A 4.94-g sample of an oxide of chromium contains 3.06 g of chromium.Calculate the simplest formula for the compound. A)CrO₅ B)Cr₂O C)CrO₂ D)CrO E)Cr₂O₃

Question

Quizplus · Accepted Answer

First, calculate the mass of oxygen in the sample: 
Mass of oxygen = Mass of the compound - Mass of chromium 
Mass of oxygen = 4.94 g - 3.06 g = 1.88 g

Next, convert the masses to moles: 
Moles of chromium = 3.06 g / 52.0 g/mol = 0.0588 mol 
Moles of oxygen = 1.88 g / 16.0 g/mol = 0.1175 mol

Divide both moles by the smaller value to get the mole ratio: 
Moles of chromium / 0.0588 = 1 
Moles of oxygen / 0.0588 = 2

Round these ratios to the nearest whole number to get the subscripts in the empirical formula: 
CrO2

Reduce the subscripts, if necessary: 
The formula cannot be reduced further, so the empirical formula is CrO2. However, the question asks for the simplest formula, so we can divide both subscripts by 2 to get the simplest formula: 
CrO

A 494-G Sample of an Oxide of Chromium Contains 3