What You Need to Know
Experimental techniques in chemistry are all about choosing the right tool for the right job. Different apparatus measure different quantities with different levels of accuracy. The IGCSE expects you to not only know what each piece of apparatus does, but also why you'd choose one over another, and how to use it correctly.
The Four Big Ideas
- Measuring accurately: The apparatus you choose depends on whether you need an approximate or precise measurement.
- Following procedure: Titrations and other techniques have strict steps that must be followed precisely — small errors become big ones.
- Understanding solutions: The language of solutions (solute, solvent, saturated) is crucial for planning and describing experiments.
- Evaluating apparatus: Every tool has pros and cons. Examiners love asking you to evaluate which is "best" for a given task.
Chapter Overview
- Apparatus for Measurements – Time, temperature, mass, liquid volume, gas volume
- Solutions – The language: solvent, solute, saturated, filtrate, residue
- Acid-Base Titrations – The procedure, common errors, indicators
1. Apparatus for Measurements
Chemistry is about measuring things: time, temperature, mass, and volume. Each measurement needs the right apparatus. Let's go through each one.
Measuring Time
You measure time using a stopwatch or stopclock. These are usually accurate to 1–2 decimal places, meaning they show you down to tenths or hundredths of a second.
- Units: Normally seconds or minutes. For very slow reactions (like rusting), you might use hours or even days.
- Key conversion: 1 minute = 60 seconds. This matters more than you'd think in the exam.
⚠️ Common Mistake: Time Units
If your stopwatch shows 1:30, that's 1 minute and 30 seconds. This is NOT 1.30 minutes — it's 1.5 minutes. Better yet: convert it to seconds: 90 seconds. This avoids all confusion and is what examiners prefer to see.
Measuring Temperature
You measure temperature using a thermometer or a digital temperature probe.
How they work:
- Traditional thermometer: Uses uniform expansion/contraction of a liquid (usually alcohol or mercury) as temperature changes. A simple glass tube with a scale.
- Digital temperature probe: Uses an electrical sensor to detect heat and display it on a screen. More precise (can read to 0.1°C).
- Precision: Lab thermometers usually read to ±0.5°C or ±1°C. Digital probes can be much more precise: ±0.1°C.
- Units: Always degrees Celsius (°C).
- When to choose which: Use a digital probe if you need high precision or automation (e.g., recording temperature over time). Use a traditional thermometer for simpler experiments.
Measuring Mass
You measure mass using a digital balance. These are standard in any chemistry lab.
How to use a digital balance correctly
1. Tare it (zero it): Press the "TARE" or "ZERO" button to reset the display to 0.00 g before placing anything on it.
2. Wait for it to settle: After placing your object on the balance, wait a few seconds for the reading to stabilise before recording it.
3. Read the value: Digital balances typically show readings to 2 decimal places (e.g., 5.43 g).