Calculate The Percentage Composition of Each of The Following Srbr2

Strontium bromide (SrBr₂) is an ionic compound composed of strontium cations (Sr²⁺) and bromide anions (Br^-). Calculating its percentage composition by mass and by moles helps understand its chemical makeup and properties.

What is SrBr2?

Strontium bromide is a white crystalline solid that dissolves in water to form a colorless solution. It's used in analytical chemistry, as a source of bromide ions, and in some specialized applications in optics and electronics.

The compound has a molar mass of approximately 229.37 g/mol, calculated by summing the atomic masses of strontium and bromine:

Molar mass of SrBr₂ = Atomic mass of Sr + 2 × Atomic mass of Br
= 87.62 g/mol + 2 × 79.90 g/mol
= 87.62 + 159.80 g/mol
= 247.42 g/mol

Note: The actual molar mass may vary slightly due to isotopic variations.

How to Calculate Percentage Composition

Percentage composition by mass is calculated using the formula:

Percentage by mass = (Mass of element / Molar mass of compound) × 100

For percentage composition by moles, we use:

Percentage by moles = (Number of moles of element / Total number of moles in compound) × 100

Step-by-Step Calculation

Determine the molar mass of the compound (SrBr₂ = 247.42 g/mol)
Find the atomic mass of each element:
- Strontium (Sr) = 87.62 g/mol
- Bromine (Br) = 79.90 g/mol
Calculate the percentage of each element by mass:
- % Sr = (87.62 / 247.42) × 100 ≈ 35.42%
- % Br = (2 × 79.90 / 247.42) × 100 ≈ 64.58%
For percentage by moles:
- SrBr₂ contains 1 mole of Sr and 2 moles of Br
- Total moles = 1 + 2 = 3 moles
- % Sr by moles = (1/3) × 100 ≈ 33.33%
- % Br by moles = (2/3) × 100 ≈ 66.67%

Example Calculation

Let's calculate the percentage composition of 247.42 grams of SrBr₂:

Element	Mass (g)	Percentage by Mass	Percentage by Moles
Strontium (Sr)	87.62	35.42%	33.33%
Bromine (Br)	159.80	64.58%	66.67%

This shows that strontium makes up about 35% of the mass and 33% of the moles in SrBr₂, while bromine constitutes the remaining percentages.

FAQ

What is the difference between percentage by mass and percentage by moles?: Percentage by mass considers the actual weight of each element, while percentage by moles considers the number of atoms or molecules of each element relative to the total.
Why is the percentage by mass of bromine higher than by moles?: Bromine has a higher atomic mass (79.90 g/mol) compared to strontium (87.62 g/mol), so it contributes more to the mass percentage despite having fewer moles in the compound.
How does temperature affect the percentage composition?: Percentage composition is a fundamental property of a compound and doesn't change with temperature under normal conditions. It's based on the chemical formula and atomic masses.
Can I use this calculator for other compounds?: Yes, the same method applies to any compound. Just input the atomic masses and the formula to calculate the percentage composition.