Lesson 8: Qualitative Analysis & Unknown Organic Identification
Demonstrating understanding of organic chemical structure, properties, and reactions for NCEA Level 2 Chemistry.
🎯 Ngā Whāinga Akoranga | Learning Intentions
Qualitative chemical tests used to identify unknown organic liquids (litmus test, NaHCO3, Br2 water, MnO4-/H+, Cr2O72-/H+, water solubility/phase separation).
Design a systematic elimination flowchart to distinguish between 5 unknown organic bottles based on experimental observations and chemical reasoning.
🎥 Media Anchor & Pedagogical Scaffold
Qualitative Identification of Unknown Organics
Video Clip: Qualitative Analysis — chemical tests to identify unknown compounds | GCSE, CSEC, and CAPE Chemistry (gSquared Academy) (Runtime: 11m 30s).
🧠 1. Before Viewing (Activate & Predict)
If you are given 5 unlabelled clear liquids in a chemistry lab, what experimental steps allow you to safely identify each compound?
👁️ 2. During Viewing (Watch With a Job)
- Test table: as you watch, create a table with columns: Functional group tested | Reagent used | Positive result | What it indicates.
- Bromine water test: when would you add bromine water to an unknown organic compound, and what does a colour change (or no change) tell you?
- Unknown identification: the video shows how to build an argument from tests. If a compound turns bromine water colourless but does NOT react with sodium carbonate, what functional group can you confirm or eliminate?
🗣️ 3. After Viewing & Kaiako Move (Process & Apply)
Kaiako Move: Conduct the '5 Unknowns' qualitative analysis practical under timed exam-style conditions.
Immediate Task: Complete Section 8 of your Organic Portfolio: Unknown Identification Qualitative Flowchart & Justification Log.
⚡ Whakaoho | Do Now: Organic Recall Challenge (10 mins)
Four bottles, no labels. A cyclohexene, a primary alcohol, a carboxylic acid and an alkane. You have litmus, sodium hydrogencarbonate, bromine water and acidified dichromate.
Two minutes, before touching anything: write the order you would run the tests in, and why that order. A good sequence eliminates the most possibilities with the fewest tests — that is the actual skill being assessed.
📖 Activity 1: Core Reaction Mechanism & Structure Analysis (25 mins)
Run your scheme (20 min). Following the safety brief, work through your test order on the four unknowns. Record every observation, including the negatives — a test that does nothing is evidence. Identify each bottle and state which single observation was decisive for each one.
Defend it (5 min). Swap identifications with another pair. Where you disagree, settle it with observations rather than opinion, and if neither has decisive evidence, name the one extra test that would.
📝 Activity 2: Level 2 Chemistry Portfolio Task & Merit/Excellence Scaffolding (20 mins)
Organic Portfolio — Section 8. Submit: (1) your test sequence with the reasoning for the order; (2) a full observation table including negative results; (3) four identifications, each justified by a named decisive observation and the structural reason that observation occurs.
🏫 Kaiako Planning & Pedagogy Notes
NCEA Level 2 Alignment: Direct preparation for NCEA Level 2 Chemistry (External) (Demonstrate understanding of the properties of selected organic compounds). Emphasise linking observations and reagents to molecular structure for Merit/Excellence grades.