A student carried out an experiment to determine the number of moles of water of crystallisation in a hydrated salt, by mass loss upon heating.
The student obtained a lower value for the water of crystallisation than expected. Which of the following explains why?
The crystals were not heated strongly enough and some water remained in the crystals at the end.
The tube was covered in soot from incomplete combustion during the heating process.
Some crystals were lost from the tube during the heating process.
What can be done to close the gap?