CHEMISTRY COMMUNITY

Jaclyn Schwartz 2D

The way I did it was to first find the pOH (14-pH), then find the concentration of the -OH by using 10^-pOH. This will act as the X in the ICE table Next, we can solve for our missing/needed value by setting up the equation Kb=[BH][OH]/[B] where be is our original base and BH is its conjugate acid,...

Jaclyn Schwartz 2D

Yeprem wrote:I completely forgot to add [B] with [BH+] to find the [B] formal:(
Thank you

Thanks for clarifying this! I have been stuck on this for so long. This helped make it clear what B formal is!

Jaclyn Schwartz 2D

Yep! A general rule is if its an acid use Ka, and if its a base use Kb. And to convert between the two you can use this equation Ka x Kb = 1 x 10^-14! Hope that helps!

Jaclyn Schwartz 2D

If the pH goes below pKa, that means the acidity of the solution becomes stronger than the pKa. When this occurs, the protonated species of HA will become more predominant, HA becomes neutral and A- is charged.

Jaclyn Schwartz 2D

I recommend looking at the problem and see what units you are given, with any problem given for any test! And if the units happen to include pressure, temperature, volume, or moles, then the Ideal Gas Law will probably be the equation for you to use to find the missing variable!

Jaclyn Schwartz 2D

Hi! I was wondering if someone could double check my work because I can not seem to get the correct answer! Here is my problem: The Kb for an amine is 3.107×10−5. What percentage of the amine is protonated if the pH of a solution of the amine is 9.128 ? Assume that all OH− came from the reaction of ...

Jaclyn Schwartz 2D

Hi! Its so bad once you think it through. First I always set up a partial pressures. Then make an ice chart and then plug everything back into the partial pressure equation! Kp=[pPCl5]/[pPCl3][pCl2] ice PCl3 + Cl2 --- PCl5 i 0 0 0.025 c +x +x -x e x. x. 0.025-x Kp=[0.025-x]/[x][x]=399 And solve from...

Jaclyn Schwartz 2D

Partial Pressures are only for gases in this course!

Jaclyn Schwartz 2D

I figured my error out! thanks tho!

Jaclyn Schwartz 2D

For question 9, I cant get the right answer no matter how hard I try. Here is the problem and my values? At equilibrium, the concentrations in this system were found to be [N2]=[O2]=0.100 M and [NO]=0.600 M. N2(g)+O2(g)↽−−⇀2NO(g) If more NO is added, bringing its concentration to 0.900 M, what will ...

Jaclyn Schwartz 2D

Yes! if that how the equation is written, thats how they will be discussed. But with many of these equilibrium equations, you can write the equations either way, but will need to pay attention to K, Q, and other values that will change if you switch directions. Hope that helps!

Jaclyn Schwartz 2D

For question 5, I understand how to cancel all the equations and convert the k values. But how do we combine the k values for the total K? I used equations Ka and Kc and was able to convert them but how to you combine the two new k values? And tips would be appreciated!

Jaclyn Schwartz 2D

The gas constant is a constant. So any time a constant is mentioned it means it will always be the same specific number. An similar example is pi; it is always 3.14. So the gas constant is always equals 8.3144598 J/mol·K.

Jaclyn Schwartz 2D

I believe it would! Logically it makes a lot of sense

Jaclyn Schwartz 2D

P is for pressure, V is for volume, n is number of moles of gas, R is the gas constant, T is for temperature

Jaclyn Schwartz 2D

Partial pressure is just the pressure the gas would have in the container if it was by itself. All the partial pressures add up to the total pressure of the container. But each gas is exerting its own pressure on the container. Hope that helps!

Jaclyn Schwartz 2D

I don't believe we will cover it in this course. But you can always email him to make sure! But in the syllabus it didn't seem to mention it

Jaclyn Schwartz 2D

H20 is only included if it is in gaseous form. Other wise, in liquid or solid, it isn't needed to be included.

Jaclyn Schwartz 2D

An inert gas is the same as a noble gas. It's "inert" because it is unreactive and doesn't bond often.

Jaclyn Schwartz 2D

I usually start with the order the molecules will appear. Then the name of them. And then the oxidation number

Jaclyn Schwartz 2D

For the most part I would assume pH testing would follow lewis acid and bases.

Jaclyn Schwartz 2D

So the charge doesn't really have a name when naming compounds. However, it determines how many of each molecule there is. Like Na+ and Cl-, it going to have a 1 to 1 ratio to create NaCl. However Mg2+ and Cl-, would have MgCl2 (two chlorides). So that is how the charges can sometime come into play....

Jaclyn Schwartz 2D

For this course, c will always be a constant and represent the speed of light

Jaclyn Schwartz 2D

In a triple bond, there is one sigma bond and two pi bonds. I believe sigma bonds are end to end while pi bonds are side to side bonds.

Jaclyn Schwartz 2D

I believe they are the same thing

Jaclyn Schwartz 2D

non-polar molecules are symmetrical and have no dipole movement. Polar molecule are non-symmetrical and have dipole movement.

Jaclyn Schwartz 2D

wait could you further explain what you mean? All that means, in each orbital there is only 2 electrons that are both spinning different ways. To denote that they are spinning in opposite direction we give it +1/2 or -1/2. It doesn't matter if the negative or positive comes first because all this n...

Jaclyn Schwartz 2D

The spin state just simply means the directions the electrons are spinning in their orbital. So in each orbital there can only be 2 electrons. And in that orbital, they are both spinning different ways. And to denote that, we have the 4th quantum number denoting that its either +1/2 or -1/2.

Jaclyn Schwartz 2D

For ionization energy trend, it increases left to right because more energy is needed to remove the electrons from their valence shells. Like in group 1 and 2, they have low ionization energy because they give their electrons, often becoming cation. And in group 7, they have high ionization energy b...

Jaclyn Schwartz 2D

I usually look at the formula. Acids are electron acceptors. So if you are to look at charges, H+ is what it will break into water. If it starts with H, it's most likely an acid because it will be the electron pair receptor. Bases are electron donors and in water will usually break into OH-. Bases m...

Jaclyn Schwartz 2D

My rule of thumb is usually look at the formula. If it starts with H, it's most likely an acid because it will be the electron pair receptor. Bases might have an OH in them as an electron pair donor. If that doesn't get you an answer, look at the structures and see which would be donating an electro...

Jaclyn Schwartz 2D

That just means the lewis structure forms a circle or ring in the structure. It's not linear like most of our lewis structures that we do. And in that sapling question I believe that the cyclic structure is that the carbon atoms form a triangle and the hydrogens branch off from that. I hope that was...

Jaclyn Schwartz 2D

Yes! 40. has 2 numbers in front of the decimal while 40 is only one sigfig because the zeros after don't count. That summary will be pretty helpful^^

Jaclyn Schwartz 2D

To be honest, it's very difficult to memorize the whole chart with bond angles. While you can think it out, it's very difficult and conceptual. My advice would be to find a chart you like and use it.This is one of the charts I use often and it helps me.

Jaclyn Schwartz 2D

Resonance structures are structures that are structurally similar, usually just multiple options. An example is CO3 2-, all similarly structured but with different spots for the double bond. In question 17, they all have the same molecular formula but have different structures so they aren't resonan...

Jaclyn Schwartz 2D

I agree with everyone! I would probably say electronegativity would be the most important but Atomic radius, electron affinity, and ionization energy are important as well. But instead of trying to just memorize trends, try to think of why that trend occurs. For atomic radius it increases as you go ...

Jaclyn Schwartz 2D

In chem 14a it hasn't mattered too much if you're keeping track of states. But it is a good habit to get into. For most of the material we are doing now it won't affect your answers. But it will eventually matter later. Usually most states are given to you in the equation, and if not, it's possible ...

Jaclyn Schwartz 2D

Yes it does have an effect! When adding more electrons, it makes the ion more negative. This leads to more electron electron repulsion. This means an increase the size of the ion radius.

Jaclyn Schwartz 2D

It is talking about removing the electron from the outmost orbital because that requires the lowest energy. Everyone orbital after that requires much more energy.

Jaclyn Schwartz 2D

You will needs to know what ms is, which is the spin. For what we have to know in 14a it basically indicates one specific electron in the orbital vs when they don't mention ms it usually is has 2. Hopefully that makes sense! But you wont have to try to differentiate between +1/2 and -1/2

Jaclyn Schwartz 2D

I don't know if this will help but I remember it by how the elements want to complete the octet. For example elements in group one and two aren't trying to fill their valence shell so low they have low electronegativity. While group 7 really wants to fill their valence shell and only needs one more ...

Jaclyn Schwartz 2D

I usually look at charge or position on the periodic table of the element or ion. The most basic definitions are a lewis acid is an electron pair acceptor and a lewis base is an electron pair donor. As said above, lone pairs usually indicate donors. Acids usually needs electrons is another hint as w...

Jaclyn Schwartz 2D

What are some good formal charge equations? Or easier ways to remember them? Cuz I have seen multiple ways people find the formal charge and a tad confused.

Jaclyn Schwartz 2D

The reason electronegativity decreases down the periodic table is because the atomic radius increases. An increases in the radius means there are more shells and the electrons are farther away so there is less of an attraction.

Jaclyn Schwartz 2D

How do you determine which resonance structure is best based on formal charge? Alittle confused on the process

Jaclyn Schwartz 2D

Ya it took me awhile to figure it out as well. But look at the electronegative atoms with lone pairs and the hydrogen atoms. The 4 hydrogens are able to form 4 hydrogen bonds with electronegative atoms. There are 2 nitrogen with a lone pair each so they can form a hydrogen bond each so that is 2 mor...

Jaclyn Schwartz 2D

I would assume because in an orbital there is 2 options of which way it "spins". So +1/2 and -1/2 is to differentiate between them

Jaclyn Schwartz 2D

Yes there is a difference! Atomic radius is the most common term, which is the distance to the atoms nucleus. A covalent radius is when you measure the distance between two covenantally bonded atoms and take half the distance.

Jaclyn Schwartz 2D

For the most part its guess and check work which can get tedious, but just use the formula charge equation to help if you need. The more you do the better you will get at them so don't worry! You got it.

Jaclyn Schwartz 2D

The brackets help indicate that the molecule is an ion, and the charge outside the brackets is the total charge of the ions.

Jaclyn Schwartz 2D

arisawaters3D wrote:How do you know when it's best to use a double bond as opposed to using a single bond and a lone pair?

If you want to lower the number of bonds. Because in a double bond creates a double bond, while a single bond will leave two lone pairs, one lone pair on each of the atoms in the bond.

Jaclyn Schwartz 2D

CO2 has double bonds in it, so it can attract and accept electrons. This qualifies it as a Lewis Acid. I hope that helps!
If you look at the reaction between H20 and C02 can possibly help too.

Jaclyn Schwartz 2D

How can we determine which resonance structure is most plausible based on formal charge and oxidation number? This is referencing problem 9 from sapling. I know how to get those numbers but based on that information how do we determine which resonance structure?

Jaclyn Schwartz 2D

Can someone explain what London dispersion forces are? And how to differentiate between how strong the forces are?

Jaclyn Schwartz 2D

Thank You!

Jaclyn Schwartz 2D

I am a tad confused on what the question means when they ask for number of photons? sapling #4 is a similar to what I'm asking. Also how would you find the number of protons as well?

Jaclyn Schwartz 2D

How would I find the energy of an electron based on the wavelength? This is based on question 13 of sapling

Jaclyn Schwartz 2D

I don't believe there is any official rules to do it. Just that 2 dots are paired and a single is an unpaired electron, so make sure to keep track of that!

Jaclyn Schwartz 2D

DMaya_3C wrote:Does electronegativity have any connection with a molecule being polar or nonpolar?

Yes it does! That's what cause polar bonds, the electronegativity difference cause there to be uneven sharing of electrons.

Jaclyn Schwartz 2D

The elements that do not follow the octet rule are H, He, Li, and Be. They are in 1s and 2s orbitals so they can not get a full valence shell. I believe there are others but these are the only one discussed so far.

Jaclyn Schwartz 2D

I don't believe he will be testing us on it. You can always email your ta to ask! but because it was so brief I wouldn’t be too worried.

Jaclyn Schwartz 2D

Both ways should be fine! My ta did it one way but a couple of the other kids in my discussion did it the way you did and she said it was okay. If it is getting you the right answer you should be good. It's just a different form of units.

Jaclyn Schwartz 2D

Yes, that is exactly right! Using fractions and non-whole numbers makes it more difficult to solve. And when you multiply by 2 on each side, it does not unbalance the equation because you are doing it to both sides.

Jaclyn Schwartz 2D

You always fill 4s orbital first, except with Cr and Cu. 4s has a lower energy so it fills before 3d. Just follow the order above^^ and it will work for most of the time.

Jaclyn Schwartz 2D

Atomic radius decreases from left to right and increases as you go down. It increases as you go down because the number of energy levels increases, so there is a greater distance between the nucleus and the outermost orbital. From left to right it decreases because of the charges of the nucleus pull...

Jaclyn Schwartz 2D

Just knowing the general trends of electronegativity will be usual for the midterm and can aid you when trying to determine other problems. For the most part, electronegativity increases from left to right and decreases as you go down the period table.

Jaclyn Schwartz 2D

Question 19 is confusing to me. Could someone help explain it?

Jaclyn Schwartz 2D

My TA said not to worry about it. She said it was a poorly set up question but we did not have to worry about those parts

Jaclyn Schwartz 2D

You have unlimited amounts to retake. But it will count your attempts

Jaclyn Schwartz 2D

Thank you for that! Very helpful!

Jaclyn Schwartz 2D

What was the issue? Were you able to type numbers? you may have been stuck on the setting where it puts the number below the letter, just without the letter there. So I would try using the arrow keys to go left and right. If that doesn't work, try to exit out and reset. If that doesn't work fro you ...

Jaclyn Schwartz 2D

This question is alot simpler than you think! To start you multiple the percent of CaCl by the total mass. That will you give you the grams of CaCl in the solution. Next just subtract the mass of the CaCl from the total mass of solution, which will give you the mass of the water. And thats it! hoped...

Jaclyn Schwartz 2D

The reason that 950000 only has 2 sig figs is because it does not have a decimal after the last zero. So the only numbers that count for sig figs are 9 and 5 which make 2 sig figs. 80060 has 4 sig figs because in between 8 and 6 the zeros count. However the zero after 6 does not count because it flo...

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