Week of Oct 24

Monday

Reviewed for 2b test. Since I want you to take test w/o calculator I showed some sample problems that you could expect and some tricks for solving them w/o a calculator.  Most of the class was spent working problems or working on your alkali carbonate lab.

Tuesday

Test day. Test was too long. Will have to finish tomorrow.

Wednesday

I am out sick. We will finish test on Friday.  Today I want you to do 3 things

  1. watch these 2 videos & take notes
  2. update your online portfolio
  3. work on your alkali carbonate lab

Thursday:

Community Day – no class

Friday:

Today you finished your test and then the rest of the block to work on the packets.

The packets are not numbered, but if you number each page starting with the Unit outline as page 1 and numbering even the empty back pages…

  • do page 3 based on video 1 above
  • do some of page 6 – just predicting the products and balancing w/o worrying if a reaction happens yet.  See this video for help on single replacement.
  • do page 7 & 8.  The rules for finding oxidation states are on pages 7 and 9 (page 9 has examples)
  • do page 12-13 using notes that start on bottom of page 9 or this video or this video .

 

 

 

Week of 10/17

Monday:

Today we worked on gravimetric analysis problems. We started by reviewing double displacement reactions in the packet and then I went over a typical ga problem.  The rest of class you worked on textbook problems.

Tuesday:

Today we started with the nomenclature quiz.  After that you worked on designing a lab to determine the alkali metal in an alkali metal carbonate.

Wednesday:

No class b/c of PSATs

Thursday:

Worked on designing the lab to determine alkali metal. Here are example procedures.

HW: Chemical formulas lab due Friday morning!

Friday:

Alkali Metal Carbonate Lab

Example Avogadro Lab Conclusion:

The Determination of Avogadro’s Number Lab was used to estimate Avogadro’s number experimentally. It’s also used to find the dimensions of an atom and determine the validity of the Oil Slick method of estimating Avogadro’s number. The experimental method used to determine Avogadro’s number was the oil slick method, which uses Oil (containing oleic acid and ethanol), lycopodium powder and water. The results of this experiment found that the Oil Slick method is not a valid method of determining Avogadro’s number as there is too much error involved in the process and false assumptions were made about the properties of the oil slick and molecule.

The mass and volume of oleic acid in a drop of oil was calculated by weighing several then dropped into a mixture of lycopodium powder and water. The ethanol in the oil then evaporated or dissolved in the water leaving the oleic acid(C17,H33COOH). The oleic acid displaced the water/lycopodium mixture as the oleic acid is nonpolar and the water is polar so the two don’t form a solution (also the water doesn’t dissolve the lycopodium, the powder rests on top of the water so when the water is displaced so is the powder, allowing to see the area of the oil slick). The nonpolar oleic acid lycopodium powder and formed a roughly circular monolayer(one molecule thick) slick on the surface of the water. The diameter of the circle formed was measured and then used, along with the volume of the oleic acid to estimate Avogadro’s number. We performed this procedure for three trials. To achieve more consistent results during this procedure, we had the same individual perform a specific task (ex. measuring the diameter of the slick, dropping the oil) for each trial.

Our group did the calculation of Avogadro’s number two different ways. For one set of calculations it was assumed that the height of one molecule of oleic acid was 20 atoms tall and for the other calculation it was assumed that one molecule was 19 atoms tall. Both these heights were supported as possible by a three dimensional model we formed of oleic acid. The calculated values for Avogadro’s number when using a molecule height of 20 atoms were: 1.12 x 1022 molecules (98.14%, 10.7 cm), 1.07 x 1022 molecules (98.22%, 10.9 cm), and 1.36 x 1022 molecules (97.74%, 11.1 cm). The calculated values for Avogadro’s number when using a molecule height of 19 atoms were 1.00 x 1022 molecules (98.34% error, 10.7 cm), 1.01 x 1022 molecules (98.32%, 10.9 cm) and 1.12 x 1022 molecules (98.04%, 11.1 cm). The difference between the use of 19 or 20 atoms made no appreciable difference on the result.

Our data is not valid because of the high percent error in our estimate of Avogadro’s number and the inaccuracy of our results. The percent error was over 98% for every trial that was conducted. The extreme inaccuracy in our calculations of Avogadro’s number can be contributed to several factors. This experiment made several assumptions, that if false, would’ve led to miscalculations and an incorrect estimate of Avogadro’s number. The assumption that the oil slick is one monolayer tall could be incorrect. If it was incorrect, it would invalidate the results of all the calculations made based on the idea that the layer was one molecule deep. This in turn would affect our results for Avogadro’s number. For instance, if the oil slick was actually five molecules tall, the average calculation for Avogadro’s number would be 5.35X1023, which is distinctly different from the result we found operating under the assumption that it was a monolayer. The assumption that the molecule was 20 atoms tall or 19 atoms tall could also be incorrect. It’s more likely that the Oleic Acid molecule is 19 atoms tall as when we did our calculations and accounted for 19 atoms in the height of the molecule, the percent error of Avogadro’s number was smaller. The average percent error using 20 atoms was 98.03%, whereas the average percent error for 19 atoms was 98.23%. Though the difference in percent error is small, the 20 atoms calculation still are closer to the accepted value it can be inferred that the molecule is more likely to be 20 atoms as opposed to 19 atoms.

Our experiment was also not accurate due to a systematic error made in measuring the diameter of the oil slick, which would lead to miscalculations in estimating Avogadro’s number. The average diameter of the oil slick was 10.9, but if you calculate the diameter of the oil slick by working backwards from Avogadro’s number, it’s closer to 17. The largest diameter, 11.1 cm, had a smaller percent error than the two smaller diameters of 10.7 cm and 10.9. The 11.1 cm had a percent error of 97.74% (assuming that the molecule is 19 atoms tall) and the 10.7 cm and 10.9 cm diameters have percent errors of 98.14% and 98.22%. If we were to increase the diameter of the oil slick to 17 cm and readjust the calculations, the estimate of Avogadro’s number is now 1.616 x 1023. The percent error of the new calculation is 73.16%, which is still high, but substantially lower than the original calculations, which had an average diameter of 10.9 cm and a percent error of 98.04%. As we increase the diameter of the oil slick, the estimate of Avogadro’s number gets closer to the accepted value.

As our estimates of Avogadro’s number are inaccurate, but relatively precise, it can be assumed that a systematic error was made in measuring the oil slick. When we measured the oil slick, we measured the largest diameter and the smallest diameter and averaged the two values, using the average as the diameter. This could’ve led to the diameter being smaller than it actually was. In addition, the circle formed by displacing the water and lycopodium powder was not even close to a perfect circle. It had many irregularities in its curve and diameter, which could’ve led to incorrect measurements of the diameter. The mass of the added lycopodium powder to the water could’ve added more resistance to the oil slick, making it harder to displace the water. Since it was harder to displace, the water wouldn’t have been pushed back as far, and thus the diameter was smaller than it actually should’ve been.

Even accounting for systematic error in measuring the diameter of the oil slick, there was still a percent error of 73.16%. This could’ve been due to the assumption that the height of the oil slick was only one monolayer, or we could have miscalculated the amount of oleic acid in one drop. If the amount of oleic acid in one drop had been too much, it would’ve decreased the estimate of Avogadro’s number, putting it further from the accepted value. It’s likely that we overvalued the weight of oleic acid in one drop of oil, leading to us underestimating Avogadro’s number.

This method was proven to not be a valid way to estimate Avogadro’s number. This was due to the tremendous amount of error that can not be accounted for when calculating on the molecular level. One major flaw was the fact that the desired thin film of lycopodium powder could not be achieved, this would lead to the oil not taking the shape of a perfect circle. Without having a perfect circle measuring an accurate diameter is practically impossible, and when calculating on the subatomic level having this measurement off can drastically jar the results. To improve this experiment a better substitute for the lycopodium powder should be used. The substitute should be able to settle in one uniformly thin layer across the surface of water, allowing for the oil slick to take the shape of a perfect circle. However, it should be noted that this experiment has a large amount of variables to control, requires measurements of the utmost accuracy and makes many assumptions. Therefore it is highly recommended that a different method should be used for those looking to execute an experiment with a low percent error.        

 

 

Week of 10/10

Monday:

No school. Columbus Day.

Tuesday:

Review of molarity and dilutions, including solutions with common ions and molarity of ions.

Wednesday

Electrolyte lab.  I described how to make solutions, you guys made solutions using volumetric glassware than we measured conductivity of each of the 0.1 M solutions. The last bit of class you put data in spreadsheet

HW: Answer questions on google classroom. For grades see Lab rubric Content section.

Thursday:

 

Today we went over neutralization reactions – including how to write complete ionic and net ionic reactions.  You learned what a spectator ion is.  We did some volumetric analysis problems from the textbook and then learned to name acids.  Here’s today’s notes.

HW: Acid naming practice. Review naming for Tuesday’s quiz. Finish electrolyte lab.

Week of 10/3 + SCIENCE SUMMER OPPORTUNITIES

Monday:

Today we started with about an hour working limiting reactant problems from the packet.  I showed two other methods for finding the limiting reactant. Then I showed how to solve combustion analysis problems and you had about 10 minutes to work on textbook problems for this (3.16, 3.63, 3.103, 3.120).   Today’s notes. For the last 25 minutes of class you broke up into groups based on color of paper (one color per group) and then took turns explaining the math behind each of the methods.  Lastly you decided on procedures in your group – how much you will use, how long and how many times you will heat.  My requirements are that your final result give you 3 sig figs and that you have a reason for each procedural step.  I will provide a mixture that is between 25 and 80% sodium bicarbonate.

Video: Empirical Formula from Combustion Analysis (for AP! but there is a typo! The compound is not made of C, O and N, but C, H and N. On Youtube)

HW: Work on textbook and packet problems. Test is Thursday. We will review on Wed.

Tuesday:

Today we did the determination of composition of a mixture lab. I also added on that you would dehydrate the alum crystals and see if you actually got a compound with 12 waters of hydration… This unfortunately took more than one class to complete =( so we continued with the lab on Wed.

Wednesday:

Today you finished up both the determination of composition of a mixture and the alum crystals lab. Test was postponed to Friday B block.

Thursday:

Today you worked problems from packet and textbook in preparation for tomorrow’s test on stoichiometry.

Friday:

Today you had until 10 am to study/ work practice problems and then we started the test on stoichiometry.

HW: Review molarity and dilutions.  Videos 2. b.1.2 and 2.b.1.5 Do #1 and 2 on page 2 of packet. Here’s more basic molarity practice if you need it.

Summer Science Opportunities:

VASTS

For current high school juniors only: This is a fabulous program. Do not hesitate for your high school junior to apply. The online application deadline is October 30, 2016.

Here is the link for more information and to apply:  http://www.vasts.spacegrant.org/  .  Students get 2 free college credits for completing the online course. The top students are selected for the summer academy at NASA Langley and get 2 more free credits!

Here are a few videos made by students that attended our summer academies:

 

Week one 2016:    https://www.youtube.com/watch?v=MC82l-G8pig

 

Week one 2015:  https://www.youtube.com/watch?v=yunJ3iA6ZBc

 

Week 3 2013:  http://www.youtube.com/watch?v=iYkVlAVHxpc

 

 

VESSS

For CURRENT 11th and 12 graders only:  VIRGINIA EARTH SCIENCE SYSTEMS SCHOLARS!!!  Click the link for more information and the application. The online application deadline is October 30, 2016.

 

http://www.vsgc.odu.edu/VESSS/

 

The Virginia Earth System Science Scholars (VESSS) program is an interactive on-line science, technology, engineering and mathematics learning experience, highlighted by a seven-day residential summer academy at NASA Langley Research Center in Hampton, Virginia. Students selected to participate in the program are immersed in NASA-related research through interaction with scientists, engineers and technologists. The program is a partnership between the Virginia Space Grant Consortium and NASA Langley Research Center with assistance from Hampton University. The Virginia Earth System Science Scholars program propose to build on the success of the award-winning Virginia Aerospace Science and Technology Scholars (VASTS) program, a program which has offered dual enrollment credit, through TNCC, to over 2900 students since 2008.

 

VESSS 2016 Week 1: https://www.youtube.com/watch?v=psyxMvAGViM

 

VESSS 2016 Week 2: https://www.youtube.com/watch?v=lNGbVpA0g9w