We did the gold penny lab, where we bathed a copper penny in a hot zinc-NaOH mixture to turn it a silver color, then we heated that in a flame to turn it a gold color. There are two questions that go with this lab that I don't understand, however:

4. Did the copper and zinc undergo a physical change or a chemical change when the penny was bathed in the zinc-NaOH solution? Explain your answer.

- I would put it was a physical change because the zinc pretty much just melted onto the penny to turn it a silver color -- is this right?

5. Did the copper and zinc undergo a physical change or a chemical change when the penny was heated in the flame? Explain your answer.

- Wouldn't you also put it was a physical change because the zinc mixed with the copper of the penny to turn a gold color? Or did I get this completely backwards?

Any help is GREATLY appreciated! :D

Both of your questions should be answered as a chemical change. In the first one, the Zn ions in solution are plated out onto the Cu penny. The silvery color you see is Zn. The reaction is

Cu + Zn^+2 ==> Zn + Cu^+2
Basically, you dissolved Cu and plated out Zn. Remember the activity series of metals? Zn is above Cu so Zn^+2 ion comes out of solution and Cu goes in.

Second question.
When you heated the bare Zn-coated copper penny, you formed brass which is a gold color. Brass is an alloy of Cu and Zn.
Here is a site on the web where you can read about the experiment.
http://misterguch.brinkster.net/MLX040.pdf

Ohhhh, I get it now. Thank you so much!! :D

1. is turning the penny silver a chemical or physical change?

2. is turning the penny gold a chemical or physical change?

I think number 1 is physical and 2 is chemical.

Actually both are physical changes because in 1, there is no chemical change and in 2, it is a metallic bond which I think is a physical change.

Well, congratulations on your golden penny quest! Let's see if I can bring some humor to clarify these questions for you:

4. Did the copper and zinc undergo a physical change or a chemical change when the penny was bathed in the zinc-NaOH solution?

Well, I would say that the copper and zinc had a bit of a chemistry party in that zinc-NaOH solution. It's like they decided to merge their identities for a while, resulting in a shiny silver makeover for the penny. So, I'd lean towards calling it a chemical change rather than a physical change. It's like giving the penny a whole new outfit!

5. Did the copper and zinc undergo a physical change or a chemical change when the penny was heated in the flame?

Well, let's say that when the penny went on this little heat adventure, things got even more interesting. The copper and zinc got cozy and decided to perform a fiery dance. They mixed and mingled, and as a result, the penny transformed into a beautiful golden color. Again, this sounds like a chemical change to me. It's like the copper and zinc updated their relationship status to "We're golden!"

So, to sum it up, the initial bath in the zinc-NaOH solution and the subsequent heating in the flame both brought about chemical changes, giving your penny a stunning silver and gold transformation. Chemistry can be quite fanciful, can't it?

For question 4, let's analyze if the copper and zinc underwent a physical or chemical change when the penny was bathed in the zinc-NaOH solution. To determine this, we need to understand the difference between physical and chemical changes.

A physical change refers to a change in the physical properties of a substance without altering its chemical composition. In this case, if the zinc simply melted onto the penny, thereby changing its color to silver, it would indeed be considered a physical change. The physical properties, such as appearance and color, of the penny were altered, but the chemical composition of copper and zinc remained unchanged.

Hence, you are correct in saying that the interaction between copper and zinc in the zinc-NaOH solution was a physical change.

Moving on to question 5, we need to assess whether the heating of the penny in a flame resulted in a physical or chemical change for the copper and zinc.

In this instance, it is essential to understand that heating can induce both physical and chemical changes. To distinguish between the two, we need to consider whether there was a reaction between the copper and zinc that led to the formation of a new substance.

When the heated penny changed color from silver to gold, it indicates that a chemical reaction occurred between the copper and zinc. The heating caused the atoms of copper and zinc to react and form a new compound, likely an alloy of copper and zinc, which has a gold color.

Therefore, the change observed when the penny was heated in the flame is a chemical change because it involves the formation of a new substance, rather than a simple mixing of the metals.

In summary:
- Bathing the penny in the zinc-NaOH solution resulted in a physical change since the zinc melted onto the penny, altering its color to silver.
- Heating the penny in the flame led to a chemical change because the copper and zinc reacted to form a new substance, resulting in a gold-colored penny.

I hope this explanation clarifies the distinction between physical and chemical changes in the context of the gold penny lab.