I hope everyone made it through the lovely weather we experienced Sunday and yesterday. I have submitted grades to the Registrar, they should be visible within a day. The average on the final exam was around 140/200. If you would like to see your final exam, stop by my office. I do not return final exams, but if you'd like to take a look at it you are welcome to do so.
I hope everyone has a great break and I look forward to seeing many of you back in class next semester. Don't forget about Lewis and VSEPR structures, we'll need them to get started in January....
2008/12/16
2008/12/11
Questions...
A few questions came in overnight.....
just like exam #4, are there going to be an "explanation" section about trends in the periodic table or is it going to be "circle which one is bigger/smaller, has higher first ionization energy..."?
Yes, there will be questions where you will be expected to explain your answer.
could you give a brief explanation of endothermic vs exothermic in reaction...i remember i got a couple of those wrong. it seems like it should be straight forward but it's not always!
Endothermic reactions require heat, exothermic reactions liberate heat. The "trick" question here usually involves water freezing. To make water freeze, you must remove heat from the system, so freezing water (or any substance) is an exothermic process, even though it "feels cold" if you were to hold it in your hand.
Other questions, let me know. See you in a few hours...
just like exam #4, are there going to be an "explanation" section about trends in the periodic table or is it going to be "circle which one is bigger/smaller, has higher first ionization energy..."?
Yes, there will be questions where you will be expected to explain your answer.
could you give a brief explanation of endothermic vs exothermic in reaction...i remember i got a couple of those wrong. it seems like it should be straight forward but it's not always!
Endothermic reactions require heat, exothermic reactions liberate heat. The "trick" question here usually involves water freezing. To make water freeze, you must remove heat from the system, so freezing water (or any substance) is an exothermic process, even though it "feels cold" if you were to hold it in your hand.
Other questions, let me know. See you in a few hours...
2008/12/10
Tomorrow...
I will be in my office by 8am tomorrow, if you have any last minute questions feel free to stop by.
The 1-Question Final Exam
A few people have asked for the answer to this question, so......
325.0mL of 0.825M sodium carbonate solution reacts with 11.348L of hydrogen chloride gas at 1.082atm pressure and 17.28°C to produce carbon dioxide gas, liquid water, and sodium chloride. How many grams of carbon dioxide gas can be produced by this reaction? If all of the sodium chloride that can be produced by this reaction is dissolved in enough water to make 450.0mL of solution, what will be the concentration of sodium chloride in the solution?
First, we need a balanced chemical equation. This is a gas forming reaction.
Na2CO3(aq) + 2 HCl(g) --> H2O(l) + CO2(g) + 2 NaCl(aq)
{Remember, carbonic acid spontaneously decomposes to water and carbon dioxide gas.}
Now we've got a couple stoichiometry problems...
(0.825 mols Na2CO3/L sol'n)(0.3250L sol'n)(1mol CO2(g)/1mol Na2CO3(aq))(44.009 g CO2/mol CO2 ) = 11.8g CO2(g)
((1.082atm)(11.348L HCl(g))/(0.08206 L.atm/mol.K)(290.43K))(1mol CO2(g)/2mol HCl(g))(44.009 g CO2/mol CO2 ) = 11.3g CO2(g)
Since the HCl(g) produces less product, it must be the limiting reagent, so this reaction can produce 11.3g of CO2(g).
Knowing that HCl(g) is the limiting reagent, we can calculate the amount of NaCl produced by this reaction:
((1.082atm)(11.348L HCl(g))/(0.08206 L.atm/mol.K)(290.43K))(2mol NaCl(aq)/2mol HCl(g)) = 0.515197 mols NaCl(aq) {NOTE: yes, this is too many sig figs, but it's the middle of a problem so I do not want to round off to the correct number of sig figs yet...}
If this amount of NaCl is dissolved in enough water to make 450.0mL of solution, the concentration is:
0.515197mols NaCl / 0.4500L sol'n = 1.145M NaCl(aq)
325.0mL of 0.825M sodium carbonate solution reacts with 11.348L of hydrogen chloride gas at 1.082atm pressure and 17.28°C to produce carbon dioxide gas, liquid water, and sodium chloride. How many grams of carbon dioxide gas can be produced by this reaction? If all of the sodium chloride that can be produced by this reaction is dissolved in enough water to make 450.0mL of solution, what will be the concentration of sodium chloride in the solution?
First, we need a balanced chemical equation. This is a gas forming reaction.
Na2CO3(aq) + 2 HCl(g) --> H2O(l) + CO2(g) + 2 NaCl(aq)
{Remember, carbonic acid spontaneously decomposes to water and carbon dioxide gas.}
Now we've got a couple stoichiometry problems...
(0.825 mols Na2CO3/L sol'n)(0.3250L sol'n)(1mol CO2(g)/1mol Na2CO3(aq))(44.009 g CO2/mol CO2 ) = 11.8g CO2(g)
((1.082atm)(11.348L HCl(g))/(0.08206 L.atm/mol.K)(290.43K))(1mol CO2(g)/2mol HCl(g))(44.009 g CO2/mol CO2 ) = 11.3g CO2(g)
Since the HCl(g) produces less product, it must be the limiting reagent, so this reaction can produce 11.3g of CO2(g).
Knowing that HCl(g) is the limiting reagent, we can calculate the amount of NaCl produced by this reaction:
((1.082atm)(11.348L HCl(g))/(0.08206 L.atm/mol.K)(290.43K))(2mol NaCl(aq)/2mol HCl(g)) = 0.515197 mols NaCl(aq) {NOTE: yes, this is too many sig figs, but it's the middle of a problem so I do not want to round off to the correct number of sig figs yet...}
If this amount of NaCl is dissolved in enough water to make 450.0mL of solution, the concentration is:
0.515197mols NaCl / 0.4500L sol'n = 1.145M NaCl(aq)
2008/12/08
Last day....
Exam 4 was returned today, average was ~110/150. Based on your 3 highest exam scores and Mastering Chemistry, I would estimate the current grade cutoffs at: 90.% = A, 80.% = B, 68% = C, 55% = D. Those cutoffs may shift around a little once the final exam scores are entered, but they shouldn't move significantly.
Don't forget, as stated in the syllabus, if you do not take the final exam, you fail the course regardless of previous performance.
As I mentioned in class, I have been tempted in the past to give a 1-question final exam. I do not actually do this because it would be exceptionally stressful for both you and me, but if I were to give a 1-question final exam, the question would probably look something like this:
325.0mL of 0.825M sodium carbonate solution reacts with 11.348L of hydrogen chloride gas at 1.082atm pressure and 17.28°C to produce carbon dioxide gas, liquid water, and sodium chloride. How many grams of carbon dioxide gas can be produced by this reaction? If all of the sodium chloride that can be produced by this reaction is dissolved in enough water to make 450.0mL of solution, what will be the concentration of sodium chloride in the solution?
If you have any other questions, stop by my office or email me. I will post answers to any emailed questions to the class blog. Good luck with your preparation and I'll see you on Thursday (or sooner...).
Don't forget, as stated in the syllabus, if you do not take the final exam, you fail the course regardless of previous performance.
As I mentioned in class, I have been tempted in the past to give a 1-question final exam. I do not actually do this because it would be exceptionally stressful for both you and me, but if I were to give a 1-question final exam, the question would probably look something like this:
325.0mL of 0.825M sodium carbonate solution reacts with 11.348L of hydrogen chloride gas at 1.082atm pressure and 17.28°C to produce carbon dioxide gas, liquid water, and sodium chloride. How many grams of carbon dioxide gas can be produced by this reaction? If all of the sodium chloride that can be produced by this reaction is dissolved in enough water to make 450.0mL of solution, what will be the concentration of sodium chloride in the solution?
If you have any other questions, stop by my office or email me. I will post answers to any emailed questions to the class blog. Good luck with your preparation and I'll see you on Thursday (or sooner...).
2008/12/04
Exam questions....
A couple questions have come in for tomorrow's exam.....
Just wondering if any like light waves, Hz questions from chapter seven are
going to be on the test..?!
That info is fair game for the exam...BUT think about how much time we spent on it. We spent maybe a day or two on that info, but we spent WEEKS talking about electron configurations, periodic trends, Lewis structures, VSEPR... The exam will reflect this, if there is a question about light, it will probably be a small question...
could you please explain how to determine which charges are best for elements?? i'm having a hard time understanding just how to find the ones your looking for, could you explain in an email??
Relatively stable ions are formed by relatively stable electron configurations. Electrons are relatively stable when: 1)all the shells are full; 2)all the subshells are full; 3)the subshells are half full. Let's look at a couple examples.
1) Sodium forms a relatively stable ion with a +1 charge because when a sodium atom loses an electron it has the same electron configuration as neon, which has full shells.
1s22s22p63s1 --> 22s22p6
2) Zinc forms a relatively stable ion with a +2 charge because when a zinc atom loses two electrons all of the occupied subshells are full.
[Ar]4s23d10 --> [Ar]3d10
3) Manganese forms a relatively stable ion with a +2 charge because when a manganese atom loses 2 electrons all of the occupied subshells are either full or half full.
[Ar]4s23d5 --> [Ar]3d5
If you're looking for stable ions, write out the electron configuration for the neutral atom and look at how many electrons you have to add or remove to get to full or half full subshells.
I'll be off-line until tomorrow morning, if you have other questions either drop me an email or post a comment to the blog and I'll answer them as soon as I get in. If you notice a question posted to the blog and would like to help out your classmates, feel free to post a follow-up comment to answer the question. See you all tomorrow.
Just wondering if any like light waves, Hz questions from chapter seven are
going to be on the test..?!
That info is fair game for the exam...BUT think about how much time we spent on it. We spent maybe a day or two on that info, but we spent WEEKS talking about electron configurations, periodic trends, Lewis structures, VSEPR... The exam will reflect this, if there is a question about light, it will probably be a small question...
could you please explain how to determine which charges are best for elements?? i'm having a hard time understanding just how to find the ones your looking for, could you explain in an email??
Relatively stable ions are formed by relatively stable electron configurations. Electrons are relatively stable when: 1)all the shells are full; 2)all the subshells are full; 3)the subshells are half full. Let's look at a couple examples.
1) Sodium forms a relatively stable ion with a +1 charge because when a sodium atom loses an electron it has the same electron configuration as neon, which has full shells.
1s22s22p63s1 --> 22s22p6
2) Zinc forms a relatively stable ion with a +2 charge because when a zinc atom loses two electrons all of the occupied subshells are full.
[Ar]4s23d10 --> [Ar]3d10
3) Manganese forms a relatively stable ion with a +2 charge because when a manganese atom loses 2 electrons all of the occupied subshells are either full or half full.
[Ar]4s23d5 --> [Ar]3d5
If you're looking for stable ions, write out the electron configuration for the neutral atom and look at how many electrons you have to add or remove to get to full or half full subshells.
I'll be off-line until tomorrow morning, if you have other questions either drop me an email or post a comment to the blog and I'll answer them as soon as I get in. If you notice a question posted to the blog and would like to help out your classmates, feel free to post a follow-up comment to answer the question. See you all tomorrow.
2008/12/03
Ready for the exam?
Today we finished up our discussion of the MO diagram of oxygen and went through a few questions in review for the exam on Friday. If you have any other questions, let me know, I'll post answers to the blog.
Don't forget the Chem Club meeting tonight and your Mastering Chemistry assignment.
Don't forget the Chem Club meeting tonight and your Mastering Chemistry assignment.
2008/12/01
Chem Club meeting this week
Don't forget that the Chem Club will be meeting this Wednesday, SL104, 7pm.
VB, Hybrid orbitals, LCAO-MO
Today we looked at how hybrid atomic orbitals can be used to understand the shapes and angles predicted by VSEPR. We used this idea of adding and subtracting orbitals to look at molecules and took an initial look at some molecular orbital diagrams for "simple" diatomics.
There is a new Mastering Chemistry assignment posted, due Thursday. This is the last MC assignment for the semester.
For those of you who will be continuing on in Chem 210, keep your book! We will be using the same book in Chem 210. If you are continuing in my class, you will also continue to use Mastering Chemistry. You should be able to continue using the same MC account, they're valid for at least a year (maybe 18 months?). If you are moving over to Dr. Edvenson's class, I don't know if you will be using MC.
There is a new Mastering Chemistry assignment posted, due Thursday. This is the last MC assignment for the semester.
For those of you who will be continuing on in Chem 210, keep your book! We will be using the same book in Chem 210. If you are continuing in my class, you will also continue to use Mastering Chemistry. You should be able to continue using the same MC account, they're valid for at least a year (maybe 18 months?). If you are moving over to Dr. Edvenson's class, I don't know if you will be using MC.
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