It should remain constant because of the law of conservation of mass and because the flask is sealed no mass will escape
You have to do it to see the results
The first thing you do before performing anything in the laboratory is to read the procedure and prepare the materials needed. Next, if you already have the solution where you are supposed to take your 20 mL sample, then have it near you. Then, prepare a volumetric flask (750 mL) and a 20-mL pipette. Wash the pipette 3 times with the sample solution. If your diluent is water, wash the flask 3 times with water. Now, get 20 mL of sample from your parent solution, then add it to the flask (previously washed with water). Finally, add water until the mark in the flask and make sure that the water added is up to the mark based on the lower meniscus reading to be accurate in the amount inside the flask. <span />
Answer: The percent yield of the reaction is 77.0 %
Explanation:
According to stoichiometry:
2 moles of 
produces = 2 moles of 
2.18 moles of is produced by=
of
Mass of =
percent yield =
