Slime Lab

In this lab, we were cross-linking Elmer’s glue with Sodium borate.  We were trying to figure out how the physical properties of the polymer change because of cross-linking.  Also, we had to find out how adding more agents would change it.  We predicted that if we mix the Elmer’s glue with the Sodium borate, then it will change it’s state of matter and the more you add the bigger the change.
When we added the water to the glue, it’s texture became more like flowing liquid and not like melted marshmallows.  Mixing the borax with the other beaker of water was just like mixing sugar or salt into any liquid.  When we were pouring the borax into the glue, it made a hole where I was pouring the water/borax solution.  Almost instantaneously it began to form a solid form.  To the left, is what the solid looked like when we first started stirring.

We performed a “slime test.”  On a scale of sliminess of 1 to 5, we gave it a 4.  It smelt like glue.  It looked like half melted marsh mellows before we rolled it into a ball.  Also, it looked like egg whites.  When we attempted to bounce it, it would bounce with one large initial bounce then 3-4 small ones.  Next, when we tried pulling them apart slowly/quickly they both ripped apart a second or two after we began.  When we’d poke our finger through it slowly, the slime would form around it.  If we were to do it faster, the finger would poke through nearly instantaneously.  For our final test, we had to time how long it’d take for it to flatten.  It took 3 minutes 34 seconds. This was my drawing when it first started.

In conclusion, our hypothesis was correct.  The glue changed from liquid to solid within seconds of pouring it in. Doing this experiment brought us closer together and made us all more comfortable with each other.

ChemThink: Chemical Reactions

1. Starting materials in a chemical reaction are called reactants.
2. The ending materials in a chemical reaction are called products.
3. The arrow indicates a chemical change has taken place.
4. All reactions have one thing in common: there is a rearrangement of the chemical bonds.
5. Chemical reactions always involve breaking old bonds, forming new bonds, or both.
6. In all reactions we still have all of the atoms at the end that we had at the start.
7. In every reaction there can never be any new atoms or missing atoms.
8. Chemical reactions only change the position and bonds of the atoms that are already
there.
9. If we use only the atoms shown, we’d have 2 atoms of H and 2 atoms of O as reactants. This would make 1 molecule of H2O, but we’d have 1 atom of O leftover. However, this reaction only makes H2O.
10. So to make H2O from oxygen gas and hydrogen gas, the balanced equation would be:

2 H2 + O2 ----> 2 H2O

11. This idea is called the Law of Conservation of Mass.
12. There must be the same mass and the same number of atoms before the reaction (in the reactants) and after the reaction (in the products).
13. What is the balanced equation for this reaction? 2 Cu + O2 ! 2 CuO
14. In the unbalanced equation there are: Reactants ----> Products

Cu atoms    1    Cu atoms 1

O atoms      2    O atoms 1

15. To balance this equation, we have to add two molecules to the products because this reaction doesn’t make lone atoms.
16. When we added a molecule of CuO, now the number of O atoms is balanced but the number of Cu atoms.
17. The balanced equation for this reaction is 2 Cu + O2 ----> 2 CuO
18. What is the balanced equation for this reaction? 1 CH4 + 2 O2 ---->  2 H2O + 1 CO2
19. What is the balanced equation for this reaction? 1 N2 + 3 H2 ----->  2 NH3
20. What is the balanced equation for this reaction? 2 KClO3 ----> 2 KCl + 3 O2
21. What is the balanced equation for this reaction? 4 Al + 3 O2 ----->  2 Al2O3

SUMMARY
1) Chemical reactions always involve breaking old bonds, forming new bonds, or both.
2) The Law of Conservation of Mass says that the same atoms must have the same mass and number of atoms before and after the bond.
3) To balance a chemical equation, you change the number in front of each substance until there are the same number of each type of atoms in both reactants and products.

3 Demonstrations by Miss Leland

Our teacher, Miss Leland performed three demonstrations.  One with Ethanol, another with Hydrochloric Acid and Zinc, and the last with baking soda/vinegar. To begin with, she put Ethanol into a soda bottle and swirled it around.  It was transforming into a gas. When heat (energy) was added it was supposed to launch forwards, but instead it just stayed lit for a few seconds and went out.  Next, she combined baking soda and vinegar.  The baking soda and vinegar combined int oCarbon Dioxide.  After they were mixed together, she lit two candles.  She poured the gas over the candles and they both suddenly went out.  This is because fire needs oxygen to continue burning.  So, when we poured the Carbon Dioxide over it, it went out because Carbon Dioxide is the opposite of Oxygen.  Since the fire was surrounded by CO2 (Carbon Dioxide), it didn't have the Oxygen required for it to maintain the chemical reaction required for the flame to stay consistent.  Finally, we did the test with Hydrochloric Acid (HCl) and Zinc (Zn).   We created ZnCl2 + H2.  We also applied heat part of the way through it.  Heat or energy can at times be a catalyst that is needed to start or speed up the chemical reaction.  Once the Zinc was introduced, it bubbled and released steam (gas).  The gas was Hydrogen.  We then added fire and it sped up the process.  The Zinc was broken into small pieces by the end of the reaction.

Chemical Reactions and Temperature Lab

In this experiment, we dropped an Alka-Seltzer into different temperatures of water to see what would dissolve faster.  We predicted that the hotter the temperature got the faster it would dissolve.  The hot water was at 50 degrees Celsius and it took 20 seconds to fully dissolve.  The room temperature water was at 25.1 degrees Celsius and took 27 seconds.  Finally, the cold water took a minute and 56 seconds to dissolve at 0.8 degrees Celsius.

Alka-Seltzers are made of NaHCO3 and once you combine it with H2O you create CO2.  The CO2 are in the bubbles created by the two, Sodium bicarbonate and water, combining.  The heat makes the water molecules bounce off each other faster to break the tablet faster. 

Melting and Freezing of Water Lab

We predicted that the freezing water would be at -2 degrees Celsius and the melting water would be 3.5 degrees Celsius.  The actual temperature for the freezing water was -2.364 degrees Celsius.  Also, the melting water temperature was 3.268 degrees Celsius. 

This is the freezing water's progression.

This is the melting water's progression.  The temperature probe immediately froze once we stopped stirring the probe around.

Once, we put it into our warm tap water it completely melted within three minutes.  The temperature for the freezing water went down while vise versa for the melting water.