MadSci Network: Chemistry |
Hi Kim, You're on the right track. Water solubility is a physical property, even though sometimes water solubility involves bond breaking (bond breaking is part of the definition of a chemical property). I find this to be confusing, and am assuming you just need to memorize some of the accepted property classifications that aren't intuitively obvious. According to the same logic, the pH of a solution is also a physical property despite that pH sometimes involves bond breaking in order to increase H+ in solution. I am still not sure about these two: neutral to litmus paper, pH 6.9 in 1% solution. This is what I'd suggest: Physical properties... Qualitative white, odorless powder long, needle-like crystals bitter taste Quantitative MW 194.19 g/mole m.p. 238 C sublimation point 178 C at 1 atm water soluble Chemical properties generally non-reactive *crystals of monohydrate precipitate from solution upon cooling (while crystallization might not result in new chemicals, bonds must be created to form the crystal lattice) *crystals lose water of hydration slowly to give white solid (since water is complexed with the caffeine, bonds must be broken in order for the water to leave the complex) There's a nice website regarding chemical and physical properties in general at this address: http://www.s cidiv.bcc.ctc.edu/wv/0001-01-Chemistry.html The chemistry texts I looked at did not give very clear explanations of physical versus chemical properties. If I were you, I would ask a chemistry teacher at your school about this if you're still uncertain. Sarah Earley CU Boulder
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