how do you determine the number of waters of hydration per formula unit? the general formula
Suppose you had a sample of MgSO4.7H2O that weighed 61.62g before heating an 30.1 after heating.
loss in weight is 61.62-30.1 = 31.52
30.1 is the mass H2O lost.
30.1 is the mass MgSO4 without the water.
molar mass MgSO4 = 120.37
molar mass H2O = 18
mols = g/molar mass
mols MgSO4 = 30.1/120.27 = 0.25
mols H2O = 31.52/18 = 1.75
So the ratio is 0.25 mol MgSO4 to 1.75 mols H2O. You want whole numbers to fit here. The way you do that is to divide both numbers by the smaller of the two; i.e.
mols MgSO4 = 0.25/0.25 = 1
mols H2O = 1.75/0.25 = 7
So the empirical formula is MgSO4.7H2O
To determine the number of waters of hydration per formula unit, you need to analyze the chemical formula of the hydrate compound. A hydrate is a compound that contains water molecules chemically bound to its formula unit. The general formula of a hydrate is represented as follows:
AnHydrate • nH2O
where "AnHydrate" represents the formula of the anhydrous (without water) compound, and "n" represents the number of water molecules attached per formula unit.
To determine the value of "n", you can follow these steps:
1. Determine the molar mass of the anhydrous compound (AnHydrate).
2. Determine the molar mass of the whole hydrate compound (AnHydrate • nH2O).
3. Calculate the molar mass of water (H2O).
4. Find the mass of water by subtracting the molar mass of the anhydrous compound (step 1) from the molar mass of the hydrate compound (step 2).
5. Divide the mass of water (step 4) by the molar mass of water (step 3) to find the number of moles of water.
6. Finally, divide the number of moles of water (step 5) by the number of moles of the anhydrous compound (step 1) to determine the number of waters of hydration per formula unit.
By following these steps, you can calculate the number of waters of hydration in a given hydrate compound.