Percent Composition By Mass

Summary

This video tutorial explains how to calculate percent composition by mass, a key concept in chemistry. Using examples like water (H₂O), iron(III) chloride (FeCl₃), and glucose (C₆H₁₂O₆), the script walks through the steps of finding the percentage of an element in a compound. It covers how to determine molar masses of individual elements and compounds, perform the necessary division, and convert the result into a percentage. The video provides clear, step-by-step instructions, ensuring viewers understand how to apply the formula for percent composition and solve related problems.

Takeaways

• 😀 Percent composition by mass refers to the percentage of a specific element's mass in a compound, calculated using a simple formula.
• 😀 The formula for percent composition is: (Total molar mass of the element / Molar mass of the whole compound) × 100%.
• 😀 To calculate percent composition, first determine the molar mass of both the element and the entire compound.
• 😀 In the case of H₂O, the molar mass of hydrogen is calculated by multiplying the number of hydrogen atoms (2) by the atomic mass of hydrogen (1.01 g/mol).
• 😀 The molar mass of water (H₂O) is obtained by adding the molar masses of hydrogen and oxygen (2 × 1.01 + 1 × 16.00), resulting in 18.02 g/mol.
• 😀 For the example of H₂O, the percent composition of hydrogen is found to be 11.2%.
• 😀 When calculating for iron(III) chloride (FeCl₃), the molar mass is determined by adding the molar masses of iron and chlorine (1 × 55.85 + 3 × 35.45).
• 😀 The percent composition of iron in FeCl₃ is calculated to be 34.43%.
• 😀 For an organic compound like C₆H₁₀O₄, the molar mass of carbon is calculated by multiplying the number of carbon atoms (6) by the atomic mass of carbon (12.01 g/mol).
• 😀 In the case of C₆H₁₀O₄, the percent composition of carbon is determined to be 49.29%.
• 😀 Remember to round the final result of percent composition based on the significant figures of the given values in the problem.

Q & A

What is percent composition by mass?

Percent composition by mass is the percentage of the total mass of a compound that is due to a specific element. It is calculated by dividing the molar mass of the element by the molar mass of the entire compound and multiplying by 100.

How do you calculate the percent composition by mass of an element in a compound?

To calculate percent composition, first find the molar mass of the compound by adding the atomic masses of all elements in the formula. Then, find the molar mass of the element of interest, divide it by the molar mass of the compound, and multiply by 100.

In the example of water (H₂O), what is the first step to calculate the percent composition of hydrogen?

The first step is to calculate the molar mass of water (H₂O) by adding the molar mass of hydrogen (1.01 g/mol) for 2 hydrogen atoms and oxygen (16.00 g/mol) for 1 oxygen atom, resulting in 18.02 g/mol.

What is the percent composition by mass of hydrogen in H₂O?

The percent composition of hydrogen in H₂O is 11.2%. This is calculated by dividing the molar mass of hydrogen (2.02 g/mol) by the molar mass of water (18.02 g/mol), then multiplying by 100.

How do you calculate the molar mass of a compound like FeCl₃?

To calculate the molar mass of FeCl₃, add the molar mass of iron (55.85 g/mol) and chlorine (35.45 g/mol) for 3 chlorine atoms, resulting in a total of 162.20 g/mol.

What is the percent composition by mass of iron in FeCl₃?

The percent composition of iron in FeCl₃ is 34.43%. This is calculated by dividing the molar mass of iron (55.85 g/mol) by the molar mass of FeCl₃ (162.20 g/mol), then multiplying by 100.

Why is it important to round the final result when calculating percent composition?

It is important to round the final result to the appropriate number of significant figures, based on the precision of the given data, to ensure accuracy and consistency in scientific calculations.

In the compound C₆H₁₀O₄, what is the molar mass of carbon?

In C₆H₁₀O₄, the molar mass of carbon is calculated by multiplying 6 carbon atoms by the molar mass of carbon (12.01 g/mol), resulting in 72.06 g/mol.

How do you calculate the percent composition of carbon in C₆H₁₀O₄?

To calculate the percent composition of carbon in C₆H₁₀O₄, divide the molar mass of carbon (72.06 g/mol) by the molar mass of the entire compound (146.16 g/mol), and multiply by 100, resulting in 49.29%.

What does the term 'molar mass' refer to in the context of percent composition?

Molar mass refers to the mass of one mole of a substance, measured in grams per mole. It is calculated by summing the atomic masses of the elements in the compound, accounting for the number of atoms of each element.