Video Transcript
Phosphorite, a sedimentary rock containing phosphate minerals, is reacted with sulfuric acid to produce calcium phosphate and calcium superphosphate. What are the respective chemical formulas for calcium phosphate and calcium superphosphate?
Phosphorite, which is also called phosphate rock, is primarily used in industry for the creation of fertilizers. The element phosphorus is particularly important to add to fertilizers because it’s needed to create ATP, which cells use for energy. Phosphorite is the primary source of the element phosphorus, but it’s insoluble in water, making it inconvenient to apply as a fertilizer, but it’s treated with an acid to produce water-soluble phosphate salts.
In this question, we’re told the phosphorite was treated with sulfuric acid, which produced the phosphate-containing salts calcium phosphate and calcium superphosphate. We need to determine the chemical formulas for these two phosphate salts. From the names of these two chemical species, we can assume they contain calcium ions and the phosphate group.
To determine the correct chemical formula for calcium phosphate, we need to make sure we have the correct number of calcium and phosphate ions so that the compound is neutral overall. One way we can do this is using arithmetic, treating the charges as positive and negative numbers. If we have three calcium ions, each with a plus two charge, and two phosphate ions, which have a charge of negative three, we’ll end up with a compound that’s neutrally charged. We can also use this shortcut to create the chemical formula where we just swap the charges of the ions. Either way, we’ll arrive at the correct chemical formula for calcium phosphate, Ca3(PO4)2.
Now, we need to determine the chemical formula for calcium superphosphate. Calcium superphosphate contains calcium ions and the dihydrogen phosphate ion instead of the phosphate ion. We need two hydrogen phosphate ions for every calcium ion so that we end up with a neutrally charged compound. So, calcium superphosphate’s chemical formula is Ca(H2PO4)2.
The respective chemical formulas for calcium phosphate and calcium superphosphate are Ca3(PO4)2 and Ca(H2PO4)2.
