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Q & A: chemical vs. physical properties

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Most recent answer: 10/24/2017
Q:
Hello,My name is Ananth Ramaswamy and I am a 7th grader at Chaboya Middle School in San Jose, California. We had a question in class regarding physical and chemical properties of matter. We were given 6 items: 1. A solution has a mixture of blue and green colors 2.The collected sample smells like rotten eggs 3. The density of a sample is 1g/cm3 and it boils at 100˚C 4. Analysis reveals the formula of a sample is C6H6 5. Results show that a sample is highly toxic 6. The collected sample is very reactive in room airWe then had to say whether each of these items was a physical or chemical property. For my answer I wrote that the mixture of colors, the smell of the sample, and the density of the sample were all physical properties. I then wrote that the chemical formula, results show that a sample is toxic, and that the sample is reactive in room air were all chemical properties. However, when we graded this question in class, my teacher said that the chemical formula of a substance is a physical, not chemical, property.I was not sure of this, so I began researching to find out whether the chemical formula of a substance is a physical or chemical property. I then started reading about oxidation states, which furthered strengthened my belief that the chemical formula of a substance is a chemical property. Also, the chemical formula of a substance does not tell you anything about the physical characteristics of a substance.I then sent an e-mail to my teacher asking her my question about whether the chemical formula is a physical or chemical property. I also gave my reasoning for why I thought it was a chemical property. The next day, she discussed the question with me. She told me that she had asked an 8th grade science teacher, who told her that the chemical formula is a physical property. She said that since the chemical formula is doing nothing to change the chemical identity of the substance, it is not a chemical property; it is a physical property. I told her about oxidation states and I said that my thinking was that the chemical formula is a name which describes the elements that react to form a substance, and it does not describe any of the physical characteristics of the substance. Since I knew that reactivity is a chemical property, I believe that the chemical formula is also a chemical property. My teacher also told me that you could say the boiling point of a substance is a chemical property, though it is actually a physical property. She then compared this to the chemical formula by saying that the chemical formula could also be argued to be a chemical property, but it is actually a physical property. She also said something about electrons being unrelated to the chemical formula of a substance.Now I am extremely confused. I still believe that the chemical formula is a chemical property; however, I am still not entirely sure of this. I found your website and I thought that even though it is a physics website I could ask my question and clarify my doubts. Sincerely,Ananth Ramaswamy
- Ananth (age 12)
San Jose, California, United States
A:

Ananth, we're very glad to help out with this question. What you ask is important because issues like it come up very often in education.

What's not important is whether we choose to call some property "physical" or "chemical". Who cares? Does it change any of our predictions for what happens in the world? There is not some "true" answer to these naming questions hiding out in the universe somewhere. 

I'm a physicist. My dad was a chemist. We talked about science often. We never once asked whether what we were talking about was "physical" or "chemical" because thinking about those names would just be a distraction from the key questions of "what's happening?" , "How would it change if you change various conditions?" and so on.

 

Mike W.


(published on 10/24/2017)

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