EXPERIMENT SECTION DATE POSTLABORATORY ASSIGNMENT . A 0200-g sample of cobalt me

Question

EXPERIMENT SECTION DATE POSTLABORATORY ASSIGNMENT . A 0200-g sample of cobalt metal reacted with hydrochloric acid according to the following balanced chemical equation: Co(s)+2 HCI(aq)CoCl2(ag)+ 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. Calculate the STP molar volume for hydrogen Umol 2. A 0.130-g sample of an unknown metal (X) reacted with hydrochloric acid according to the following chemical equation: 2 X(s) 6 HCI(aq)2XCl3(aq) + 3 H2(g) The volume of hydrogen gas collected over water was 92.0 mL at 20 °C and 763 mmHg. Calculate the atomic mass of the unknown metal and identify the metal from the periodic table. g/mol

Explanation / Answer

Ans 1

Volume V = 87.5 mL x 1L/1000 mL = 0.0875 L

Temperature T = 20 + 273 = 293 K

Pressure of dry gas = Barometric pressure - Vapor pressure of water at 293 K

= 763 - 17.5 = 745.5 mmHg x 1atm/760mmHg

= 0.9809 atm

Moles of H2 gas = PV/RT

= 0.9809 atm x 0.0875 L / 0.0821 L-atm/mol-K x 293K

= 0.003568 mol

Volume at STP = (0.003568 moles)x(0.0821 L atm / K mole)(273 K) / (1.00 atm)

V = 0.07997 L

Molar volume = 0.07997 L / 0.003568 moles

= 22.41 L/mol

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