What is the minimum mass of magnetite Fe3O4, a iron ore, from which 7.5kg of pure iron could be extracted? Be sure your answer has a unit symbol, if necessary, and is rounded to the correct number of significant digits.

7.5kg Fe x (1000g / 1kg) x (1mol Fe / 55.845g Fe) x (1 mol Fe3O4 / 3 mol Fe) x (231.53 g Fe3O4 / 1 mol Fe3O4) =

10364.849136g
10.364849136kg

10. Kg Fe3O4

Well to my expert knowledge and my exquisite calculations i think the the negative ion # 412 is the key to sucess

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.