Mass in a chemistry lab is primarily measured using a balance. These balances are carefully calibrated to ensure accurate measurements, usually in grams.
Types of Balances Used
Several types of balances are common in a chemistry laboratory, each with varying degrees of precision:
- Analytical Balances: These are highly sensitive instruments capable of measuring mass to a high degree of accuracy (typically to the nearest 0.0001 g or 0.1 mg). They are used when very precise measurements are crucial for experiments and calculations.
- Top-Loading Balances: These balances are less sensitive than analytical balances but can handle larger masses. They are often used for general weighing purposes when high precision is not required.
- Microbalances: These balances offer extremely high precision, capable of measuring mass in micrograms (µg). They are used for specialized applications where minute mass changes need to be detected.
Using a Balance: Key Considerations
To obtain accurate mass measurements, several factors must be considered:
- Calibration: Balances must be regularly calibrated using standard weights to ensure accuracy. This compensates for any drift in the instrument's performance over time.
- Leveling: The balance must be placed on a stable, level surface. Most balances have adjustable feet and a bubble level to ensure proper leveling.
- Taring/Zeroing: Before measuring the mass of a substance, the balance should be tared (zeroed) with any container (e.g., a weighing boat or flask) that will hold the substance. This eliminates the container's mass from the final measurement.
- Environmental Factors: Air currents, vibrations, and temperature fluctuations can affect balance readings. Balances are often placed in a draft-free environment or have enclosures to minimize these effects.
- Sample Handling: Samples should be handled carefully to avoid contamination or loss of material. Static electricity can also affect the measurement of powders, so antistatic devices are sometimes used.
Example Procedure
Here's a simplified procedure for measuring the mass of a solid using an analytical balance:
- Ensure the balance is clean and level.
- Turn on the balance and allow it to warm up.
- Place a weighing boat on the balance pan.
- Tare the balance to zero.
- Carefully add the solid to the weighing boat until the desired mass is reached.
- Record the mass displayed on the balance.
- Carefully remove the weighing boat and solid.
- Clean the balance if any spills occurred.
