Empirical Formula & Molecular Formula Determination From Percent Composition

The Organic Chemistry Tutor
12 Aug 201711:00
EducationalLearning
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TLDRThis educational video script teaches viewers how to determine the empirical formula of a compound from its percent composition and how to derive the molecular formula given the molar mass. It walks through two examples: one with a compound containing carbon, hydrogen, and oxygen, and another with carbon, hydrogen, and nitrogen. The process involves converting mass percentages to grams, calculating moles, identifying the smallest mole ratio, and adjusting to find whole numbers for the empirical formula. For the molecular formula, the script explains multiplying the empirical formula's subscripts by the ratio of the compound's molar mass to the empirical formula's molar mass.

Takeaways
  • 🧪 To find the empirical formula of a compound from percent composition, convert percentages into grams based on a 100-gram sample of the compound.
  • 📊 Calculate the number of moles for each element by dividing the mass of the element by its atomic mass.
  • 🔍 Identify the smallest number of moles among the elements to determine the empirical formula's subscripts.
  • 🔢 Divide the moles of each element by the smallest moles value to simplify the ratio to whole numbers.
  • 🌐 The empirical formula is represented with the lowest whole number ratios of atoms of each element.
  • 🔬 If given the molar mass of a compound, determine the molecular formula by comparing it to the molar mass of the empirical formula.
  • ⚖️ Calculate the molar mass of the empirical formula by summing the products of the atomic masses and their respective subscripts.
  • 📈 Divide the molar mass of the compound by the molar mass of the empirical formula to find a multiplier for the empirical formula's subscripts.
  • 🔑 Multiply the subscripts of the empirical formula by the calculated multiplier to obtain the molecular formula.
  • 📝 When given the grams of elements directly, convert them to moles and follow the same steps as with percent composition to find the empirical formula.
  • 🎓 Understanding how to convert between empirical and molecular formulas is crucial for analyzing chemical compounds.
Q & A

  • What is the purpose of the video?

    -The video aims to explain how to determine the empirical formula of a compound from its percent composition and how to find the molecular formula if the molar mass is given.

  • How do you convert percent composition into grams for a 100-gram compound?

    -You multiply the percentage of each element by 100 to get the grams of that element in a 100-gram sample of the compound.

  • What is the molar mass of carbon, and how is it used to convert grams of carbon into moles?

    -The molar mass of carbon is 12.01 grams per mole. It is used by dividing the grams of carbon by the molar mass to get the number of moles.

  • How many moles of carbon are in 52.14 grams of carbon?

    -Dividing 52.14 grams by the molar mass of carbon (12.01 g/mol) gives approximately 4.34 moles of carbon.

  • What is the molar mass of hydrogen, and how is it used to find moles of hydrogen?

    -The molar mass of hydrogen is 1.008 grams per mole. It is used by dividing the grams of hydrogen by this molar mass to find the moles of hydrogen.

  • How many moles of hydrogen are in 13.13 grams of hydrogen?

    -Dividing 13.13 grams by the molar mass of hydrogen (1.008 g/mol) gives approximately 13.026 moles of hydrogen.

  • What is the process to determine the empirical formula of a compound?

    -The process involves converting the grams of each element to moles, identifying the smallest number of moles, and then dividing each mole value by the smallest one to get whole number ratios, which become the subscripts in the empirical formula.

  • How do you find the molecular formula if the molar mass of the compound is known?

    -First, calculate the molar mass of the empirical formula. Then, divide the given molar mass of the compound by the molar mass of the empirical formula to find a multiplier. Multiply the subscripts of the empirical formula by this number to get the molecular formula.

  • What is the empirical formula for a compound with 20.32 grams of carbon, 5.12 grams of hydrogen, and 7.9 grams of nitrogen?

    -Following the process, the empirical formula is determined to be C3H9N.

  • How do you calculate the molar mass of the empirical formula C3H9N?

    -Add up the molar masses of all the atoms in the empirical formula: (3 * 12.01 for carbon) + (9 * 1.008 for hydrogen) + (14.01 for nitrogen) to get the molar mass.

  • Given the molar mass of a compound and its empirical formula, how do you determine the molecular formula?

    -Divide the molar mass of the compound by the molar mass of the empirical formula to get a whole number. Multiply the subscripts of the empirical formula by this number to obtain the molecular formula.

Outlines
00:00
🧪 Finding Empirical Formula from Percent Composition

This paragraph explains how to determine the empirical formula of a compound using its percent composition by mass. The process involves converting percentages to grams based on a 100-gram sample, then calculating moles of each element using their atomic masses. The example given uses a compound with 52.14% carbon, 13.13% hydrogen, and 34.73% oxygen. The moles of each element are calculated and then divided by the smallest number of moles to find the simplest whole number ratio, resulting in the empirical formula C2H6O. The paragraph also introduces the concept of finding the molecular formula from the empirical formula when the molar mass of the compound is known.

05:03
🔍 Calculating Molecular Formula from Empirical Formula

This paragraph continues the discussion by explaining how to find the molecular formula of a compound when its molar mass is provided. Using the empirical formula C2H6O and the molar mass of the compound (138.204 g/mol), the paragraph demonstrates the calculation of the molecular formula. The molar mass of the empirical formula is determined, and the given molar mass of the compound is divided by this value. The result is used to multiply the subscripts of the empirical formula, yielding the molecular formula C6H18O3. Additionally, a second example is provided, where the empirical formula is derived from given masses of carbon, hydrogen, and nitrogen, and then used to calculate the molecular formula based on a provided molar mass.

10:04
📚 Summary of Finding Empirical and Molecular Formulas

The final paragraph summarizes the process of finding both empirical and molecular formulas of compounds. It reiterates the method of converting percent composition or given masses into moles, determining the empirical formula by finding the simplest whole number ratio, and then using the molar mass to find the molecular formula. The paragraph concludes by emphasizing the importance of these formulas in understanding the composition of compounds and thanks the viewers for watching the educational content.

Mindmap
Keywords
💡Empirical Formula
The empirical formula of a compound is the simplest whole number ratio of atoms present in the compound. It is a fundamental concept in chemistry for identifying the composition of a substance. In the video, the empirical formula is derived from the percent composition of elements within a compound, which is essential for understanding the basic makeup of the substance.
💡Percent Composition
Percent composition refers to the proportion of each element in a compound expressed as a percentage of the total mass. It is a key starting point in the script for determining the empirical formula, as it provides the initial data from which the mass of each element in the compound is calculated.
💡Molar Mass
Molar mass is the mass of one mole of a substance, typically measured in grams per mole (g/mol). It is used in the script to convert the mass of elements in a compound into moles, which is a necessary step for finding the empirical and molecular formulas.
💡Moles
Moles are a measure used in chemistry to express amounts of a chemical substance. The script uses moles to convert the mass of each element into a comparable unit, which allows for the calculation of the empirical formula by determining the ratio of atoms in the compound.
💡Atomic Mass
Atomic mass is the mass of an individual atom of an element, usually given relative to the carbon-12 standard. In the script, the atomic masses of carbon, hydrogen, and oxygen are used to convert their respective masses in grams to moles, which is crucial for finding the empirical formula.
💡Molecular Formula
The molecular formula of a compound shows the exact number of atoms of each element in a molecule of the compound. The script explains how to derive the molecular formula from the empirical formula by using the molar mass of the compound, which is a more detailed representation of the compound's composition.
💡Subscripts
In the context of the script, subscripts refer to the numerical coefficients in the empirical formula that indicate the ratio of atoms of each element. They are determined by dividing the moles of each element by the smallest number of moles to achieve whole numbers.
💡Compound
A compound is a substance formed when two or more chemical elements are chemically bonded together. The script discusses how to determine the empirical and molecular formulas of compounds, which are essential for understanding their chemical properties and structure.
💡Calculation
Calculations are performed throughout the script to convert percentages and masses into moles, and then to determine the ratios that lead to the empirical formula. These calculations are fundamental to the process of understanding the composition of compounds.
💡Whole Number Ratio
A whole number ratio is the simplest form of expressing the relative amounts of elements in a compound, which is achieved by dividing the number of moles of each element by the smallest number of moles. The script emphasizes the importance of whole number ratios in determining the empirical formula.
💡Contextualization
Contextualization in the script refers to the process of understanding the terms and concepts within the specific narrative of finding the empirical and molecular formulas. It helps to clarify how each concept is applied in the process of chemical analysis.
Highlights

Introduction to determining the empirical formula from percent composition.

Explanation of converting percent composition into grams for a 100-gram compound basis.

Method to convert grams of each element into moles using atomic masses.

Calculation example for converting 52.14 grams of carbon into moles.

Conversion of 13.13 grams of hydrogen into moles with the molar mass of hydrogen.

Conversion of 34.73 grams of oxygen into moles using the molar mass of oxygen.

Identifying the smallest number of moles to simplify the ratio.

Process of dividing each mole quantity by the smallest value to find whole number ratios.

Determination of the empirical formula C2H6O.

Introduction to finding the molecular formula given the molar mass of a compound.

Calculation of the molar mass of the empirical formula C2H6O.

Method to determine the molecular formula by comparing molar masses.

Example calculation for deriving the molecular formula C6H18O3.

Explanation of finding the empirical formula from given grams of elements.

Conversion of 20.32 grams of carbon, 5.12 grams of hydrogen, and 7.9 grams of nitrogen into moles.

Determination of the empirical formula C3H9NO.

Calculation of the molar mass of the empirical formula C3H9NO.

Derivation of the molecular formula C12H36N4 from the empirical formula and given molar mass.

Summary of the process for finding empirical and molecular formulas from composition data.

Transcripts

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Chemistry FormulasEmpirical FormulaMolecular FormulaElemental AnalysisMolar MassPercent CompositionChemical CalculationCompound AnalysisScientific MethodEducational Video