
Estimate check: M is about 40, and 25 ÷ 40 = 0.625. The full calculation agrees ✓
Question: What mass of calcium carbonate, CaCO₃, contains 0.350 mol?
Step 1 — molar mass. Ca = 40.078, C = 12.011, O = 15.999
M(CaCO₃) = 40.078 + 12.011 + (3 × 15.999) = 40.078 + 12.011 + 47.997 = 100.086 g mol⁻¹
Step 2 — direction. Moles given, mass wanted → multiply.
Step 3 — calculate. m = 0.350 × 100.086 = 35.030
m = 35.0 g
Estimate check: M ≈ 100, so 0.35 mol should weigh about 35 g ✓
Worked in full in Mass ↔ Mole Conversion — The Central Skill of Stoichiometry.
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