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Is there a interaction between a graphite pencil and and a eraser. For example, if I drew a line on a piece of paper and then erased that, what interaction is occurring?

Is it a Van der Waals interaction with intermolecular forces or is something else?

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  • $\begingroup$ Hello and welcome to Chemistry.SE! If you have any questions about the site I suggest you start off with the short tour. Good luck! $\endgroup$ – airhuff Feb 22 '17 at 0:39
  • $\begingroup$ @airhuff This is a good question. Maybe it needs a little bit of edit. But it's good $\endgroup$ – Mockingbird Feb 22 '17 at 4:24
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    $\begingroup$ @Mockingbird, agreed. My first thought is that the Van der Waals interactions between the graphite and eraser are just stronger than those between the graphite and the paper, but I hope someone has a more thorough answer than that ;) Do you have any ideas? $\endgroup$ – airhuff Feb 22 '17 at 5:51
  • $\begingroup$ I also share the same thought.. $\endgroup$ – Mockingbird Feb 22 '17 at 6:33
  • $\begingroup$ It's called friction which is mechanical and not "chemical". Does the rubber erase the graphite if you just put it on your scribbles and don't rub it? I find that most chemists forget about the simple world of mechanics all too fast. Apply a thin layer of something on a surface and then rub it -> it vanishes. Must be hydrogen bonding, right? Wrong. Call it Pauli repulsion if you want $\endgroup$ – AMT Feb 22 '17 at 15:38
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There was much discussion in the comments to the OP regarding whether erasing a pencil mark is a chemical process or merely a mechanical process, akin to removing an oil spill with high pressure water (my analogy). But I think the answer to "Is it a Van der Waals interaction with intermolecular forces" is clearly yes.

Although the classic "pencil head" eraser generally requires a vigorous rubbing action to rapidly remove a pencil mark, even this can be done in a manner that shows pencil marks that had been bound to the paper via intermolecular forces are transferred to a material having a stronger affinity for the pencil mark than does the paper.

This Wikipedia article discusses several types of erasers that clearly illustrate a chemical process rather than a mechanical one is dominating the removal of the pencil mark. For example, regarding the "poster putty" type of eraser the article states:

"...poster putty works much the same as traditional kneaded erasers, but with a greater tack or lifting strength...Repeatedly touching the putty to a drawing pulls ever more medium free..."

A "gum" eraser also clearly works by adsorbing graphite from paper. As the gum is dabbed or lightly rubbed on the pencil mark, the intermolecular forces holding the graphite to the paper are weaker than the intermolecular forces between the graphite and the erasure. The following photo from the above Wikipedia article shows that the graphite in the used eraser has accumulated over time. There is no evidence of paper or other material having accumulated along with the material from the pencil mark.

gum erasers

Furthermore, one can imagine using different materials that should make for good erasers if the pencil marks are simply being removed by the mechanical action of an eraser. For example, if that's the case, shouldn't you be able to remove the pencil mark by rubbing it off with a piece of wood, one's finger, another piece of paper, a fingernail, etc.?

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  • $\begingroup$ You can erase the pencil marks with your finger. I'm not convinced by your arguments. One type of eraser absorbs graphite quite heavily, so all erasers function via "van der waals" interaction? I've mentioned in the comments that this by itself is an extremely vague term. So why do you need to rub your eraser then? The way I understand it, it is 1) rubbing the eraser thus loosening the graphite 2) some kind of absorption process by the material to prevent smearing, is this correct? $\endgroup$ – AMT Mar 20 '17 at 9:36

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