Electrolyte Lab

Electrolyte Lab

  1. Each group will make 50 mL of the following solutions using a volumetric flask.
    1. a 0.1 M solution of calcium acetate monohydrate
    2. a 0.1 M solution of sodium acetate trihydrate
    3. a 0.1 M Sucrose (C12H22O12) solution
    4. a 0.1 M solution of potassium chloride
    5. a 0.1 M solution of strontium chloride hexahydrate
    6. 100 mL of a 0.1 M solution of Calcium chloride
    7. 100 mL of a 0.1 M solution of sodium chloride
    8. 1 L of a solution that is 0.1 M NaCl and 0.1 M CaCl2
  2. Each group will then pour their solution into a large labeled test tube to allow for the conductivity to be tested.
  3. Obtain a conductivity meter and change the setting to the 0-2000 microsiemen/cm setting.
  4. Calibrate your conductivity meter:
    • To calibrate: put the lever in the center position (0-200 microS/cm)
    • Click the sensor menu, click calibrate, choose the conductivity sensoor
    • click the one-point calibration button, then click “Calibrate Now”
    • Type in 0 if calibrating in air or 1000 if using solution. Press keep.
  5. Measure the conductivity for each group.  Be sure to rinse and completely dry you conductivity tester between solutions.  Make sure to use the same conductivity tester for all the solutions.  If you don’t get results that seem reasonable (larger values for substance that have more ions) than calibrate your sensor
  6. Make a bar graph of the compound vs. conductivity in order from most to least.
  7. Make a bar graph of # of ions vs conductivity in order from most conductive to least
  8. Which solutions are strong electrolytes, weak electrolytes and nonelectrolytes?  Explain, using data to justify.
  9. Is there any data that supports the idea that there are two ions in sodium chloride and sodium acetate? How about 3 ions in the calcium compounds?
  10. What would you predict about how does solution 9 compare with 7 and 8? Does the data support the hypothesis? Justify your thinking w/ data.
  11.  Draw a molecular level picture of your solution and one other.  Collect pictures of other solutions.  Make sure any that you have in common with other groups match. Make sure your pictures match your label of strong/weak/nonelectrolyte.

Week of 9/29

Monday:
Today we started w a couple questions from the homework. 5a on the last page asks for volume of water and it is important to note that you can’t use 22.4 L for that. Water is a liquid according to the reaction so must use the density of water. If u did not know the density of water is 1 g/ml then u should now.

I also mentioned some items/ expectations for the test, but this is not exhaustive…

  • stoichiometry like in packet and textbook
  • limiting reactants
  • percent yield
  • drawing pics and explaining of limiting reactants (including what is left over)
  • combustion analysis

HW: textbook probs, lab, packet of stoichiometry problems

Tuesday: test!

Wednesday: Today we reviewed the process of dissolving for both ionic and covalent compounds and I gave the definition of electrolyte.  We worked on 4.20 in the textbook which turned out to be extremely confusing, but actually was really good because it uncovered alot of conceptual problems that would have led to major confusion and difficulty later if we didn’t get it cleared up.  Hopefully, it is cleared up for all of you, but if not…read! Watch beginning chem videos here (9.b.1 to 9.b.5).  This all took about an hour and 15 min.  The last 20 minutes, I showed how to solve various problems.  Notes are here.

  • basic molarity (but see chem 1 videos for more if you need it)
  • molarity w/ multiple solutions
  • dilutions
  • molarity mixing two solutions
  • dealing w/ mass percent.

Homework: textbook problems and packet (page 1 on molarity of ions, page 2 on molarity w/ multiple solutions and dilutions)

Thursday: Start electrolyte lab.

  1. Warm-up: how to make a dilution / how much water to add
  2. Making dilutions using volumetric glassware

Friday: acid naming, analysis for electrolyte lab, time to work on homework problems. The electrolyte lab didn’t work VERY well, but some groups had some data that made sense.  Next year I will try it with the 0 – 2000 setting and have kids calibrate before hand.  I think it will work better! Did not have students do too much with analysis, just went through data from the group with the best data as a class and had them make some notes in their lab notebooks.  For those of you that need naming help…check out videos from first year chem here.

Week of 9/22

Monday: We spent the first 15 minutes working out the difficulties of submitting the labs online and going over the latest test.  Then we did the “Green Chemistry Mixtures Lab.” We just did the pre-lab. My goal was to a) work through a really hard problem on your own without me explaining it first. This is often how you will encounter chemistry problems in the future! and b) see that there are many different ways to solve stoichiometry problems, creativity is helpful, and you don’t need to just memorize a process for figuring out all problems.  At the end of class I asked you to reflect on the activity

  • How did you feel during this activity?
  • How well did your group work together? What did you do well and what could have been better?
  • How was it explaining and listening to other explanations?

In hindsight I think it would be helpful to have copies of the math for each of the 3 methods for each of you for discussion during that time.

Tuesday: Today is too short to do a lab so we’re going to work on combustion analysis problems. Here’s the notes.

Wednesday: Do the mixtures lab

Thursday: Limiting Reactants: demo then notes. Page w pictures in packet.

Friday: More limiting reactants. Started w sim. Had students draw pics. Rest of period to work.

Week of 9/15

Monday: Hydrate lab.  In groups you worked on procedures and data table and then completed two trials to determine formula of hydrate.

Tuesday: Review for test. See unit outline for objectives.  Today’s review problems are here.

Answers to HW problems that are not blue:

3.13: find the moles of C6H6 by dividing by molar mass of C6H6. Since the number of molecules in a given amount of moles is always the same no matter the substance, the moles of C6H6 = moles NH3 to have same # of molecules of both substances.  Multiply moles found by molar mass of NH3. Answer: a

3.14) B

3.15) D

3.18) part 2

a) the molar mass of XCl2 is 100 g/ 0.25 mol = 400 g/mol and the molar mass of YCl2 = 125 g/ 0.50 mol = 250 g/mol

b) If you have 1.0 moles of each compound the number of chloride ions is the same because 1 mole represents the same number of molecules of each compound and each compound has 2 Cl’s per molecule.

c) For 1 mol you have 400 g of X and 250 g of Y. The mass of X is larger than the mass of Y because the formula weight of XCl2 is larger and since the amount of chlorine is the same in each sample, the mass due to chlorine is the same, the thing making XCl2 heavier is X.

d) The mass of chloride ions present in 1.0 mole of each is the same because both 1.0 mole samples contain the same number of molecules and each molecule has the same number of Cl’s

e) what are the molar masses of X and Y.   X = (400 – 2*35.45) = 329.1 g/mol.  The molar mass of Y is 250 – 70.9 = 197.1

f)  200 g of XCl2 is 1/2 a mole.  1/2 a mole i 3 x 10^23 molecules, for each 1 molecule there is 1 X ion so there’s 3.0×10^23 X2+ ions.  but each molecule has 2 Cl’s so there will be 6.0 x 10^23 Cl’s

g)Grams of Y ions in 250 g.  If one mole of the compound is 250 g, than there is one mole present meaning, one mole of Y ions which is just the molar mass of Y: 197.1 g/mol

h) Molar mass of YBr3 = 197.1 + 3*79.9 = 435.8 g/mol

Wednesday: Test and time to work on hydrate lab.  Hydrate lab write-up should include

  • Group procedures shared with me on google docs
  • Group data table if typed
  • Individual data table if handwritten. Take a picture and post in google classroom.
  • Individual clearly labeled calculations for formula. Take a picture and post in google classroom.
  • Typed conclusion (follow checklist and see rubric attached to the syllabus). Post in google classroom.

Thursday: No class b/c of short Thursday.

Friday: Today we started the stoichiometry unit. Here’s the notes.  We started by drawing molecular level picture and going over meaning of coefficients, what happens when you double coefficients, etc. Then on to practice sheet w/ grids to fill in, practicing mole ratios in our heads. Then 3.8 in textbook: various meanings at molecular level, mass, mole level.  Emphasis here is conservation of mass and that you cannot just use mass ratio, must use mole ratio!  Then you had time to do other book problems. After the break I gave notes on % yield and we worked through the 3 types of percent yield problems. It worked out very nicely to have you guys answer “how much N2 is left over on the second question.” There were at least 2 different ways to solve this problem and someone in class found each one!  Same thing for the third type of problem.  I didn’t have to show any of you how to do it – just help a few through it.  If you need to see videos on percent yield check out unit 2 page which has links to relevant chem 1 videos.   Unit outline for textbook problems.

Week of 9/8

Monday: Today we started by getting labs turned in which was kind of a pain…not sure how this ELN thing is gonna go.  Would be better if labs were typed.  We went over what’s on test (unit outline objectives), did some more naming instruction and practice as well as balancing reactions practice.  At the end we finished up the mass spec packet #4,5. The take-away from #5 is the idea of molecular ion giving the molecualr weight of a compound.  I also mentioned that some mass spec may be comprised of multiple elements, that might require more information to interpret.  Answers can be found in today’s notes.

Here’s some review pages from last year’s packets.

Tuesday Quiz, homework none

Wednesday: We started with dimensional analysis review – one in which you were unfamiliar with the context (electrolysis of Cu) and a cubed metric example.  Then we did an activity that shows how Avogadro’s number was derived/ why it was derived (so that you have enough atoms such that the mass on the periodic table is grams instead of amu).  Then we did some mole practice in the text book. See unit outline for problems.  During the second half of class we did the Empirical formula chemtivity distinguishing between empirical and molecular formulas as well as ionic compounds that have formula units and covalent compounds that have molecules.  We ended with the idea of the atom ratio = the mole ratio

Thursday: A short class, we finished the empirical formula packet, went over the last problem and learned how to determine molecular formula from molecular weight.

Friday: First 1/2 we spent doing these mole problems and some more challenging empirical formula problems that are on the unit outline. I am glad I made the time to do this, this year as there was a lot of learning happening as you worked through the problems! The last half we went over hydrates: what they are and how to get their formulas.  The 2nd half I assigned you to groups to work on designing a hydrate lab to determine the formula of alum.  Once in groups you got ipads and looked up some example labs. Most of you thought your hydrate was going to change color, but that is not the case so I def have to remember to clarify that next year.  The point of doing research was to find differences in the way others designed their labs.  I also needed to clarify that we’re looking for differences in the details, not the overall method.  I handed out the checklist so that as you write your procedures you know what I’ll be looking for.  FRIDAY’s NOTES

Homework: continue with book problems if you haven’t finished yet. Test Tuesday.

Monday: review

Tuesday: quiz