[JonathanEyoon]

I'm lost on a question that my teach assigned for homework and was wondering if someone on here could help me with it. The problem is as follows.


Chromic Acid is a dark solid that melts at 197 celcius. When heated gently, it gives off a gas. After the gas evolution stops, a dark red solid remains that melts at a different temperature than 197 celcius.

a.) Have the chromic acid molecules been changed by the heating process? Explain your answer.

b.) Is the dark red solid that remains after heating still chromic acid? Explain your answer

c.) Was this a chemical change or a physical change? Explain your answer.


I'm honestly stuck on all three parts. Thanks alot

[enahs]

What is chromic acid? Is it a pure compound?

[JonathanEyoon]

I'm not sure what it is but the questions are aimed I believe at thinking about the physical, chemical, extensive, intensive properties as well as any physical change and chemical changes.

[enahs]

Search the internet or your books for more info on Chromic Acid. It is a mixture, it is not one pure compound. I am sure it is in your book, but the boiling point, or melting, etc, of mixtures of compounds is not the same as that of one of the pure compounds. If they have distinct enough boiling points (as an example), you can purify some compounds by driving off the lower boiling point compound. Simplified.

Look in your book and the internet about physical properties of mixtures.

[JonathanEyoon]

I looked in my book during this entire time, consulted with a couple buddies and it's not in the book and we are still clueless 


Apparently the teacher is not interested in what kind of acid it is. She stated it can be Succinic Acid or Chromic Acid or some other kind but the thing she's looking for is if we can use our knowledge of physical properties, chemical properties, mixtures, compounds, and other things we've learned to answer the questions....which we're having such a hard time with.  Help 

[JonathanEyoon]

For part a) the only thing I can come up with is

When heating up the chromic acid mixture gently, the molecules of chromic acid have changed due to a process of distillation.  The gas that was given off when heated was part of the chromic acid which was a physical property where the melting point is 197 Celsius.  Now that the melting point has changed, I can only say that it has underdone a chemical change where the composition of the chromic acid is different.


How did I do?

[JonathanEyoon]

Any help is greatly appreciated  I have a major test on this since I have  a test in a few hours.

[Arkcon]

Like your teacher says, this is not a question on the properties of chromic acid.  This question is all about part C -- is this a physical change ( example: melting of an ice cube by heating) or a chemical change (example:  charing sugar by heating) and how can you tell? That's what you should search your notes and text book for.  It's unlikely the exam will have this same exact question.  Parts A and B seem to ask the same question as part C, just in different ways.

[AWK]

May be dehydration
H2CrO4 = CrO3 + H2O
Water is a gas over 100 C