Lab Practical

---
target: 30/30
author: Senior Sibling
name: lab-practical
description: >-
  12th Grade 30-mark Practical Exams (PCMB/PCMC). 
  Covers Volumetric Analysis, Salt Analysis, Physics Experiments, and Viva strategy.
---

# Lab Practical & Viva — Securing the 30/30

In Grade 12, the Practical exam is **30 Marks**. It is evaluated by an **External Examiner**. You need a perfect Lab Record, a functional project, and a confident Viva performance.

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## 🧪 Chemistry Experiments (30M)

### 1. Volumetric Analysis (8 Marks)
- **Experiment:** Determination of concentration/molarity of $KMnO_4$ solution by titrating it against a standard solution of **Oxalic Acid** or **Ferrous Ammonium Sulphate (Mohr's Salt)**.
- **Viva Logic:**
    - *Why is $H_2SO_4$ added?* (To provide acidic medium and prevent $MnO_2$ precipitation).
    - *Why don't we use $HCl$ or $HNO_3$?* ($HCl$ is oxidized by $KMnO_4$, $HNO_3$ is itself an oxidizing agent).
    - *What is the indicator?* ($KMnO_4$ is a self-indicator).

### 2. Salt Analysis (8 Marks)
- **Experiment:** Identification of one **Cation** and one **Anion** in a given salt.
- **Anions:** Carbonate, Sulphide, Sulphite, Nitrite, Sulphate, Chloride, Bromide, Iodide, Nitrate, Oxalate, Acetate, Phosphate.
- **Cations:** $Pb^{2+}, Cu^{2+}, As^{3+}, Al^{3+}, Fe^{3+}, Mn^{2+}, Zn^{2+}, Ni^{2+}, Co^{2+}, Ca^{2+}, Sr^{2+}, Ba^{2+}, Mg^{2+}, NH_4^+$.
- **Viva Logic:** Confirmatory tests (e.g., Brown Ring test for Nitrate, Chromyl Chloride test for Chloride).

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## 🔭 Physics Experiments (30M)

### 1. Section A & B Experiments
- **Current Electricity:** Ohm's Law (12th depth), Meter Bridge (Finding resistance/specific resistance), Potentiometer (Comparing EMF or finding Internal Resistance).
- **Optics:** Focal length of Convex Lens/Mirror using $u-v$ method, Refractive index of a glass slab/liquid using Traveling Microscope.
- **Semiconductors:** V-I characteristics of P-N junction diode and Zener diode.

### 2. Viva Strategy
- *Meter Bridge:* Why should the balance point be in the middle ($40-60 cm$)? (For maximum sensitivity).
- *Potentiometer:* Why is it preferred over a voltmeter? (It draws no current at null point, giving true EMF).

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## 🧬 Biology Experiments (30M)

1.  **Spotting:** Identification of slides/models (e.g., T.S. of Testis/Ovary, Meiosis stages, Blastula stage).
2.  **Major Experiment:** Isolation of DNA from plant material (e.g., Spinach/Pea).
3.  **Minor Experiment:** Study of pollen germination on a slide.

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## ✍️ The "Senior Sibling" Viva Protocol
- **Appearance:** Wear a clean lab coat. Keep your hair tied/neat. 
- **The First Question:** Most examiners ask "What is your favorite chapter?". Always have one chapter (e.g., Electrostatics or Coordination Compounds) mastered deeply for this.
- **Honesty:** If you don't know an answer, say "I am unable to recall at the moment, sir/ma'am" instead of guessing wildly.

**Command Integration:** Use `/viva-bot [Subject]` to simulate a mock viva session with an external examiner persona.