Answer
$MgSO_{4}\times7H_{2}O$
Work Step by Step
Divide the mass of the dehydrated salt by its molar mass to get the moles of salt.
$\frac{2.41g}{120.366\frac{g}{mol}}= 0.020mol\ MgSO_{4}$
Divide the difference between the hydrated mass and dehydrated mass of the salt by the molar mass of water to find out how many moles of water were present in the hydrated salt.
$4.93-2.41= 2.52g\ H_{2}O$
$\frac{2.52}{18.015\frac{g}{mol}}=0.140mol\ H_{2}O$
Now Divide the moles of water by the moles of salt to get the number of moles of water per the number of moles of salt which will be the same as molecules of water per molecules of salt.
$0.140\div0.020=7$
Therefore the formula is: $MgSO_{4}\times7H_{2}O$
