20. What prediction did Mendeleev make that came true less than 20 years later?
He said that the periodic table would be developed into 18 families.
He predicted the atomic numbers of unknown elements.
He said that three new elements would be discovered.
He predicted that a total of 112 elements would be discovered.

20. What prediction did Mendeleev make that came true less than 20 years

later?

He said that the periodic table would be developed into 18 families.

He predicted the atomic numbers of unknown elements.

He said that three new elements would be discovered.

He predicted that a total of 112 elements would be discovered.

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%