ANSWERS 1. Yes or No depending on what your hypothesis was to begin with. (Answers will vary for the second part of the questions). 2. Leaves changing colors during autumn, forest fires caused by lightning or careless humans, dead animals decaying after they die, digestion of food by animals, photosynthesis by plants and algae, metals rusting or oxidizing when they come in contact with oxygen (and water), sulfuric acid in acid rain dissolving limestone, etc. 3. Here are the 12 substances: a) baking soda b) Borax c) pink lemonade d) corn starch e) KCl f) CaCl2 1) vinegar 2) carbonated soda 3) iodine 4) water 5) PVA 6) washing soda solution *(some of the liquids contained the universal indicator solution and turned a certain color due to their pH) 4. The mass of the PRODUCTS that formed will be the same as the REACTANTS that were mixed together at the start of the chemical reaction. Remember, matter cannot be created of destroyed. If you start with 101 grams of reactants then you will end up with 101 grams of products. Sometimes the products might be in the form of a gas which might cause your mass to be less after the reaction has taken place (this is due to the gases escaping the container or bag you performed that experiment in). BONUS QUESTION: How do you know a chemical reaction has taken place when reactants are mixed together? Answers will vary, but should include evidence of a chemical reaction (color change, heat increase, became colder, precipitate formed, gas produced, pH changed (determined by color change), or a new substance was formed. MAKING OF SILVER AND FALLING SNOW ANSWERS MAKING SILVER OUT OF COPPER WIRE 1. The copper wire is dissolving into the solution of silver nitrate AgNO3. The solution is turning blue because the copper is dissolving into the solution. 2. Silver (yes silver) is collecting on the copper wire. It is coming from the silver nitrate solution. Copper is being dissolved into the solution, 3. It is a single replacement reaction. This is due to Cu (copper) and Ag (silver) trading places. The copper is being replaced by silver. Copper is now bonding with NO 3 and silver is all by itself forming “silver” crystals on the copper wire. 4. Test tube #1 has the most silver because it is more CONCENTRATED. This means it has more silver to react with the copper wire. This is because test tube “A” was not diluted with water like test tube “B”. 5. I could add more copper, more silver nitrate (AgNO3), increase the surface area of the copper (coil it like in the book’s example), increase the temperature of the solution or use a more concentrated silver nitrate solution and not dilute it with H2O like I did. 6. Sketches and explanations will vary. FALLING SNOW 1. The solvent was the water (it dissolved most of the boric acid) and the boric acid was the solute. 2. Some of the boric acid mixed with the water, but not all of it because the solution was SATURATED (full, no more room, no occupancy, please wait for the next elevator because this one is FULL). 3. Yes, boric acid is slightly soluble in water. There was less viable boric acid crystals in the water compared to the amount before the water was added. Since matter cannot be destroyed some of the boric acid must have dissolved into the water to form a boric acid solution. 4. More boric acid crystals would be on the bottom of the bottle. The added boric acid would not dissolve in the water (see #2). 5. I could have increased the temperature of the water (stuff dissolves better in hot water vs. colder water because the water molecules spread out when heated – more room for boric acid to dissolve), added more water (in a bigger bottle of course), or some other ways (stir or shake more vigorously), but the first two are the best. 6. Since not all the boric acid was able to dissolve, we would say the solution is SATURATED and that is why some solute was left on the bottom. 7. See # 5 above or not add as much boric acid in the first place. * Note: by adding more water I am diluting the concentrated boric acid solution and I am also changing its concentration. 8. Sketches and explanations will vary. Disappearing Water (Electrolysis) Lab 1. Oxygen collects at the positive electrode (anode) because oxygen is negatively charged (it takes away electrons from the hydrogen). Oxygen is more electronegative and is missing two valence electrons so it more aggressive at taking the electrons away from hydrogen. Since oxygen is negatively charged (an ion) it is attracted to the “positive” electrode (opposites attract in nature). 2. Hydrogen collects at the negative electrode (cathode) because the hydrogens are positively charged (they lose their electrons to the more electronegative oxygen). Since hydrogen is positively charged (an ion) it is attracted to the “negative” electrode (opposites attract in nature). 3. How much hydrogen should you have theoretically you should collect twice the amount of hydrogen compared to oxygen (because it is H2O – two hydrogens for every one oxygen). Some reasons it was not exactly 2 to 1 are: i. The gases could have dissolved in the water bath and not completely collected in the test tube ii. The oxygen reacts with the electrode and causes some rust – this means some of the oxygen is lost to the formation of another product (Fe2O3) that is taking place with another reaction. iii. The test tub graduations are sometimes challenging to read (not very precise). iv. Some of the gases might have escaped from test tubes depending on position over the electrodes. v. Anything else that you uncovered from your research. 4. By lighting a wooden splint and placing it in each test tube. If there was a “pop” or little explosion it was the test tube with the hydrogen. If the wooden splint reignited or the flame got more intense or bigger it was the test tube with the oxygen. 5. Most likely not. The ocean is HUGE and the amount of energy would be enormous (more than all the 6V batteries we have). The reaction is a decomposition reaction. If you have enough oxygen, hydrogen and energy (example: lightning) the reaction would result in the synthesis reaction of water (H + O). Even if students did this hydrogen being so unstable would likely react with other elements (one of them being oxygen) and synthesis water that would return back to the sea (as rain). 6. The reaction stopped because the water was no longer in contact with one of the electrodes. This means the electrical current could no longer “flow”. This causes the reaction to stop because all the reactants at the one electrode where finished reacting to form products (it is similar to running out of gas in your car). The solution would be to expose the electrode to the water bath to restart the reaction and flow of electrical current through the water. THE ACIDS & BASES RAINBOW LAB (ANSWERS) 1. A. Vinegar B. Apple Juice C. Banana Juice D. H2O (neutral pH) E. Soap F. Ammonia H. NaOH 2. Yes. First, there was a physical change (the color changed). Second, the reason the color changed is because the universal indicator works by forming bonds differently (good sign of a chemical reaction) with the chemicals in the solution depending on the pH of the solution. This means that there is a chemical change depending on the pH. 3. It stays reddish. It did not go to purple because test tube “A” was more concentrated. 4. The color goes from orange to blue. After I add “A” it turns back to orange or red. It actually goes back to orange and not very red because the solution was not as concentrated as the basic solution that was added. All the solutions are relatively dilute compared to the concentrated liquids I made them from originally. 5. Yes, these reactions are reversible. That means they can go back and forth to form new products. You could have taken any of the test tubes and added the opposite pH chemical (acid to a base and base to an acid) and the color would have kept changing depending on the overall solution pH. 6. Not ALL reactions are reversible. When you burn a tree down (hopefully you are not going to do this), the reaction only goes one way. You cannot easily take all the ashes, smoke and gases you produced in the reaction and put the poor tree back together again. 7. I have to neutralize the acid so it does not eat away and destroy the drain (metal pipes) and all the pretty little fish in the ocean (that would be bad, very bad). 8. The color turns to a green/blue. It is due to their being more concentrated basic solutions. “I GOT WORMS AND SO DO YOU” LAB Post Lab Questions: 1. Yes, a chemical reaction occurred. New products were formed. The new product was a long chained polymer worm that allowed many sodium alginate monomers to crosslink and form calcium alginate long chained polymer worms. The product (the worms) had different physical and chemical properties compared to the sodium alginate and calcium chloride solution. 2. A polymer is a substance that consists of small, repeating patterns of structural units (monomers). 3. A polymer is like when you take paper clips and attach them together. They each are one simple part, but can become something very large and complex as more and more pieces are added together. Other analogies will work as well. 4. They are smooth, wet and slippery. It will stretch a little, but will break if you stretch it too far. This is because the crosslinks will break with too much tension. When you stretch it the force on the crosslinks is too great and the worm breaks into two pieces. 5. Polymers are used in clothing (thread), plastics, glues, latex paint, silk worm and spider silk, and many other products that are a result of long chains. Much of ourselves are polymers (muscle tissue, carbohydrates, DNA, RNA, etc). One example of a polymer in the real world is Kevlar. It is used in bullet proof vest and other protective equipment (motor cycle protective wear). It is a thread that is extremely strong and can be woven into a very long chain for use in clothing to make them more resistant to bullets. 6. Answers and pictures will vary. 7. Wet, smooth, colors, amorphous solid, slippery, fun to play with, break if stretch too far, jumble up if squished together, etc. 8. 9. 10. 11. 12. 13. 14. Polyvinyl Alcohol Slime All Over Post Lab Questions: 1. Yes, a chemical reaction occurred. A new product was formed that had different physical and chemical properties. The new product was a long chained polymer slime that acted like a very viscous (thick) liquid and a solid. I guess you could say it was an amorphous solid. 2. After mixing all the reactants a material that could be drawn out into a long, pliable (malleable) material formed. It was similar to the polymer worms made earlier. 3. They are smooth, wet and slippery. It will stretch a little, but will break if you stretch it too far. This is because the crosslinks will break with too much tension. When you stretch it the force on the crosslinks is too great and the slime blob breaks into two pieces. It feels cool to the touch because of the high moisture content. The moisture removes heat from your hands as it evaporates away. 4. It is both a solid and a liquid. We tend to call matter that is both an amorphous solid. 5. DNA, RNA, muscle tissue, plastics, slime, carbohydrates, Kevlar, clothing threads (Nylon, polyester, cotton, etc.) and many, many more. 6. Yes. It contains carbon atoms. Compounds that are organic contain carbon. Organic compound have two unique properties: they are or once came from living organisms and they burn. Inorganic means a substance does not contain carbon and is of a non-living origins. 7. Answers and pictures will vary. 8. Wet, smooth, colors, transparent, amorphous solid, slippery, fun to play with, break if stretch too far, glows in the dark* (with zinc sulfide).
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