A solution contains 5.85 g of NaCl in 500 g of water. Calculate its molality.

📘 Complete Step-by-Step Solution

📌 Given Data

Mass of NaCl = 5.85 g

Mass of water = 500 g

Na = 23, Cl = 35.5

🔵 Step 1: Calculate Molar Mass of NaCl

Molar Mass of NaCl

= Na + Cl

= 23 + 35.5

= 58.5 g mol⁻¹

🟢 Step 2: Calculate Moles of NaCl

Moles = Mass ÷ Molar Mass

= 5.85 ÷ 58.5

= 0.10 mol

✅ Moles of NaCl = 0.10 mol

🟠 Step 3: Convert Mass of Water into kg

Molality is calculated using the mass of solvent in kilograms.

500 g = 500 ÷ 1000 kg

= 0.5 kg

🟣 Step 4: Apply the Molality Formula

Molality (m) = Moles of solute ÷ Mass of solvent (kg)

m = 0.10 ÷ 0.5

= 0.20 mol kg⁻¹

🎬 3D-Style Solution Animation

NaCl particles are dissolved in water.

Na⁺ Cl⁻ H₂O H₂O Cl⁻ Na⁺

5.85 g NaCl → 0.10 mol NaCl

500 g water → 0.5 kg solvent

0.10 ÷ 0.5 → 0.20 mol kg⁻¹

✅ Final Answer

Molality = 0.20 mol kg⁻¹

= 0.20 m

🎯 Important Formula

Molality (m) = Moles of solute ÷ Mass of solvent in kg

m = n / W(kg)