How was the empirical formula mass of 141.94g/mol found? What are some easy steps I can use so I can remember for next time I calculate?

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How was the empirical formula mass of 141.94g/mol found?

What are some easy steps I can use so I can remember for next time I calculate?

### Determining Empirical and Molecular Formulas II

A white powder is analyzed and found to contain 43.64% phosphorus and 56.36% oxygen by mass. The compound has a molar mass of 283.88 g/mol. What are the compound’s empirical and molecular formulas?

#### Solution

**Where are we going?**
To find the empirical and molecular formulas for the given compound.

**What do we know?**
- Percent of each element
- Molar mass of the compound is 283.88 g/mol

**What information do we need to find the empirical formula?**
- Mass of each element in 100.00 g of compound
- Moles of each element

**How do we get there?**

**What is the mass of each element in 100.00 g of compound?**
- Phosphorus (P): 43.64 g
- Oxygen (O): 56.36 g

**What are the moles of each element in 100.00 g of compound?**

\[ \text{Moles of P} = 43.64 \, \text{g} \times \frac{1 \, \text{mol P}}{30.97 \, \text{g P}} = 1.409 \, \text{mol P} \]

\[ \text{Moles of O} = 56.36 \, \text{g} \times \frac{1 \, \text{mol O}}{16.00 \, \text{g O}} = 3.523 \, \text{mol O} \]

**What is the empirical formula for the compound?**
Dividing each mole value by the smaller one gives:

\[ \frac{1.409}{1.409} = 1 \text{ P} \quad \text{and} \quad \frac{3.523}{1.409} = 2.5 \text{ O} \]

This yields the formula \( \text{PO}_{2.5} \). Since compounds must contain whole numbers of atoms, the empirical formula should contain only whole numbers. To obtain the simplest set of whole numbers, we multiply both numbers by 2 to give the empirical formula \( \text{P}_2\text{O}_5 \).

**What is the molecular formula for the compound?**
Compare the empirical formula mass to the
Transcribed Image Text:### Determining Empirical and Molecular Formulas II A white powder is analyzed and found to contain 43.64% phosphorus and 56.36% oxygen by mass. The compound has a molar mass of 283.88 g/mol. What are the compound’s empirical and molecular formulas? #### Solution **Where are we going?** To find the empirical and molecular formulas for the given compound. **What do we know?** - Percent of each element - Molar mass of the compound is 283.88 g/mol **What information do we need to find the empirical formula?** - Mass of each element in 100.00 g of compound - Moles of each element **How do we get there?** **What is the mass of each element in 100.00 g of compound?** - Phosphorus (P): 43.64 g - Oxygen (O): 56.36 g **What are the moles of each element in 100.00 g of compound?** \[ \text{Moles of P} = 43.64 \, \text{g} \times \frac{1 \, \text{mol P}}{30.97 \, \text{g P}} = 1.409 \, \text{mol P} \] \[ \text{Moles of O} = 56.36 \, \text{g} \times \frac{1 \, \text{mol O}}{16.00 \, \text{g O}} = 3.523 \, \text{mol O} \] **What is the empirical formula for the compound?** Dividing each mole value by the smaller one gives: \[ \frac{1.409}{1.409} = 1 \text{ P} \quad \text{and} \quad \frac{3.523}{1.409} = 2.5 \text{ O} \] This yields the formula \( \text{PO}_{2.5} \). Since compounds must contain whole numbers of atoms, the empirical formula should contain only whole numbers. To obtain the simplest set of whole numbers, we multiply both numbers by 2 to give the empirical formula \( \text{P}_2\text{O}_5 \). **What is the molecular formula for the compound?** Compare the empirical formula mass to the
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