How many grams is 0.125 moles of sio2?

First, you need grams but you have moles.
Find out the total molar mass of SiO₂
Si = 28.085 g/mol Si
O₂ = 32 g/mol O₂
Add them together to get the molar mass
28.085 g/mol Si + 32 g/mol O₂ = 60.085 g/mol SiO₂
Multiply the molar mass of SiO₂ by the number of moles you have of the same substance:
60.085 g/mol SiO₂ × 0.125 mol SiO₂ =
7.51 grams SiO₂

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. 

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