0
$\begingroup$

I'm an electrical engineer and not a chemist, so please excuse me if this is obvious.

When soft-soldering electronic parts, we’re normally taught to clean copper of oxides (like using flux and so on) before soldering. Also I’ve observed that when heating copper to $\ce{\approx 200 ^\circ C}$ copper changes colour and builds an oxide layer. So why is copper considered a noble metal? Shouldn’t it be resistant to oxidation?

If the definition of noble metal is “less oxidation” instead of “no oxidation": Does that mean that gold and silver also build a small oxide layer in the $\pu{25 ^\circ C} - \pu{200 ^\circ C}$ temperature range?

Improve this question
$\endgroup$
6
  • 7
    $\begingroup$ Nobel metal is a very woolly concept without much scientific basis. Silver and mercury are pretty reactive too. I would not give much time to the concept. $\endgroup$
    – Waylander
    Apr 18, 2020 at 9:22
  • 4
    $\begingroup$ Even Pt oxidises, who's Cu? $\endgroup$
    – Zenix
    Apr 18, 2020 at 9:34
  • 1
    $\begingroup$ In context of chemistry of metals, the adjective noble means more or less they do not dissolve in non oxidating acids. But copper slowly dissolves even in vinegar in oxygen presence. $\endgroup$
    – Poutnik
    Apr 18, 2020 at 10:35
  • 1
    $\begingroup$ To my understanding "noble metal" meant that those metals frequently found in the metallic form in nature rather than an ionic form. Gold silver platinum and copper were all discovered as they can be readily obtained straight from the ground without smelting an ore. Most modern copper is mined as an ore and smelted to the metallic form, but substantial amounts of the metallic form do naturally occur. Many metals resist bulk oxidation by forming a protective surface oxide layer. $\endgroup$
    – Max Power
    Apr 18, 2020 at 21:50
  • 2
    $\begingroup$ Pure gold(24 karat gold) does not tarnish at all but if that is alloyed with other metals, it tends to tarnish(onecklace.com/tips/does-real-gold-tarnish). As for silver, it is easily tarnished from oxygen and moisture(ncbi.nlm.nih.gov/pmc/articles/PMC5111099) and is common knowledge that silver reacts with sulfur in air to form black $\ce{Ag2S}$. See: chemistry.stackexchange.com/questions/78882/… $\endgroup$
    – Nilay Ghosh
    May 2, 2020 at 5:21

0

Reset to default

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Browse other questions tagged or ask your own question.