What mass of iron is required to replace over from 8.00 g of silver nitrate dissolved in water

Assume that Fe(II) is used
The chemical equation will be as follows:
2 AgNO3 (aq) + Fe2+ ---> Fe(NO3)2 (aq) + 2 Ag 

From the periodic table:
molar mass of silver = 107.87 gm
molar mass of nitrogen = 14 gm
molar mass of oxygen = 16 gm

molar mass of silver nitrate = 107.87 + 14 + 3(16) = 169.87 gm

number of moles in 8 gm = mass / molar mass = 8 / 169.87 = 0.047 moles

From the balanced chemical equation, we can see that two moles of silver nitrate reacts with one mole of iron(II), therefore, the ratio is 2:1

number of moles of Fe(II) required to react with 0.047 moles of silver nitrate can be calculated as follows:
number of moles of Fe(II) = 0.047 x (1/2) = 0.0235 moles

To get the mass, multiply the number of moles by the molar mass of iron as follows:
mass of required iron = 0.0235 x 55.845 = 1.312 gm

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. 

answer: mole of the gas

answer: mole of the gasexplanation:

answer: mole of the gasexplanation: this is because 1 mole of a gas is 22.4dm³, which is use in ideal gas