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6: Chemical Composition

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    Chapter 6 is concerned with the amounts of substances which participate in chemical reactions, the quantities of heat given off or absorbed when reactions occur, and the volumes of solutions which react exactly with one another. These seemingly unrelated subjects are discussed together because many of the calculations involving them are almost identical in form. The same is true of the density calculations, and of the calculations involving molar mass and the Avogadro constant.

    • 6.1: Counting Nails by the Pound
      The size of molecule is so small that it is physically difficult, if not impossible, to directly count out molecules. However, we can count them indirectly by using a common trick of "counting by weighing".
    • 6.2: Counting Atoms by the Gram
      In chemistry, it is impossible to deal with a single atom or molecule because we can't see them or count them or weigh them. Chemists have selected a number of particles with which to work that is convenient. Since molecules are extremely small, you may suspect this number is going to be very large and you are right. The number of particles in this group is Avagadro's number and the name of this group is the mole.
    • 6.3: Formula Mass- The Mass of a Molecule or Formula Unit
      Formula masses of ionic compounds can be determined from the masses of the atoms in their formulas.
    • 6.4: Counting Molecules by the Gram
      The molecular mass of a substance is the sum of the average masses of the atoms in one molecule of a substance. Calculations for formula mass and molecular mass are described. Calculations involving conversions between moles of a material and the mass of that material are described. Calculations are illustrated for conversions between mass and number of particles.
    • 6.5: Chemical Formulas as Conversion Factors
      Using formulas to indicate how many atoms of each element we have in a substance, we can relate the number of moles of molecules to the number of moles of atoms.  In any given formula the ratio of the number of moles of molecules (or formula units) to the number of moles of atoms can be used as a conversion factor.
    • 6.6: Mass Percent Composition of Compounds
      Chemists often need to know what elements are present in a compound and in what percentage. The percent composition is the percent by mass of each element in a compound.
    • 6.7: Mass Percent Composition from a Chemical Formula
      The percent composition of a compound can also be determined from the formula of the compound. The subscripts in the formula are first used to calculate the mass of each element in one mole of the compound. This is divided by the molar mass of the compound and multiplied by 100%.
    • 6.8: Calculating Empirical Formulas for Compounds
      An empirical formula tells us the relative ratios of different atoms in a compound. The ratios hold true on the molar level as well. A process is described for the calculation of the empirical formula for a compound based on the percent composition of that compound.
    • 6.9: Calculating Molecular Formulas for Compounds
      A procedure is described that allows the calculation of the exact molecular formula for a compound.

    6: Chemical Composition is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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