A 3.48 gram sample of sodium sulfate hydrate lost 1.35 gram of water when heated to constant weight. What is the formula of the hydrate?
this is what I did, but I am stuck.
Na2SO4 . H2O------> NA2SO4+H20
So the mass of water is what? The loss due to water is the 1.35. How much is left?
3.48 - 1.35 = ?? must be the mass of the anhydrous Na2SO4.
So determine moles Na2SO4 and moles H2O. Convert those moles to small whole numbers just as if you had a percentage problem and want to know the empirical formula.
To determine the formula of the hydrate, you need to use the information about the mass of the compound and the mass of water lost during heating.
Step 1: Calculate the molar masses of sodium sulfate (Na2SO4) and water (H2O).
- The molar mass of Na2SO4 = 2(Na) + S + 4(O) = 2(23.0) + 32.1 + 4(16.0) = 142.1 g/mol
- The molar mass of H2O = 2(H) + O = 2(1.0) + 16.0 = 18.0 g/mol
Step 2: Calculate the number of moles of sodium sulfate and water.
- Moles of Na2SO4 = Mass of Na2SO4 / Molar mass of Na2SO4
- Moles of Na2SO4 = 3.48 g / 142.1 g/mol
- Moles of Na2SO4 = 0.0245 mol
- Moles of H2O = Mass of H2O lost / Molar mass of H2O
- Moles of H2O = 1.35 g / 18.0 g/mol
- Moles of H2O = 0.075 mol
Step 3: Determine the ratio of moles between Na2SO4 and H2O.
The ratio of moles of Na2SO4 to water can be obtained by dividing the number of moles of each substance by the smallest number of moles.
- Divide the moles of Na2SO4 and H2O by 0.0245 (the smallest number of moles):
- Moles of Na2SO4 = 0.0245 mol / 0.0245 mol = 1
- Moles of H2O = 0.075 mol / 0.0245 mol = 3.06 (approximately)
From the ratio, we can conclude that the formula of the hydrate is Na2SO4ยท3H2O, meaning that for every one mole of sodium sulfate, there are three moles of water.