Solutions – Mixing Things Up Like a Chemist!
Imagine making tea: you mix sugar (solid) into water (liquid). That’s a solution—one of the most important concepts in chemistry! Let’s break it down simply.
Foundation Knowledge (What You Need First)
✅ Atoms & Molecules (Topic 2)
✅ The Mole Concept (Topic 3)
✅ Basic Math (multiplication, division)
1. What is a Solution?
A solution is a homogeneous mixture (same throughout) of:
🔹 Solute – The substance being dissolved (e.g., sugar).
🔹 Solvent – The substance doing the dissolving (e.g., water).
📌 Fun Fact: Air is a gas solution (oxygen, nitrogen mixed evenly)!
2. Concentration – How “Strong” is Your Solution?
Chemists measure concentration in different ways:
A. Mass Percent (%)
= (Mass of solute ÷ Mass of solution) × 100
Example:
If you dissolve 10g of salt in 90g of water, what’s the mass %?
- Mass % = (10g ÷ 100g) × 100 = 10% salt solution.
📌 Real-Life Use: Bottles of hydrogen peroxide show 3% or 6% concentrations.
B. Molarity (M) – The Most Common Unit!
= Moles of solute ÷ Liters of solution
Example:
If 0.5 moles of NaOH are dissolved in 2L of water, what’s the molarity?
- Molarity = 0.5 moles ÷ 2L = 0.25 M NaOH.
📌 Pro Tip:
- 1 M = 1 mole per liter (like a “standard recipe”).
- Lab chemicals often use molarity (e.g., “0.1 M HCl”).
C. Molality (m) – When Temperature Matters!
= Moles of solute ÷ Kilograms of solvent
📌 Key Difference:
- Molarity uses liters of solution (volume changes with temperature).
- Molality uses kg of solvent (mass doesn’t change with temperature).
3. Dilution – Making Solutions Weaker
Sometimes you need to reduce concentration by adding more solvent.
🔹 Formula:
M₁V₁ = M₂V₂
(Initial Molarity × Initial Volume = Final Molarity × Final Volume)
Example:
How much water is needed to dilute 100 mL of 6 M HCl to 2 M?
- 6 M × 100 mL = 2 M × V₂ → V₂ = 300 mL (so add 200 mL water).
📌 Lab Hack: Always add acid to water (not water to acid!) to avoid splashes.
4. Solubility – Why Doesn’t Oil Mix with Water?
Not all substances dissolve equally! Factors affecting solubility:
🔹 Temperature – Hot water dissolves more sugar than cold.
🔹 Polarity – “Like dissolves like”:
- Polar solvents (e.g., water) dissolve polar/ionic solutes (e.g., salt).
- Non-polar solvents (e.g., oil) dissolve non-polar solutes (e.g., grease).
📌 Fun Demo: Try mixing oil + water + food coloring—it’s like a lava lamp!
5. Colligative Properties – Changing Solutions’ Behavior
These depend on how many particles are dissolved, not their identity:
🔹 Boiling Point Elevation – Adding salt raises water’s boiling point.
🔹 Freezing Point Depression – Antifreeze lowers water’s freezing point.
📌 Real-Life Uses:
- Salting roads in winter (melts ice).
- Ice cream makers use salt to freeze cream faster.
Summary (Cheat Sheet!)
🧪 Solution = Solute + Solvent.
📊 Concentration = Mass %, Molarity (M), Molality (m).
💧 Dilution = M₁V₁ = M₂V₂.
🌡️ Solubility depends on temperature & polarity.
❄️ Colligative Properties = Boiling/freezing point changes.
Try It Yourself!
- What’s the molarity if 0.2 moles of NaCl are dissolved in 0.5 L water?
- How much 5 M HCl is needed to make 1 L of 1 M HCl?
- Why does salt melt ice? (Hint: Colligative properties!)
(Answers: 1) 0.4 M, 2) 200 mL, 3) Lowers freezing point!)
Now you’re a solution expert! 🎉