Calculating Percent Composition and Empirical Formulas

Why is understanding percent compositions and percentages important in chemistry?

• To calculate the speed of chemical reactions

• To measure the temperature of reactions

• To identify the composition of unknown compounds

• To determine the color of compounds

What does the law of definite composition state?

• Compounds are always in a gaseous state

• Elements can change their properties

• Compounds have a definite composition and ratio

• Compounds can have varying compositions

How do you calculate percent by mass?

• Mass of element multiplied by mass of compound, divided by 100

• Mass of compound multiplied by mass of element, divided by 100

• Mass of compound divided by mass of element, multiplied by 100

• Mass of element divided by mass of compound, multiplied by 100

What is the molar mass of HNO3?

• 87.43 grams

• 30.03 grams

• 60.06 grams

• 63.02 grams

How much iron can be obtained from 125 grams of Fe2O3?

• 69.94 grams

• 87.43 grams

• 125 grams

• 63.02 grams

What is the first step in finding the empirical formula of a compound?

• Write the chemical equation

• Determine the molecular formula

• Assume 100 grams of the compound

• Convert masses to moles

In the example given, what is the empirical formula for a compound with 40.0% carbon, 6.70% hydrogen, and 53.3% oxygen?

• C2H4O2

• C3H6O3

• C4H8O4

• CH2O

What is the purpose of converting percent composition to moles in empirical formula calculations?

• To simplify the chemical equation

• To measure the temperature of the reaction

• To determine the ratio of elements

• To find the molecular formula

What is the next step after determining the empirical formula in finding the molecular formula?

• Calculate the molar mass of the empirical formula

• Write the chemical equation

• Determine the percent composition

• Convert masses to moles

If the empirical formula is CH2O and the molar mass is 60.06 grams, what is the molecular formula?

• C4H8O4

• C2H4O2

• CH2O

• C3H6O3