3/12/09
Lab Report
How much Water and How much Salt?
Introduction:
When we were first presented with this experiment, I was excited to discover the results, although I was a little bit confused about where we were supposed to begin. This experiment, which produced common table salt, was conducted over the course of several days. The assignment was to make a procedure given the molarity, formula, reactants, and products, along with our previous knowledge, and determine the amount of water from the reaction. When we first began the experiment, we were told that we needed to find how much water not only from the reaction, but also from the reactants. Later in the experiment, this was changed to simply finding the water from the reaction. We were told that the molarity of the NaOH solution was 3M and the molarity of the HCl was 12 M. The products of NaOH and HCl are H2O +NaCl. We needed to use our knowledge of neutrality in order to neutralize the solution. Since we were not given a procedure, as we normally are, the first day or two was devoted to simply discovering what steps we were supposed to take. When we first began, we thought that we needed to separate the NaOH and HCl and boil them separately before combining them. However, we were later told that those steps were not necessary. The formulas that we had to use were only necessary for calculating the final results. That formula was C=mol/L, with C being concentration, mol meaning moles, and L meaning liters. Although our hypothesis did not include the exact mass of the water, we predicted that there would be more water than salt. This experiment was very challenging at first, although it proved to be very interesting towards the end.
Hypothesis:
We hypothesized that there would be a greater amount of water than salt, although we were not exactly positive why that would be the case. Furthermore, we believed that the solutions would be neutral when we first combined them, as we would measure the appropriate amounts. We knew that we had to boil the water out in order to find the amount of salt, and consequently, the amount of water. Additionally, we used the knowledge that we gained from the alcohol fermentation experiment that was demonstrated earlier in the year. From this experiment, we knew we needed to boil out one of the components in order to find the other. We made these hypotheses based on our knowledge of neutrality and stochiometry.
Materials:
• NaOH
• HCl
• 2 small graduated cylinders
• 1 glass rod
• 2 100 mL beakers
• 1-2 pipettes
• 1 roll of paper towels
• 1 analytical balance
• 1-2 strips of pH paper
• Calculator
• Pencil
• Paper
• 1 Bunsen burner
• 1 stand
• 1 wire mesh square
• 1 starter/lighter
• 1 crucible and top
• Clock
• Baking soda
• Vinegar
• 1 pair of tongs
• 1 clear, plastic tray
Methods:
1. Gather all supplies and materials necessary for the experiment.
2. Measure out 4 mL of the 3M NaOH and 1 mL of the 12M HCl into separate graduated cylinders. However, finding these precise measurement will be very difficult. To make this process easier, pour around 10 mL of each solution into a separate beaker. To make sure that the solution does not run down the side of the container, place a glass rod in the center of the beaker. Using a pipette, drop the correct amount of acid or base into the graduated cylinder. For the HCl, be sure to measure it out under the hood, as it will produce a cloud.
3. Find the mass of a 100 mL empty beaker. Record this number.
4. Pour the two solutions into the beaker. Using the glass rod, place a drop of the solution onto the pH paper. If the pH paper does not turn green, add the necessary amounts of acid or base. Record all information.
5. Using a pipette and an analytical balance, find the mass of one drop from the pipette. Take more than one sample and then calculate the average. Using the density formula, determine the volume of one drop.
6. Find the mass of the beaker. Find the mass of the solution. Record all information.
7. Set up the burner and all necessary materials for the later step.
8. Place the empty crucible on top of the burner and allow the flame to pass over it for 5 minutes. This will purify the crucible. Allow the crucible to cool for around 2-3 minutes.
9. Find the mass of the empty crucible.
10. Pour the neutral solution into the crucible.
11. Using a burner, place the crucible above the flame. Pass the flame gently over the crucible. Check the amount of water every minute or so to see how much water is left. When there is only white salt and no water left, turn the burner off. This will eventually evaporate the water out, leaving only the salt. Allow the crucible to cool.
12. Find the mass of the salt by finding the mass of the crucible. Record these results.
13. Subtract the amount of salt from the total mass. This will give you the amount of water.
14. Record your results and data.
15. Clean up all materials and workspace. When pouring out the solutions, you must neutralize them. For the acid solution, or HCl, pour a little bit of baking soda into the graduated cylinder/beaker. For the base solution, or NaOH, pour a little bit of vinegar into the graduated cylinder/beaker. This will neutralize the solutions and make them safe to go down the drain.
*If you are not completing your experiment in one sitting, cover the acid and base to ensure accurate results.
Data/Results:
# of drops of acid Added 2 drops Added 5 drops Added 10 drops Added 0 drops
# of drops of base Added 0 drops Added 0 drops Added 0 drops Added 3 drops
Color/Is it neutral? Dark blue=too basic Blue=too basic Red=too acidic Light green=neutral
Note: These numbers are after we realized that the initial solution was not neutral. This is the amount of acid/base that we added to the first solution.
Note: On Word, this is in a chart. Look at the numbers as if it were on a chart. Read vertically. Example (first column): Added 2 drops of acid, 0 drops of base, result=dark blue=too basic.
Mass of drops (g):
0.0207 g(1 drop)
0.0341 g(2 drops)
0.0648 g(3 drops)
0.0889 g(4 drops)
Average mass of 1 drop:0. 0112 g
Density=mass/volume
Density of water=1
Mass of drop-0.0112
1=0.0112/V
V= 0.0112 mL (1 drop)
Mass of empty graduated cylinder=25.93 g
Mass of empty beaker=50.83 g
Mass of beaker with neutral solution=56.0763 g
Mass of solution=56.0763-50.83=5.2463 g
Mass of empty crucible=15.5217 g
Mass of crucible after heating=15.8483 g
Amount of NaOH used=0.0121 moles=0.48 g
- 3M=moles/L
- 0.0112 x 3=0.0336 grams
- 4 mL + 0.0336=4.0336
- 4.0336/1000=0.0040336 L
- 3M=moles/0.0040336
- Moles=0.0121
- 0.0121 x 40=0. 48 g
Amount of HCl used=0.014 moles= 0.52 g
- 12M=moles/L
- 0.0112 x 17=0.1904 g
- 1 mL + 0.1904=1.1904
- 1.1904/1000=0.0011904 L
- 12M=moles/0.0011904
- Moles=0.014
- 0.014 x 36.458=0.52 g
Mass of NaCl at the end of the experiment=15.8483-15.5217=0.3266 g
0.3266 g/58.44=0.006 moles
Mass of H2O at the end of the experiment=5.2463-0.3266=4.92 g
4.92 g/ 20.16= 0.24 moles
Actual/Theoretical Yield
Theoretical Yield= 4mL of 3M NaOH + 1 mL of 12M HCL-->NaCl +H2O
C=mol/v mol=cv
HCl=(12M)(0.001)=0.012 moles
NaOH=(3M)(0.004)=0.012 moles
0.012 mol NaCl x 58.44=0.7 grams=Theoretical (under perfect conditions)
0.3266=Actual=Experimental yield
% yield=Actual/Theoretical x 100
0.3266 g/0.7 x 100=46.66%
Discussion/Analysis:
Our hypothesis, which was that the amount of water would be greater than the amount of salt, was proven correct. Although some of our water spilled out of the crucible, our hypothesis was still proven, as the mass of the NaCl was 0.3226 grams while the mass of the H2O was 4.92 grams. However, the second part of our hypothesis, which was that the solution would be neutral the first time we combined it, was not correct. We made four more attempts at achieving a neutral point by adding drops of acid or base, depending on what color the pH paper turned. Although we did have to try four times, when the pH paper turned red, we only had to add three more drops. Drops do not have a lot of volume, and we knew that we would only have to add a small amount of acid or base in order to achieve neutrality, since we did not measure out a large quantity of volume at the beginning of the experiment. Furthermore, the moles of base are not exactly equal to the moles of acid. This is due to the margin of error. The NaOH is not new, so it has absorbed more water due to this fact. Also, other people left the NaOH open, which caused it to be exposed to the air. Saying this, our moles of acid compared to our moles of base are very close nonetheless. Additionally, we had to revise our procedure many times before we got our final product. The first class in which we were presented with this experiment we simply thought of ideas on how to approach this experiment. Our first idea was too arithmetical, and Mr. Schoudel wanted us to find the results by experimentation. This led to us revising our procedure once again. Furthermore, we used our knowledge from the alcohol fermentation lab that we observed earlier in the year. We knew that in that experiment, Mr. Schoudel boiled out the alcohol, which is something very similar to what we wanted to do. If we had a more accurate procedure from the beginning of the experiment, we could have performed it more efficiently. However, there were many obstacles and challenges that we had to overcome, as this was the first time we were presented with a lab without a procedure. Although I am very pleased with how the experiment turned out, there would be some improvements that I would make. First, I would place the flame over the crucible filled with solution more slowly. Although we tried our best to do this, we held the flame under the crucible for just a moment too long, which caused a tiny bit of water to spill out of the crucible. Although it was just a small amount of water, it still changed the outcome of the experiment. Also, I would move more efficiently the next time. Although we did finish the experiment, we had to stay after class for around five more minutes. If we had known exactly what we had to do, we could have been more efficient. Finally, I would make sure that we made all of our measurements on the analytical balance. Although we made the majority of them on the analytical balance, we used a regular balance for two or three measurements. Since science is such a precise subject, every decimal place counts. There is a great margin for error in every experiment we perform, as we are subjected to many different variables, such as the old NaOH. These are variables that we cannot control, so we have to do our best to work around them. Although I could make changes, I am extremely pleased with the way we executed the experiment.
Conclusion
This experiment was exciting, interesting, and challenging for me. I never knew that we could produce table salt so easily. This experiment was interesting, as I really wanted to discover the results and answers to the experiment. Getting around the different obstacles was challenging, but we were able to perform a great experiment. This experiment used our previous knowledge and the information that we are learning and forced us to think critically about it. I can say that I understand more about products and reactants, neutrality, and other topics than I did before. Once our procedure was completed, the experiment was much less challenging. However, making us create our own procedure was another step and another obstacle. I think that we handled the experiment very well, and really applied the chemistry knowledge that we had. Although I was a little concerned at first about the experiment, as I did not know how it was going to go, I enjoyed performing this experiment very much.
