24.6g of hydrated salt of MgSO4.xH2O gives 12g of anhydrous MgSO4 on heating. what is the value of x?
Answers
Explanation:
Explanation:
The idea here is that heating the hydrate will drive off the water of evaporation and leave behind the anhydrous salt.
In your case, the anhydrous salt is magnesium sulfate,
MgSO
4
. Since you know that after complete dehydration the mass of the sample is equal to
4.82 g
, you can say that the hydrate contained
4.82 g
→
MgSO
4
Use the molar mass of the compound to convert this to moles
4.82
g
⋅
1 mole MgSO
4
120.37
g
=
0.04004 moles MgSO
4
Now, the difference between the mass of the hydrate and the mass of the anhydrous salt will be equal to the mass of water of hydration.
You can thus say that the hydrate contained
mass of hydrate
9.86 g
−
mass of anhydrous salt
4.82 g
=
mass of water of hydration
5.04 g
Use the molar mass of water to convert this to moles
5.04
g
⋅
1 mole H
2
O
18.015
g
=
0.2798 moles H
2
O
The number of waters of hydration is given by the number of moles of water present for every
1
mole of anhydrous salt.
In your case, you know that
0.04004 moles MgSO
4
→
0.2798 moles H
2
O
This means that
1
mole of magnesium sulfate will have
1
moles MgSO
4
⋅
0.2798 moles H
2
O
0.04004
moles MgSO
4
=
6.988
≈
7
Therefore, you can say that the chemical formula of the hydrate is
MgSO
4
⋅
7
H
2
O
→
magnesium sulfate heptahydrate
The Value Of x Is 7
GIVEN
Weight of MgSO₄.xH₂O = 24.6 gram
Weight of MgSO₄ = 12 grams.
TO FIND
The value of x.
SOLUTION
We can simply solve the above problem as follows-
On heating, a hydrate will remove the water of hydration and leave anhydrous salt as a residue.
So, After complete dehydration -
Weight of salt = 12 grams
Number of moles = Given weight/molecular weight
= 12/120
0.1 moles.
We can say that -
weight of hydrate - the weight of anhydrous salt = the weight of water of hydration.
24.6 - 12 = 12.6
Weight of water of hydration = 12.6 grams.
According to stoichiometry
1 mole of H₂0 = molar mass of H₂O = 18grams
So,
18 grams = 1 mole of H₂O
12.6 grams =
= 0.7 moles.
We can observe that,
0.1 moles of MgSO₄ have 0.7 moles of water of hydration.
We know that,
Number of moles of hydration = moles of water per moles of anhydrous salt.
Therefore,
1 mole of Magnesium sulfate will have -
0.7 moles of water / 0.1 mole of magnesium sulfate
= 7
The chemical formula of the hydrate is MgSO₄.7H₂O
Hence, the value of x is 7
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