g chemist accidentally leaves an open beaker containing 250.0 mL of a 0.500 M NaHCO3(aq) solution on a lab bench. They return a few weeks later to find that the volume of the solution has decreased to 75.0 mL. What is the molarity of this partially evaporated solution, assuming the solute does not evaporate

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant. 

Cis the answer ur welcome if i get it wrong u don't have to me