Where's the evidence?

Guiding Question: What are some signs that a chemical reaction has taken place?

Hypothesis: I believe that there are many signs that show chemical change or chemical reaction. The mixture or the color of different elements could change color. The state and the tempereature could also change. It would become colder or warmer, depending on the chemical reaction. Another sign that a reaction occured would be bubbling or combustion (explosion).

The Materials Used

We used many different types of materials for this lab, as many different experiments took place. We used baking soda, vinegar, sugar, copper sulfate, sodium carbonate, zinc, hydrochloric acid (HCl), calcium chloride, aluminum foil (copper), starch and iodine.

Data table with all observations:

Reactions	Observations Before Reaction	Predictions	Observations During Reaction	Observations After Reaction
Baking Soda (Soda bicarbonate) + vinegar	Vinegar looks like water, but has a strong alcohol scent. Baking soda is a white powdery substance.	I think that once the two substances mix, a white liquid could form.	The moment we put vinegar into baking soda, the mixture started foaming and rising up the test tube.	The mixture turned powdery and stuck to the sides of the test tube.
Sugar + heat	To provide the heat, we used a wax candle, and we put the sugar into a tin foil.	The sugar will probably become quite warm and caramelize.	During the reaction, smoke was released, and it had a strong smell. The sugar turned brown, and while it was over the flame, it was a brown substance, which had a gooey consistency.	After a while, the caramel cooled down, and it completely got stuck onto the foil, as it went back to its original state of matter.
Copper Sulfare + Sodium Carbonate	The sodium carbonate is a colorless liquid, while copper sulfate is bright blue.	I think that the mixture will just turn a light blue color.	The mixture precipitated, and turned into a form of a solid. Also, the mixture turned light piercing blue, probably because the copper sulfate into the sodium carbonate.	The solid broke apart, and the denser piece went to the bottom of the now colorless liquid, while the less dense one floated at the top.
Zinc piece + Hydrochloric acid (HCl)	Zinc is a solid, yet powdery metal, and HCl is a water-like liquid, that is very toxic.	I believe that the zinc will probably just start fizzing.	The zinc started getting all bubbly and it started fizzing. The smell was really disgusting, because hydrogen gas was released. The zinc turned black and dissolved.	After the reaction, the zinc was still fizzing, but the HCl liquid has turned completely white.
Calcium chloride + Sodium Carbonate	Both liquids look like water and are completely see-through (colorless). However, both have a distinct smell.	I think that nothing interesting will happen, and that the two liquids will probably form another colorless mixture.	The two liquids formed a white, cloudy mixture, and they also precipitated.	The mixture pretty much remained the same, the only difference was the fact that the solid fell to the bottom of the tube.
Copper Sulfate + aluminum foil	Copper sulfate Is a bright blue liquid, while the aluminum foil is a shiny, bendable, sheet of metal.	I am not really sure about what could happen, but the aluminum foil could dissolve.	The foil started getting bubbles on it, and during the reaction it looked white, and small parts of the foil fell off when I shook the test tube.	Two days after the reaction took place, we found out that the foil completely changed it’s color and it turned crimson red.
Starch + Iodine	The starch is a white powder used for baking, while iodine is a very red liquid, that looks like blood.	I think that the two materials won’t mix, because they have a lot of different physical and chemical properties.	When iodine and starch DID mix, the liquid was a purple color. The more iodine we added, the darker it got.	The purple started settling at the bottom of the test tube, while the rest of the liquid went back to being colorless.

Analysis of my results:

1. How do the results of each reaction compare with your prediction?
Most of my predictions were right, even though some chemical reactions really took me by surprise. When the aluminum foil and the copper sulfate, I really didn't expect the foil to become so red, and to start falling apart inside the tube. Also, the fomaing of baking soda and vinegar caught me by surpsrise, as I didn't expect such a severe reaction between these two common substances. However, we knew in advance that some substances could e very toxic and reactive, so we could know what to expect.
2.  How did you know when each reaction was over?
In most cases, it was obvious to see when the reaction was over. If the mixture stopped bubbling, that meant the reaction was over, and that the chemical changes have aleady taken place. Also, if the color completely stopped changing, we would know that the reaction is over. The end of a reaction could be marked by the cooling down of a mixture, or the stop in temperature change.
3. What was the evidence of a chemical reaction in all results?
The evidence of a chemical reaction was what was left of the reaction after it took place. When the sugar was burned, the evidence of a chemical reaction was the caramelized sold sugar that was stuck to the aluminum foil. It's color and state had been changed. Another evidence of a chemical reaction would be the newly-formed mixture left when two or more materials mix. This mixture could have a different color, smell, etc.
4. Were there any endothermic or exothermic reactions?
Exothermic reactions took place throughout this lab. Exothermic reactions that can be explosive and they release heat. One example where heat and smoke was released when zinc was mixed with hydrochloric acid. When the metal started fizzing, the mizture released warm energy, as well a hydrogen gas.  However, during this lab, no endothermic reactions were experienced, since nothing cooled down dramatically.
5. Were the products always the same as what you started with?  How do you know?
The products were never the same as they started with. In a chemical reaction the whole chemical structure of molecules changes, and they can never go back to their original states. I know that the substances and mixtures are not the same because their color changes, their original state cannot be retrieved, and they could have strong scents.

Conclusion:

What are some signs that a chemical reaction has taken place? There are many sings that can show that a chemical reactions occured. Firstly, there could be a color change in the mixture. The texture could change, as well, so the way something feels changes. We also know a chemical reaction has taken place when a new substance is formed. For example, when zinc was mixed with hydrochloric acid, hydrogen gas was released. We can also know that a chemical reaction has taken place when something combusts (explodes) or precipitates. Most of the reactions came to the end, because once the bonds create, and once the elements are mixed with each other, they stop reacting.

Further Inquiry:

If I could change anything about this lab, I would probably add some more known substances, to see how household items, and items that are familiar react with each other. This would have probably made the lab more interesting. However, overall, I believe that this was one of the most interesting labs we did, and it was one of my personal favorites.