Which of the following must NOT be done when using an analytical balance?

• A. Weighing Warm Objects In The Balance.
• B. Placing The Sample Not At The Center But On The Side Of The Pan.
• C. Touching The Samples Or Sample Containers With Your Bare Fingers.
• D. Closing The Draft Shield Before Reading The Result.

Answer: (D)

The main idea here is that a precision analytical balance is extremely sensitive to disturbances from heat, drafts, and handling. Any of these can cause a reading to drift or be inaccurate, so proper technique focuses on minimizing those disturbances.

Closing the draft shield before reading the result is something you should not do because the shield is there to shield the pan from air currents during weighing. If you close it too early, you can trap air and heat around the pan and create unstable conditions that affect the measurement. The safer approach is to allow the reading to stabilize, then close the shield to protect the balance from drafts for subsequent measurements. The other practices are clearly problematic: weighing hot objects creates convection and drift, placing the sample off-center misaligns the load, and touching samples with bare fingers transfers oils and residues that alter mass.