Final answer:
When a gas is collected over water, manipulating the eudiometer to equalize the water levels inside and outside corrects for the vapor pressure of water in the gas. Not following this procedure would result in an overestimation of the calculated molar mass of the gas.
Step-by-step explanation:
When a gas is collected over water, the manipulation of the eudiometer to equalize the water levels inside and outside is done to correct for the vapor pressure of water in the collected gas. Water has a vapor pressure that depends on temperature, and this pressure adds to the total pressure inside the eudiometer, affecting the measurement of the gas pressure. By equalizing the water levels, the partial pressure of water vapor can be determined and subtracted from the total pressure to obtain the true pressure of the gas.
If this process is not followed, the calculated molar mass of the gas would be higher than the actual molar mass. This is because the incorrect measurement of the gas pressure would include the additional pressure from the water vapor, leading to an overestimation of the gas density. As a result, the calculated molar mass would be higher than the actual mass.