Identifying metal blocks..

Discussion in 'Supporting Physics' started by clairelucas, May 19, 2017.

  1. I have just received an order of 2x2cm metal blocks. Given that zinc and tin are very similar in weight, so I can't hand on heart say which is definitely which, is there any other way to correctly identify them? I'm tempted to just label them the same thing anyway for density experiments, but if we use them for anything else...? don't want to be caught out!
     
    GeorgetheScienceTech likes this.
  2. Pop them in a little dilute HCL. Zn will "bubble".
     
  3. Hi Claire. Allan's suggestion is a good one however the acid will cause some damage to the block. Why not determine which is wch by a non-destructive method - density measurements. Zn has a density of 7.140 g/mL while Sn has a density of 7.310 g/mL.:);)
     
  4. That was my first thought- 2x2cm blocks should have masses of 57ish and 58ish, -my 4 blocks range from55.8 to 59, 3 at 57 or below. I have just labelled the two lighter ones as zinc, 2 heavier as Tin. If I can't tell, hopefully neither will anyone else...!
     
  5. Carol Taylor

    Carol Taylor Footsore

    instead of dropping them in acid why not drip acid on them?
     
  6. If they are ever used for anything other than density calculations, I may try. They are so shiny and new, don't want to spoil them... at least till they get nicked. Despite every box of labelled metal clearly having the number of blocks on them, and asking the teachers to count 'em back in again, lose at least 1 every couple of lessons they're used....
     
  7. Nick Mitchener

    Nick Mitchener COMMITTEE


    What is it with teachers and counting? I give them segmented trays so they only need to check each segment has something in it, just a quick glance, still some fail.
     
  8. Former_user

    Former_user Guest

    Nick :D The million dollar question!
     
    Tonytech likes this.
  9. could you use them in photoelectric effect demo? zinc would work i don't think tin would? just a thought
     
  10. PhysicsSimon

    PhysicsSimon COMMITTEE

    That's a good idea as long as they've got the stuff, the UV light must be less than 286nm with zinc (we've a low pressure mercury discharge lamp which emits mainly UVC light at 253nm). I'm not sure what the wavelength is for Tin to work but a bit of googling suggests it's less than UV, be into the X ray band.
     
  11. I'm assuming photoelectric demo is an 'A'level expt... not usual for only up to KS4. If its simple and could use anything we already have, may consider it..
     
  12. PhysicsSimon

    PhysicsSimon COMMITTEE

    Charge up a gold leaf electroscope which has some freshly polished zinc on top - shine visible light on it & it retains its charge - swap this for UV (see above for wavelengths) & you can watch it lose the charge in seconds. We have an add on with a piece of glass - this time it retains its charge proving that the UV won't go through glass (or at least the relevant wavelengths won't).

    the real point is that this proves that light (electromagnetic waves) exists in small packets (quanta) - you could shine light of the wrong wavelength on it for ever & it won't budge (or not for that reason anyway)...... most definitely A level - some proper physicist may be along in a mo to explain properly (at heart I'm a humble mechanical engineer)
     
    clairelucas likes this.
  13. Zinc is naturally dull grey and is very hard to polish. Tin is silvery grey in color (like most metals) when polished and darker when unpolished

    You could try gentle rub with lambs wool (very very fine steel wool) or sandpaper
     
    clairelucas likes this.
  14. Nick Mitchener

    Nick Mitchener COMMITTEE

    polished is perhaps not the right term, you just need a surface free from oxide, rubbing with wire wool will be fine. You are not looking for a mirror finish just access to the zinc itself rather than through an oxide layer.
     
  15. I'm not a Physics expert but this doesn't seem like Rocket Science to me. Why can't the density be determined and the identity of the said metals(s) can be found from published tables?:);)
     
  16. Nick Mitchener

    Nick Mitchener COMMITTEE

    it should be I think, the metals are in handy cubes. However Zinc is 97.54% of the density of Tin, and being that close means you need to be fairly accurate when measuring. They do look completely different as density blocks I find.
     
  17. Hello

    How about you measure the heat capacity of these blocks?

    Tin has a specific heat capacity of 0.21 J/gK while Zinc has, almost double, 0.387 J/gK. That should be significant enough to distinguish the blocks without harming them.

    So long :D
     
  18. I don't have the blocks but is not zinc non magnetic and tin weakly magnetic... would a strong magnet show that difference?? I don't know the answer!!
     
  19. I've just tried, but not magnetic enough to be noticeable...
     
  20. Wouldn't that have been just too easy!
     
    clairelucas likes this.