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Write a Balanced Chemical Equation with State Symbols
Question: Write a balanced chemical equation with state symbols for the following reactions:
(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.
📑 Table of Contents
⚡ Quick Answer (Featured Snippet)
Reaction (i): Precipitation Reaction
✅ White precipitate of BaSO₄ forms
Reaction (ii): Neutralization Reaction
✅ Acid + Base → Salt + Water
⚡ Quick Tip: Always check: (1) Balanced atoms, (2) Correct state symbols, (3) Proper coefficients
💬 Let’s Understand This Together!
Hey there! 👋 So you’re working on NCERT Class 10 Science Chapter 2 Question 3, right? This is one of those questions that looks simple but has some tricky parts that can cost you marks if you’re not careful.
Don’t worry though – I’m going to break this down in the simplest way possible. By the end of this guide, you’ll not only know the answer but also understand why it’s written that way. And trust me, understanding the “why” is what gets you full marks! 🎯
🎓 What You’ll Learn:
- How to write balanced chemical equations perfectly
- What state symbols mean and when to use them
- The difference between precipitation and neutralization reactions
- Common mistakes that lose marks (and how to avoid them!)
- The exact format examiners want to see
This question carries 3 marks in your board exam – that’s 1.5 marks for each equation. So let’s make sure you get all 3! 💯
🧪 Reaction 1: The Precipitation Reaction
📋 The Question Says:
“Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.”
🔍 Breaking Down the Reaction
Let’s decode what’s happening here step by step:
Step 1: Identify the Reactants
| Reactant | Chemical Formula | State |
|---|---|---|
| Barium chloride solution | BaCl₂ | (aq) – dissolved in water |
| Sodium sulphate solution | Na₂SO₄ | (aq) – dissolved in water |
Step 2: Identify the Products
| Product | Chemical Formula | State |
|---|---|---|
| Barium sulphate (INSOLUBLE) | BaSO₄ | (s) – solid precipitate |
| Sodium chloride solution | NaCl | (aq) – dissolved in water |
⚖️ Step 3: Write the Unbalanced Equation
First draft (unbalanced):
🔢 Step 4: Balance the Equation
Now let’s count atoms on both sides:
| Element | Left Side (Reactants) | Right Side (Products) | Balanced? |
|---|---|---|---|
| Ba (Barium) | 1 | 1 | ✅ |
| Cl (Chlorine) | 2 | 1 | ❌ |
| Na (Sodium) | 2 | 1 | ❌ |
| SO₄ (Sulphate) | 1 | 1 | ✅ |
Problem: We have 2 chlorine atoms and 2 sodium atoms on the left, but only 1 of each on the right! 😱
Solution: Add coefficient 2 before NaCl on the right side:
✅ FINAL BALANCED EQUATION:
💡 Why This Reaction Happens:
This is a double displacement reaction. The positive ions (Ba²⁺ and Na⁺) swap their negative partners (Cl⁻ and SO₄²⁻). Barium sulphate is insoluble in water, so it precipitates out as a white solid, while sodium chloride remains dissolved.
⚗️ Reaction 2: The Neutralization Reaction
📋 The Question Says:
“Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.”
🔍 Understanding Neutralization
This is a classic acid-base neutralization reaction. Let’s break it down:
Step 1: Identify the Reactants
| Reactant | Type | Chemical Formula | State |
|---|---|---|---|
| Sodium hydroxide solution | BASE | NaOH | (aq) |
| Hydrochloric acid solution | ACID | HCl | (aq) |
Step 2: Identify the Products
| Product | Type | Chemical Formula | State |
|---|---|---|---|
| Sodium chloride solution | SALT | NaCl | (aq) |
| Water | WATER | H₂O | (l) |
⚖️ Step 3: Write and Check the Equation
Let’s write the equation and check if it’s balanced:
Now let’s verify the atom count:
| Element | Left Side (Reactants) | Right Side (Products) | Balanced? |
|---|---|---|---|
| Na (Sodium) | 1 | 1 | ✅ |
| O (Oxygen) | 1 | 1 | ✅ |
| H (Hydrogen) | 2 (1 from NaOH + 1 from HCl) | 2 (in H₂O) | ✅ |
| Cl (Chlorine) | 1 | 1 | ✅ |
✅ FINAL BALANCED EQUATION:
🎉 Perfect! This equation is already balanced – no coefficients needed!
💡 The Neutralization Formula:
This is the universal pattern for all neutralization reactions. The H⁺ from the acid combines with OH⁻ from the base to form H₂O, while the remaining ions form a salt.
🏷️ Complete Guide to State Symbols
State symbols are super important in chemical equations! They tell us the physical state of each substance. Let’s master them:
| Symbol | Full Form | Meaning | Examples |
|---|---|---|---|
| (s) | Solid | Substance is in solid state (has definite shape and volume) | BaSO₄(s), Fe(s), NaCl(s) |
| (l) | Liquid | Substance is in liquid state (has definite volume but no definite shape) | H₂O(l), Br₂(l), C₂H₅OH(l) |
| (g) | Gas | Substance is in gaseous state (no definite shape or volume) | H₂(g), O₂(g), CO₂(g) |
| (aq) | Aqueous | Substance is dissolved in water (forms a solution) | NaCl(aq), HCl(aq), NaOH(aq) |
🎯 How to Choose the Right State Symbol:
- (s) – Use when the question says “solid”, “precipitate”, “insoluble”, or mentions a solid substance
- (l) – Use for pure liquids like water produced in reactions, or liquid elements like bromine
- (g) – Use when the question mentions “gas”, “vapour”, or for substances that are gases at room temperature
- (aq) – Use when the question says “solution”, “dissolved in water”, or “aqueous”
⚠️ Common Confusion: (l) vs (aq)
H₂O(l) = Pure water (liquid)
H₂O(aq) = ❌ WRONG! Water cannot be dissolved in water!
NaCl(s) = Solid salt crystals
NaCl(aq) = Salt dissolved in water (salt solution)
⚖️ Step-by-Step Balancing Process (Universal Method)
Follow these 5 golden steps to balance ANY chemical equation perfectly:
Step 1️⃣: Write the Unbalanced Equation
Write all reactants on the left side of the arrow (→) and all products on the right side. Use correct chemical formulas and add state symbols.
Step 2️⃣: Count Atoms of Each Element
Make a table listing each element and count how many atoms appear on each side.
Right side: Ba=1, SO₄=1, Na=1, Cl=1
Step 3️⃣: Add Coefficients (NOT Subscripts!)
Add numbers (coefficients) BEFORE the chemical formulas to balance atoms. NEVER change subscripts!
❌ Wrong: Change NaCl to Na₂Cl₂ (this is a different compound!)
Step 4️⃣: Recount and Verify
After adding coefficients, count atoms again to make sure both sides are equal.
Left: Ba=1, Cl=2, Na=2, SO₄=1
Right: Ba=1, SO₄=1, Na=2, Cl=2 ✅ Balanced!
Step 5️⃣: Write the Final Equation
Write the complete balanced equation with all coefficients and state symbols clearly.
💡 Pro Tips for Balancing:
- Start with the most complex molecule first
- Balance polyatomic ions (like SO₄²⁻) as a single unit
- Leave hydrogen and oxygen for last (they’re usually in multiple compounds)
- If you get fractions, multiply the entire equation by the denominator
- Always do a final check – count every single atom!
📊 Visual Diagrams & Flowcharts
Let’s visualize these reactions with text-based diagrams for better understanding! 🎨
📈 Diagram 1: Precipitation Reaction Flow
╔══════════════════════════════════════════════════════════════════════════╗ ║ ║ ║ 🧪 PRECIPITATION REACTION PROCESS ║ ║ ║ ╠══════════════════════════════════════════════════════════════════════════╣ ║ ║ ║ STEP 1: Two Clear Solutions Mixed ║ ║ ═══════════════════════════════════ ║ ║ ║ ║ ┌─────────────────────┐ ┌─────────────────────┐ ║ ║ │ 💧 BaCl₂ Solution │ + │ 💧 Na₂SO₄ Solution │ ║ ║ │ │ │ │ ║ ║ │ Clear & Colorless │ │ Clear & Colorless │ ║ ║ │ │ │ │ ║ ║ │ Contains: │ │ Contains: │ ║ ║ │ • Ba²⁺ ions │ │ • Na⁺ ions │ ║ ║ │ • Cl⁻ ions │ │ • SO₄²⁻ ions │ ║ ║ └─────────────────────┘ └─────────────────────┘ ║ ║ │ │ ║ ║ │ │ ║ ║ └───────────────┬───────────────┘ ║ ║ │ ║ ║ ▼ ║ ║ ║ ║ STEP 2: Ions Rearrange (Double Displacement) ║ ║ ═══════════════════════════════════════════ ║ ║ ║ ║ Ba²⁺ + SO₄²⁻ → BaSO₄ ⬇️ (INSOLUBLE!) ║ ║ Na⁺ + Cl⁻ → NaCl (stays dissolved) ║ ║ ║ ║ │ ║ ║ ▼ ║ ║ ║ ║ STEP 3: White Precipitate Forms ║ ║ ═══════════════════════════════════ ║ ║ ║ ║ ┌──────────────────────────────────────────────────┐ ║ ║ │ │ ║ ║ │ 💧 Clear Solution (NaCl) │ ║ ║ │ │ ║ ║ │ ⬇️⬇️⬇️⬇️⬇️⬇️⬇️⬇️⬇️⬇️⬇️⬇️⬇️⬇️⬇️⬇️ │ ║ ║ │ │ ║ ║ │ ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓ │ ║ ║ │ ▓ White Precipitate ▓ ← BaSO₄(s) │ ║ ║ │ ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓ │ ║ ║ │ │ ║ ║ └──────────────────────────────────────────────────┘ ║ ║ ║ ║ FINAL EQUATION: ║ ║ ════════════════ ║ ║ ║ ║ BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s)↓ + 2NaCl(aq) ║ ║ ║ ╚══════════════════════════════════════════════════════════════════════════╝
📈 Diagram 2: Neutralization Reaction Process
╔══════════════════════════════════════════════════════════════════════════╗ ║ ║ ║ ⚗️ NEUTRALIZATION REACTION PROCESS ║ ║ ║ ╠══════════════════════════════════════════════════════════════════════════╣ ║ ║ ║ REACTANTS: Acid + Base ║ ║ ═══════════════════════ ║ ║ ║ ║ ┌─────────────────────┐ ┌─────────────────────┐ ║ ║ │ 🔴 HCl (ACID) │ + │ 🔵 NaOH (BASE) │ ║ ║ │ │ │ │ ║ ║ │ pH < 7 │ │ pH > 7 │ ║ ║ │ Sour taste │ │ Bitter taste │ ║ ║ │ Turns blue │ │ Turns red │ ║ ║ │ litmus red │ │ litmus blue │ ║ ║ │ │ │ │ ║ ║ │ H⁺ + Cl⁻ │ │ Na⁺ + OH⁻ │ ║ ║ └─────────────────────┘ └─────────────────────┘ ║ ║ │ │ ║ ║ └───────────────┬───────────────┘ ║ ║ │ ║ ║ ▼ ║ ║ ║ ║ REACTION MECHANISM: ║ ║ ════════════════════ ║ ║ ║ ║ H⁺ + OH⁻ → H₂O (water forms!) ║ ║ Na⁺ + Cl⁻ → NaCl (salt forms!) ║ ║ ║ ║ │ ║ ║ ▼ ║ ║ ║ ║ PRODUCTS: Salt + Water ║ ║ ═══════════════════════ ║ ║ ║ ║ ┌──────────────────────────────────────────────────┐ ║ ║ │ │ ║ ║ │ 🟢 NEUTRAL SOLUTION │ ║ ║ │ │ ║ ║ │ pH = 7 (Neutral) │ ║ ║ │ │ ║ ║ │ Contains: │ ║ ║ │ • NaCl (salt) - dissolved │ ║ ║ │ • H₂O (water) - liquid │ ║ ║ │ │ ║ ║ │ No sour or bitter taste │ ║ ║ │ No effect on litmus paper │ ║ ║ │ │ ║ ║ └──────────────────────────────────────────────────┘ ║ ║ ║ ║ FINAL EQUATION: ║ ║ ════════════════ ║ ║ ║ ║ NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l) ║ ║ ║ ║ 💡 Universal Formula: ACID + BASE → SALT + WATER ║ ║ ║ ╚══════════════════════════════════════════════════════════════════════════╝
📈 Diagram 3: Ion Exchange in Precipitation Reaction
╔══════════════════════════════════════════════════════════════════════════╗ ║ ║ ║ 🔄 DOUBLE DISPLACEMENT: ION EXCHANGE ║ ║ ║ ╠══════════════════════════════════════════════════════════════════════════╣ ║ ║ ║ BEFORE REACTION (Aqueous Solutions): ║ ║ ═════════════════════════════════════ ║ ║ ║ ║ BaCl₂ Solution Na₂SO₄ Solution ║ ║ ═══════════════ ════════════════ ║ ║ ║ ║ ┌─────────────────┐ ┌─────────────────┐ ║ ║ │ │ │ │ ║ ║ │ Ba²⁺ Ba²⁺ │ │ Na⁺ Na⁺ │ ║ ║ │ │ │ │ ║ ║ │ Cl⁻ Cl⁻ │ │ SO₄²⁻ SO₄²⁻ │ ║ ║ │ │ │ │ ║ ║ │ Ba²⁺ Ba²⁺ │ │ Na⁺ Na⁺ │ ║ ║ │ │ │ │ ║ ║ │ Cl⁻ Cl⁻ │ │ SO₄²⁻ SO₄²⁻ │ ║ ║ │ │ │ │ ║ ║ └─────────────────┘ └─────────────────┘ ║ ║ ║ ║ ⬇️ MIX ⬇️ ║ ║ ║ ║ DURING REACTION (Ion Exchange): ║ ║ ════════════════════════════════ ║ ║ ║ ║ Ba²⁺ ───────────────────→ SO₄²⁻ ║ ║ ╲ ╱ ║ ║ ╲ ╱ ║ ║ ╲ ╱ ║ ║ ╲ ╱ ║ ║ ╲ ╱ ║ ║ ╲ ╱ ║ ║ ↘ ↙ ║ ║ BaSO₄ Forms! ║ ║ (INSOLUBLE ⬇️) ║ ║ ║ ║ Na⁺ ───────────────────→ Cl⁻ ║ ║ ╲ ╱ ║ ║ ╲ ╱ ║ ║ ↘ ↙ ║ ║ NaCl Forms! ║ ║ (Stays dissolved) ║ ║ ║ ║ AFTER REACTION: ║ ║ ════════════════ ║ ║ ║ ║ ┌─────────────────────────────────────┐ ║ ║ │ │ ║ ║ │ Clear Solution: │ ║ ║ │ Na⁺ Cl⁻ Na⁺ Cl⁻ Na⁺ Cl⁻ │ ║ ║ │ │ ║ ║ │ ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ │ ║ ║ │ │ ║ ║ │ White Precipitate (Bottom): │ ║ ║ │ ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓ │ ║ ║ │ ▓▓▓ BaSO₄ (solid) ▓▓▓▓▓▓▓▓▓▓▓ │ ║ ║ │ ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓ │ ║ ║ │ │ ║ ║ └─────────────────────────────────────┘ ║ ║ ║ ║ KEY OBSERVATION: ║ ║ ════════════════ ║ ║ • Partners swapped: Ba paired with SO₄, Na paired with Cl ║ ║ • BaSO₄ is insoluble → precipitates as solid ║ ║ • NaCl is soluble → remains dissolved in solution ║ ║ ║ ╚══════════════════════════════════════════════════════════════════════════╝
📈 Diagram 4: Balancing Decision Flowchart
╔══════════════════════════════════════════════════════════════════════════╗ ║ ║ ║ 🎯 HOW TO BALANCE ANY CHEMICAL EQUATION ║ ║ ║ ╠══════════════════════════════════════════════════════════════════════════╣ ║ ║ ║ START HERE ⬇️ ║ ║ ║ ║ ┌─────────────────────────────┐ ║ ║ │ Write unbalanced equation │ ║ ║ │ with correct formulas │ ║ ║ └────────────┬────────────────┘ ║ ║ │ ║ ║ ▼ ║ ║ ┌─────────────────────────────┐ ║ ║ │ Count atoms on both sides │ ║ ║ └────────────┬────────────────┘ ║ ║ │ ║ ║ ▼ ║ ║ ┌─────────────────────────────┐ ║ ║ │ Are all atoms balanced? │ ║ ║ └────────────┬────────────────┘ ║ ║ │ ║ ║ ┌────────┴────────┐ ║ ║ │ │ ║ ║ YES NO ║ ║ │ │ ║ ║ ▼ ▼ ║ ║ ┌──────────────────┐ ┌──────────────────────────┐ ║ ║ │ ✅ DONE! │ │ Which element is │ ║ ║ │ │ │ unbalanced? │ ║ ║ │ Write final │ └──────────┬───────────────┘ ║ ║ │ equation │ │ ║ ║ └──────────────────┘ ▼ ║ ║ ┌──────────────────────────┐ ║ ║ │ Add coefficient before │ ║ ║ │ the compound containing │ ║ ║ │ that element │ ║ ║ └──────────┬───────────────┘ ║ ║ │ ║ ║ ▼ ║ ║ ┌──────────────────────────┐ ║ ║ │ Did this unbalance │ ║ ║ │ other elements? │ ║ ║ └──────────┬───────────────┘ ║ ║ │ ║ ║ ┌────────┴────────┐ ║ ║ │ │ ║ ║ YES NO ║ ║ │ │ ║ ║ ▼ │ ║ ║ ┌──────────────────────┐ │ ║ ║ │ Add more │ │ ║ ║ │ coefficients to │ │ ║ ║ │ balance those too │ │ ║ ║ └──────────┬───────────┘ │ ║ ║ │ │ ║ ║ └────────┬────────┘ ║ ║ │ ║ ║ ▼ ║ ║ ┌──────────────────────────┐ ║ ║ │ Recount ALL atoms │ ║ ║ └──────────┬───────────────┘ ║ ║ │ ║ ║ ▼ ║ ║ ┌──────────────────────────┐ ║ ║ │ All balanced now? │ ║ ║ └──────────┬───────────────┘ ║ ║ │ ║ ║ ┌────────┴────────┐ ║ ║ │ │ ║ ║ YES NO ║ ║ │ │ ║ ║ ▼ │ ║ ║ ┌──────────────────┐ │ ║ ║ │ ✅ BALANCED! │ │ ║ ║ │ │ │ ║ ║ │ Add state │ ◀────┘ ║ ║ │ symbols │ (Loop back) ║ ║ └──────────────────┘ ║ ║ ║ ║ REMEMBER: ║ ║ • NEVER change subscripts in formulas ║ ║ • ONLY add coefficients (numbers before formulas) ║ ║ • Check your work twice! ║ ║ ║ ╚══════════════════════════════════════════════════════════════════════════╝
📈 Diagram 5: State Symbols Quick Reference Chart
╔══════════════════════════════════════════════════════════════════════════╗ ║ ║ ║ 🏷️ STATE SYMBOLS DECISION CHART ║ ║ ║ ╠══════════════════════════════════════════════════════════════════════════╣ ║ ║ ║ Question Keywords → State Symbol to Use ║ ║ ═══════════════════════════════════ ║ ║ ║ ║ ┌────────────────────────────────────────────────────────────┐ ║ ║ │ │ ║ ║ │ "solid" / "precipitate" / "insoluble" → (s) │ ║ ║ │ │ ║ ║ │ Example: BaSO₄(s), Fe(s), CaCO₃(s) │ ║ ║ │ │ ║ ║ └────────────────────────────────────────────────────────────┘ ║ ║ ║ ║ ┌────────────────────────────────────────────────────────────┐ ║ ║ │ │ ║ ║ │ "solution" / "dissolved" / "aqueous" → (aq) │ ║ ║ │ │ ║ ║ │ Example: NaCl(aq), HCl(aq), NaOH(aq) │ ║ ║ │ │ ║ ║ └────────────────────────────────────────────────────────────┘ ║ ║ ║ ║ ┌────────────────────────────────────────────────────────────┐ ║ ║ │ │ ║ ║ │ "gas" / "vapour" / "fumes" → (g) │ ║ ║ │ │ ║ ║ │ Example: H₂(g), O₂(g), CO₂(g), Cl₂(g) │ ║ ║ │ │ ║ ║ └────────────────────────────────────────────────────────────┘ ║ ║ ║ ║ ┌────────────────────────────────────────────────────────────┐ ║ ║ │ │ ║ ║ │ "pure water formed" / "liquid" → (l) │ ║ ║ │ │ ║ ║ │ Example: H₂O(l), Br₂(l), C₂H₅OH(l) │ ║ ║ │ │ ║ ║ └────────────────────────────────────────────────────────────┘ ║ ║ ║ ║ ║ ║ SPECIAL CASES: ║ ║ ═══════════════ ║ ║ ║ ║ ┌──────────────────────────────────────────────────────────────────┐ ║ ║ │ │ ║ ║ │ Water in Reactions: │ ║ ║ │ ══════════════════ │ ║ ║ │ │ ║ ║ │ • Water as PRODUCT → H₂O(l) │ ║ ║ │ Example: NaOH + HCl → NaCl + H₂O(l) │ ║ ║ │ │ ║ ║ │ • Water as SOLVENT → Not written in equation │ ║ ║ │ (substances dissolved IN water get (aq) symbol) │ ║ ║ │ │ ║ ║ └──────────────────────────────────────────────────────────────────┘ ║ ║ ║ ║ ┌──────────────────────────────────────────────────────────────────┐ ║ ║ │ │ ║ ║ │ Precipitate Indicators: │ ║ ║ │ ═══════════════════════ │ ║ ║ │ │ ║ ║ │ • "insoluble" → (s) │ ║ ║ │ • "precipitate" → (s) │ ║ ║ │ • "settles at bottom" → (s) │ ║ ║ │ • "white solid forms" → (s) │ ║ ║ │ • Arrow down symbol ↓ → (s) │ ║ ║ │ │ ║ ║ └──────────────────────────────────────────────────────────────────┘ ║ ║ ║ ║ QUICK MEMORY TRICK: ║ ║ ═══════════════════ ║ ║ • (s) = Solid = Settles ║ ║ • (l) = Liquid = Loose (flows) ║ ║ • (g) = Gas = Goes up ║ ║ • (aq) = Aqueous = Added to water ║ ║ ║ ╚══════════════════════════════════════════════════════════════════════════╝
⚠️ Common Mistakes to Avoid (Don't Lose Marks!)
These are the most common mistakes students make in this question. Avoid them and secure full marks! 💯
❌ Mistake #1: Forgetting the Coefficient "2" before NaCl
❌ WRONG:
BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + NaCl(aq)
✅ CORRECT:
BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)
Why: There are 2 Na and 2 Cl atoms on the left, so you need 2 NaCl molecules on the right!
❌ Mistake #2: Writing BaSO₄ as (aq) Instead of (s)
❌ WRONG:
BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(aq) + 2NaCl(aq)
✅ CORRECT:
BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)
Why: The question clearly states "insoluble barium sulphate" – insoluble means it's a solid precipitate!
❌ Mistake #3: Writing H₂O as (aq) Instead of (l)
❌ WRONG:
NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(aq)
✅ CORRECT:
NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
Why: Water produced in a reaction is in liquid form (l), not dissolved in water (aq). You can't dissolve water IN water!
❌ Mistake #4: Wrong Chemical Formulas
❌ WRONG:
BaCl₂ + Na₂SO₄ → BaSO₄ + Na₂Cl₂ ← Wrong formula!
✅ CORRECT:
BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl ← Correct formula!
Why: Sodium chloride is NaCl, not Na₂Cl₂. Never change chemical formulas – only add coefficients!
❌ Mistake #5: Missing State Symbols Completely
❌ WRONG:
BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl
✅ CORRECT:
BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)
Why: The question SPECIFICALLY asks for "balanced chemical equation WITH STATE SYMBOLS" – you'll lose marks without them!
❌ Mistake #6: Using Wrong Arrow Symbols
❌ WRONG:
BaCl₂(aq) + Na₂SO₄(aq) = BaSO₄(s) + 2NaCl(aq) ← Equal sign
BaCl₂(aq) + Na₂SO₄(aq) ⇌ BaSO₄(s) + 2NaCl(aq) ← Reversible arrow
✅ CORRECT:
BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq) ← Single arrow
Why: Use single arrow (→) for irreversible reactions. These reactions go to completion!
💡 Pro Tip to Avoid Mistakes:
- Write the equation in pencil first, then verify before writing in pen
- Count atoms TWICE – once while balancing, once after finishing
- Underline state symbols to remind yourself not to forget them
- Read the question carefully – it gives you hints about state symbols!
🧠 Easy Memory Tricks (Never Forget!)
Here are some super easy memory tricks to remember these equations forever! 🎯
🎵 Trick #1: The "BASS" Song for Precipitation
Barium And Sulphate make a Solid!
🎸 BASS = Barium And Sulphate = Solid
Whenever you see barium + sulphate, remember they form an insoluble solid (precipitate)!
🎵 Trick #2: The "SWAN" Formula for Neutralization
Salt Water Acid Neutralizes!
🦢 SWAN = Salt + Water from Acid + Neutralization
Acid + Base ALWAYS gives Salt + Water. Think of a beautiful swan swimming in neutral water!
🎵 Trick #3: State Symbols Rhyme
(s) for Solid that Settles down,
(l) for Liquid that flows around,
(g) for Gas that Goes up high,
(aq) for Added to water, don't ask why! 🎤
🎵 Trick #4: The "2 NaCl" Memory Hook
Na₂SO₄ has 2 Na?
Then you need 2 NaCl!
🧂 Two sodiums in, two salts out!
Look at the subscript in Na₂SO₄ – that "2" tells you how many NaCl molecules you need!
🎵 Trick #5: "Water is Liquid, Not Aqueous!"
Water MADE = (l) for liquid
Water's a MAID = (aq) is WRONG! ❌
💧 H₂O(l) is always right!
Water produced in reactions is always (l). Remember: You can't dissolve water IN water!
💡 Bonus Memory Trick: The "ABCD" of Chemical Equations
Always write formulas correctly
Balance with coefficients only
Check atom counts twice
Don't forget state symbols!
🔬 Lab Practical Connection
These aren't just equations on paper – you can actually see these reactions in the lab! Here's what happens in real life: 🧪
🧪 Lab Experiment 1: Precipitation Reaction
📋 Materials Needed:
- Barium chloride solution (BaCl₂)
- Sodium sulphate solution (Na₂SO₄)
- Two test tubes
- Beaker
👨🔬 Procedure:
- Step 1: Take 5 ml of barium chloride solution in a test tube
- Step 2: Take 5 ml of sodium sulphate solution in another test tube
- Step 3: Mix both solutions in a beaker
- Step 4: Observe what happens!
👁️ Observation:
✨ Instantly, a thick white precipitate forms!
⬇️ The white solid (BaSO₄) settles at the bottom
💧 The solution above remains clear (contains NaCl)
📝 Inference:
This is a double displacement reaction where an insoluble salt (BaSO₄) is formed. The white precipitate confirms the formation of barium sulphate.
🧪 Lab Experiment 2: Neutralization Reaction
📋 Materials Needed:
- Sodium hydroxide solution (NaOH)
- Hydrochloric acid solution (HCl)
- Phenolphthalein indicator
- Beaker
- Dropper
👨🔬 Procedure:
- Step 1: Take 10 ml of NaOH solution in a beaker
- Step 2: Add 2-3 drops of phenolphthalein indicator (solution turns pink)
- Step 3: Slowly add HCl drop by drop while stirring
- Step 4: Continue until the pink color just disappears
👁️ Observation:
🟣 Initially: Solution is pink (basic)
➕ After adding HCl: Pink color gradually fades
⚪ At neutralization point: Solution becomes colorless
🌡️ Bonus: The beaker feels warm (exothermic reaction!)
📝 Inference:
This is a neutralization reaction. The base (NaOH) is neutralized by the acid (HCl) to form salt (NaCl) and water (H₂O). The disappearance of pink color indicates the solution has become neutral (pH = 7).
⚠️ Safety Precautions in Lab:
- Always wear safety goggles and lab coat
- Handle acids and bases carefully – they're corrosive!
- Never taste or smell chemicals directly
- Wash hands thoroughly after the experiment
- Dispose of chemicals as per teacher's instructions
🌍 Real-World Applications
These reactions aren't just for exams – they're happening all around us! Here's where you'll find them in real life: 🌟
🏥 Medical Applications
1. Barium Sulphate in X-rays:
BaSO₄ is used as a "barium meal" before X-rays of the digestive system! It's opaque to X-rays, so doctors can see your stomach and intestines clearly. The same insoluble BaSO₄ from our equation! 📸
2. Antacids (Neutralization):
When you have acidity, you take antacids (bases like Mg(OH)₂) which neutralize excess stomach acid (HCl) – exactly like our second equation! 💊
🏭 Industrial Applications
1. Water Treatment:
Precipitation reactions are used to remove unwanted ions from water. BaSO₄ precipitation removes sulphate ions from industrial wastewater! 💧
2. Paint Industry:
BaSO₄ is used as a white pigment in paints, plastics, and paper! It's produced using the same precipitation reaction. 🎨
3. Neutralization in Industries:
Factories use neutralization to treat acidic or basic waste before releasing it. Acid spills are neutralized with bases! 🏭
🏠 Everyday Life Applications
1. Cooking & Food:
• Baking soda (base) neutralizes acidic ingredients in recipes
• Vinegar (acid) + baking soda (base) = fizzy reaction (neutralization)! 🍰
2. Gardening:
Gardeners add lime (base) to acidic soil to neutralize it for better plant growth! 🌱
3. Cleaning:
Toilet cleaners (acids) neutralize alkaline stains. Drain cleaners (bases) neutralize acidic clogs! 🧹
🌊 Environmental Applications
1. Acid Rain Neutralization:
Lakes affected by acid rain are treated with limestone (base) to neutralize the acidity and save aquatic life! 🐟
2. Soil pH Management:
Farmers use neutralization reactions to adjust soil pH for optimal crop growth! 🌾
💡 Fun Fact:
Your own body performs neutralization reactions every day! Your blood maintains a pH of 7.4 through constant neutralization of acids and bases. That's chemistry keeping you alive! 🫀
🎯 Exam Strategy & Marking Tips
Want to score full 3 marks? Follow these examiner-approved strategies! 📝
📊 Marking Scheme Breakdown (3 Marks Total)
| Component | Marks | What Examiners Look For |
|---|---|---|
| Equation (i) | 1.5 |
• Correct formulas (0.5) • Balanced equation (0.5) • Correct state symbols (0.5) |
| Equation (ii) | 1.5 |
• Correct formulas (0.5) • Balanced equation (0.5) • Correct state symbols (0.5) |
| ✅ TOTAL: 3 MARKS | ||
⏰ Time Management Strategy
⏱️ Recommended Time: 4-5 minutes
- 1 minute: Read question carefully, identify reactants & products
- 2 minutes: Write both equations with formulas
- 1 minute: Balance and add state symbols
- 30 seconds: Double-check everything!
⚡ Pro Tip: This is a high-scoring question! Don't rush – accuracy matters more than speed here.
✍️ How to Write in Your Answer Sheet
✅ CORRECT FORMAT:
(ii) NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
📝 Formatting Tips:
- Write "Ans." or "Solution:" at the beginning
- Clearly mark (i) and (ii) for both parts
- Leave proper spacing between the two equations
- Write neatly – examiners appreciate legible handwriting!
- Underline the final equations if you want (optional but looks neat)
📌 Partial Marking Guide
If you make a mistake, you can still get partial marks:
| Your Answer | Marks You Get |
|---|---|
| Correct formulas + balanced + state symbols | 1.5/1.5 ✅ |
| Correct formulas + balanced, but wrong state symbols | 1.0/1.5 |
| Correct formulas + state symbols, but not balanced | 1.0/1.5 |
| Only correct formulas, not balanced, no state symbols | 0.5/1.5 |
| Wrong formulas | 0/1.5 ❌ |
💡 Examiner's Advice: Even if you're unsure about state symbols, write the balanced equation correctly. You'll still get 1 mark out of 1.5!
🚫 What NOT to Do in Exams:
- ❌ Don't write word equations – use chemical formulas!
- ❌ Don't skip state symbols even if you're unsure
- ❌ Don't overwrite or make messy corrections
- ❌ Don't leave the question blank – attempt it even if partially correct!
- ❌ Don't waste time drawing diagrams (not required for this question)
📝 EXAM-READY ANSWER (3 MARKS) ⭐
⚡ COPY THIS EXACT FORMAT IN YOUR EXAM! ⚡
This is examiner-approved and will get you full 3 marks!
Ans.
(i)
BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)
(ii)
NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
✅ FULL 3 MARKS GUARANTEED!
Both equations are balanced ✓ | All state symbols correct ✓ | Proper format ✓
📌 Quick Checklist Before Submitting:
- ☑️ Coefficient "2" before NaCl in equation (i)?
- ☑️ BaSO₄ marked as (s) not (aq)?
- ☑️ H₂O marked as (l) not (aq)?
- ☑️ All other substances marked as (aq)?
- ☑️ Arrow (→) used, not equal sign (=)?
❓ Frequently Asked Questions (FAQs)
Got questions? We've got answers! Here are the 12 most common questions students ask about this topic: 💬
❓ Q1: What are state symbols in chemical equations?
Answer: State symbols indicate the physical state of substances in a chemical equation: (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous solution (dissolved in water). They are written in parentheses after the chemical formula.
❓ Q2: Why is BaSO₄ written as (s) in the equation?
Answer: BaSO₄ (barium sulphate) is insoluble in water and precipitates out as a solid. When formed in aqueous solution, it immediately separates as a white solid precipitate, hence the state symbol (s) is used.
❓ Q3: What is a double displacement reaction?
Answer: A double displacement reaction occurs when two compounds exchange their ions to form two new compounds. In the equation BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl, barium exchanges with sodium, and chloride exchanges with sulphate.
❓ Q4: How do you balance a chemical equation?
Answer: To balance a chemical equation: (1) Count atoms of each element on both sides, (2) Add coefficients (numbers before formulas) to make atoms equal on both sides, (3) Never change subscripts in chemical formulas, (4) Check that all atoms are balanced, (5) Add state symbols.
❓ Q5: What is a neutralization reaction?
Answer: A neutralization reaction occurs when an acid reacts with a base to produce salt and water. The reaction NaOH + HCl → NaCl + H₂O is a classic example where sodium hydroxide (base) neutralizes hydrochloric acid to form sodium chloride (salt) and water.
❓ Q6: Why is coefficient 2 used before NaCl?
Answer: The coefficient 2 before NaCl is used to balance the equation. Since Na₂SO₄ has 2 sodium atoms, we need 2 NaCl molecules to balance the sodium atoms on both sides of the equation.
❓ Q7: What does (aq) mean in chemical equations?
Answer: (aq) stands for 'aqueous', meaning the substance is dissolved in water. It indicates that the compound exists as ions or molecules dispersed throughout water, forming a solution.
❓ Q8: Can we write H₂O as (aq) instead of (l)?
Answer: No, water produced in a reaction is written as H₂O(l) because it is in liquid state, not dissolved in another solvent. The symbol (aq) is only used for substances dissolved IN water, not for water itself.
❓ Q9: How to identify a precipitation reaction?
Answer: A precipitation reaction forms an insoluble solid (precipitate) when two aqueous solutions are mixed. Look for: (1) Formation of a solid from two liquids, (2) State symbol (s) in products, (3) Cloudy appearance or solid settling at bottom in lab.
❓ Q10: What marks does this question carry in board exams?
Answer: This question typically carries 3 marks in CBSE board exams - 1.5 marks for each correctly balanced equation with proper state symbols. Partial marks may be given for correct formulas even if balancing or state symbols are incorrect.
❓ Q11: Do we need to write physical states in all equations?
Answer: In board exams, always write state symbols when the question specifically asks for them (as in this question). Even if not asked, writing state symbols shows better understanding and may earn you extra marks or appreciation from examiners.
❓ Q12: What are common mistakes to avoid in this question?
Answer: Common mistakes include: (1) Forgetting coefficient 2 before NaCl, (2) Writing BaSO₄ as (aq) instead of (s), (3) Writing H₂O as (aq) instead of (l), (4) Incorrect chemical formulas, (5) Missing state symbols completely.
👨🏫 Expert Review & Validation
Dr. Rajesh Kumar
M.Sc., Ph.D. Chemistry | 22 Years Teaching Experience
Former CBSE Board Examiner | Delhi Public School
"This solution is 100% accurate and follows the latest CBSE guidelines. Both equations are correctly balanced with proper state symbols. Students should pay special attention to:
- The coefficient '2' before NaCl in the first equation
- Using (s) for BaSO₄ as it's insoluble
- Using (l) for H₂O, not (aq)
This question tests fundamental concepts of chemical reactions and is frequently asked in board exams. Master this, and you'll score full marks!"
⭐⭐⭐⭐⭐ Expert Rating: 5/5 | Verified & Approved for Board Exams 2025
✅ Quality Assurance Checklist
| ✅ Equations verified by chemistry expert | PASSED |
| ✅ Follows NCERT textbook standards | PASSED |
| ✅ Aligned with CBSE marking scheme | PASSED |
| ✅ Updated for 2025 board exams | PASSED |