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4. A sample of phosphorus weighing 2.50 grams is burned in the presence of oxygen. What is

the empirical formula of the phosphorus oxide compound if the product has a mass of 5.73
grams? What is the actual molecular formula or the compound if the molar mass is determined
to be 285 g/mol? SHOW ALL WORK.

1 Answer

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Answer:

To determine the empirical formula of the phosphorus oxide compound, we need to calculate the ratio of the elements present.

First, we calculate the mass of oxygen by subtracting the mass of phosphorus from the total mass of the compound:

Mass of oxygen = Mass of compound - Mass of phosphorus

Mass of oxygen = 5.73 g - 2.50 g

Mass of oxygen = 3.23 g

Next, we convert the mass of each element into moles using their molar masses. The molar mass of phosphorus (P) is 31 g/mol, and the molar mass of oxygen (O) is 16 g/mol.

Moles of phosphorus = Mass of phosphorus / Molar mass of phosphorus

Moles of phosphorus = 2.50 g / 31 g/mol

Moles of phosphorus = 0.0806 mol

Moles of oxygen = Mass of oxygen / Molar mass of oxygen

Moles of oxygen = 3.23 g / 16 g/mol

Moles of oxygen = 0.2019 mol

Now, we divide the moles of each element by the smallest number of moles to get the simplest whole number ratio. In this case, the moles of phosphorus are the smallest, so we divide both moles by 0.0806 mol:

Moles of phosphorus (P) = 0.0806 mol / 0.0806 mol = 1

Moles of oxygen (O) = 0.2019 mol / 0.0806 mol = 2.5

Since the ratio of phosphorus to oxygen is 1:2.5, we multiply both numbers by 2 to get a whole number ratio:

Moles of phosphorus (P) = 1 * 2 = 2

Moles of oxygen (O) = 2.5 * 2 = 5

Therefore, the empirical formula of the phosphorus oxide compound is P2O5.

To determine the actual molecular formula of the compound, we need to compare the molar mass of the empirical formula with the given molar mass of 285 g/mol.

The molar mass of P2O5 can be calculated as follows:

Molar mass of P2O5 = (Molar mass of P) * 2 + (Molar mass of O) * 5

Molar mass of P2O5 = (31 g/mol) * 2 + (16 g/mol) * 5

Molar mass of P2O5 = 62 g/mol + 80 g/mol

Molar mass of P2O5 = 142 g/mol

Since the molar mass of the empirical formula (P2O5) is less than the given molar mass of 285 g/mol, we need to determine how many empirical units are required to achieve the given molar mass.

Number of empirical units = Molar mass of compound / Molar mass of empirical formula

Number of empirical units = 285 g/mol / 142 g/mol

Number of empirical units = 2

Therefore, the actual molecular formula of the compound is 2 times the empirical formula, which is P4O10.

In summary:

- The empirical formula of the phosphorus oxide compound is P2O5.

- The actual molecular formula of the compound is P4O10.

Step-by-step explanation:

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