Grade 11 Chemistry: Physical/Chemical Change Help

[JimmyRay]

Hi I have just started grade 11 chemistry... We're reviewing from grade nine a bit and in class we did an experiment where we had copper(II) sulfate in a test tube and we heated it, and then let it cool and added water...

Ok well we have to classify this as a physical or chemical change.. but really I can't tell because when its heated it looses its color, and a change of color would be chemical, but then when water is added, its color is back... and it APPEARS to be the same substance...that would mean it's a physical change?

Ive also noticed there arnt many basic websites for chemistry help (stuff like this, physical chemical changes, grade 9-10 review)... I'd like to know if anyone has some...

Any sort of help would be appreciated...

 

[Gokul43201]

You dilemma is well justified. The terms "physical change" and "chemical change" are outdated, ill-defined and really should be thrown out of textbooks.

Both your lines of reasoning are (broadly) correct, as per "definitions". In general, however, convention requires that hydration/dehydration in inorganic compounds be considered physical changes. There's a very fuzzy area between clearly physical and clearly chemical changes, and such processes (as the above) lie in this fuzzy region, so it takes a convention to define where the line exists between the two.

I strongly recommend you write down exactly what you wrote here, stating both lines of argument.

 

[Padford]

i always refer to www.chemguide.co.uk, it's well layed out, nothing too fancy, but it's really helpful. I'm not sure if Grade 11 is the same as year 11 in england - but I'm in year 12, and this website helps no end.

 

[JimmyRay]

Hmm... I see... thanks for the replies guys

Well it's not a big deal because it's just a lab, we're going to have a small OPEN BOOK quiz on it, but we have to use our notes hmm... See the problem is the teacher won't tell us the answer... We have to observe... and for this level I think she just wants us to say physical or chemical... So basically what you said (gokul) was that it's a physical change because... ?

What do you mean when you say hydration/dehydration ?

 

[MusicMonkey]

Hydration means the addition of a water molecule and dehydration means the removal of a water molecule.

 

[GCT]

Hi I have just started grade 11 chemistry... We're reviewing from grade nine a bit and in class we did an experiment where we had copper(II) sulfate in a test tube and we heated it, and then let it cool and added water...

Ok well we have to classify this as a physical or chemical change.. but really I can't tell because when its heated it looses its color, and a change of color would be chemical, but then when water is added, its color is back... and it APPEARS to be the same substance...that would mean it's a physical change?

Ive also noticed there arnt many basic websites for chemistry help (stuff like this, physical chemical changes, grade 9-10 review)... I'd like to know if anyone has some...

Any sort of help would be appreciated...

Well in any physical process the result of the change yields the same products and reactants (compounds, elements, etc...). In this case I imagine that the change in color is either due to the different charge states of iron when it is solvated (and perhaps crystal field splitting of transition metal applies), all in all I would identify it as a chemical change. However, I believe your text should definitely give you the answer to this problem and it may conversely be physical change.

 

[Gokul43201]

So basically what you said (gokul) was that it's a physical change because... ?

Honest answer : because I think that's how your text might have it. (if you have your 9th grade text, see how it defines physical and chemical change) The reasoning may be something to the effect that the change is "easily" reversible. Reversibility appears in most high school textbook definitions of a physical change.

However, in my opinion, it is more of a chemical change, as GeneralChemTutor has explained above. There is definitely a ligand effect involved.

As such I would again recommend that you answer what you believe is the complete answer, rather than just picking anyone (unless this is an online tutorial where you can only check one box) Moreover, none of us here can tell you what the "correct" answer is supposed to be.