Question

A 0.200-g sample of cobalt metal reacted with hydrochloric acid according to the following balanced chemical equation: Co (s) + 2 HCl (aq) ➝ CoCl2 (aq) + H2 (g) The volume of hydrogen gas collected over water was 87.5 mL at 20 °C and a barometer reading of 763 mm Hg. Referring to Example Exercise 1, the adjusted volume of the H2 gas is

Answer 1

V H2(g) = 83.13 mL

Step-by-step explanation:

Dalton's law:

• Pgas = Pbar - P*H2O

∴ vapor pressure (P*)

⇒ P*H2O(20°C) = 17.5 mmHg

∴ Pbar = 763 mmHg

⇒ PH2 = 763 mmHg - 17.5 mmHg = 745.5 mmHg = 0.9809 atm

• Co(s) + 2 HCl(aq) → CoCl2(aq) + H2(g)

∴ Mw Co(s) = 58.933 g/mol

⇒ mol Co(s) = ( 0.200 g Co )×( mol/58.933 g ) = 3.394 E-3 mol Co

⇒ n H2(g) = ( 3.394 E-3 mol Co )( mol H2 / mol Co ) = 3.394 E-3 mol H2(g)

ideal gas:

• PV = RTn

∴ R = 0.082 atm.L/K.mol

∴ T = 20°C ≅ 293 K

the adjusted volume H2(g):

⇒ V H2(g) = ((0.082 atm.L/K.mol)(293 K)(3.394 E-3 mol)) / (0.9809 atm)

⇒ V H2(g) = 0.08313 L

⇒ V H2(g) = 83.13 mL