CHEMISTRY COMMUNITY

Marylyn Makar 1B

Hi! So both [H3O+][OH-] = 1.0 * 10^-14 and (Ka)(Kb) = 1.0 * 10^-14 because 1.0 * 10^-14 is the autoprotolysis constant of water. This constant, or Kw, comes from the autoprotolysis of water reaction where two water molecules react to produce OH- and H30+. In this reaction, if you multiply the concen...

Marylyn Makar 1B

Hi! Work is not a state property because it is proportional to the distance an object moved, which means that work is dependent on the path taken. Similarly, heat is not a state property either because it depends on how the system changes from initial to final state.

Marylyn Makar 1B

Hi! So the question asks what the pH is for acetic acid. In order to find the pH, we must first find the concentration of H30 + because the definition of pH is -log [H30+]. When you find the concentration of [H30+] at equilibrium, you are then able to find the pH of the acetic acid.

Marylyn Makar 1B

Hi! Yes, what you described definitely makes sense! It also helps to think that Kw is a constant so Ka and Kb have to balance each other out, meaning if Ka is high than Kb must be low.

Marylyn Makar 1B

Hi ! So if Ka is large, then it is a stronger acid and if the Kb is large, then it is a stronger base. If Ka is small, then it is a weaker acid and if Kb is small, then it is a weaker base.

Marylyn Makar 1B

And to clarify, should we use 10^-3 or 10^-4 as the threshold to when we can ignore the +/- x to avoid a quadratic equation? Lavelle has mentioned both. Hi! I think it is safer to use 10^-4. If you want to use 10^-3, you can double check that it is fine to use by making sure x is less than 5% of th...

Marylyn Makar 1B

Hi! I just wanted to add that organic acids are generally weak. For example, acids containing a carboxyl group (like COOH) are weak acids.

Marylyn Makar 1B

Hi! So I believe that all amphiprotic compounds are amphoteric as well but the opposite is not always true. Amphiprotic compounds can act as a proton donor and proton acceptor. Amphoteric compounds have both acidic and basic character but that does not necessarily mean that they are amphiprotic as w...

Marylyn Makar 1B

Hi! I was wondering if Le Chatlier's Principle is applied when there is a change in temperature since K changes?

Marylyn Makar 1B

Hi! K does not change because the reaction returns to the same P/R ratio eventually by shifting either right or left. For example, if the pressure doubles (the volume halves), then Q will change and be different than K but the reaction will shift to the right in order to return back to equilibrium. ...

Marylyn Makar 1B

Hi! I think that usually you will get a positive and negative value from the quadratic formula, so you do not have to worry about getting 2 positive values.

Marylyn Makar 1B

Hi! What exactly does an ideal gas mean?

Marylyn Makar 1B

Hi! I'm pretty sure we have to use Kelvin for temperature

Marylyn Makar 1B

Hi! Can you go over how to tell which molecules show least covalent character? For example NaCl vs KCl and HF vs. HBr? Also what is the difference between polarizability and polarizing power? Also how can you tell what is a weak acid and weak base? Last question lol, what is the difference between h...

Marylyn Makar 1B

Hi! Yes chelating ligands and polydentate ligands are the same thing :)

Marylyn Makar 1B

Hi! I am a little confused on the difference between hard and soft water? So is hard water alkaline and soft water acidic? Or is it the other way around ? Also is soft water the one with the soapy feel?

Marylyn Makar 1B

Hi! Are alkaline solutions the same thing as a basic solution?

Marylyn Makar 1B

Hi! T-shaped molecular geometry is different than trigonal planar because it has 3 bonds and 2 lone pairs while trigonal planar molecular geometry only has 3 bonds and 0 lone pairs.

Marylyn Makar 1B

Hi! What's the difference between pH values and pKa values?

Marylyn Makar 1B

Hi! How do you know when you have an unhybridized orbital and how do you know how many unhybridized orbitals to have? For example, how do you know that CO2 has 2 unhybridized 2p orbitals?

Marylyn Makar 1B

Hi! What exactly is the porphyrin ligand in a heme complex?

Marylyn Makar 1B

Hi! You can tell the ionic charge of an element by looking at the periodic table but this is only possible for the s-block and p-block. For example, the charge of group 1 elements is +1, group 2 is +2, group 13 is +3, group 14 is +4/-4, group 15 is -3, group 16 is -2, and group 17 is -1.

Marylyn Makar 1B

Hi! So with the example of hypochlorous acid, hypobromous acid, and hypoiodus acid from today's lecture, we cannot predict their acid strength based on bond length because they all form the same bond of O-H. When these acids dissolve in water, the bond of O-H breaks and the O is left with a negative...

Marylyn Makar 1B

Hi! I was just thinking about this the other day! I definitely do remember seeing answers on Chemistry Community pop up when I searched a chem question in high school! Now I know what Chemistry Community actually is lol :)

Marylyn Makar 1B

Hi! During lecture 23 when Dr. Lavelle was talking about sp2 hybridization for ethene, he wrote that it forms sp3 hybrid orbitals. I was confused because I thought ethene formed sp2 hybrid orbitals? Could anyone clarify this? Thank you.

Marylyn Makar 1B

Hi! Ligands are electron rich species, such as Lewis bases, that interact with a transition metal. Because they are Lewis bases and are electron pair donors, they can form a coordinate covalent bond with transition metals which are usually cations. Sometimes these ligands have multiple electron lone...

Marylyn Makar 1B

Hi! You can find your saved drafts by clicking on your name in the upper right hand corner and then click user control panel. Then click overview and on the left hand side click manage drafts. Hope that helps!

Marylyn Makar 1B

Hi! I believe that the platinum atom of the cisplatin molecule covalently binds to the N7 position of a guanine.

Marylyn Makar 1B

Hi! Yes, we should have 40 posts by this Sunday.

Marylyn Makar 1B

Hi! Lone pairs push down on the bonded electrons because the repulsion strength of a lone pair-bonding pair is greater than the repulsion between a bonding pair-bonding pair. The lone pairs thus push down on the bonding pairs and slightly distort the bonding angles. This is what was in the lecture a...

Marylyn Makar 1B

Hi! Polarizing power refers to small, highly charged cations (I like to remember it like they're tiny but mighty). Polarizability refers to bigger atoms with lots of electrons that are easily distorted.

Marylyn Makar 1B

Hi! So the real structure of molecules with resonance is called a resonance hybrid. This resonance hybrid spreads multiple bond character over a molecule and lowers its energy, causing it to be more stable. This is why the best representation of molecules with resonance is a resonance hybrid because...

Marylyn Makar 1B

Hi! So this refers to Schrodinger's equation. The energy that we get out of Schrodinger's equation matches the energy of a specific orbital and can be compared to spectroscopic data. The higher the energy, the larger the orbital (meaning s,p,d,f). Also, Schrodinger's equation squared represents the ...

Marylyn Makar 1B

Hi! The trend for electronegativity is the same as ionization energy. So, electronegativity increases from left to right across a period and decreases down a group. However, this trend does not apply to the noble gases because they do not want another electron. In the case of N and S, nitrogen would...

Marylyn Makar 1B

Hi! Are there ever any valence electrons in the d orbital since it is never the outermost shell?

Marylyn Makar 1B

Hi! In Lecture #17, Dr. Lavelle says that -250 kJ/mol is the magnitude of attractive interactions between Na+ and Cl-. What exactly is the mole of? Is it per mole of Na+ and Cl- together or per mole of bonds?

Marylyn Makar 1B

He subtracted 1 electron because the ammonium had a positive charge. This means the ammonium had to lose 1 electron to be positively charged.

Marylyn Makar 1B

Hi! Dr. Lavelle mentioned in one of his lectures before that if two elements are close together on the periodic table, then they will form a covalent bond. If two elements are on opposite sides of the periodic table and bind, then they will most likely form an ionic bond.

Marylyn Makar 1B

Hi! This number is the magnitude of attractive interactions between the two ions. The number is negative because energy is being released, which is favorable.

Marylyn Makar 1B

I am in it right now. Make sure you are signed in with SSO first using this: https://ucla.zoom.us
And the zoom link is on CCLE

Marylyn Makar 1B

Hi! Yes you are right. An expanded valence shell means that an atom has more than 8 valence electrons.

Marylyn Makar 1B

Dr. Lavelle just said in his office hours that we do not need to know how to do part d for that question and he will update the outline to omit part d.

Marylyn Makar 1B

Hi! So formal charge is calculated by calculating the number of valence electrons minus the sum of the number of lone pair electrons plus the number of shared electrons divided by 2, or FC= V- (L + S/2) So oxygen has 6 valence electrons since it is in the 6th group excluding the d-block. In SO4, oxy...

Marylyn Makar 1B

Hi! Why does nuclear charge increase across a period? I know increasing nuclear charge causes the atomic radii to decrease across a period but I cannot figure out why. Thanks!

Marylyn Makar 1B

Hi! Yes you can use the second equation (the Rydberg equation) but the first equation just helps you to better understand what is going on. The first equation helps you to clearly recognize if the Energy is being emitted ( a negative value for E) or absorbed (a positive value for E).

Marylyn Makar 1B

Hi! You have to do 333.6 J/g x 423 g first. Then you use E=hc/λ and plug in 819x10^-9 m for λ and find E. Once you have this energy in J/ photon, you can find the number of photons. You just take what you got from your first calculation ( 141,113 J) and divide it by what you got in your second calcu...

Marylyn Makar 1B

Hi! Does light in the atomic spectra experiment behave like a wave or a particle?

Marylyn Makar 1B

Hi! I would start off by balancing nitrogen first and getting 2C10H15N + O2 -> CO2 + H2O + CH4N2O Then, balance the carbon to get 2C10H15N + O2 -> 19CO2 + H2O + CH4N2O Now we can balance hydrogen to get 2C10H15N + O2 -> 19CO2 + 13H2O + CH4N2O Lastly we balance oxygen to get the final equation of 2C1...

Marylyn Makar 1B

Hi! When do we use the Einstein equation E=hv versus the equation E=pc?

Marylyn Makar 1B

Hi! Yes, it only applies to metals because the original experiment was done by shining light on a metal surface to measure the energy needed to eject electrons from the surface.

Marylyn Makar 1B

It should be given to you. A detector is the only thing that can find the wavelength. Wavelength can be calculated if you are given frequency by doing λ=c/v

Marylyn Makar 1B

Hi! Yes, I believe no nodal plane means that there is no electron density distribution of 0 in the s plane.

Marylyn Makar 1B

What exactly is electron density?

Marylyn Makar 1B

Hi! Yes, I believe a longer wavelength is the same as a larger wavelength.

Marylyn Makar 1B

What does electron transition mean?

Marylyn Makar 1B

Since the energy levels of an electron are quantized, it is not possible to have a middle energy level between n=1 and n=2 for example. There is no such thing as n=1.5 because light does not act like a continuous wave when it interacts with these electrons.

Marylyn Makar 1B

The Balmer series occurs in the visible region and involves the n=2 state. Th Lyman series occurs in the UV region and involves the n=1 state. Which state the electron is in is random. However, all the electrons do eventually come back to the ground state, which is n=1.

Marylyn Makar 1B

Hi! So since c= λv, we can rearrange that equation to solve for v which is v=c/λ. Now we can substitute c/λ for v in the equation E=hv and we get E=hc/λ. I think you got mixed up and thought E=hc/v which is wrong. Hope that helps!

Marylyn Makar 1B

Hi! I got an email from my TA that we have to have an external webcam that we can plug into a computer and move around independently of a laptop screen/desktop. So a built-in camera on a laptop will not work.

Marylyn Makar 1B

I also found this different sheet hyperlinked under Math Assistance on Dr. Lavelle's website if that helps!

https://lavelle.chem.ucla.edu/wp-conten ... ussion.pdf

Marylyn Makar 1B

Oh I see! I used the molar mass of 2H20 instead of just H20 to calculate the number of moles in H20. That's what messed up my answer in case anyone was wondering what my mistake was. Thanks again!

Marylyn Makar 1B

Hi! For question 19 in the limiting reactant calculation post-module assessment, I keep getting H2O as the limiting reactant but that is not the answer. Could anyone help me get the right answer? Thanks. 19.) For the following reaction if 1.00 x 102 g H2O reacts with 1.00 x 102 g CaC2 identify the l...

Marylyn Makar 1B

In section H of the fundamentals in the ebook, it defines reagents as all chemicals available in a lab. The book also says that a reagent is only called a reactant when it is being used in a particular reaction. So there is a difference in the terms.

Marylyn Makar 1B

Chemistry Community is available to everyone even if you have never taken 14A. However, only students currently enrolled in the class are allowed to post on chemistry community. Just look up chemistry community on google and you will be able to find it.

Marylyn Makar 1B

In this problem, CaCO3 is a limiting reactant. Now, the moles of a limiting reactant determine how much product can be formed. Therefore, we can figure out how many moles there are in CaCO3 and determine how many moles of CO2(a product) will be produced based on the 1:1 molar ratio between CaCO3 and...

Search found 65 matches