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Chemistry LibreTexts

8: Stoichiometry and the Mole

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  • We have already established that quantities are important in science, especially in chemistry. It is important to make accurate measurements of a variety of quantities when performing experiments. However, it is also important to be able to relate one measured quantity to another, unmeasured quantity. In this chapter, we will consider how we manipulate quantities to relate them to each other.

    • 8.1: Introduction
    • 8.2: The Mole
      The mole is a key unit in chemistry. The molar mass of a substance, in grams, is numerically equal to one atom's or molecule's mass in atomic mass units.
    • 8.3: The Mole in Chemical Reactions
      Balanced chemical reactions are balanced in terms of moles. A balanced chemical reaction gives equivalences in moles that allow stoichiometry calculations to be performed.
    • 8.4: Atomic and Molar Masses
      The mass of moles of atoms and molecules is expressed in units of grams.
    • 8.5: Making Molecules- Mole to Mass (or vice versa) and Mass-to-Mass Conversions
      We have used balanced equations to set up ratios, now in terms of moles of materials, that we can use as conversion factors to answer stoichiometric questions, such as how many moles of substance A react with so many moles of reactant B. We can extend this technique even further. Recall that we can relate a molar amount to a mass amount using molar mass. We can use that ability to answer stoichiometry questions in terms of the masses of a particular substance, in addition to moles.
    • 8.6: Mole-Mass and Mass-Mass Calculations
      Mole quantities of one substance can be related to mass quantities using a balanced chemical equation. Mass quantities of one substance can be related to mass quantities using a balanced chemical equation. In all cases, quantities of a substance must be converted to moles before the balanced chemical equation can be used to convert to moles of another substance.
    • 8.7: Solution Concentration and Solution Stoichiomentry
      Solution concentrations are typically expressed as molarities and can be prepared by dissolving a known mass of solute in a solvent or diluting a stock solution. The concentration of a substance is the quantity of solute present in a given quantity of solution. Concentrations are usually expressed in terms of molarity, defined as the number of moles of solute in 1 L of solution.
    • 8.8: Solution Concentration- Molarity
      Another way of expressing concentration is to give the number of moles of solute per unit volume of solution. Of all the quantitative measures of concentration, molarity is the one used most frequently by chemists. Molarity is defined as the number of moles of solute per liter of solution. The symbol for molarity is MM or moles/liter. Chemists also use square brackets to indicate a reference to the molarity of a substance.
    • 8.9: Stoichiometry
      Quantities of substances can be related to each other using balanced chemical equations.
    • 8.10: Solution Stoichiometry
      Double replacement reactions involve the reaction between ionic compounds in solution and, in the course of the reaction, the ions in the two reacting compounds are “switched” (they replace each other). Because these reactions occur in aqueous solution, we can use the concept of molarity to directly calculate the number of moles of reactants or products that will be formed, and hence their amounts (i.e. volume of solutions or mass of precipitates).
    • 8.11: Reactions of Acids and Bases
      When an acid and a base are combined, water and a salt are the products. Salts are ionic compounds containing a positive ion other than H+ and a negative ion other than the hydroxide ion, OH-. Double displacement reactions of this type are called neutralization reactions. Salt solutions do not always have a pH of 7, however. Through a process known as hydrolysis, the ions produced when an acid and base combine may react with the water to produce slightly acidic or basic solutions.