CHEMISTRY COMMUNITY

Sarah Salam 1J

The specific heat capacity depends on knowing the mass, heat capacity doesn't so we use that when we don't know the mass.

Sarah Salam 1J

Could someone explain how they solved for the amount of CS2 produced? I've tried a couple of different ways and I'm not getting the right answer, I was using the heat abosorbed = moles * standard enthalpy equation to solve for moles, then grams.

Sarah Salam 1J

I believe we were given an example where the X was negligible in a quadratic equation. It just depends on whether X is small enough, under 10^-4.

Sarah Salam 1J

You add pKa and pKb because they are logarithmic values, and based on their properties adding them is like multiplying Ka and Kb.

Sarah Salam 1J

You'll have to look at the equation PV=nRT and see if the question is asking you to solve for one of these variables using what you are given. That would mean you are given or can solve for the rest of the variables.

Sarah Salam 1J

Use an ICE table to solve for x, and use -logx to find the pH, and use x/concentration X 100 to find percentage.

Sarah Salam 1J

Like Michael said, strong acids and bases dissociate completely, so one important thing to keep in mind would be that weak ones don't dissociate completely, and we can calculate the percentage that it did, which we did in the homework.

Sarah Salam 1J

When you set your equation equal to Kb, did you arrange it like x^2/M-x (this is how I thought of it)? And when you solved it, did you use the M value to divide the x value when you were getting the percentage? That's the only thing I could think of when I compared my work to yours.

Sarah Salam 1J

The way I solved this question is by finding the pOH since we have the Kb by subtracting the pH from 14. Then I found x by finding 10 to the power of the negative pOH. I used that and the Kb we were given to find molarity, and used the x and molarity value to find the percentage protonated.

Sarah Salam 1J

What key words should we look for in order to determine if we should be using Ka and Kb? This concept caused me a few issues with the homework In the homework, you'd need to use Ka when solving for a weak acid, and Kb when solving for weak bases. You solve for one by dividing 1x10^-14 by the other....

Sarah Salam 1J

Yes, because they are asking about the pH of the weak base, you'll need to find Kb first, and then solve the way you would have with Ka.

Sarah Salam 1J

Partial pressure is for each gas present, the total pressure is all pressures combined.

Sarah Salam 1J

A reaction that produces more products than reactants favors the right side. A reaction that has more reactants than products favors the left.

Sarah Salam 1J

They're noble gases! And they're different because they don't react, so they aren't affecting the equilibrium reaction like other gases would.

Sarah Salam 1J

They don't dissolve or change volume, and so they don't affect equilibrium, so their concentration doesn't matter.

Sarah Salam 1J

It depends on the units that are given in the question. One R value is in J/K*mol and the other is L*atm/K*mol, so you would look at what units are present or that you could convert to and use the corresponding R value.

Sarah Salam 1J

It's D because the will not stop, but equilibrium means the reactions will produce equal amounts of products and reactants at same time.

Sarah Salam 1J

I know that en is C2H4(NH2)2, and I believe that there are two other compounds with similar abbreviations. What are those, and what is important to know about these compounds?

Sarah Salam 1J

In the Friday's lecture, electronegativity was mentioned with acid bonds. How do they relate to increasing electronegativity?

Sarah Salam 1J

How do we find the oxidation number of a metal to get the Roman numeral when naming a compound?

Sarah Salam 1J

Lily Mohtashami wrote:So is tetradentate different than tetrahedron and square-planar complex?

Kind of, tetradentate refers to the binding sites of the ligand, while tetrahedral and square planar are molecular geometries. Denticity can determine possible geometries.

Sarah Salam 1J

Why is the octahedral geometry the only one with a coordination number of 6?

Sarah Salam 1J

Hi, this confused me too, but from what I saw I believe electron geometry groups can include molecular geometry shapes based off of bond angles.

Sarah Salam 1J

No, you will need to draw the Lewis structure to determine if the bonds are single, double or triple.

Sarah Salam 1J

Is there a full list of shapes we could use to practice each one? Should I just write down what Dr. Lavelle went over in lecture, or are there more?

Sarah Salam 1J

One of the sapling questions suggested using dipole arrows to solve it. I solved it without them, but how could we use dipole arrows? What do they show?

Sarah Salam 1J

How can we recognize a delocalized pi bond?

Sarah Salam 1J

Sigma bonds are single bonds, pi bonds are double or triple bonds. All bonds include sigma bonds.

Sarah Salam 1J

Generally ionic bonds are going to have a higher melting point because of their stronger bonds and bond energy, but if I'm not mistaken there are a few exceptions based on other factors.

Sarah Salam 1J

Ionic bonds are formed by nonmetals and metals, since metals usually have few valence electrons, they will give their electrons to nonmetals. Covalent bonds are when an electron is being shared between two atoms, usually these are nonmetals.

Sarah Salam 1J

I think it was mentioned in a lecture that Pauli's exclusion principle and Hund's rule can be used to find the ground state electron configuration. I'm still a little confused by finding configurations, so what is this process and how are these involved?

Sarah Salam 1J

I'm still confused by the different orbitals, and how to make configurations with them, even though I remember them from high school. Does anyone have any resources that I could use to practice and understand these on a basic level?

Sarah Salam 1J

You'll want to use periodic table trends to determine the electronegativity of the atom in question and what it is bonded to.

Sarah Salam 1J

Oh, that clears it up, thank you!

Sarah Salam 1J

When would electrons be parallel? I'm a bit confused on what Hund's rule is saying about this.

Sarah Salam 1J

We use the idea of neighboring atoms for reference, or it could be atoms that they are bonded to, in the case of ionic and covalent radius.

Sarah Salam 1J

Do we always make an expanded octet if we can? Also, the professor explained why they are ok, but I didn't fully understand the explanation. What does it have to do with orbitals?

Sarah Salam 1J

Be has 2 valence electrons, and Li tends to lose an electron and go down to two instead of going up to 8, so they do not form an octet.

Sarah Salam 1J

The point of making it into BF4 was to show how the octet can be completed with a coordinate covalent bond, since BF3 usually behaves as a Lewis acid.

Sarah Salam 1J

What does it mean for something to be highly distorted? I know that it relates to polarization, and the model with the ion and cation in the lecture helped me understand what is happening, but I don't understand what is making that happen or how to recognize it. Does this only refer to electrons and...

Sarah Salam 1J

Could someone please walk me through this problem using the deltaE = -hR/n^2-(-hR/n^2) method that he showed in the lecture? I've used the deltaE=hv equation to solve for the total change in energy, which I got to be 7.55*10^-20 J. I then substituted that into the equation with the necessary consta...

Sarah Salam 1J

Avogadro's constant is the number of something in a mole. It can be the number of atoms in something, molecules in something, it is just a number without units.

Sarah Salam 1J

For better conceptual understanding, what is the maximum?

Sarah Salam 1J

Can someone explain the process for solving #27 in the atomic spectra post module? The meter was defined in 1963 as 1,650,763.73 wavelengths of radiation emitted by krypton-86 (it has since been redefined). What is the wavelength of this krypton-86 radiation? To what region of the electromagnetic sp...

Sarah Salam 1J

Some Heisenberg uncertainty questions ask about the minimum uncertainty and some ask about the maximum. Is there a difference in the way we solve for this or the answers? What is the maximum referring to?

Sarah Salam 1J

I believe it was that increasing the intensity of the light did not eject electrons, like it should have with only wave properties.

Sarah Salam 1J

What is the m in Ek=1/2mv^2 equation? Where does this come from?

Sarah Salam 1J

I believe your comment counts, but as far as the email somebody else mentioned goes you will want to make sure you are posting your questions in the right topic sections to get points for your posts.

Sarah Salam 1J

As far as understanding goes, that's up to how comfortable you are with the bookwork. I found the workshops I've went to very helpful because the UA will go through the problem after letting you work on it, so if you get stuck that will hopefully clarify the problem immediately. You don't need to do...

Sarah Salam 1J

According to the video modules, kinetic energy is the energy of the photon or light minus the work function. Also called excess energy.

Sarah Salam 1J

I believe Prof. Lavelle mentioned in either a video module or a lecture that combustion specifically is a reaction with O2 to make H2O and CO2, so I think it is safe to assume that a question asking about combustion will be that equation.

Sarah Salam 1J

I'm not sure but using units throughout the question may help you get partial credit if you were to mess up the final answer. Otherwise, I've found it at least helps you keep track of your work if you need to fix something.

Sarah Salam 1J

I can get to the homework problems through CCLE but how do I get to the textbook with the free trial?

Sarah Salam 1J

What do the 1-bromopropane and the magnesium represent in the equation as pictured in the problem? Because as far as I've solved it I did not reference those elements In this particular question we were told the 1-bromopropane was in excess, so I think those elements were just there to complete the...

Sarah Salam 1J

In questions where we are trying to find the empirical formula from given masses, like Sapling question #9 or the nicotine example, where we have found the moles of the molecule and we multiply it by the amount of atoms in that molecule, can someone explain the next steps and why they work?

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