Experimental Techniques - Apparatus for measurement

Measurement of Volume (Liquids): Measuring cylinders are used for approximate volumes. For high precision, a volumetric pipette is used for fixed volumes (e.g., $10.0 \text{ cm}^3$ or $25.0 \text{ cm}^3$), while a burette is used for variable volumes (accurate to $\pm 0.05 \text{ cm}^3$).

Measurement of Volume (Gases): A gas syringe is the most common apparatus for measuring the volume of gas evolved in a reaction. Alternatively, gas can be collected over water in a graduated tube if the gas is not soluble in water (e.g., $H_2$ or $O_2$).

Measurement of Mass: Electronic balances are used to measure mass, usually recorded in grams ($g$) to two or three decimal places for accuracy in stoichiometry.

Measurement of Temperature: Thermometers (alcohol or mercury-in-glass) or digital thermistors measure temperature in degrees Celsius ($^\circ\text{C}$); the SI unit is Kelvin ($K$).

Measurement of Time: Stopwatches or digital timers are used to measure the rate of reaction by timing the interval in seconds ($s$) or minutes ($min$).

Precision and Parallax Error: When reading volumes in glassware, the eye must be level with the bottom of the meniscus (the curve of the liquid) to avoid parallax error.

Apparatus Selection: The choice of apparatus depends on the required precision. For example, a $250 \text{ cm}^3$ beaker is unsuitable for measuring $25.0 \text{ cm}^3$ of a reagent accurately; a pipette or burette must be used.