Percent Composition By Mass

The Organic Chemistry Tutor
12 Aug 201717:00
EducationalLearning
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TLDRThis educational video script explains how to calculate the percent composition of elements in a compound. It demonstrates the process using sucrose and other compounds, detailing the steps to find the molar mass and then the mass percentage of each element. The script also includes a problem-solving example to determine the molar mass of an unknown molecule from the mass percentage of nitrogen, illustrating the application of these concepts in chemistry.

Takeaways
  • 🧪 The formula for mass percent is the mass of an element divided by the total mass of the compound, multiplied by 100.
  • 📊 Mass percent can be calculated using either the grams of the element or the molar mass in grams per mole.
  • 🌐 The molar mass of a compound is found by summing the atomic masses of all the atoms in the compound's formula.
  • 📝 Example calculation: For sucrose (C12H22O11), the molar mass is calculated and then used to find the mass percent of carbon, hydrogen, and oxygen.
  • 📉 The mass percent of each element in a compound should add up to 100%, which serves as a check for calculation accuracy.
  • 🔍 To find the mass percent of an element, multiply the total atomic mass of that element in the compound by 100 and divide by the molar mass of the compound.
  • 📚 The periodic table provides the necessary atomic masses for calculating molar masses and mass percents.
  • 📈 The script demonstrates calculations for multiple compounds, including C5H9NO2 and comparing carbon mass percentages in CH4, C2H7N, C5H11OH, C6H12O6, and CO2.
  • 🏆 The compound with the highest percentage of carbon by mass among the given examples is CH4 (methane) at 74.87%.
  • 🔢 If the mass percent and the number of atoms of an element in a molecule are known, the molar mass of the molecule can be calculated.
  • 🔑 The script concludes with a method to find the molar mass of an unknown compound given the mass percent and atomic mass of a single element within it.
Q & A

  • What is the formula for calculating the mass percent of an element in a compound?

    -The mass percent of an element is calculated by dividing the mass of the element by the total mass of the compound, and then multiplying by 100.

  • How can you find the molar mass of a compound using the periodic table?

    -You can find the molar mass of a compound by summing the atomic masses or molar masses of all the atoms present in the compound as listed in the periodic table.

  • What is the molar mass of sucrose (C12H22O11) in grams per mole according to the video?

    -The molar mass of sucrose is 342.296 grams per mole.

  • How do you calculate the percentage by mass of carbon in sucrose?

    -You multiply the atomic mass of carbon (12.01) by the number of carbon atoms (12), divide the result by the molar mass of sucrose (342.296), and then multiply by 100 to get the percentage by mass of carbon, which is approximately 42.1%.

  • What is the percentage by mass of hydrogen in sucrose?

    -The percentage by mass of hydrogen in sucrose is calculated by multiplying the atomic mass of hydrogen (1.008) by the number of hydrogen atoms (22), dividing by the molar mass of sucrose, and then multiplying by 100, which gives approximately 6.5%.

  • How do you determine the mass percent of oxygen in a compound like sucrose?

    -You multiply the atomic mass of oxygen (16) by the number of oxygen atoms, divide by the molar mass of the compound, and then multiply by 100. For sucrose, this results in approximately 51.4%.

  • What is the molar mass of the compound C5H9NO2 as given in the video?

    -The molar mass of the compound C5H9NO2 is 115.132 grams per mole.

  • How can you verify if the mass percentages of elements in a compound add up correctly?

    -By adding the mass percentages of all the elements in the compound, it should equal 100% if calculated correctly.

  • What is the mass percent of carbon in methane (CH4) according to the video?

    -The mass percent of carbon in methane is approximately 74.87%.

  • How can you find the molar mass of a molecule if you know the mass percent of a single element and the number of atoms of that element?

    -You can use the formula where the mass percent of the element divided by 100 equals the atomic mass of the element divided by the molar mass of the compound. Solving for the molar mass gives you the unknown value.

  • What is the molar mass of a molecule that contains a single nitrogen atom with a mass percent of 13.32%?

    -The molar mass of such a molecule would be 105.18 grams per mole.

Outlines
00:00
🧪 Calculating Percent Composition of Elements

This paragraph introduces the concept of calculating the percent composition of an element in a compound. The formula for mass percent is given as the mass of the element divided by the total mass, multiplied by 100. The example of sucrose (C12H22O11) is used to demonstrate the calculation process, starting with finding the molar mass of the compound using atomic weights from the periodic table. The mass percent of carbon in sucrose is calculated by summing the mass of all carbon atoms (12 x 12.01), dividing by the molar mass of sucrose (342.296 g/mol), and multiplying by 100 to get 42.1%. The same method is applied to hydrogen and oxygen to find their respective mass percentages, and the sum of these percentages is verified to be 100%.

05:01
📚 Detailed Calculation of Percent Composition for C5H9NO2

The second paragraph continues the theme of percent composition by calculating the mass percentages of each element in the compound C5H9NO2. The molar mass of the compound is determined by multiplying the number of atoms of each element by their respective atomic masses and summing these products. The mass percentages of carbon, hydrogen, nitrogen, and oxygen are calculated by dividing the total mass of each type of atom by the molar mass of the compound and multiplying by 100. The results are 52.16% for carbon, 7.88% for hydrogen, 12.1% for nitrogen, and 27.85% for oxygen. The paragraph concludes with a brief mention of a problem involving the comparison of carbon content in different compounds.

10:03
🔍 Determining the Molar Mass from Percent Composition

This paragraph presents a method to find the molar mass of an unknown molecule when the mass percent of a single element and the number of atoms of that element are known. Using the given mass percent of nitrogen (13.32%) in a molecule with a single nitrogen atom, the formula for mass percent is rearranged to solve for the molar mass (x). The atomic mass of nitrogen (14.01) is used in the calculation, and after algebraic manipulation, the molar mass of the compound is found to be 105.18 g/mol. This demonstrates how to reverse-engineer the molar mass of a compound from its elemental composition.

Mindmap
Keywords
💡Percent Composition
Percent composition is a way to express the mass of an element in a compound as a percentage of the total mass of the compound. It is a fundamental concept in chemistry for understanding the proportion of elements within a substance. In the video, the concept is used to calculate the mass percentage of carbon, hydrogen, and oxygen in various compounds, such as sucrose and other organic molecules.
💡Mass Percent
Mass percent is the ratio of the mass of a particular element in a compound to the total mass of the compound, expressed as a percentage. It is a key term in the script, as the video demonstrates how to calculate mass percent for elements like carbon, hydrogen, and oxygen in different compounds, which is essential for understanding their proportionate presence.
💡Molar Mass
Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is calculated by summing the atomic masses of all atoms in a molecule. In the video, molar mass is used to find the total mass of compounds like sucrose and C5H9NO2, which is then used to calculate the mass percent of individual elements.
💡Atomic Weights
Atomic weights are the ratio of the average mass of atoms of an element to 1/12 of the mass of an atom of carbon-12. They are used to calculate the molar mass of a compound. In the script, atomic weights of carbon, hydrogen, and oxygen are used to determine the molar mass of sucrose and other compounds, which is crucial for finding the percent composition.
💡Sucrose
Sucrose, with the chemical formula C12H22O11, is a common sugar used as an example in the video to demonstrate the calculation of percent composition by mass. The script walks through the process of finding the molar mass of sucrose and then using it to calculate the mass percent of carbon, hydrogen, and oxygen in the compound.
💡C5H9NO2
C5H9NO2 is a chemical formula representing a compound with five carbon atoms, nine hydrogen atoms, one nitrogen atom, and two oxygen atoms. It is used in the video as another example to illustrate the calculation of the molar mass and the mass percent of each element within the compound.
💡Elemental Analysis
Elemental analysis is the process of determining the elemental composition of a compound, typically expressed as mass percent. In the video, elemental analysis is performed on various compounds to find the mass percent of carbon, hydrogen, and other elements, which helps in understanding their chemical makeup.
💡Compound
A compound is a substance formed when two or more chemical elements are chemically bonded together. In the context of the video, compounds like sucrose and C5H9NO2 are analyzed to determine the mass percent of the elements they contain, which is essential for understanding their chemical properties and structure.
💡Mole
A mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as the number of particles (atoms, molecules, etc.) in 12 grams of pure carbon-12. It is foundational in calculating molar mass and percent composition, as seen in the video when determining the mass percent of elements in compounds.
💡Chemical Formula
A chemical formula represents the elemental composition of a substance, indicating the types of atoms and their proportions in the compound. In the script, chemical formulas like C12H22O11 for sucrose and C5H9NO2 are used to identify the elements present and calculate their respective mass percentages.
💡Calculation
Calculation, in the context of the video, refers to the mathematical processes used to determine the molar mass of compounds and the mass percent of individual elements within those compounds. The script provides step-by-step calculations for various compounds, emphasizing the importance of accurate computation in chemical analysis.
Highlights

Introduction to calculating the percent composition of an element in a compound.

Explanation of the mass percent formula: mass percent = (mass of element / total mass) * 100.

Use of atomic weights or molar mass from the periodic table for calculation.

Example calculation of the molar mass of sucrose (C12H22O11).

Calculation of the percent by mass of carbon in sucrose.

Method to verify calculations by ensuring the sum of element percentages equals 100%.

Demonstration of calculating the percent composition for hydrogen and oxygen in sucrose.

Example calculation for the compound C5H9NO2, including molar mass and individual element percentages.

Explanation of how to calculate the mass percent of each element in a compound.

Comparative analysis of carbon percentage in various compounds (CH4, C2H7N, C5H11OH, C6H12O6, CO2).

Identification of CH4 as having the highest carbon percentage by mass among the given compounds.

Problem-solving approach for determining the molar mass of a molecule with a given mass percent of nitrogen.

Algebraic method to find the molar mass of an unknown compound from the mass percent of nitrogen.

Final determination of the molar mass of a compound with 13.32% nitrogen by mass.

Emphasis on the importance of knowing the number of atoms of an element to calculate the molar mass of an unknown molecule.

Conclusion summarizing the method for finding the percent composition of elements in molecular compounds.

Transcripts

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ChemistryPercent CompositionMolar MassElemental AnalysisEducationalAtomic WeightsCalculationCompound AnalysisScience TutorialMolecular Formulas