Molar Mass and Percent Composition

This video tutorial explains how to find the percent composition by mass of each element in potassium chloride (KCl). It begins with calculating the molar mass of the compound, followed by determining the molar mass of individual elements, potassium and chlorine. The video demonstrates the calculation of the percent composition for each element, showing that potassium makes up 52.45% and chlorine 47.55% of KCl. The tutorial concludes by verifying that the sum of these percentages equals 100%, reinforcing the concept of percent composition.

What is the first step in finding the percent composition by mass of a compound?

• Identify the physical state of the compound

• Calculate the density of the compound

• Find the molar mass of the compound

• Determine the number of atoms in the compound

What is the molar mass of potassium used in the calculation?

• 52.45 grams per mole

• 74.55 grams per mole

• 39.10 grams per mole

• 35.45 grams per mole

How many potassium atoms are present in KCl?

• Two

• One

• Three

• Four

What percentage of KCl's mass is made up by potassium?

• 35.45%

• 39.10%

• 52.45%

• 47.55%

What is the molar mass of chlorine used in the calculation?

• 74.55 grams per mole

• 52.45 grams per mole

• 39.10 grams per mole

• 35.45 grams per mole

How many chlorine atoms are present in KCl?

• Four

• One

• Three

• Two

What percentage of KCl's mass is made up by chlorine?

• 47.55%

• 52.45%

• 39.10%

• 35.45%

What should the sum of the percent compositions of all elements in a compound be?

• 100%

• 75%

• 50%

• 150%

What is the final step in verifying the percent composition calculations?

• Recalculate the molar mass

• Check if the sum is close to 100%

• Recount the number of atoms

• Recheck the periodic table values