CHEMISTRY COMMUNITY

OwenSumter_2F

I think we will also learn more about how temperature affects things in a later chapter!

OwenSumter_2F

I'm having problems with Sapling Week 2 #5. The question is: The Kb for an amine is 2.666×10−5. What percentage of the amine is protonated if the pH of a solution of the amine is 9.976 ? Assume that all OH− came from the reaction of B with H2O. I tried to work backwards by finding the pOH from the p...

OwenSumter_2F

Yes, you'll have to memorize the strong acids and bases, they should be in your textbook. As for conjugate bases/acids, they are what's left of an acid/base respectively after taking away or adding an H+

OwenSumter_2F

Just be wary about using left/right as opposed to reactants/products as you may have a reverse reaction or something!

OwenSumter_2F

In addition, anything with both H₃O⁺ and OH^- will multiply to the K_W, just normally not the same number

OwenSumter_2F

In addition, anything with both H₃O⁺ and OH^- will multiply to the K_W, just normally not the same number

OwenSumter_2F

If it makes more sense, try working out the K value of a reaction one way, and then try working out the K value when it is reversed. You will find that the two K values are reciprocals of each other.

OwenSumter_2F

Awesome thank you, that clears up my confusion! :)

OwenSumter_2F

K is the more common equilibrium constant, and as a general rule we will most likely be working with K, as that is what a reaction will tend to level off to.

OwenSumter_2F

So with the equilibrium constant formula being K= [C]^c[D]^d/[A]^a[B]^b, how do we found those concentrations?

OwenSumter_2F

I am reading through textbook topic 5G and I am confused on what an activity is. Is it just a broader term for the concentrations of certain pieces of an equilibrium or is it something else?

OwenSumter_2F

Also make sure to take into account that Lewis acids and bases correspond to donating lone pair electrons, while Bronsted acids and bases correspond to donating H⁺ ions.

OwenSumter_2F

Also make sure given any of the four components (pH, pOH, OH^- levels, H⁺ levels) that you can get the other three, as seen in the Sapling homework for this week.

OwenSumter_2F

You would need more context dealing with bases. An acid only gives off protons if it has a base or bases to give them to. A polyprotic acid can release more than one proton but it doesn't have to. In fact, it is much easier for it to donate only one than two or more.

OwenSumter_2F

Also you can be pretty confident with weak acids or weak bases if they don't follow the general formula for the strong versions (i.e. a metal and OH for strong bases and a starting H for strong acids). Obviously some specifics will have to be memorized but you can use some process of elimination if ...

OwenSumter_2F

Also make sure you consider charge. If a base is neutral, its conjugate acid will be + charged. If a base is -, its conjugate acid will be neutral, and so on.

OwenSumter_2F

If it's polydentate, then it'll be able to bind to those sites, we won't be getting that deep into the actual reality of it in this class.

OwenSumter_2F

It's better if you know them, but you probably won't be tested on knowing the exact names and numbers and rather how to use them.

OwenSumter_2F

I'd definitely suggest mnemonics for some of the less common ones but try to remember some of the more common ones.

OwenSumter_2F

Also one thing I was struggling with is that if there are two or more ligands that need a prefix, put each in front of each ligand, rather than just 1 prefix.

OwenSumter_2F

So the question on Sapling Q1 is to give the systematic name of this coordination compound: [Co(NH₃)₄Cl²]Cl. I thought the answer was tetra ammine chloro cobalt (II) chloride, but that isn't correct. What part am I doing wrong?

OwenSumter_2F

This is also featured in multiple sapling questions about hybridization, where it focuses on one central atom and then another.

OwenSumter_2F

For the common shapes, it should be fairly easy to know those angles since we work with them regularly. For shapes with lone pair electron density areas, those bond angles would be smaller than normal but different for each molecule, and we won't have to calculate those.

OwenSumter_2F

Also check that you didn't accidentally switch the answers for the two molecules, because what you got is correct. Also you could try refreshing the page or something.]

OwenSumter_2F

From what I'm seeing, there is a PCL₃ question which would be sp3 and a PBr₅ question which would be the sp3d you are talking about.

OwenSumter_2F

You would have to find the formal charge to see what has the lowest formal charge, which is what you want.

OwenSumter_2F

To add on to what the others have said, if you are asked to give the most probable Lewis structure, you would give the last one with the lowest formal charge, however resonance is all possible structures.

OwenSumter_2F

It has to do with the chemical formula and composition. In this example, the H connects to the O for some reason, maybe it was already in a molecule with it and two molecules joined or because it is forming a Hydrogen bond, but it does not always have to bond with the central atom.

OwenSumter_2F

Furthermore, most questions of electron configuration won't ask for the electron spin since it is a 50/50 and you can't know more without more context. That being said, if you see a question where the answer for electron spin is something such as 0 or 1 you know it is wrong.

OwenSumter_2F

It is easier in my opinion to think of it as a spectrum rather than absolutes. For example, on homework problems asking for the molecule that is most ionic in character, it would be the molecule with the highest difference in electronegativities. So viewing it as such instead of strict rules helps m...

OwenSumter_2F

Also, as far as molecular shape goes, bonds don't change the shape whether they are single or double or triple, yet lone pairs can.

OwenSumter_2F

I found this guide for oxidation numbers online that I thought was helpful also.

OwenSumter_2F

Yeah, resonance structures are normally pretty redundant with large amounts of atoms, so it's pretty tricky to remember each atom you've used with double bonds and which you've haven't. Every individual atom gets a fair shot, not just the atom types.

OwenSumter_2F

Like others said, find the one with the least formal charge, but if resonance is in question, you'll want both types with an arrow pointing between the two.

OwenSumter_2F

This is also seen on Sapling Q10, where it asks you to arrange 5 bonds from most ionic to most covalent. This is found by the largest differences in electronegativity, or the farther away the two atoms are on the periodic table. It is more useful to know this as a spectrum.

OwenSumter_2F

Got it, so it relates back to orbitals and where on the periodic table it is?

OwenSumter_2F

And then the second number, the subscript, is the amount of orbitals in each subshell.

OwenSumter_2F

Yes, these are primarily theoretical and if new elements were discovered with these higher orbitals we would know how to handle them!

OwenSumter_2F

Normally for answers for problems in this class, we won't be getting really weird and large mole numbers, it will normally be something like 2:2:1, so if you get some really weird combo like 13:27:6 you may have done something wrong in rounding or in the calculations, but usually rounding will be ab...

OwenSumter_2F

As the title says, how do we know when an element will have more than 8 electrons? Is it just when making a structure and we realize we need more bonds, or is it something we can predict beforehand? Thanks!

OwenSumter_2F

You can think of them conceptually the same way if that helps you visualize it, but they are two different numbers and concepts.

OwenSumter_2F

Also, unless a question specifically asks for a certain unit, you can usually use the base unit (meters, grams, etc.). And if a problem does want for example picometers, having 1.5 x 10^-8 is just as correct as 150 x 10^-10.

OwenSumter_2F

To provide a bit of reasoning why, sig figs are used to show how certain you are of a certain number. So if a certain number i.e. 20 has two zeroes after the decimal place, it means you are certain that it is 20.00 up to those two decimal places. Rather than if you only had 20, you would be certain ...

OwenSumter_2F

This is something that was always kind of confusing to me, but what helped me was that the E=hv equation is the energy of a single photon. So to find the total amount of photons, you would take the given energy and divide it by the energy of a single photon.

OwenSumter_2F

Also, in equations, velocity and frequency shouldn't be used together in the same step for what we're working on. For example, velocity should only be found working with kinetic energy of an electron or with momentum in the Heisenberg Uncertainty Principle, otherwise frequency will be used such as i...

OwenSumter_2F

For our normal discussion section time, do we join the regular zoom link first and then follow instructions of the TA or do we just join the zoom through the midterm straight away?

OwenSumter_2F

The question will also most likely have the experimental yield shown somewhere, so if that is in kilograms or milligrams or something to that effect it would be best to put the theoretical yield into that unit as well, this will make it simpler if you have to do a percent yield equation.

OwenSumter_2F

Also some certain conversions such as between metric units (i.e. kilograms -> grams or meters -> nanometers) won't be on the equation sheet as that is something we are expected to know, so I would make sure you have that down. :)

OwenSumter_2F

It is also covered in textbook section 1D

OwenSumter_2F

And also, memorizing the names of chemical formulas is just for quicker work, in actuality it would be nearly impossible to memorize a whole lot of them, so you can eventually know some ones you work with often, but it's not a necessity.

OwenSumter_2F

To add on to what Truman said, they are the same formula, one is just shorter (E=hv). The other, E=hc/λ is the combination of E=hv and c=λv, it is just there to show how the two equations work together.

OwenSumter_2F

So I was just wondering, since when we use the mass of electrons in the de broglie equation we use 9.11x10^-31kg, do we always use kilograms, and then do we always use meters, or does it not matter?

OwenSumter_2F

I'm having some trouble with this problem. 1B.7 Sodium vapor lamps, used for public lighting, emit yellow light of wavelength 589 nm. How much energy is emitted by (a) an excited sodium atom when it generates a photon; (b) 5.00 mg of sodium atoms emitting light at this wavelength; (c) 1.00 mol of so...

OwenSumter_2F

Also, try not to round your numbers until the final answer, or else your answer may be off a couple of decimal points.

OwenSumter_2F

This was also confusing to me, but I was able to rationalize by thinking of Avogadro's number or moles not as just used for elements or molecules but as a number that can be used for any purpose. Therefore, you can look at it in simpler terms, such that if I had a ten pencil boxes with 3 pencils in ...

OwenSumter_2F

Also, as an additional note, try not to round your numbers until the final answer, otherwise you could be off by a few decimal points.

OwenSumter_2F

Also, using g or mg or any other unit like that is perfectly fine, it is just a convenience for us. It would be very annoying having to write 3.2x10^-6kg in every lab working with small amounts.

OwenSumter_2F

I think its mostly just how you work best and to make it simpler to you. If you want to memorize or get in the habit of knowing basic naming conventions for compounds, that will make it a quicker and easier process for you in the future, however you should be fine either way.

OwenSumter_2F

Yes, it depends on how precise your calculation is. For example, if your graduated cylinder measured to the hundredths place, you could measure exactly 100.00mL of water. But if the graduated cylinder only measured to the tenths place, you could measure exactly 100.0mL of water. Even if there is exa...

OwenSumter_2F

Formula units are the term for ionic compounds, such as molecules for a regular compound or atoms for atoms.

OwenSumter_2F

I'm having trouble with how to approach this problem: "A solution is prepared by dissolving 0.500 g of KCl, 0.500 g of K 2 S, and 0.500 g of K 3 PO 4 in 500. mL of water. What is the concentration in the final solution of (a) potassium ions; (b) sulfide ions?" How do I find the concentrati...

OwenSumter_2F

No, the empirical formula will either be the same as the molecular or smaller due to it being a ratio at the most simplified form. For example, Glucose C₆H₁₂O₆ would simplify even further than you thought, going to CH₂O.

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