Final answer:
The number of moles of hydrogen gas produced when strontium reacts with water is calculated using the volume of gas and standard temperature and pressure conditions. The result should theoretically match the mole quantity of strontium reacted, which indicates the stoichiometry of the chemical reaction.
Step-by-step explanation:
The student reacted strontium with water and recorded the volume of hydrogen gas produced. To determine the number of moles of hydrogen gas, we can use the ideal gas law, PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant, and T is the temperature. Assuming standard temperature and pressure (STP), 1 mole of a gas occupies 22.4 liters. Therefore, having 0.12dm³ or 0.12 liters of hydrogen gas, we calculate the moles of hydrogen gas (H₂) as follows:
n(H₂) = volume of H₂ at STP / molar volume at STP = 0.12 L / 22.4 L/mol = 0.005356 moles of H₂.
The student processed 0.438g of strontium, which they found to correspond to 0.005 moles of Sr. Given that strontium reacts with water in a 1:1 molar ratio to produce hydrogen gas according to the reaction:
Sr + 2H₂O → Sr(OH)₂ + H₂,
The calculated moles of hydrogen gas should theoretically match the moles of strontium used if the reaction goes to completion. In this case, the result is slightly different, so either there is an error in the experiment or the reaction did not go to completion.