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What's the empirical formula of a compound composed of 22.55% P and 77.45% Cl?

A) PCl2
B) PCl4
C) PCl3
D) PCl5

The most likely empirical formula is choice C:

Explanation:

The empirical formula of a compound gives the molar ratio between atoms of each element in this compound. For example, in the formula , the molar ratio between atoms and atoms is one-to-five.

Assume that the percentages here refer to the composition of this compound by the mass of each element. To find the empirical formula of this compound, start by converting the mass ratio to the molar ratio.

For simplicity, consider a sample of this compound. This

How many moles of atoms and atoms would that be? Look up the relative atomic mass of these two elements on a modern periodic table:

In other words, the mass of one mole of atoms would be , while the mass of one mole of atoms would be . Therefore, in this imaginary sample:

Calculate the ratio between and :

.

Taking the reciprocal might make this ratio more apparent:

.

In other words, there should be approximately three time as many atoms as atoms in this compound. That likely corresponds to the empirical formula .

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%

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explanation: