Key is one approach to identify something unknown?

If a polyatomic ionic compound has gained two hydrogen ions, then how does its name begin?

How can a give a full method for the experiment of separating sand from water by filtration? 1-materials 2-steps 3-conclusion also for water and salt separated by the evaporation or distillation process

What is the percent by mass of magnesium sulfate in mgso4.7h2o