does rust affect the mass of a metal?

Answer 1

If a metal rusts, its mass will change slightly.

In the case of Iron, Fe, rusting into Iron (III) Oxide, Fe2O3, the object's mass will increase to the addition off Oxygen to the material.
The chemical reaction is as follows,
4 Fe + 3 O2 --> 2 Fe2O3
4 moles of Iron combine with 3 moles of Oxygen gas to form 2 moles of Iron (III) Oxide.
If the material was pure Iron to start out with, through the rusting process the Iron will pick up additional Oxygen atoms to form the heavier compound Iron Oxide.

The molar mass of Iron is: 55.85 g/mol
The molar mass of Oxygen gas, O2, is: 32 g/mol
The molar mass of Iron (III) Oxide is: 159.7 g/mol

For every 1 gram of Iron which reacts, 1.43 grams of Iron Oxide is formed. The increase in mass comes from the Oxygen.

This assumes that the Iron Oxide produced in the reaction stays on the original object and does not flake off. If it does flake off, the mass of the Iron in the Iron Oxide will no longer be counted with the mass of the object, and the object's apparent mass will decrease.
Throughout this process, the mass of the Iron and the mass of the Oxygen will not change. The change only results due to the fact that you are either counting or not counting some of the material before/after you take the object's mass.
If this process were to take place in a closed container and the entire container's mass were to be measured before and after, nothing would change.

Answer 2

Yes...

rust is the result of the oxidation of iron... oxygen combines with the iron atoms to form iron oxide. So you could look at it two ways... if you're interested in just the mass of the original metal, it's less, as the iron that combined with oxygen is no longer 'iron'. If you're interested in the mass of the rusted metal bar you're holding in your hand, it's more... because now that it's oxidized, the weight of the original iron is now combined with the weight of the oxygen that formed the rust in the first place (assuming you don't flake the rust off).

either way - the mass is effected.

Answer 3

Yes, The metal has reacted with O2 to form an oxide, increasing the mass.

Answer 4

Rust is actually heavier than iron. It is an addition reaction. iron + oxygen makes iron oxide. Then when all the iron is oxidized it is rusted away. So yes it does effect mass.

Answer 5

Strictly speaking, when metal oxidizes, it adds oxygen from the atmosphere, and so it would get heavier.

Answer 6

of course "erosion" just as in the earth eventually there will be no mass

Answer 7

yes