Combustion and Carius Method Combined Concept

 

❓ Concept Question

How do we calculate percentage of hydrogen using $CO_2$ and $AgBr$ data in organic analysis problems?

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🖼 Concept Image

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✍️ Short Concept

This concept is based on:

👉 Carbon estimation from $CO_2$
👉 Halogen estimation using $AgBr$
👉 Percentage composition method.

Main idea:

First calculate:

$$\%C$$

and

$$\%Br$$

Then remaining percentage gives hydrogen.

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🔷 Step 1 — Carbon from $CO_2$💯

From combustion:

$$1 \text{ mole } CO_2 \rightarrow 1 \text{ mole } C$$

Mass ratio:

$$\frac{12}{44}$$

So:

$$\text{Mass of Carbon} = \text{Mass of }CO_2 \times \frac{12}{44}$$

Used in combustion analysis questions.

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🔷 Step 2 — Bromine from $AgBr$

In Carius method:

$$AgBr$$

helps determine bromine amount.

Since:

$$1\text{ mole }AgBr \rightarrow 1\text{ mole }Br$$

Mass ratio:

$$\frac{80}{188}$$

So:

$$\text{Mass of Br} = \text{Mass of AgBr} \times \frac{80}{188}$$

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🔷 Step 3 — Mass Conservation Rule

Organic compound contains:

$$C,H,Br$$

Hence:

$$\text{Total mass} = C+H+Br$$

So hydrogen is obtained by difference:

$$H= \text{Total}-(C+Br)$$

Very important shortcut in JEE problems.

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🔷 Step 4 — Percentage Formula

Percentage of element:

$$\%\text{ element} = \frac{\text{mass of element}}{\text{total mass}} \times100$$

Used for:

$$\%C,\ \%H,\ \%Br$$

calculations.

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🔷 Step 5 — Mole Conversion Idea

Basic formula:

$$\text{Moles} = \frac{\text{Mass}}{\text{Molar Mass}}$$

This helps find:

$$x:y:z$$

ratio in molecular formulas.

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🔷 Step 6 — JEE Trap Alert 🚨

❌ $CO_2$ mass ko direct carbon mass maan lena

❌ $AgBr$ ka molar mass wrong lena

❌ Hydrogen by difference method bhool jaana

Remember:

$$\text{Remaining percentage} \rightarrow H$$

in many organic analysis questions.

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✅ Final Takeaway

For organic analysis:

$$CO_2 \rightarrow C$$
$$AgBr \rightarrow Br$$

Then:

$$H=\text{Remaining percentage}$$

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⭐ Golden JEE Insight

Always remember:

$$1\text{ mole }CO_2 \rightarrow 1\text{ mole }C$$
$$1\text{ mole }AgBr \rightarrow 1\text{ mole }Br$$

These direct mole relations save huge calculation time.

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📚 Related Topics

• Silver Halide Formation in Organic Analysis
• Faraday Law and Nernst Equation Combined Concept
• Mole Fraction of CO2 After Combustion Calculation