ANAND CLASSES Study Material and Notes to understand the key difference between 1 Molar and 1 Molal solutions with a simple explanation and practical numerical example. Learn which one is more concentrated and why, ideal for JEE, NEET, and CBSE students.
🔍 What is Concentration?
Concentration means how much solute is present in a given amount of solvent or solution.
The more solute in a given amount of liquid, the more concentrated the solution is.
🧪 What is 1 Molar (1 M)?
- Molarity (M) = Moles of solute / Liters of solution
- So, 1 M means: 1 mole of solute is dissolved in 1 liter of the total solution (solute + solvent combined).
🔸 That 1 liter includes both:
- The solute (like salt or sugar)
- The solvent (like water)
🧪 What is 1 Molal (1 m)?
- Molality (m) = Moles of solute / Kilograms of solvent
- So, 1 m means: 1 mole of solute is dissolved in exactly 1 kilogram of solvent only (not the total solution).
🔸 The final volume of the solution may be more than 1 liter, but that doesn’t matter in molality. It depends only on the mass of solvent.
⚖️ So, Which One Is More Concentrated?
Let’s compare 1 M and 1 m for the same solute (say, NaCl):
🟦 In 1 M solution:
- 1 mole of NaCl is dissolved in 1 liter of solution.
- Since solute also takes up space, the amount of water used is less than 1 kg (maybe around 0.95 kg).
🟩 In 1 m solution:
- 1 mole of NaCl is dissolved in exactly 1 kg of water.
- The final volume may be more than 1 liter (maybe 1.05 L), but we don’t care about volume in molality.
👉 So, in 1 molal, we’re using less liquid (just 1 kg of water), while in 1 molar, the solution includes more total volume (solute + some extra water).
✅ Therefore: 1 molal is more concentrated than 1 molar.
💡 Simple Analogy:
Imagine making lemon juice 🍋:
- 1 M = 1 spoon of lemon juice in a 1-liter jug of drink
- 1 m = 1 spoon of lemon juice in exactly 1 kg of water (which is slightly less than 1 liter)
Who do you think will get the sourer drink?
👉 The one with less water – so 1 molal is more concentrated.
📌 Key Differences Table:
| Property | Molarity (1 M) | Molality (1 m) |
|---|---|---|
| Based on | Volume of solution (L) | Mass of solvent (kg) |
| Affected by temperature? | ✅ Yes (volume changes) | ❌ No (mass doesn’t change) |
| Concentration | Less (more total volume) | More (fixed amount of solvent) |
| Units | mol/L | mol/kg |
Let’s make this very, very simple — like a fun story. 😊
🧪 Imagine Two Friends Are Making Salt Water:
Friend A makes 1 Molar (1 M) salt water:
- He takes 1 spoon of salt.
- Then he adds water until the total water + salt = 1 bottle (1 liter).
📌 So he uses less water, because the bottle must fit both salt + water.
Friend B makes 1 Molal (1 m) salt water:
- He takes 1 spoon of salt.
- Then he takes exactly 1 kg of water (about 1 full bottle).
- He does not care how big the final bottle is — just uses 1 kg of water.
📌 So, he uses more water than Friend A.
🔍 Who has the stronger (more concentrated) salt water?
Let’s look:
| Friend | Salt (solute) | Water (solvent) | Concentration |
|---|---|---|---|
| A (1 M) | 1 spoon | Less than 1 kg | More concentrated ✅ |
| B (1 m) | 1 spoon | 1 kg | Less concentrated ❌ |
✅ Final Answer (Simple):
✔️ 1 Molar (1 M) is actually more concentrated than 1 Molal (1 m)
because it uses less water for the same amount of salt.
💡 Easy Trick to Remember:
- Molarity (M) → based on volume → less water used → more concentrated
- Molality (m) → based on mass (kg of water) → more water used → less concentrated
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🔹 Written by: Neeraj Anand
🔹 Published by: Anand Technical Publishers under Anand Classes
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