Another mass composition problem | Chemistry | Khan Academy

Khan Academy
27 Aug 200906:41
EducationalLearning
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TLDRIn this educational video script, the presenter explores the empirical formula of a hypothetical substance composed of hydrogen, oxygen, and sulfur. Starting with 100 grams of the mixture, the presenter calculates the moles of each element and simplifies the ratios to determine the empirical formula. The process involves understanding molar mass and mole calculations, leading to the conclusion that the substance is sulfuric acid (H2SO4), a compound known for its strong acidic properties.

Takeaways
  • 🧪 The script discusses determining the empirical formula of a substance with a given mass composition.
  • 🔍 It begins with a hypothetical scenario of having a bottle of a substance with specific percentages of hydrogen, oxygen, and sulfur.
  • 📊 The substance is 2.04% hydrogen, 65.3% oxygen, and 32.65% sulfur by mass.
  • 📚 The process starts by assuming 100 grams of the substance for calculation purposes.
  • 📉 The mass of each element in grams is calculated based on the given percentages: 2.04g of hydrogen, 65.3g of oxygen, and 32.65g of sulfur.
  • ⚗️ The atomic mass units (amu) for hydrogen, oxygen, and sulfur are considered to convert grams to moles.
  • 🔢 Hydrogen has an atomic mass of 1 amu, resulting in 2.04 moles of hydrogen.
  • 🌀 Oxygen's atomic mass is 16 amu, leading to 4.08 moles of oxygen from the given mass.
  • ⚠️ Sulfur's atomic mass is 32 amu, and the calculation yields 1.02 moles of sulfur.
  • 📐 The mole ratios of hydrogen, sulfur, and oxygen are determined to be 2:1:4.
  • 🔑 The empirical formula derived from the mole ratios is H2SO4, which is sulfuric acid.
Q & A

  • What is the purpose of the video script?

    -The purpose of the video script is to solve an empirical formula problem involving a substance composed of hydrogen, oxygen, and sulfur, and to determine its empirical formula.

  • What is the mass percentage composition of the substance in the script?

    -The substance is composed of 2.04% hydrogen, 65.3% oxygen, and 32.65% sulfur.

  • How does the script suggest assuming the total mass of the substance?

    -The script suggests assuming a total mass of 100 grams for the substance to simplify calculations.

  • What is the mass of hydrogen in grams if the total mass is 100 grams?

    -If the total mass is 100 grams, the mass of hydrogen is 2.04 grams (2.04% of 100 grams).

  • What is the mass of oxygen in grams in the same 100 grams of substance?

    -The mass of oxygen in 100 grams of the substance is 65.3 grams (65.3% of 100 grams).

  • What is the mass of sulfur in grams in the 100 grams of substance?

    -The mass of sulfur in 100 grams of the substance is 32.65 grams (32.65% of 100 grams).

  • How many moles of hydrogen are there in 2.04 grams of hydrogen?

    -There are 2.04 moles of hydrogen in 2.04 grams, since the atomic mass of hydrogen is 1 gram per mole.

  • How many moles of oxygen are there in 65.3 grams of oxygen?

    -There are 4.08 moles of oxygen in 65.3 grams, given that the atomic mass of oxygen is 16 grams per mole.

  • How many moles of sulfur are there in 32.65 grams of sulfur?

    -There are 1.02 moles of sulfur in 32.65 grams, since the atomic mass of sulfur is 32 grams per mole.

  • What is the empirical formula of the substance based on the moles of each element?

    -The empirical formula of the substance is H2SO4, which corresponds to sulfuric acid.

  • Why does the script mention Port Sulfur in Louisiana in relation to sulfur's smell?

    -The script mentions Port Sulfur in Louisiana to illustrate sulfur's characteristic smell, which is similar to rotten eggs, due to the sulfur processing that took place there.

Outlines
00:00
🧪 Determining the Empirical Formula

The speaker introduces a problem involving a substance composed of hydrogen, oxygen, and sulfur. They provide the mass percentages of each element in the substance and proceed to calculate the empirical formula. The process begins by assuming 100 grams of the substance and determining the grams of each element present. The speaker then calculates the number of moles for each element based on their atomic masses. Hydrogen has an atomic mass of 1, oxygen 16, and sulfur 32. The calculations reveal 2.04 moles of hydrogen, 4.08 moles of oxygen, and 1.02 moles of sulfur. These molar ratios are then used to deduce the empirical formula.

05:09
🔍 Finalizing the Empirical Formula

Continuing from the previous explanation, the speaker concludes the calculation of the empirical formula. They find that for every mole of sulfur, there are two moles of hydrogen and four moles of oxygen. This ratio is confirmed by multiplying the moles of sulfur by the respective coefficients. The speaker then states that the empirical formula of the substance is H2SO4, identifying it as sulfuric acid. The explanation emphasizes the importance of understanding molar ratios in determining the composition of a compound.

Mindmap
Keywords
💡Empirical formula
The empirical formula is a representation of a compound that shows the simplest whole number ratio of atoms in a molecule. In the video, the speaker is trying to determine the empirical formula of a substance based on its mass composition. This is a key concept as it helps in understanding the molecular structure of the substance.
💡Mass composition
Mass composition refers to the proportion of each element in a compound by mass. In the script, the mass composition of the substance is given as 2.04% hydrogen, 65.3% oxygen, and 32.65% sulfur. This information is crucial for determining the empirical formula, as it provides the basis for calculating the moles of each element.
💡Moles
Moles are a measure used in chemistry to express amounts of a chemical substance, defined as the number of elementary entities (such as atoms or molecules) in a given sample. In the video, the speaker calculates the moles of hydrogen, oxygen, and sulfur to determine the empirical formula. This concept is central to the process of understanding how many atoms of each element are present in a given mass of the substance.
💡Atomic mass
Atomic mass is the mass of an atom, typically expressed in atomic mass units (amu). It is used to calculate the moles of an element in a substance. In the script, the atomic masses of hydrogen (1 amu), oxygen (16 amu), and sulfur (32 amu) are used to determine the moles of each element in the substance.
💡Hydrogen
Hydrogen is a chemical element with the symbol H and atomic number 1. It is the lightest element in the periodic table and is a component of the substance being analyzed in the video. The speaker calculates that there are 2.04 grams of hydrogen in 100 grams of the substance, which corresponds to 2.04 moles.
💡Oxygen
Oxygen is a chemical element with the symbol O and atomic number 8. It is a major component of the Earth's atmosphere and is also present in the substance being analyzed. The script mentions that 65.3 grams of oxygen are in 100 grams of the substance, which translates to 4.08 moles of oxygen.
💡Sulfur
Sulfur is a chemical element with the symbol S and atomic number 16. It is a non-metal that is mentioned in the script as part of the substance's composition. The speaker finds that 32.65 grams of sulfur are in 100 grams of the substance, which corresponds to 1.02 moles of sulfur.
💡Ratio
In chemistry, a ratio is the relationship between the quantities of different elements in a compound. The speaker uses the ratios of moles of hydrogen, oxygen, and sulfur to determine the empirical formula. The ratio is essential in simplifying the formula to the smallest whole numbers.
💡Sulfuric acid
Sulfuric acid is a compound with the formula H2SO4. It is mentioned in the video as the empirical formula of the substance being analyzed. The speaker concludes that the empirical formula, based on the mass composition and moles calculated, is consistent with that of sulfuric acid.
💡Mole concept
The mole concept is a fundamental idea in chemistry that allows for the conversion of mass to the number of particles (atoms, molecules, ions, etc.). In the script, the mole concept is used to calculate the number of moles of each element in the substance, which is essential for determining the empirical formula.
Highlights

Introduction to a more complex mass composition problem with a non-2:1 ratio.

A substance is described with percentages of hydrogen, oxygen, and sulfur.

Assumption of 100 grams of the substance for calculations.

Calculation of grams of hydrogen based on the total mass.

Conversion of grams of hydrogen to moles using atomic mass.

Explanation of the atomic mass unit and its relation to moles.

Calculation of moles of oxygen from its mass and atomic mass.

Introduction of the atomic mass of oxygen and its calculation.

Calculation of moles of sulfur using its atomic mass.

Description of sulfur's atomic mass and its significance.

Determination of the molar ratio of hydrogen, sulfur, and oxygen.

Explanation of how the molar ratios lead to the empirical formula.

Identification of the empirical formula as H2SO4.

Discussion on the practical implications of sulfuric acid.

Emphasis on the precision of the problem setup for educational purposes.

Final summary of the empirical formula derivation process.

Transcripts

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Related Tags
Chemistry AnalysisEmpirical FormulaHydrogenOxygenSulfurMole CalculationScientific MethodEducational ContentChemical CompositionTeaching AidSulfuric Acid