i neeed help determining whether the following changes are chemical or physical and why. i have some guesses but i wanted to have them verified. thanks. =)
1) mixing chalk and vinegar: chem. b/c it bubbles
2) mixing starch and iodine: physical b/c the iodine dissoles and the satrch falls to the bottom of the beaker, (but the mixture turns purple)
3) ammonia abd iron (III) chloride: physical b/c the mixture eventually settles out,(but there is a color change.)
please help me to verify. thanks
1) correct
2) read http://en.wikipedia.org/wiki/Iodine_test and guess again
3) wrong. The color change is a clear indication of a chemical reaction.
Sure! I'd be happy to help you verify your guesses about whether these changes are chemical or physical. Let's go through each scenario one by one:
1) Mixing chalk and vinegar: Chemical change. Your reasoning is correct - the bubbling indicates a chemical reaction is taking place. In this case, the acetic acid in vinegar reacts with the calcium carbonate in chalk to produce carbon dioxide gas, water, and a compound called calcium acetate.
2) Mixing starch and iodine: Chemical change. Contrary to your initial guess, this is actually a chemical change. The iodine molecules interact with the starch molecules to form a dark blue or purple complex, known as the starch-iodine complex. While the starch may appear to fall to the bottom, it is still participating in a chemical reaction with the iodine, resulting in the color change.
3) Mixing ammonia and iron (III) chloride: Chemical change. Though you initially suggested it may be a physical change due to settling out, the color change indicates a chemical reaction. When ammonia and iron (III) chloride react, they form a new compound called iron (III) hydroxide, which is a brown precipitate. The formation of a precipitate and the change in color indicate a chemical reaction has occurred.
In summary, all three scenarios involve chemical changes because new substances are formed as a result of reactions between the different substances.