Why did one liter of have a greater mass than the other liter prepared by a different method

Nobody can answer your question, because we have no idea
what belongs after the word "... of ...", so we don't know what
substance(s) you're talking about. 

All we can say for sure is that the first method produces the substance
with greater density, because it has more mass in the same volume.

It will take annabelle 4 hours to complete her homework. if it took her 3 hours to finish 75%, then it probably took her 1 hour for every 25% she finished. if she finished 75%, she has 25% left to be done or 100% complete. 25% = 1 hour. so 3 hours + 1 hour = 4 hours or 100% complete

It won't lose or gain electrons if it's a covalent bond it shares the electrons with another atom or atoms. if it is an ionic bond it will lose the 3 electrons on the outer shell and become a positively charged ion.  credit goes to @sunshinebaby of answers.yahoo.com.