What is the formula mass of strontium phosphate? Show your calculation. 357.83 amu b_ 421.83 amu 182.59 amu d. 715.66 amu 452.80 amu
The Correct Answer and Explanation is:
To find the formula mass of strontium phosphate, Sr₃(PO₄)₂, follow these steps:
Step 1: Identify the elements and number of atoms
The chemical formula Sr₃(PO₄)₂ means:
- Sr (Strontium): 3 atoms
- P (Phosphorus): 2 atoms (because (PO₄)₂ means 2 phosphate groups)
- O (Oxygen): 8 atoms (4 from each phosphate group × 2 = 8)
Step 2: Use the atomic masses from the periodic table
- Sr (Strontium): 87.62 amu
- P (Phosphorus): 30.97 amu
- O (Oxygen): 16.00 amu
Step 3: Multiply and add
Mass of 3 Sr atoms:3×87.62=262.86 amu3 × 87.62 = 262.86\ \text{amu}3×87.62=262.86 amu
Mass of 2 P atoms:2×30.97=61.94 amu2 × 30.97 = 61.94\ \text{amu}2×30.97=61.94 amu
Mass of 8 O atoms:8×16.00=128.00 amu8 × 16.00 = 128.00\ \text{amu}8×16.00=128.00 amu
Total formula mass:262.86+61.94+128.00=452.80 amu262.86 + 61.94 + 128.00 = \boxed{452.80\ \text{amu}}262.86+61.94+128.00=452.80 amu
Final Answer:
Correct choice: e. 452.80 amu
Explanation
The formula mass of a compound is the sum of the atomic masses of all atoms in its formula unit. It represents the mass of one formula unit of an ionic compound in atomic mass units (amu). Strontium phosphate, Sr₃(PO₄)₂, is an ionic compound made of strontium ions and phosphate ions.
We start by analyzing the chemical formula. The subscript 3 next to Sr shows there are three strontium atoms. The (PO₄)₂ tells us that there are two phosphate groups. Each phosphate group contains one phosphorus atom and four oxygen atoms, so two groups contribute 2 phosphorus atoms and 8 oxygen atoms.
Next, we refer to the periodic table for the atomic masses: strontium is approximately 87.62 amu, phosphorus is 30.97 amu, and oxygen is 16.00 amu. We multiply the atomic mass of each element by the number of atoms in the compound. After calculating each contribution separately, we add them together to get the total formula mass.
This calculation gives us:
- Strontium: 262.86 amu
- Phosphorus: 61.94 amu
- Oxygen: 128.00 amu
Adding these yields a total formula mass of 452.80 amu.
This value matches option e, making it the correct answer. This mass tells us how much one formula unit of Sr₃(PO₄)₂ weighs in atomic mass units and is essential for converting between moles and grams in chemistry calculations.
