Answer:
There are found 3 water molecules per formula unit in a partially dehydrated sample of sodium sulfate with a formula mass of 197 amu.
Explanation:
The fully hydrated form of sodium sulfate is the decahydrate has structural formula of Na2SO4*10H2O
The molar mass of the decahydrate is 323 amu
When heated the hydrated salt loses water.
The molecular mass is now 197 amu
Na2SO4 has a molecular mass of 142.04 amu
1 molecule of water has a molecular mass of 18 amu
Before heating, the mass of Na2SO4*10H2O = 323 amu
After heating, the mass of Na2SO4*nH20 = 197 amu
The mass of nH2O lost = 323-197 = 126 amu
1* H2O has a molecular mass of 18 amu
n = 126/18 = 7
The mass after heating - the mass of Na2SO4 = The mass of nH2O
197 - 142 = 55
The mass of nH2O / the mass of 1*H2O = n
55/ 18 = 3
This partially dehydrated sample of sodium sulfate is Na2SO4*3H2O
There are found 3 water molecules per formula unit in a partially dehydrated sample of sodium sulfate with a formula mass of 197 amu.
