Question

2.8% hydrogen, 9.8% nitrogen,20.5% nickel, 44.5% oxygen, and 22.4% sulfur

determine empirical formula for compounds

Answer 1

assume you have 1000g

then moles
of H=28g/1.007= 27.8 moles H
of Ni=205g/58.7=3.49 moles Ni
of O=445/16=22.8 moles O
of S=224/32= 7 moles of S

Now take the lowest number, divide it into all the others:
H=27.8/3.49=7.96
Ni=3.49/3.49=1
O=22.8/3.49=6.53
S=7/3.49=2
These are mole ratios of elements. Notice that O is six and a half, we need ratios in whole numbers. So double all numbers.
H=16
Ni=2
O=13
S=4

I wonder if it contains hydrate.. We could pull 8H2O out, and leave
Ni2 S4O5 which looks like a dead end. What if 7 waters were pulled out, we are left wiht
Ni2 H2 S4 O6 or Ni2 (HS2O3)2 which is leads us to
(Ni(HS2O3))2.7H2O
Nickel(+1) compounds are normally found in complex ligands. I am not certain this compound exists in nature. Hypo thiosulfates themselves are not all that common in complexes.

check my math, small errors lead to crazy conclusions.

Answer 2

I think N was left out of the calculations.
H = 2.8/1 = 2.8
N = 9.8/14 = 0.7
Ni = 20.5/58.7 = 0.349
O = 44.5/16 = 2.78
S = 22.4/32.1 = 0.698

Divide everything by 0.349 and round to whole numbers gives
H = 8
N = 2
Ni = 1
O = 8
S = 2
Ni(SO4)2(NH2)2

Answer 3

However, I am unfamiliar with that compound.