Final answer:
By calculating the mass and moles of water and the moles of anhydrous strontium nitrate, we deduce a molar ratio of approximately 4, leading to the correct option is 3 hydrate formula of Sr(NO₃)₂ • 4H₂O.
Step-by-step explanation:
To determine the correct formula for the hydrate of strontium nitrate, we start by understanding that the mass of water lost upon heating is equal to the difference in mass between the hydrated salt and the anhydrous salt. Subtracting the mass of the anhydrous salt from the initial mass of the hydrate gives us the mass of water in the hydrate:
Mass of water = Mass of hydrate - Mass of anhydrous salt
= 1.056 g - 0.788 g
= 0.268 g
Now we can find the moles of water by dividing the mass of water by its molar mass (18.02 g/mol):
Moles of water = Mass of water / Molar mass of water
= 0.268 g / 18.02 g/mol
≈ 0.01487 mol
Next, we calculate the moles of anhydrous strontium nitrate using its molar mass (211.6 g/mol):
Moles of Sr(NO₃)₂ = Mass of Sr(NO₃)₂ / Molar mass of Sr(NO₃)₂
= 0.788 g / 211.6 g/mol
≈ 0.003725 mol
To find the molar ratio of water to strontium nitrate, divide the moles of water by the moles of strontium nitrate:
Molar ratio (H₂O:Sr(NO₃)₂) = Moles of water / Moles of Sr(NO₃)₂
= 0.01487 mol / 0.003725 mol
≈ 4
Since the molar ratio is approximately 4, the correct formula for the hydrate is Sr(NO₃)₂ • 4H₂O.