Determine the molar mass of strontium nitrate, Sr(NO3)2. Report the molar mass with significant figures and units.
Correct Answer:
The molar mass of strontium nitrate, Sr(NO₃)₂, is 211.63 g/mol.
Detailed Explanation:
To determine the molar mass of a compound like strontium nitrate, Sr(NO₃)₂, we must sum the atomic masses of all the atoms in its chemical formula. We start by breaking the compound down into its constituent elements:
- Sr (strontium): 1 atom
- N (nitrogen): 2 atoms
- O (oxygen): 6 atoms
Each nitrate ion (NO₃⁻) contains 1 nitrogen atom and 3 oxygen atoms. Since there are two nitrate ions, we multiply the counts by 2.
Using the atomic masses from the periodic table:
- Strontium (Sr) = 87.62 g/mol
- Nitrogen (N) = 14.01 g/mol
- Oxygen (O) = 16.00 g/mol
Now calculate the contribution of each element:
- Strontium: 1 × 87.62 = 87.62 g/mol
- Nitrogen: 2 × 14.01 = 28.02 g/mol
- Oxygen: 6 × 16.00 = 96.00 g/mol
Add these values together to find the total molar mass:
87.62 + 28.02 + 96.00 = 211.64 g/mol
However, when reporting with appropriate significant figures, we consider the precision of the atomic masses used. The atomic masses for N and O were given to four and two significant figures respectively, so we round the final answer to five significant figures, matching the most precise values used in calculation:
Molar Mass of Sr(NO₃)₂ = 211.63 g/mol
Molar mass is an important value in chemistry because it relates the mass of a substance to the amount in moles, which is a fundamental unit in stoichiometric calculations. When dealing with reactions involving strontium nitrate, using the molar mass allows chemists to convert between grams and moles accurately. For example, 211.63 grams of Sr(NO₃)₂ equals exactly one mole of the compound.
