Cleaning Silver

[Teresa]

Hi to anyone who comes online over the holidays!
I have a question regarding cleaning silver:
Over Christmas when the silver cutlery needed cleaning, an old army technique was used: ie dipping the tarnished silver into water containing dissolved table salt and a sheet of alfoil, and then wiping dry.
It was like magic!
Can somebody explain the chemistry behind this?
Regards
Teresa

[Robb]

Hi Teresa,

Relatively easy question to answer,

Basically what is happening is that an electrochemical cell has been made.

The Silver has formed one electrode and the Foil the other. Table salt is added to give a conductive free ion path for electrons to travel.

So what does this all mean?

The Silver is much lower in the activity series of metals, The Al foil much higher, therefore the aluminium is giving electrons up and these electrons are dropping into solution.

The imbalance of charge then causes the Silver to attract electrons to its surface which in turn reduces the metal, (only at the surface of the metal).

(Just as if the Al foil and Silver were a set of terminals on a battery, one Negative and the other Positive respectively).

Hence, why the silver is cleaned.

Hope this has given some insight into your query.

Happy New Year ahead,

Robb.....

[Teresa]

Thank you for you reply Robb, you are always so prompt to answer queries. Thank you!

Further to Robb’s reply. In between the time when I posted the query and Robb replying I found extra information at http://scifun.chem.wisc.edu/HomeExpts/TARNISH.html

Basically it explains that the tarnish on silver is silver sulfide.

When silver is cleaned with abrasive polishes you remove the silver sulfide compound, which is a physical change.

However when you put the silver, which is tarnished into the salt solution with the aluminium foil, you create an electrochemical cell and the chemical reaction as follows:
3 Ag2S + 2 Al 6 Ag + Al2S3

Hence it is better to clean silver using the latter method as you don’t lose silver, which is especially important if the item is silver coated.
This could be used as an example of the difference between physical and chemical change.

I found this interesting and thought it might be of interest to others too.

Best wishes for 2007
Kind regards
Teresa

[Steph]

I tried this over the weekend. Brilliant results with a minimum of effort! Thanks for the tip.