Chapter 12: Experimental Techniques and Chemical Analysis — Part 1

01 Measurement Apparatus

Selecting the appropriate apparatus is essential for accuracy and precision in chemical experiments.

• Measuring Time: Stopwatches are used to measure or control the duration of reactions. They are more accurate than analogue clocks, often measuring to the nearest millisecond. However, accuracy depends on the user's reaction time, which introduces human error.
• Measuring Temperature: Liquid-in-glass thermometers are common in laboratories due to their low cost and ease of use. They typically have an uncertainty of ±0.5°C. Disadvantages include limited ranges and potential parallax error.
• Measuring Mass: Digital balances provide fast, accurate readings, typically to 2 decimal places (or even micrograms). Balances must be tared (zeroed) before use and kept away from air currents.
• Measuring Volume of Liquids:
  • Burettes: Used to measure and deliver accurate volumes, commonly in titrations. The scale is read from top to bottom (0.00 cm³ is at the top).
  • Volumetric Pipettes: Used to deliver one specific, fixed volume (e.g., 10 cm³ or 25 cm³) consistently.
  • Measuring Cylinders: Used for approximate volumes. They are less accurate than pipettes but simpler and quicker to use.
• Measuring Volume of Gases: Gas syringes are used to collect gas from a reaction or deliver gas into a closed system. They are highly accurate but sensitive to temperature and pressure changes.

02 Key Definitions

• Solvent: A substance that dissolves a solute.
• Solute: A substance that is dissolved in a solvent.
• Solution: A mixture of one or more solutes dissolved in a solvent.
• Saturated Solution: A solution containing the maximum concentration of solute that can dissolve at a specified temperature.
• Filtrate: The liquid or solution that has passed through a filter.
• Residue: The substance that remains after filtration, evaporation, or distillation.