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### EXAMPLE - Equation Stoichiometry with Mixtures:

Calcium dihydrogen phosphate, Ca(H2PO4)2, which is used in the production of triple superphosphate fertilizers, can be formed from the reaction of phosphoric acid with apatite, Ca5(PO4)3F, in apatite ore.

2Ca5(PO4)3F  +  14H3PO4      10Ca(H2PO4)2  +  2HF

a.  What is the maximum mass of Ca(H2PO4)2 that can be formed from the reaction of excess phosphoric acid solution with the Ca5(PO4)3F in 8.50 x 104 kilograms of an apatite ore that is 81.7% Ca5(PO4)3F?

b.  If an apatite ore is 81.7% Ca5(PO4)3F, what is the minimum mass necessary to produce 8.0 x 103 kg of Ca(H2PO4)2?

Solution:

a.  Remember that percentages convey a ratio that can be used as a conversion factor (Section 8.4). Thus, 81.7% Ca5(PO4)3F in apatite ore can be described as

This conversion factor can be used to convert between mass of ore and mass of the pure substance Ca5(PO4)3F. The following shows one way to work this problem.

### =  1.61 x 105 metric tons Ca(H2PO4)2

b. For this calculation, the percentage provides a conversion factor that converts from mass of Ca5(PO4)3F to mass of the apatite ore.

### =  4.2 x 103 kg ore

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