Empirical and Molecular Formulas

The video tutorial explains how to determine the empirical formula from mass composition. It begins with a review of calculating mass composition using H2O as an example. The tutorial then demonstrates how to convert mass composition back to an empirical formula through examples involving mercury and chlorine, and magnesium and iodine. The process involves assuming a 100-gram sample, calculating moles, and determining the ratio of elements to find the empirical formula.

What is the empirical formula of water, given its molecular formula is H2O?

• H2O

• HO

• H2O2

• OH

If a compound is 75% mercury and 25% chlorine by mass, what is the first step to find its empirical formula?

• Convert mass percentages to grams

• Find the molecular formula

• Calculate the molar mass

• Determine the density

How many moles of mercury are in 75 grams, given its atomic mass is 200?

• 1 mole

• 0.5 moles

• 0.375 moles

• 0.25 moles

What is the empirical formula for a compound with a 1:2 ratio of mercury to chlorine?

• Hg2Cl

• Hg2Cl2

• HgCl

• HgCl2

In the example with magnesium and iodine, what is the mass of one mole of iodine?

• 24 grams

• 200 grams

• 127 grams

• 35 grams

What is the empirical formula for a compound with a 1:2 ratio of magnesium to iodine?

• MgI2

• MgI

• Mg2I

• Mg2I2

Why is it useful to assume 100 grams when calculating empirical formulas from mass percentages?

• It simplifies the conversion to moles

• It is the standard unit of measurement

• It avoids calculation errors

• It is easier to remember

What is the atomic mass of magnesium used in the example?

• 127

• 24

• 200

• 35

What is the significance of Avogadro's number in these calculations?

• It determines the molecular formula

• It is used to calculate density

• It measures atomic mass

• It represents the number of atoms in a mole

What is the main takeaway from the examples discussed in the video?

• Empirical formulas can be derived from mass composition

• Empirical formulas are only theoretical

• Molecular formulas are always the same as empirical formulas

• Mass composition is irrelevant to chemical formulas