Final answer:
The volume of hydrogen gas produced is measured when reacting zinc with an acid while keeping the volume of the acid and mass of zinc constant. This measures the reactivity and stoichiometry of the reaction, and the volume of gas can be calculated using the ideal gas law.
Step-by-step explanation:
When the volume of acid is kept the same and the mass plus size of zinc used is the same each time, what is usually measured is the amount of hydrogen gas produced from the chemical reaction between zinc and the acid. The reaction follows the equation:
Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g).
In such an experiment, the controlled variables are the volume of acid and the mass of zinc, which ensure a consistent reaction environment. The dependent variable, which is the volume of hydrogen gas produced, can be calculated by using the ideal gas law, PV = nRT, where P is the pressure, V is the volume of gas, n is the number of moles of gas, R is the ideal gas constant, and T is the temperature in Kelvin. Conversions of units may be necessary, such as converting mm Hg to atm for pressure or degrees Celsius to Kelvin for temperature. By measuring the volume of hydrogen gas produced in the reaction, one can deduce the reactivity or the stoichiometric relationships in the reaction.