CHEMISTRY COMMUNITY

MMckinney_4H

For number 34, why are two moles of OH produced for every mole of CaO?

MMckinney_4H

Anybody have a thorough explanation on how to determine strength of bases? I recognize that BrO- is the conjugate base for HBrO so it would be pretty strong but how do I know definitively that it is stronger than C17H19O3N or any other base?

MMckinney_4H

How do we know which one to use between isocyano and cyanido-kN?

MMckinney_4H

The first would be tetrahedral with two of the oxygens on one S and the other one on the other S. (b) There would be two tetrahedral shapes about the carbons with the Be in between the Carbons. (c) the Hydrogens would be 120 degrees away from each other because of the lone electron forming a bent sh...

MMckinney_4H

This image shows how the molecule can attach to the metal "M" at multiple different points making it a chelate. And the video explains why chelates are more stable/how they work. https://www.youtube.com/watch?v=RM6l2JfHxg8

MMckinney_4H

The stronger/short the bond, the less likely it is to dissociate in water. This means that with longer bonds, the hydrogen is more easily released when it comes in contact with a base, so the ratio of molecules that dissociate for molecules with longer bonds is higher making it a stronger acid.

MMckinney_4H

If you picture a flow chart for electrons based on electronegativity for trichloroacetic acid, you'd see that Chlorine would be pulling the electrons from Carbon resulting in Carbon needing the electron from the covalent bond with the other Carbon even more. From here, the Oxygens would be far less ...

MMckinney_4H

Water itself is amphoteric as it can form hydronium ions and hydroxide ions when introduced to an acid or base respectively. Zinc Oxide and Aluminum hydroxide are both amphoteric as well. I believe that when an amphoteric compound come is contact with water, both can act as an acid or as a base so p...

MMckinney_4H

Bases often have an electron pair that is available for bonding which allows it to accept Hydrogen ions. Whereas the acid is able to dissociate because of differences in electronegativity between a hydrogen atom and other atoms in the molecule. If you look at a chemical equation you can figure out w...

MMckinney_4H

The difference between a weak acid and a strong acid is the amount of it that dissociates in water. Not every Carboxylic Acid molecule will dissociate when it comes in contact with water whereas something like Hydrochloric Acid would have every molecule dissociate.

MMckinney_4H

Bond lengths can help describe how strong a bond is between two atoms. The shorter the bond, the stronger it is. This is why double bonds are shorter than single. Dissociation energy is related because it is the energy it takes to break the bond between two atoms. If the bond length is shorter, the ...

MMckinney_4H

What creates the actual dipole is the arrangement of the atoms in the molecule. So, looking at the molecular formula itself is of little help. You should draw out the lewis structure of the molecule and look at the electronegativity difference between atoms that are bonded to each other. This will g...

MMckinney_4H

You should look at the electronegativity of the atoms bonded in the molecule. The larger the difference in electronegativity, the stronger (more polar) the dipole.

MMckinney_4H

Just learn all of the possible molecular shapes presented as you don't know which ones will be on the test and don't want to be caught unawares.

MMckinney_4H

Imagine an AX5 shape. You have five equally spaced atoms bonded to the A. In an AX4E shape, it's the same situation except the lone pair repels the bonding pairs more than a bonding pair would repel others. So, to be most stable, the molecule wants the least amount of repulsion (the reason why we sp...

MMckinney_4H

What happened @Kavee Dodampahala ????

MMckinney_4H

No they don't the dipole moment is a result of the structures not the other way around. Also, unlike with induced dipole moment, the dipole moment doesn't really change, so the only thing that could influence it is the original structure.

MMckinney_4H

It would be two because there are two Cls that can be part of the OSCl bond angle.

MMckinney_4H

There's a lone pair on the central atom that would alter the formation to be trigonal pyramidal (not tetrahedral or trigonal planar) making the bond angles OSCl slightly less than 109.5 degrees but the ClSCl would be less because they don't have the double bond repelling them more.

MMckinney_4H

I'm also wondering about points that shouldn't have been taken away (partial credit that wasn't given) but I the syllabus says no regrades. If there is most definitely a mistake in grading how do we go about solving it?

MMckinney_4H

It's most definitely cumulative.

MMckinney_4H

Intermolecular forces are the result of chemical bonds. Chemical bonds are the sharing of transfer of electrons whereas intermolecular forces are the interactions that happen because of charges. Think about magnets A molecule acts like a single magnet. While it can connect with other magnets, they a...

MMckinney_4H

The 3 types of covalent bonds that we've learned of are polar, non-polar, and coordinate. The first two differ because of electronegativity differences (or lack thereof) between the atoms in the molecule. A coordinate covalent bond is when the an atom in a molecule doesn't have its valence shell fil...

MMckinney_4H

Molecules with more intermolecular forces will have a lower vapor pressure. Water's hydrogen bonds make it have a lower vapor pressure. It's very similar to why water's boiling point would be higher than that of diethyl ether.

MMckinney_4H

If it only had one double bond, it would be less stable than having all three double bonds, so you'd actually want it to have three.

MMckinney_4H

Given that we can't look up stuff during the midterm, what would be the best way of figuring out which one goes in the middle for this situation?

MMckinney_4H

If he is going to grade us on whether or not we know how to draw resonance structures, he will ask us to draw them. There may be resonance structures of the most stable lewis structure for a given molecule, but we shouldn't have to draw them unless specified.

MMckinney_4H

As the polarizing power of a cation increases with size, for the first 3 columns, as you move to right, their polarizing power decreases and as you move down, the polarizing power increases. But it's much better to be able to compare polarizing power from the size and charge than to figure out some ...

MMckinney_4H

The charge of the anion isn't considered as really affecting the polarizability outside of the size of the anion (which is affected by the charge) I don't believe. The focus is more on the size of the cation, its charge and the size of the anion.

MMckinney_4H

First, I just set up the molecule as described in the problem. From there, I added all of the 22 other electrons onto the atoms to give them octets. At first I gave Cl 6 free electrons, Oxygen 4, Nitrogen 0 and each of the oxygens 6. However, with this setup, nitrogen didn't have an octet. So, I mov...

MMckinney_4H

viewtopic.php?t=417

Professor Lavelle actually explained this in a separate post.

MMckinney_4H

While I don't believe that there will be a review session purely dedicated to this, I believe that a few TAs are going to do a full review of all of the material which should include the fundamentals unit.

MMckinney_4H

Yes, they should all add up to -1. The individual charges can vary so long as the entire molecule's overall charge matches the given charge. But you must also keep in mind that the individual charges should be the lowest that they can be.

MMckinney_4H

Because it is an ionic compound, you would separate them, keeping the electrons by phosphorus. You go about arranging the lewis structure the same way but at the end you take the electrons from the bonds and give them to the phosphorus because it needs to end up with a charge of -3 as phosphorus doe...

MMckinney_4H

For Formaldehyde, first note that they give you HCHO as opposed to H2CO or something of that nature. This is because you are supposed to use this as a guide to how to draw the structure. Carbon is supposed to be connected to both of the Hydrogen atoms. From here, you calculate the number of valence ...

MMckinney_4H

You'd find the element with the same amount of elements as the given configuration then add two electrons to the element that corresponds to the configuration. For example: a) chromium has the same number of elements as the given configuration then add two electrons to get Iron. So Fe2+ would have t...

MMckinney_4H

This picture really helped me out. n (the shell) represents the energy level. l (the subshell) represents the type/ shape of the orbitals. m(sub)l (the orbital) represents the actually orientation of the space that the electron can occupy.

MMckinney_4H

g orbitals do in fact exist. However, we cannot have a 4g because that would mean that the n=4 and l=3,2,1, or 0. A g orbital would only happen when l=4.

MMckinney_4H

As you increase the size of the nucleus across a period, the electrons are pulled in closer because of the higher number of protons with the electrons still being in the same shell. However, cations are smaller because when an atom loses an electron making it a cation, there is less electron-electro...

MMckinney_4H

On a previous discussion board, Professor Lavelle commented that the solutions guide has an error with this question. Link to his comment: https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=5558 Solution manual errors correction: -Solution manual states Δv = 5.0 m.s-1 -Velocity was given as 5.00 ± ...

MMckinney_4H

Atoms' numbers of protons and electrons are balanced to have a charge of 0. However, when electrons are exchanged, some atoms can either have a positive or have a negative charge depending on which atom receives an electron and which one gains one. When an electron which has a negative charge is gai...

MMckinney_4H

The frequency is how many times a wave cycle passes in one second. If the wavelength is shorter, you would get a higher frequency. It takes a wave with a longer wavelength more time to get through which is why see the lower frequency. Understanding the photoelectric effect will help draw the connect...

MMckinney_4H

The formula (Planck's Constant)(frequency)= (Energy) would be able to help you if you know the frequency. If not, use the formula (wavelength)(frequency)=(speed of light) then substitute.

MMckinney_4H

You should be able to look at the different wavelengths or frequencies in comparison to each other to find out which event goes with which radiation from knowing a little bit about each radiation. e.g. Visible light has to pair with reading because you need to see the words and we can only see visib...

MMckinney_4H

Planck's constant, the speed of light, and the mass of an electron are all good to have memorized though they should be provided on the tests. The conversion from eV to J and Rydberg's constant would also be useful. But if you don't have everything completely memorized, it isn't something to freak o...

MMckinney_4H

I don't think that it would be required of us to have them memorized as the sheet provided during tests will have the necessary constants, but after doing enough problems, it should be burned into your memory. This would also make doing problems a bit faster as you wouldn't have to search through th...

MMckinney_4H

I'm not too sure what you mean by "the wavelength of the incoming light" but it really doesn't matter where the radiation is or has come from. We simply need to know that somewhere there is radiation with a wavelength of 102.6 nm and find out the initial and final electron levels that corr...

MMckinney_4H

How am I supposed to figure out the molecular formula for Epsom salt with just knowing its name is Magnesium Sulfate Heptahydrate?

MMckinney_4H

2 mol K/ 1 mol compound isn't actually applicable for KCl as there would only be 1 mol K for 1 mol KCl. However for K2S, you would have 2 mol K for each mole of the compound. Likewise there would be 3 mol K for each mole of K3PO4

MMckinney_4H

I recognized that when the equation for the combustion of butane is balanced, there are 2 moles of Butane needed, so I just multiplied the entire equation by two so it would show that for 4 moles of Butane, there would be 16 moles of Carbon Dioxide (gas) produced.

MMckinney_4H

This is how I did it step by step.

MMckinney_4H

Which question was this?

MMckinney_4H

I really doubt that this will be tested this week as it is not specifically covered in the fundamentals listed. However for the future, since this is something that should've been covered in high school, we will likely encounter it and you should probably learn it.

MMckinney_4H

The problems specifically mentioned are:

Problems E 1, 3, 7, 9, 15, 17, 21, 23, 25, 27, 29; F 1, 3, 5, 9, 11, 13, 15, 17, 19, 23, 25;
G 5, 7, 9, 11, 13, 17, 19, 21, 23, 25; H 1, 3, 5, 7, 11, 13, 15, 17, 19, 21; L 1, 3, 5, 7, 35, 39;
M 1, 3, 5, 7, 9, 11, 15, 19

MMckinney_4H

That is the correct answer. I simply recognized that with 12 moles of ClO2, I needed 4 moles of BrF3 and this would produce double the typical amount of each product (as double the ClO2 and BrF3 was used) so I got 12 mols ClO2F as a product as well as 2 mols Br. Since I only used 4 mole of BrF3, the...

MMckinney_4H

I did it by recognizing first that Nitrogen, Carbon, and Hydrogen could have only come from the formula for caffeine because for combustion, all you need aside from the thing that is being burned is oxygen. With that I set off to find out how much of each. Nitrogen was the easiest as the problem sai...

MMckinney_4H

Overall the oxygen is the limiting factor, but for the first reaction, the phosphorous is limiting how much P4O10 is created. With the .04657125 mols of P4, you can make .04657125 mols of P4O6 as the ratio is 1:1, but you only use up .13971375 mols of O2 because the ratio between P4 and O2 in the fi...

MMckinney_4H

I'm not entirely sure what you are referring to with the term "chemical unit" but if you mean "molecular formula," then the difference between a formula unit (the empirical formula) and the molecular formula would be that the empirical formula is the ratio between the atoms in a ...

MMckinney_4H

The "M" in M(OH)(sub)2 refers to an unknown metal which you have to find based off of knowing that the two Oxygens and two hydrogens would account for 34 grams of the 74 gram molar mass of the metal hydroxide. If you subtract the 34 from 74, you find that the remaining 40 grams must be the...

MMckinney_4H

If you use the periodic table to find the molar masses of each of the elements, you find that Na has a molar mass of 22.99, Cl has a molar mass of 35.45, and K has a molar mass of 39.098. Adding Na's molar mass with that of Cl, you get that 1 mol of NaCl has a mass of 58.44 g. To find how much NaCl ...

MMckinney_4H

I know it isn't necessarily something we need to focus on, but in the review when they mentioned that despite there typically being a more dominant gas, gaseous mixtures are not considered solutions, I was wondering why not or if they are considered something else. Anyone have an explanation?

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