chemistry (solutions)

Question

Ammonium phosphate can be used as a fertilizer. 6.00 g of ammonium phosphate is dissolved in sufficient water to prepare 325 mL of solution.

What is the concentration of ammonium ions present?

Answer 1

Hello, Zoe,

The formula for ammonium phosphate is key in finding this answer. It is (NH₄)₃PO₄. Note that each molecule of ammonium phosphate releases 3 (NH₄)⁺ molecules when it dissolves. If we dissolve 1 mole of (NH₄)₃PO₄, we will create 3 moles of (NH₄)⁺ ions.

Here, we have 6.00 g of (NH₄)₃PO₄ dissolved in 325ml of solution. Let's determine how many moles of (NH₄)₃PO₄ are in 6.0g. We need the molar mass of (NH₄)₃PO₄ to calculate moles of (NH₄)₃PO₄. I get 149.1 g/mole. To find moles (NH₄)₃PO₄, divide 6.00g/(149.1g/mole). Grams cancel and moles moves to the top, and we find we have 0.040 moles of (NH₄)₃PO₄. That is dissolved in 325 ml of solution. The definition of concentration, Molar, is Moles/Liter. We have 0.40 moles of ammonium phosphate in 0.325 liter.

The Molarity of this solution is (0.040 Moles/0.325 L), or 0.124M (3 sig figs). The concentration of ammonium ions is thus 3*(0.124M) = 0.371M

Bob