Chemistry Problem: Concentration of Phosphoric Acid Solution

What is the concentration of the phosphoric acid solution?

If 15.0 mL of phosphoric acid completely neutralizes 38.5 mL of 0.150 mol/L calcium hydroxide.

Answer:

After balancing the neutralization reaction equation between phosphoric acid and calcium hydroxide, the calculations show that the concentration of the phosphoric acid solution is 0.1283 M.

Explanation: To determine the concentration of phosphoric acid that completely neutralizes calcium hydroxide, we first look at the balanced chemical equation for the neutralization reaction: H3PO4 + 3Ca(OH)2 → Ca3(PO4)2 + 6H2O According to the equation, each mole of phosphoric acid can neutralize three moles of calcium hydroxide. Given that 38.5 mL of 0.150 mol/L calcium hydroxide solution is completely neutralized, we can first determine the moles of calcium hydroxide: • Moles of Ca(OH)2 = Volume (L) × Molarity • Moles of Ca(OH)2 = 0.0385 L × 0.150 mol/L = 0.005775 mol Since one mole of phosphoric acid reacts with three moles of calcium hydroxide: • Moles of H3PO4 = Moles of Ca(OH)2 / 3 • Moles of H3PO4 = 0.005775 mol / 3 = 0.001925 mol To find the concentration of phosphoric acid, we use the volume of the phosphoric acid solution (15.0 mL or 0.015 L) and the moles of phosphoric acid: • Concentration (M) = Moles / Volume (L) • Concentration (M) = 0.001925 mol / 0.015 L = 0.1283 M Therefore, the concentration of the phosphoric acid solution is 0.1283 mol/L.