Question

57 ldeal Gas Law: Estimation of Molar Mass of Magnesium Experiment 8 QUESTIONS A POST LAB A 0.0524-g sample of magnesium is reacted with 25 mL of 3.0 M sulfuric acid as described in the experimen- tal section. The resulting hydrogen gas is colllected over water and is found to have a volume of 53.6 mL. The temperature is 25 °C and the atmospheric pressure is 762.12 mm Hg. The column of water height inside the graduated cylinder is found to be 22.9 mm. What is the height of the water column after converting to an equivalent height of mercury in mm? 1. What is the pressure of the hydrogen gas in the column in mm Hg? OT 2DA3 TMATRO 2. 3. What is the pressure in question 2 in atmospheres? b a What is the number of moles of hydrogen gas in the sample? 4. What is the number of moles of metal in the sample? 5. What is thd calculated molar mass of the metal for this trial? 6. What is the percent error in this determination? 7. holad o

Answer 1

1) mmHg are calculated:

mmHg = 22.9 mmH2O * (0.074 mmHg / 1 mmH2O) = 1.7 mmHg

2) The water vapor pressure at that temperature is 23.78 mmHg, the hydrogen pressure is calculated:

P H2 = P atm - P H2O + P Height = 762.12 - 23.78 + 1.7 = 740.04 mmHg

3) It is calculated in atmospheres:

P = 740.04 mmHg * (1 atm / 760 mmHg) = 0.974 atm

4) The moles of H2 are calculated:

n H2 = P * V / R * T = 0.974 * 0.0536 L / 0.082 * 298 = 0.0021 mol

5) The moles of gas are equal to those of metal.

6) The molar mass is calculated:

MM = g / n = 0.0524 / 0.0021 = 25 g / mol

7) The percentage of error is calculated:

% error = (25 - 24.3) * 100 / 24.3 = 2.88%

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