A student following the procedures in this lab exercise collected the following

Question

A student following the procedures in this lab exercise collected the following data: mass Mg, g 0.0243 initial syringe volume, mL 08 final syringe volume, mL 26.3 barometric pressure, torr 748 temperature, K 293.5 Calculate the value of the universal gas constant, R. What would be the volume of hydrogen gas produced by the reaction of 0100 g of magnesium metal, collected at 750 torr and 298 K? Use the value of R found in question 1. The results of this experiment are affected by the care with which each step is completed. Describe how each of the following errors would affect the calculated value of R. a. The Mg slid into the HCl in the test tube before the system was sealed off. b. The room temperature increased by 5 degree C between the time that the final volume was measured and the temperature was recorded. c. The MgO coating was not removed before the Mg sample was placed in the HCl. d. The test tube was filled with 4 mL of 0.10 M HCl instead of 4 mL of 1M HCl.

Explanation / Answer

Mg + 2HCL ---> MgCl2 + H2

1 mol H2 gas is produced from 1 mol of Mg.

moles of Mg used = 0.0243 gm/24g/mol = 0.001 moles

volume of gas produced = 26.3mL-0.8mL = 25.5 mL

                                                            = 0.0255 L

Pressure of the gas = 748 torr = 0.984 atm

PV = nRT

or, R = PV/nT

       = 0.984 * 0.0255 L /0.001 *293.5 K = 0.0855 L atm/K/mol

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