calcium metal reacts with phosphoric acid to produce calcium phosphate and hydrogen gas.

Question

calcium metal reacts with phosphoric acid to produce calcium phosphate and hydrogen gas. if 8g of calcium react calculate a.the concentration of phosphoric acid if the volume of acid that reacts is 60cm3 b.calculate the volume of hydrogen gas produced c.calculate the volume of hydrogen gas produced at step d calculate the number of molecules of hydrogen gas produced

Answer 1

3Ca(s) + 2H₃PO₄(aq) ===> Ca₃(PO₄)₂(aq) + 3H₂(g) ... balanced equation

moles of Ca = 8 g x 1 mol Ca/40 g = 0.2 moles Ca

(a) 0.2 mol Ca x 2 mol H₃PO₄/3 mol Ca = 0.133 mol H₃PO₄ reacted

60 cm³ H₃PO₄ * 1 L/1000 cm³ * x mol/L = 0.133 mol

x = 2.22 M = concentration of H₃PO₄

(b) 0.2 mol Ca x 3 mol H2/3 mol Ca = 0.2 mol H₂ gas

Volume of H₂ will depend on the temperature and pressure, but assuming this is at STP, the volume will be..

0.2 mol x 22.4 L/mol = 4.48 L = 4 L H₂ gas (1 sig. fig.)

(c) molecules of H₂ gas = 0.2 mol H₂ x 6.02x10²³ molecules/mol = 1.2x10²³ molecules = 1x10²³ molecules of H₂ (1 sig. fig.)