Lab questions help - proving

[Jessica]

1. How could you prove that dissolving the salt in water resulted in only a physical change? Would this be because the water is still water? That the salt has not affected the water?

2. How could you prove that adding Mg to HCl resulted in a chemical change?


I need help with these questions!

Here are my observations when I added salt to water and added Mg to the HCl.

Salt >>> water:
*salt sinks immediately to the botton and dissolves; no change in liquid

Mg >>> HCl:
Temp of plain HCl was 23.5 degrees Celcius.
After Mg is added, it went up to 23.6 degrees Celcius.
Observations: Mg floats up and down (it was a Mg ribbon)


For the questions, I do not know how to explain it. I need a head start and some hints, then I will try to answer the questions.
if you want me to answer the questions, I will, but I will have some trouble.



Also, why would adding Mg metal to HCl be a chemical change? The metal moved up and down and the temp got warmer, but I don't understand how it's a chemical change.

[Rusty]

Can you list the three things that can happen when atomic bonds are broken? This may help you figure out the answer to number two.

I think you already know the answer to number one. Dissolving salt in water doesn't change the water. Only the shape of the salt was altered. It didn't combine with the water molecules. This process is reversible. Explain how you can reverse the process for proof of a physical change.

[Jessica]

okay, but I don't know the 3 things that happen when atomic bonds break

[Rusty]

There are the big three - light, sound or heat is given off. There are others.

[Jessica]

okay.....you said it will help me answer #2. can you explain a little more??

[Rusty]

You said you measured a change in something during the chemical change that occurred. One of the three things I mentioned explains why that measurement was different. That is one thing you observed.
You said the other thing you observed was the movement of metal. I wouldn't think this is a chemical change, but perhaps a chemical change caused the metal to move in the liquid. Can you think of anything that would cause the object to move? Were there bubbles of any sort?

[Jessica]

yeah there were bubbles

[Rusty]

How'd the bubbles get there? What caused the acid to heat up?

[Jessica]

the Mg made the HCl heat up??????????

[Rusty]

Yes, the chemical reaction between the two compounds caused heat and bubbles to occur. The bubbles were not because the liquid was boiling. Do you know what the bubbles contained? You can find your answer by searching for "reaction between mg and hcl" on the Internet.

[Jessica]

Did it contain acid?? I looked it up on the Internet but couldn't find an answer.
In the lab, we put small pieces of antacid (broken up) into the water, and right away, it sank and lots of bubbles and foam appeared and quickly reached the top. Would that be acid? So would the bubbles contain acid?

[CrOtALiTo]

Jessica, you are doing your homework with us, jejej never mind that, but you must to find your homework in the internet or you also can to find in the library, I told you this because I don't know if it correct that we are helping you in your own homework, then I feel, you need to learn your homework correctly in your own world, I did that before, for that reason I told you this, I don't mind me the, you need help of us, but you need to study more, you believe?

[Jessica]

I got it. The bubbles are a gas, and also, since the temperature changed, it's a chemical change.

[Rusty]

Good job. Gas and heat were the results of the chemical change.