CHEMISTRY COMMUNITY

kevinchang_4I

If we look at the equation we see that Cl- and N03- are formed. Because these are the conjugate bases of two strong acids (HCl and HNO3), they do not affect the pH or pOH of the solution.

kevinchang_4I

Glycine is not polyprotic because even though it has 5 H's, it can only give away one. Usually N and C do not give away H+'s, as NH groups are more commonly bases and C does not like to be negatively charged. Since there's only one H bonded to an O, that's the only H that can be given away. Hope thi...

kevinchang_4I

Find the difference in concentration between OH- and H30+. From there plug in the value you got into pOH or pH

kevinchang_4I

Jessica Tejero 3L wrote:For number 21 what is the oxidation state of iron?

The oxidation state of iron will be 2+ because two of the nitrogens have lone pairs making their formal charges -1 each.

kevinchang_4I

Will the answers to the Minimarshmallows be posted? Thanks!

kevinchang_4I

I'm confused about the distinction between these items. Is it the salt that reacts with water to make it more acidic or is it the acid that reacts with water to make it more acidic? Same question about bases.

kevinchang_4I

What is the relationship between pH, pKa and Ka? Also how do we find Kb from Ka?

kevinchang_4I

Hybridization of electron orbitals is important for the formation of covalent bonds between atoms. For example, CH4 has hybrid orbitals, and couldn't be formed without them. Carbon naturally only has 2 unpaired valence electrons, but we know it needs 4 to bond with the hydrogens. We hybridize and ge...

kevinchang_4I

Polydentate means that it is a ligand with multiple donor atoms, or atoms with lone pairs that can bond to the central metal atom. So in order to solve this problem we have to look at which of these molecules has lone pairs. For (a) I googled the structure. Other people can recognize that all the N'...

kevinchang_4I

How do we identify how many donor atoms a ligand has? Also what is a donor atom? As an example question, how many donor atoms does something big and scary such as HN(CH2CH2NH2)2 have? Thanks!

kevinchang_4I

What is polydentate and what's its significance within this course and chemistry in general?

kevinchang_4I

In part (d) it asks to write the formula for this coordination compound:

sodium bisoxalato(diaqua)ferrate(III)

Could someone walk me through the process of finding the formula? As in what represents what and how to order it. Thank you!

kevinchang_4I

I don’t know it I can explain it clearly, but I think I can explain it simply. Basically, a high vapor pressure corresponds to low IMF because vapor pressure can be thought of as liquid evaporating. If there are low intermolecular forces then the molecules will start breaking off from each other, or...

kevinchang_4I

I’m sorry if this is a dumb question, but what is a coordination complex and what is it’s purpose?

kevinchang_4I

Hybridization of electron orbitals is important for the formation of covalent bonds between atoms. For example, CH4 has hybrid orbitals, and couldn't be formed without them. Carbon naturally only has 2 unpaired valence electrons, but we know it needs 4 to bond with the hydrogens. We hybridize and ge...

kevinchang_4I

How do we know how many hydrogen bonding sites there are? Like for example on a G-C pair how many hydrogen bonding sites are there and how do we know

kevinchang_4I

In question 2.45, there is an O with a double bond with C and 2 lone pairs. How do I hybridize the O?

kevinchang_4I

Arrange the anions Cl-, Br-, N 3-, and O 2- in order of increasing polarizability. What's the general rule of polarizability? The general rule of polarizability is the larger the atom, the more polarizable. This is because the larger the atom, the less influence the positively charged nucleus has o...

kevinchang_4I

The book actually says it's angular. This makes sense bc if we do the lewis structure for ClO2- then we see that Cl has two lone pairs on it. This "pushes" the O's downward, making it so that the angle is no longer 180 degrees. If you look at 2E.1 (a) that's kinda what our molecule looks l...

kevinchang_4I

How are we supposed to know what kind of bond something is? Like if we are given a molecule like H2O or PCl5 or SO4-, how do we identify what bonds are what?

kevinchang_4I

The electrons begin to be ejected at 1.23 x 10^15 Hz because at this point the energy of the incoming photon is enough to overcome the threshold energy of the gold surface. Remember:

Ephoton = Ethreshold + Eemitted electron

kevinchang_4I

You have the concept right, more ionic means a larger difference in electronegativity. However, all because C and F are "closer" than C and H does not mean their electro negativities are closer. H is 2.1, C is 2.5, F is 4.0. If we use these values then CF4 is clearly more ionic.

kevinchang_4I

Dipole moments arise from differences in electronegativity between atoms. Like if there is a polar atom it may induce a dipole on another atom since it has a charge.

kevinchang_4I

It usually does matter in the same way we apply negative formal charges. Because we try to apply neg charges to the most electronegative atom, we try to apply pos charges to the least electronegative atom. This is usually the central atom. However, making our formal charges zero is still the primary...

kevinchang_4I

Yes because lone pairs usually make the molecule asymmetric, causing polarity. If there are two opposite facing lone pairs then it is possible to be nonpolar

kevinchang_4I

Does anyone know of a good reference table with the names and the shapes for everything? The partial ones in the book are pretty bad and not very helpful.

kevinchang_4I

a) An excited hydrogen atom undergoes an electronic transition from n=3 to n=1. Calculate the frequency of the photon emitted. b) If a hydrogen electron goes from n=6 to n=4, will deltaE be negative or positive? Will the energy of the photon emitted be negative or positive? a) What formulas am I sup...

kevinchang_4I

(b) Matt walks in, hoping to absorb some of the potassium ions in the air to alleviate his cramps. He thinks to himself, “I wonder what the frequency of the potassium ion is?” and divides the speed of light by the wavelength to obtain a frequency of 2.671x10^16 Hz for each potassium ion. Is he corre...

kevinchang_4I

In this problem we have to use 2 equations. p*x = 1/2*hbar and p = m*v m*v*x = 1/2*hbar x(what we're looking for) = hbar / 2*m*v We have all three components, but not in the right units. 0.55 m/s must be multiplied by 2 because we are given it as a range. 1.5 g must be 1.5 x 10^3 kg, and we have to ...

kevinchang_4I

For the first question we just have to use Wavelength = Speed of light / Frequency.

It's given us the frequency, just in the wrong units, MHz not Hz. Remembering SI stuff, M = mega = 1,000,000 = 10^6.

Now we have 8.01 x 10^7 Hz

Wavelength = 3 x 10^8 / 8.01 x 10^7 = 3.74272732 meters

kevinchang_4I

I think they matter because it is another indication that electrons are not really in "bonds". They are actually always moving around and the resonance structures let us understand the different places they can be in. Also, resonance structures can show us which configurations are more sta...

kevinchang_4I

If you go to the class website lavelle.chem.ucla.edu you can find a link called "Midterm Review Sessions and Rooms" or you can try this link https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14A/Midterm_Review_Sessions_14A.pdf but idk if it will work because you need to log int...

kevinchang_4I

Ionic bonds are stronger than covalent bonds. Ionic bonds are stronger because they are formed through the attraction of opposite charges of a metallic (+) and nonmetallic ion (-). Covalent bonds are two nonmetallic atoms sharing atoms, and aren't as strong.

kevinchang_4I

Can someone explain how to identify radicals? For example can someone explain why NO2- is not a radical and CH20 is? It's part of problem 2C.1

kevinchang_4I

Valence electrons of an atom are related to the valence of an atom, but are not the same. Nitrogen has a valence of 3, meaning that it needs three more electrons for bonding, but has 5 valence electrons. This 5 is the amount in its valence shell. When we do Lewis structures we refer to the amount of...

kevinchang_4I

This problem is just asking for the electron configuration of the ions. For example, Cu (copper) usually has an electron configuration of [Ar] 3d10 4s1, but because it is asking for the configuration of the ion Cu+ then we know it has one less electron. Therefore the configuration just is [Ar] 3d10

kevinchang_4I

The first thing is that the atoms must follow the octet rule. It helps to distribute the atoms like you're passing out cards, one by one instead of giving a person all eight at a time.

kevinchang_4I

The main two will be

Ephoton = planck's constant * frequency

speed of light = wavelength * frequency

However, I think it will be important to know some derivations of these equations like

Ephoton = (planck's constant * speed of light) / (wavelength)

kevinchang_4I

I believe that the primary difference between the two is quantum mechanics says that light is both a particle, which has mass, and a wave, which has none.

kevinchang_4I

I guess you kinda have to memorize the order. It goes 1s2, 2s2, 2p6, 3s2, 3p6, 3d10, 4s2,4p6.... The exponents are keep track of the number of electrons. For example, if my electron configuration was 1s2, 2s2, 2p3, then I know my element has 7 electrons, and must be Nitrogen. This rule applies to th...

kevinchang_4I

I have a question regarding the order I'm supposed to put electron configurations. For (Ga) for example, the electron configuration is 1s1 2s2 2p6 3s2 3p6 3d10 4s2 4p1. I am confused as to why 3d10 comes before 4s2 because when looking at the periodic table it looks like it should be 4s2 3d10 4p1. I...

kevinchang_4I

For part of question D.21 it says list the subshell notation and the numbver of orbitals with the following quantum numbers. It gives a n= and l=. For example, n=5 and l=2 will be the 5d subshell. What I don't understand is how to know the orbitals. Also what are orbitals in this context? Thanks

kevinchang_4I

This problem took me forever. So because it tells us that it's UV light, when know n1 = 1. n2 is what we need to find and we have the equations to do it. wavelength = speed of light / frequency frequency = Rydberg constant * (1/n1^2 - 1/n2^2) We have wavelength and speed of light, so we can solve fo...

kevinchang_4I

Hi sorry I can't answer your question but where is the post module assessment?

kevinchang_4I

This problem gives the velocity of an emitted electron and asks for its wavelength. How do I solve this without a given work function? Thank you for the help

kevinchang_4I

The 5H2O really is a curveball.To begin with, we need to know how many moles of CuSO4 in 250 mL of a .2 M solution. This will be .05 moles of CuSO4. This is going to be 7.98 grams CuSO4. Now we must calculate CuSO4's percent composition in CuSO4 * 5H2O. Which is molar mass CuSO4 over molar mass CuSO...

kevinchang_4I

In this problem it gives us the wavelength of 102.6nm and tells us the line is in the UV spectrum. This means that n1 is going to = 1, and we must find n2. v=R((1/n1^2)-(1/n2^2)), and wavelength 102.6nm = c / v. I just don't know the algebra to find the value of n2. Thanks for the help

kevinchang_4I

Sorry I meant the moles of C, H, and N from the PRODUCTS

kevinchang_4I

This problem is a tough one. Luckily my TA did it in discussion. To find the empirical formula of caffeine you must first the moles of C, H, and N from your products. Remember the subscripts in your conversions! Leave out the O2 for now because there is O2 in the reactants. From there, find out how ...

kevinchang_4I

So 1 mol is equal to 6.02 x 10^23 atoms of whatever element you have. For example, one mol of Calcium is 6.02 x 10^23 individual atoms of Calcium. Now we combine this with the molar mass of Calcium which is around 40 grams/mol, which is also the same as saying 6.02 x 10^23 atoms of Calcium will weig...

kevinchang_4I

So 1 mol is equal to 6.02 x 10^23 atoms of whatever element you have. It is a standard unit used to simplify and streamline calculations. (Even if it doesn't seem so helpful now) For example, one mol of Carbon is 6.02 x 10^23 individual atoms of Carbon. Now we combine this with the molar mass of Car...

kevinchang_4I

When are we supposed to use the Balmer series or Lyman series when we are identifying lines? Also, how do we know what values of n1 and n2 to use, as in the book it says n2 can be anything. Also, is it always frequency (v) = R{(1/n1^2) - (1/n2^2)} for all element and energy levels?

kevinchang_4I

Hi Ryan, usually the larger atom will go first, at least that's what my TA said. He also said it is not crucial to know at the moment, and most of the time it is given.

kevinchang_4I

We must look at the ratios for this problem. For every 2 BrF3 we use we need 6 ClO2, and vice versa. Since we have 12 ClO2, we need 4 BrF3. Since we have 5 moles, it is our excess reactant.

kevinchang_4I

This problem is a tough one. Luckily my TA did it in discussion. To find the empirical formula of caffeine you must first the moles of C, H, and N from your reactants. From there, find out how many grams of each you got. There should be a difference between that value and the initial caffeine. The d...

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