Summary of Gr11S Fr Chem Analyze Elémentaire 19 20

Main Ideas and Concepts

• Elementary Analysis Overview:

  The chapter focuses on Elementary Analysis, which is divided into qualitative and Quantitative Analysis. The objective is to determine the formula of organic compounds through Quantitative Analysis.

• Quantitative Analysis:

  This analysis helps identify the relative quantity of elements (carbon, hydrogen, oxygen) in organic compounds. The Empirical Formula represents the smallest whole-number ratio of these elements.

• Finding Empirical Formulas:

  The process involves complete combustion of hydrocarbons to convert carbon to CO₂ and hydrogen to H₂O. The mass of CO₂ and H₂O produced during combustion is measured to determine the Mass Percentages of carbon, hydrogen, and oxygen.

• Calculating Mass Percentages:

  The percentage by mass for each element is calculated using the following steps:

  • For Carbon: Use the mass of CO₂ produced to find the mass of carbon.
  • For Hydrogen: Use the mass of H₂O produced to find the mass of hydrogen.
  • For Oxygen: Since the compound is made of carbon, hydrogen, and oxygen, the mass percentage of oxygen can be derived from the total being 100%.
• Formulas and Calculations:

  The Empirical Formula is derived from the Mass Percentages calculated. A specific methodology is employed to express the relationship between the Mass Percentages and the molar mass of the compound.

• Application Example:

  An example is provided where the combustion of 5 mg of an organic compound yields 12 mg of CO₂ and 6 mg of H₂O. The steps to calculate the Empirical Formula from this data are outlined.

Methodology and Instructions

• Complete Combustion Setup:

  Prepare a device for complete combustion of the Hydrocarbon. Measure the mass of the apparatus before and after the reaction.

• Mass Measurement:

  Collect the CO₂ and H₂O produced in separate tubes. Calculate the mass change in each tube to find the masses of carbon and hydrogen.

• Calculate Mass Percentages:
  • Carbon:

    Use the equation: mass of carbon = (mass of CO₂ / molar mass of CO₂) × molar mass of carbon

    Calculate the percentage: percentage of carbon = (mass of carbon / total mass) × 100

  • Hydrogen:

    Use the equation: mass of hydrogen = (mass of H₂O / molar mass of H₂O) × molar mass of hydrogen

    Calculate the percentage: percentage of hydrogen = (mass of hydrogen / total mass) × 100

  • Oxygen:

    Calculate as: percentage of oxygen = 100 - (percentage of carbon + percentage of hydrogen)

• Derive Empirical Formula:

  Use the Mass Percentages to determine the molar ratio of elements. Adjust ratios to the nearest whole numbers to formulate the Empirical Formula.

Speakers or Sources Featured

• Mansour Connerré
• Laurent Fignon

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