Suggest an explanation and method of improvement when a reaction has negative yield i.e. the mass of container with product is less than the mass of empty container. This happened to me twice in an orgo lab and I have no idea whats going on.
If the mass of the container with product is less than without then there are some possible mistakes:
- you wrote down/used the wrong mass/container
- you weighted the empty container with plug/screw cap and afterwards without
- you changed the plug/screw cap
- you had the container filled with a gas with higher density than air (common with argon), which can be a difference of some hundred mg depending on the size.
- the temperature wasn't the same, don't weigh hot/warm flasks
From my experience as TA in synthetic labs: it's most likely the second one.