Answer to Question #134556 in General Chemistry for A

Question

SAFETY: If the stopcock becomes difficult to turn, which of the following statements describe a safe approach to loosening it? More than one answer may be correct.

a)If using a Teflon stopcock, loosen the locking nut slightly.

b)Use extra force to turn the tap.

c)If using a glass stopcock, stop the experiment, empty the buret and re-grease the tap.

Answer 1

Option c and a is correct

prefer Teflon as It doesn't require grease and won't "freeze up" due to corrosion with alkali. I wouldn't buy glass unless it was unavoidable

How about the use of ptfe tape (the thin flexible sort used for sealing threads) on stopcocks (glass) A little at the top and a little at the bottom, just as grease would be applied. Worth a try.

Obviously, both glass and PTFE stopcocks have their good and bad points. Select the best for particular applications. Glass for reaents and mixtures that will contaminate teflon, teflon for applications absent temperature extrema or very aggressive reagent, and for times when grease contamination would be a major nuisance (like prep of samples for analysis.)