General Chemistry 1, Unit 7, Lesson 7.1: Percent Composition

General Chemistry 1, Unit 7, Lesson 7.1: Percent Composition

• Introduction: Water is a vital compound, a substance composed of different elements bonded together. Compounds can be simple, like water or salt, or complex, like glucose, which contain multiple elements in varying ratios. These ratios are described using chemical formulas.

• Learning Objectives: Students should be able to describe percent composition and calculate the percent composition of a given compound or molecule based on its chemical formula.

• Warm Up (Activity): Students participate in a candy-counting activity to explore the concepts of chemical formulas and percent composition in a real-world example. The activity uses different colored candies to represent elements, aiding in the understanding of the concepts.

• Calculating Percent Composition from Experimental Data: The percent composition of a compound's elements can be determined using the masses of the elements present (as measured in experiments).

• Calculating Percent Composition Using Molar Mass: The percent composition can also be calculated if the compound's molar mass and the mass of each element within the compound can determine the percent mass.

• Key Points:

  • Chemical formulas indicate the type and number of atoms in a compound.
  • The percent composition of elements in a compound represents the proportion of each element by mass in the compound.
  • Percent composition calculations can allow us to determine the relative amounts of each element in a compound.

• Key Formulas:

  • % composition = (mass of an element / mass of the compound) x 100
  • % composition = (mass of each element / molar mass of the compound) x 100

• Guide Questions: Questions related to concepts of chemical formulas and percent composition.

• Explanation of Chemical Formulas: Chemists use symbols to represent elements and formulas to represent compounds. Formulas show the ratio and the types of atoms and their numerical subscripts in compounds in a straightforward and efficient method.

• Percent Composition Determination: Each element contributes to a compound's overall mass, and the proportion of each element's mass relative to the total compound mass is the percent composition.

• Examples and Practice: Detailed examples (Examples 1 & 2) demonstrate calculating mass percent in compounds given relevant data. Additional practice exercises (Try It! 1, 2 & 3) are provided.

• Tips, Key Points and Calculating Percent Composition Using Molar Mass: These sections elaborate on aspects of understanding how to calculate a compound’s percent composition and related concepts (molar mass, relevant calculations, and the rationale behind using molar masses).