Question

A 7.300 gram sample of aluminum was quantitatively combined with a sample of selenium to form a compound. The compound weighed 39.35 grams. What is the empirical formula for this compound?

Answer 1

Answer:

The empirical formula is Al2Se3  

Explanation:

Step 1: Data given

Mass of the sample of aluminium = 7.300 grams

Mass of the compound = 39.35 grams

Molar mass of aluminium = 26.98 g/mol

Molar mass of selenium = 78.96 g/mol

Step 2: Calculate mass of selenium

Mass of selenium = mass of compound - mass of aluminium

Mass of selenium = 39.35 - 7.3 = 32.05 grams

Step 3: Calculate moles of Al

Moles Al = Mass Al/ Molar mass Al

Moles Al = 7.300 grams / 26.98 g/mol

Moles Al = 0.2706 moles

Step 4: Calculate moles of Se

Moles Se = Mass Se / Molar mass Se

Moles Se =32.05 g / 78.96 g/mol

Moles Se = 0.4059 moles

Step 5: Divide through the smallest amount of mol

Aluminium: 0.2706 / 0.2706 = 1

Selenium: 0.4059/0.2706 = 1.5

This means for each mol aluminium, we have 1.5 moles of selenium

For each 2 moles of aluminium, we have 3 moles of selenium

The empirical formula is Al2Se3  

This is aluminium(III) selenide.