# Empirical & Molecular Formula Calculations

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Category: Education

## Presentation Description

A brief comparison of empirical and molecular formula definitions is presented, followed by several worked out examples of how to determine empirical and molecular formulas.

## Presentation Transcript

### Determining Empirical Formulas (from masses):

Determining Empirical Formulas ( from masses ) Convert each mass to moles. Divide all answers by the smallest mole number. Use the quotients as subscripts in the empirical formula

### What is the empirical formula for a compound if a 2.50 g sample contains 0.900 g of calcium and 1.60 g of chlorine? :

What is the empirical formula for a compound if a 2.50 g sample contains 0.900 g of calcium and 1.60 g of chlorine? CaCl 2

### PowerPoint Presentation:

Tip: If your division of mole numbers gives you a .5 or .25 or .33…, multiply all your mole numbers by a common factor, so that you have whole numbers for your subscripts.

### PowerPoint Presentation:

What is the empirical formula of a compound that has 7.22g Ni, 2.53g P, and 5.25g O? Ni 3 P 2 O 8

### Determining Empirical Formulas (from percentages):

Determining Empirical Formulas ( from percentages ) Assume total mass is 100.g => Change “%” to grams Convert each mass to moles. Divide all answers by the smallest mole number. Use the quotients as subscripts in the empirical formula

### A compound has a percentage composition of 40.0% C, 6.71% H, and 53.3% O. What is the empirical formula?:

A compound has a percentage composition of 40.0% C, 6.71% H, and 53.3% O. What is the empirical formula? CH 2 O Assume total mass is 100. g

### Determining Molecular Formulas:

Determining Molecular Formulas Calculate the Empirical Formula (if necessary) Calculate the formula mass of the empirical formula Divide the Molecular Mass by the Empirical Mass => Quotient is the multiplier for the subscripts in the Empirical Formula

### Ascorbic acid (vitamin C) has a percentage composition of 40.9% carbon, 4.58% hydrogen, and 54.5% oxygen. Its molecular mass is 176.1 u. What is its molecular formula? :

Ascorbic acid (vitamin C) has a percentage composition of 40.9% carbon, 4.58% hydrogen, and 54.5% oxygen. Its molecular mass is 176.1 u. What is its molecular formula? C 3 H 4 O 3 Assume total mass is 100. g Empirical Formula One More Step…

### Finding the Molecular Mass…:

Finding the Molecular Mass… Empirical Formula = C 3 H 4 O 3 Empirical Mass = 88.0 u Multiply by the subscripts Molecular Formula = C 6 H 8 O 6