Search found 32 matches
- Sat Dec 08, 2018 10:15 pm
- Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
- Topic: Final Exam
- Replies: 8
- Views: 2427
Re: Final Exam
To add to the previous questions, can someone also explain the conceptual meaning of pKA and pKB?
- Sat Dec 08, 2018 7:17 pm
- Forum: Naming
- Topic: Polarizability
- Replies: 2
- Views: 447
Polarizability
What is the polarizing trend in the periodic table?
- Thu Dec 06, 2018 11:00 pm
- Forum: Bronsted Acids & Bases
- Topic: Problem J.7 - 7th Ed.
- Replies: 4
- Views: 552
Problem J.7 - 7th Ed.
The question asks us to write a chemical equation based on the formation of the resulting compound. How do we determine what base and acid we use? I know that we look at the resulting compound to determine but I am confused on exactly how to do so.
- Fri Nov 30, 2018 10:30 am
- Forum: Administrative Questions and Class Announcements
- Topic: Final
- Replies: 11
- Views: 1379
Re: Final
I also had a question about the final. Does anyone know how many questions would be on the final? Would it be similar to the midterm (8 questions)?
- Fri Nov 30, 2018 10:27 am
- Forum: Hybridization
- Topic: 2F.3b (7th Edition)
- Replies: 1
- Views: 205
Re: 2F.3b (7th Edition)
I believe we would have to draw the most stable form which is how test #3 was formatted as well. So I think as long as we can draw with a formal charge of 0 or whatever charge the molecule has on it, we should be fine.
- Fri Nov 30, 2018 10:22 am
- Forum: Electronegativity
- Topic: 7th Edition 3F.15
- Replies: 4
- Views: 2901
7th Edition 3F.15
The problem asks us to explain the difference in the boiling points between ASF3 and ASF5 but the solution manual states that ASF3 is a polar molecule and ASF5 is a nonpolar molecule. Why is it that they are different in polarity characteristics when they are the same atom but different amount?
- Sat Nov 24, 2018 1:31 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Saying Thank You to Dr. Lavelle
- Replies: 490
- Views: 634430
Re: Saying Thank You to Dr. Lavelle
Dear Dr. Lavelle, You are truly an amazing professor and I am so grateful to be part of this class. You haven't only made chemistry interesting but made it simple. Even though at times I didn't understand the homework or lecture, but I still had a supporting community such as this one where students...
- Sat Nov 24, 2018 1:21 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: vsepr model
- Replies: 3
- Views: 458
Re: vsepr model
When atoms bond to a central atom, they do it in such a way to maximize the difference between two bonds and thus confirming a molecular shape. When there are no lone pairs on the central atom, the electron geometry and molecular geometry is similar. However, when there are lone pairs involved, the ...
- Sat Nov 24, 2018 1:13 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: 4.25 6th edition: Polarity of SF4
- Replies: 4
- Views: 754
Re: 4.25 6th edition: Polarity of SF4
It has to do with electronegativity. The difference in electronegativity between Sulfure and Fluorine is 2.98 and the electronegativity is large enough for it to be a polar molecule.
- Fri Nov 16, 2018 10:59 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Sigma bond and Pi bonds
- Replies: 2
- Views: 522
Sigma bond and Pi bonds
What are the significance of sigma and pi bonds and what do they represent? How would we draw sigma and pi bonds?
- Fri Nov 16, 2018 10:50 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Shortcut
- Replies: 4
- Views: 989
Re: Shortcut
Just do the number of things attached to the atom; lone pairs counts as two things and a bond counts as one thing. So do the number of things attached - valence electrons of the atom and that is the shortcut.
- Fri Nov 16, 2018 10:40 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Test 3
- Replies: 19
- Views: 1421
Re: Test 3
I think memorizing would make it easier because knowing what shape corresponds to how many bonds and lone pairs makes it easier on the test. Also, the bond angles that aren't exact also should be memorized because it's most likely going to be on the test. My tutor told me to make flash cards to memo...
- Fri Nov 09, 2018 9:35 am
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: electron distortion
- Replies: 4
- Views: 469
Re: electron distortion
Think about it this way, if there are a concentration of electrons in one particular side of a molecule and it comes in interaction with another molecule which also has electrons but is less electronegative than the first molecule then the first molecule will push away the electrons because a negati...
- Fri Nov 09, 2018 9:27 am
- Forum: Bond Lengths & Energies
- Topic: Dipole interaction
- Replies: 3
- Views: 456
Re: Dipole interaction
Dipole-dipole interactions are between opposite partial charges on two different molecules attracting each other. It usually forms when there is a permanent dipole. So in case of a water molecule, the Oxygen is partially negative and Hydrogen is partially positive because of their electronegativity ...
- Thu Nov 08, 2018 5:22 pm
- Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
- Topic: Wednesay - 11/7 Notes
- Replies: 2
- Views: 334
Wednesay - 11/7 Notes
I couldn't make it to class this Wednesday (11/7/18) due to an appointment. It would be wonderful if someone can share their notes and, if not, the topics I should go over in the book, I would greatly appreciate your help.
Thank you very much in advance!
Thank you very much in advance!
- Thu Nov 01, 2018 10:04 pm
- Forum: Bond Lengths & Energies
- Topic: 2.25 Homework Problem
- Replies: 4
- Views: 933
Re: 2.25 Homework Problem
It has to do with electronegativity. The electronegativity of Nitrogen is greater than Phosphorus so it would pull the electrons closer making the bonds smaller. Also due to the similar sizes of Nitrogen and Fluorine, they make smaller and stronger bonds.
- Thu Nov 01, 2018 9:59 pm
- Forum: Lewis Structures
- Topic: 7th edition 2b9
- Replies: 1
- Views: 219
Re: 7th edition 2b9
The 3- is the charge on a Phosphide atom. Since Phosphorus has 5 valence electron in general but when it becomes Phosphide it gains 3 more electrons thus making it 8 valence electrons. Now, if we were to calculate the formal charge it would be #of valence electrons minus the number of electrons/bond...
- Thu Nov 01, 2018 9:52 pm
- Forum: Lewis Structures
- Topic: Lewis Structure of Glycine
- Replies: 1
- Views: 306
Re: Lewis Structure of Glycine
Well, Lavelle did say that there will be questions from the homework and since this is a homework problem, I think it would be safer to know how to draw them.
- Sat Oct 27, 2018 8:02 pm
- Forum: Lewis Structures
- Topic: Lewis Dot Structures
- Replies: 3
- Views: 455
Re: Lewis Dot Structures
It depends on what element is given and the number of bonds they can make. If the element can make double or triple bonds and it doesn't exceed the number of bonds they can make then you should be able to use it.
- Sat Oct 27, 2018 7:52 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Is homework graded for correctness or completeness?
- Replies: 5
- Views: 904
Re: Is homework graded for correctness or completeness?
I think as long as you show work and attempt the problem, most TA's will give you the full grade. Also, you might want to ask your TA how they grade the homework.
- Sat Oct 27, 2018 7:48 pm
- Forum: Student Social/Study Group
- Topic: Winter quarter scheduling
- Replies: 6
- Views: 1062
Re: Winter quarter scheduling
I have talked to my counselor as well and she advised me that if you want to take them simultaneously it could be difficult and time-consuming since labs are mostly about writing long lab reports. It's not recommended unless you feel very good at chemistry. However, it is your choice and completely ...
- Sun Oct 21, 2018 3:40 pm
- Forum: Ionic & Covalent Bonds
- Topic: Focus 2D #3 - HW Problem
- Replies: 4
- Views: 898
Focus 2D #3 - HW Problem
Which of these compounds has bonds that are primarily ionic? a) BBr3 b)BaBr2 c)BeBr2 I understand the first two and why they are covalent and ionic but BeBr2 is covalent and I don't understand why because it's a metal forming a bond with a nonmetal. The solution manual says that its due to the high ...
- Thu Oct 18, 2018 10:09 pm
- Forum: Ionic & Covalent Bonds
- Topic: Electron Configuratin
- Replies: 5
- Views: 437
Electron Configuratin
When we write the ground state for an ion such as Tl^3+ it is [Xe] 4f^145d^106s^26p^1 but then we lose 3 electrons so the final configuration would be [Xe]4f^145d^10. Why do we only remove electrons from the p-subshell and the s-subshell but never the d or f subshells?
Thank you in advance!
Thank you in advance!
- Thu Oct 18, 2018 7:48 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Class Grading
- Replies: 9
- Views: 1169
Re: Class Grading
Actually, I read some of the older post from Lavelle about curving. He said in that post "curves vary from quarter to quarter" and students can expect a 3-5% curve from the standard point scale. I hope he still continues this grade curving.
- Thu Oct 18, 2018 7:34 pm
- Forum: Properties of Electrons
- Topic: eV to J
- Replies: 7
- Views: 971
Re: eV to J
1 eV = 1.6x10^-19 Joules. So if we are given a certain number of electron volt (eV) and want it in Joules, you would set up a conversion factor. For example, 2eV to Joules would be: 2eV x ((1.6 x 10^-19 J)/1 eV)) = 3.2 x 10^-19 J. I don't think we have to memorize it, he will probably give it to us ...
- Thu Oct 18, 2018 7:27 pm
- Forum: Photoelectric Effect
- Topic: units
- Replies: 12
- Views: 1147
Re: units
As the others have said, meters is the standard use in solving for the wavelength of the photon. When we use the formula, c is the speed of light in m/s and turning nanometer into meter cancels out the meters. Finally, to represent energy we usually write it in Joules because when we use Planck's co...
- Wed Oct 10, 2018 2:13 pm
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: Periodic Table
- Replies: 3
- Views: 386
Re: Periodic Table
As the replies above me have already stated, it is safer to use the entire molar mass given in the periodic table. However, every periodic table differs in the molar mass they provide on the chart. If you have a periodic table that gives the molar mass to 5 decimal places as opposed to one that give...
- Wed Oct 10, 2018 2:06 pm
- Forum: Limiting Reactant Calculations
- Topic: Test 1
- Replies: 3
- Views: 447
Re: Test 1
Even though I have not taken the test yet, I have talked to others who have. They told me that the test has 8 questions and they were able to finish it fairly quickly leaving them time in the end. I recommend focusing on practicing the problems assigned by professor Lavelle so you know exactly what ...
- Wed Oct 10, 2018 2:03 pm
- Forum: SI Units, Unit Conversions
- Topic: Rounding Off of 5
- Replies: 7
- Views: 2599
Re: Rounding Off of 5
It depends on how many significant numbers the problem is asking for but in this case, 4.45 would be rounded to 4.5 because if you are just rounding to 4.4 it means you are rounding down which is incorrect. The .05 makes a difference in the answer so we can't disregard it by rounding down so the bes...
- Fri Oct 05, 2018 10:06 am
- Forum: Empirical & Molecular Formulas
- Topic: Empirical formula set up
- Replies: 9
- Views: 678
Re: Empirical formula set up
When we are trying to find the empirical formula, we usually take the mass percent composition and turn it into grams because percent is usually out of 100. In most cases,100 gram is convenient because it reflects the mass of each element in conjunction with the percent composition which is a fracti...
- Fri Oct 05, 2018 9:53 am
- Forum: Balancing Chemical Reactions
- Topic: How To....
- Replies: 16
- Views: 2643
Re: How To....
When balancing an equation, the state of matter might be provided by the equation but if not then there are some common ones that we should know. For example, if we have H2, O2 or N2 then we know that they are gaseous elements. However, in the case of I2, the state is solid in room temperature and B...
- Fri Oct 05, 2018 9:39 am
- Forum: Limiting Reactant Calculations
- Topic: When to use H vs H2
- Replies: 7
- Views: 1112
Re: When to use H vs H2
When you have 1 mole of H2, the molar mass will be the molar mass of Hydrogen times 2 because you have 2 atoms of hydrogen in this molecule. However, in HCl, you will only use 1.007 because there is only one atom of Hydrogen. The subscript next to the Hydrogen will indicate how much of that atom the...