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This lab experiment involved the reaction between magnesium (Mg) and hydrochloric acid (HCl) to produce hydrogen gas (H2). The purpose of this report is to present the findings and calculations related to this reaction, including the determination of the moles of hydrogen gas collected, the theoretical yield, and the percent yield. The reaction was conducted under specific conditions, and various factors that could affect the results were analyzed. Additionally, the report discusses the impact of potential errors on the calculated moles of gas collected and explains why the total pressure inside the gas collection tube is assumed to be equal to the atmospheric pressure outside of the tube.
Lastly, it considers the effect of an undetected air bubble in the gas collection tube on the calculated percent yield.
The balanced equation for the reaction conducted in this lab is as follows:
Mg(s) + 2HCl(aq) + H2O(l) -> MgCl2(s) + H2(g)
The purpose of this experiment was to determine the moles of hydrogen gas (H2) produced in this reaction and calculate the percent yield based on the theoretical yield.
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The given data includes the mass of magnesium (0.032 g), the volume of gas collected (30 mL), the barometric pressure (1.1 atm), the room temperature (22 °C), and the vapor pressure of water (19.8 torr).
The following materials were used in the experiment:
The experimental procedure involved the following steps:
Using the provided data, we can calculate the relevant values:
| Parameter | Value |
|---|---|
| Partial Pressure of H2 (atm) | 0.026 atm |
| Moles of H2 Collected (mol) | 0.00133 mol |
| Theoretical Yield of H2 (mol) | 0.0131 mol |
| Percent Yield (%) | 10.15% |
Partial Pressure of H2: To determine the partial pressure of the hydrogen gas collected, we subtracted the vapor pressure of water (19.8 torr) from the barometric pressure (1.1 atm).
The result is 0.026 atm.
Moles of H2 Collected: Using the ideal gas law, we calculated the moles of hydrogen gas collected with the formula:
n = (P * V) / (R * T)
n = (1.074 atm * 0.03 L) / (0.0821 * 295.15 K) = 0.00133 mol H2
Theoretical Yield of H2: Assuming that magnesium (Mg) was the limiting reactant, we calculated the theoretical yield of hydrogen gas (H2) with the formula:
Theoretical Yield = (Mass of Mg / Molar Mass of Mg) * (Moles of H2 / Moles of Mg)
Theoretical Yield = (0.032 g / 24.305 g/mol) * (1 mol / 1 mol) = 0.0131 mol
Percent Yield: The percent yield was calculated using the formula:
Percent Yield = (Actual Yield / Theoretical Yield) * 100
Percent Yield = (0.00133 mol / 0.0131 mol) * 100 = 10.15%
Effect of Errors on Calculated Moles of Gas Collected:
a) The measured mass of the magnesium was smaller than the true mass. This error would not affect the number of moles calculated because the mass of magnesium was not used to determine the moles of the gas.
b) The actual temperature of the hydrogen gas is less than room temperature. If the gas was cooler than its surroundings, its density would be greater, and the volume would appear to be smaller. Charles' Law states that a gas' volume is directly proportional to its temperature when the pressure is constant. Therefore, a lower temperature would result in a slightly lower calculated moles of gas collected.
Dalton's Law and Total Pressure:
Assuming that the gas collection tube was sealed and no leaks occurred, the total pressure inside the tube can be considered equal to the atmospheric pressure outside of the tube. This is based on Dalton's law of partial pressures, which states that in a mixture of gases, each gas exerts its own pressure independently. The particles inside the container exert force on the container walls, and the particles outside the container also exert force. If there were a significant difference in pressure, it would lead to the collapse or expansion of the container. Therefore, we assume that the total pressure inside and outside the tube is the same.
Effect of an Undetected Air Bubble:
If an undetected air bubble was trapped inside the gas collection tube, it would occupy space within the tube. As a result, the volume available for the collection of hydrogen gas would be reduced. This would lead to an underestimation of the moles of hydrogen gas collected. Consequently, the calculated percent yield would be lower than the actual yield due to the reduced volume available for gas collection.
In conclusion, this experiment involved the reaction between magnesium and hydrochloric acid to produce hydrogen gas. The moles of hydrogen gas collected were determined, and the theoretical yield and percent yield were calculated. Potential errors, such as a smaller measured mass of magnesium and variations in temperature, were discussed in terms of their effects on the calculated moles of gas collected. Dalton's law of partial pressures was used to justify the assumption that the total pressure inside the gas collection tube was equal to the atmospheric pressure outside. Lastly, the presence of an undetected air bubble inside the tube would lead to a reduced volume for gas collection and result in a lower calculated percent yield.
For future experiments, it is essential to ensure accurate measurements of reactants and conditions to improve the reliability of results. Additionally, careful inspection of equipment to prevent the presence of air bubbles in the gas collection tube is crucial for accurate calculations of gas moles and percent yield.
Lab Report: Magnesium and Hydrochloric Acid Reaction. (2016, Mar 07). Retrieved from https://studymoose.com/document/honors-lab-chemistry
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