After repeating vacuum drying, dry mass determinations that are within 0.3 g of one another indicate that drying is complete.

After repeating vacuum drying, dry mass determinations that are within 0.3 g of one another indicate that drying is complete.

• A. True
• B. False
• C. Not specified
• D. They must be within 0.1 g

Answer: (A)

Constant mass across repeated vacuum drying shows you’ve removed enough moisture that the sample won’t lose more mass in the future. In practice, you weigh, dry, weigh again, and compare the results. If successive dry masses are within a small tolerance, here 0.3 g, you’ve reached a stable dry mass and drying is complete. The tolerance accounts for slight balance variability and minor handling differences, so you’re not chasing an impossible zero-difference reading. Not specifying a tolerance would ignore the real-world need for a stability criterion. Requiring a tighter difference, like 0.1 g, would be more stringent than this procedure calls for and would waste time without significantly improving accuracy in many cases.

Constant mass across repeated vacuum drying shows you’ve removed enough moisture that the sample won’t lose more mass in the future. In practice, you weigh, dry, weigh again, and compare the results. If successive dry masses are within a small tolerance, here 0.3 g, you’ve reached a stable dry mass and drying is complete. The tolerance accounts for slight balance variability and minor handling differences, so you’re not chasing an impossible zero-difference reading.

Not specifying a tolerance would ignore the real-world need for a stability criterion. Requiring a tighter difference, like 0.1 g, would be more stringent than this procedure calls for and would waste time without significantly improving accuracy in many cases.