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Chemistry Lab involving extensive and intensive properties

Submitted by IDR SeMiNoLe on Wed, 09/05/2007 - 23:20

I did a lab in Chemistry where I cleaned a penny in sodium chloride and vinegar (not really relevant, but I thought I'd share the step anyway), put the penny in a mixture of sodium hydroxide and zinc over a bunsen burner, and let it sit for awhile. It turned silver, and when it did that, I took it out, and put it in distilled water. After a minute or so, I took it out and held it over the bunsen burner (which was turned up high) and it turned gold, and i took it out before it started to melt. Here are some questions I have:

1. did the copper change to gold? explain. (i put no, and my reasoning was "we were told that it wasn't"...i didn't actually know why it wasn't gold)
2. what intensive property could be used to prove your explanation? (i dont know this either)
3. list 1 extensive and 1 intensive property of the penny
4. the last change (meaning when i held the penny over the open flame) formed an alloy, was the last change physical or chemical?
5. did the last change form a compound, mixture, or new element? (i don't know =/)
6. what was the final product? (i think its brass but idk)

i need help figuring these out, but i would like a good explanation so im actually learning something

This is actually a fun lab. Your first process coats the surface with zinc (the silver look.) The heating then allows the integration of the copper and zinc to form the alloy of brass on the coins surface (the gold color.)

Thoughts (hints) to help you

1. what does conservation of matter mean?
2 & 3 particular to the penny , or amount of penny
4 & 5 into what classification of matter does alloy fit
6 i believe your right.

now, go read your chem text.

But intensive properties are properties that that depend on the type of matter not the amount of matter, so I put it's melting point. I figured that if you knew the melting points of the two, and you knew the temperature of the flame, you could tell if it was gold or not.

And I think an alloy is a mixture, which would mean that the process of combining the Copper and Zinc would be a physical change, correct?

Good thinking, yes intensive properties are particular to the type of matter.

Determining the melting point might be a little impractical,
but you might think of other physical properties with regards
to metals.

Good, now to be more specific, what kind of mixture?

Your on the right track.