Answer:
A.) PCl₅
Step-by-step explanation:
To determine the empirical formula, you need to (1) identify the atomic masses of both elements (from the periodic table), then (2) convert each element from grams to moles (via atomic masses), then (3) divide both elements by the smallest molar value of both, and then (4) construct the empirical formula.
(Step 1)
Atomic Mass (P): 30.974 g/mol
Atomic Mass (Cl): 35.453 g/mol
(Step 2)
3.72 g P 1 mole
--------------- x ------------------ = 0.120 mole P
30.974 g
21.28 g Cl 1 mole
----------------- x ------------------- = 0.600 mole Cl
35.453 g
(Step 3)
Because 0.120 mole is smaller than 0.600 mole, you need to divide both elements by this value to determine the ratio of the elements in the empirical formula.
0.120 mole P / 0.210 mole = 1.00 mole P
0.600 mole Cl / 0.210 mole = 5.00 moles Cl
(Step 4)
The molar value of each element represents the amount of each element in the formula. This value shows itself in the form of subscripts in the formula. This makes the correct empirical formula:
PCl₅