Three students are asked to discuss the percent errors obtained from this lab and explain what would account for the discrepancies seen, if any. Which student employs correct scientific reasoning? A source of error could occur if the valve did not fully seal and allowed gas to escape, this would lower the measured pressure and therefore lower the molar volume calculated. A source of error could come from adding too much water in the room temperature water bath causing more hydrogen to be formed and falsely increasing the molar volume. A source of error that causes the molar volume to be wrong is if the magnesium was the limiting reactant and therefore not enough hydrogen gas would be produced.

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Three students are asked to discuss the percent errors obtained from this lab and explain what would account for the discrepancies seen, if any. Which student employs correct scientific reasoning? A source of error could occur if the valve did not fully seal and allowed gas to escape, this would lower the measured pressure and therefore lower the molar volume calculated. A source of error could come from adding too much water in the room temperature water bath causing more hydrogen to be formed and falsely increasing the molar volume. A source of error that causes the molar volume to be wrong is if the magnesium was the limiting reactant and therefore not enough hydrogen gas would be produced.

Answer 1

A source of error could occur if the valve did not fully seal and allowed gas to escape, this would lower the measured pressure and therefore lower the molar volume calculated.

Answer 2

In evaluating the students' explanations for errors, we consider the following scientific principles: 1. **Valve not fully sealing**: If the valve does not fully seal, gas can escape, which would indeed lower the measured pressure. According to the Ideal Gas Law $PV = nRT$, a lower pressure ($P$) while keeping volume ($V$), temperature ($T$), and number of moles of gas ($n$) constant would decrease the calculated molar volume. 2. **Adding too much water**: This statement is inherently flawed. The amount of water in a water bath does not affect the formation of hydrogen gas directly; it's the chemical reaction that determines how much hydrogen is produced. The molar volume would not be falsely increased due to the amount of water. 3. **Magnesium as the limiting reactant**: If magnesium (Mg) is the limiting reactant, the reaction will be limited by the amount of available Mg, thereby producing a precise and predictable amount of hydrogen gas ($H_2$). This means the total molar volume should be measured accurately based on the amount of hydrogen gas produced. This wouldn't cause an error in the molar volume calculation itself, since limiting reactants are considered in stoichiometric measurements. Hence, the correct scientific reasoning that potentially leads to discrepancies in measured molar volume is provided by the first student regarding the valve not fully sealing.

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