Mixtures, Percentage, and Equation Stoichiometry

In many equation stoichiometry problems, we can assume that the liquids and solids in our reaction mixtures were pure. Unfortunately (for chemistry students), the real world is physically quite complex, and chemists must often work with substances that are part of a mixture. For example, apatite, Ca5(PO4)3F, which is a common reactant used to make a number of important compounds, is often added to the reaction vessel in the form of apatite ore, which is a mixture of Ca5(PO4)3F with other substances. The amount of Ca5(PO4)3F in the ore is usually described in terms of percentage. A typical apatite ore has over 75% Ca5(PO4)3F.

When one of the substances needed for a reaction is part of a mixture, our equation stoichiometry problems require a new step to convert from the mass of the mixture to the mass of the component in it that is needed for the reaction. The conversion factor needed for this step comes from the substances mass percentage.

The conversion factor that comes from the percentage can also be used at the end of an equation stoichiometry problem to convert from mass of a substance to mass of mixture that contains the substance.



Click here to see an example of how percentage is used in equation stoichiometry problems.

Click here to see an exercise.

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