Question

Oxygen gas was collected over hot water at 75 degrees Celsius. A volume of 78.3mL at a total pressure of 101kPa was obtained. The saturated vapour pressure of water at 75 degrees Celsius is 38.7kPa.

(i) What was the partial pressure of the oxygen?

(ii) What mass of oxygen was collected?

(iii) Why was hot water used?

Answer 1

1 Total puessure 10 kPa. klarer is at 75°C Pautial pressure of water vapor at 75°c = Vapor pressure of water at 75°C = 38.7kia. . Using palton's law of pautal pressure . Total puessure pautial puessure of H2O + pautial pressue of Oz - lol : 38.7+ PO2 PO₂: 62. 3 kPa Volume=78.3 mL of total volume. = 78-3 - 0.8783 wireles - Viq 1000 . ранніх рилике оо, . 62.3 ka Considering O₂ as ideal gas, using ideal gas egn: PO 2 VTi Notextu. To 75°C=15+273= 348K gas constant = 8.314 Lokia .; 62.3 X 0.0783 - 102 x 8.314% 348 malk . noze 0.00168 ... moles g 0.2 0.00168.., mass of 222. moles x molas man morning glory

Lai mass of 02: 0.00168 X 32 g/mol = 0.05376 gm :Mass of oseygen collected: 0.05376 gm. Hot water is used heue so that Onygen can be collected using water displacement method. This is applicable for gases that are insoluble in it such as 02. Hot wates will provide water vapos at 75°C. The vapor is then displaced by Oxygen & the total pressure is pautally due to collected gas & water vapa that was displaced & escaped from surface of watel. After equillibuium is reached the Dalton's law of pautial puessure can be applied & amount of gas collected can be quantified to