CHEMISTRY COMMUNITY

VioletKo3F

Is it possible to get a lower letter grade after the curve? For example, if I have a 450/500 (90%), is it possible that I'll get a B+ because the class average is too high?

VioletKo3F

Usually, you would need Ka or Kb when the question gives you a concentration of a weak acid/base and asks for the pH or pOH of the solution.

VioletKo3F

You first have to determine the orders of the individual reactants by comparing the reaction rate and concentration. For the reaction order, you would add the orders of the reactants together. For 17, it would be 1 (A) + 2 (B) + 2 (C) = 5.

VioletKo3F

Where would we find in the textbook how to do problems like 3B,C, and D? I don't think I ever came across it while doing Outline 2.

VioletKo3F

Prasanna Padmanabham 4I wrote:What edition textbook are you using? Part b on 6D.15 for me is asking about AlCl3...

Yeah it's the same question. I'm just referring to it without the Cl ions since they're not part of the equation. The answer manual uses Al(H2O)6 as the acid to calculate concentration/pH.

VioletKo3F

How do you get the Ka for Al(H2O)6? I don't think it's on either table 6C.1 or 2.

VioletKo3F

In an exothermic reaction, heat is one of the products. For an endothermic reaction, heat is required, so it can be seen as part of the reactants.

VioletKo3F

When writing the cell diagram, how do you know which phase to write?

VioletKo3F

How do you get the two half reactions for the solution? Where does K and Cl go?

VioletKo3F

Does order matter when drawing cell diagrams? For example: Au(s)|Au³⁺(aq)|| or Au³⁺(aq)|Au(s)||

VioletKo3F

How do you get the half reaction for the anode? Shouldn't O₂ and H+ be on different sides of the equation?

VioletKo3F

How are you supposed to balance out P₄ -> PH₃?

VioletKo3F

How are we supposed to balance out H2O? Can someone walk me through the steps/reasoning?

VioletKo3F

I heard from my TA that you need to know how to derive it for the final. She said points could be given based on deriving it.

VioletKo3F

When do you use a comma and when do you use | in a cell diagram?

VioletKo3F

How do you know when to add Pt to the cell diagram?

VioletKo3F

Why is the half equation Cl₂ +2e^- -> 2Cl^- when in the equation, it's Cl₂ -> Cl₂?

VioletKo3F

Can someone give a general outline of how to find oxidation number?

VioletKo3F

Why is I labeled as the reactant instead of I₂? Isn't it supposed to be the opposite?

VioletKo3F

If Gibbs is positive and spontaneous, why does it mean that it will produce more reactants?

VioletKo3F

Would there be any conceptual ideas that we should know before the test?

VioletKo3F

Isolated systems cannot exchange matter or energy. But a closed system can exchange energy.

VioletKo3F

Exothermic reactions produce heat. When the temperature is raised, there is more heat (product) so the system shifts to the reactants to maintain the equilibrium.

VioletKo3F

S, or entropy, is zero in an isothermal reversible system since it it always at equilibrium.

VioletKo3F

My TA mentioned that she would accept homework problems we did on midterm topics.

VioletKo3F

Isochoric means a constant volume.

VioletKo3F

Similar to what is was last quarter, I don't think test 2 is cumulative. It should cover the topics we learn after the midterm.

VioletKo3F

For me, the workshops are really helpful since they give you extra problems to work on. If you have questions, I suggest going to the TA office hours or the step-ups/ drop-ins.

VioletKo3F

Why do you need to subtract twice the enthalpy of formation of NO to get the total reaction enthalpy?

VioletKo3F

Jordan Young 2J wrote:Enthalpy of formation of O2 is zero because it's in its most stable form of oxygen

How would you know that it's the most stable form? Would you have to memorize it?

VioletKo3F

When calculating the enthalpy, why are only some reactants/products used to calculate it? For example, for part (a), you only use the enthalpy of formation of H2O and H2O2, and don't include O2.

VioletKo3F

The equation is pKa = -log Ka. Due to the math, a larger Ka will mean a smaller pKa.

VioletKo3F

Energy is used for the phase change, so there is no increase/decrease in temperature.

VioletKo3F

Most gases are non ideal. Any gas that has intermolecular forces and take up volume are non ideal.

VioletKo3F

An inert gas does not react. Noble gases are the elements of the rightmost column of the periodic table. Noble gases are part of inert gases, but they are not used interchangeably.

VioletKo3F

Ideal gases must follow the gas laws. They have no interaction and take up no volume.

VioletKo3F

Since density is mass over volume, you can substitute the mass in n and the volume in v in the equation pv = nrt. Once this is done, the equation can be rewritten as molar mass = dRT/P.

VioletKo3F

Volume and pressure have an inverse relationship. If the volume decreases, the air particles crash more frequently within the smaller area, increasing pressure. The opposite occurs when volume increases.

VioletKo3F

It is also important to note that ka * kb = kw, which is equal to 1.0*10^-14.

VioletKo3F

Heat is part of the products in an exothermic reaction. If the temperature is raised, there is more heat and the reaction is driven back to maintain equilibrium.

VioletKo3F

Lewis acids accept an electron pair while lewis bases donate an electron pair. If a molecule has unbonded electron pairs, it can be a lewis base by donating an electron. If a molecule's valence shells are not filled, it can accept an electron and act as a lewis acid.

VioletKo3F

In problem 5.35, how would you figure out the balanced chemical equation just from the partial pressures?

VioletKo3F

I think memorizing the strong acids and bases will help since there aren't many of them to begin with. Just assume everything else is weak.

VioletKo3F

If the product is removed, the reaction will immediately favor the forward reaction, producing more product.

VioletKo3F

Lower pH means a higher acidity and more H+ in the solutions. Stronger acids have a higher acidity and they also dissociate completely, meaning more H+.

VioletKo3F

Since the reaction is endothermic, when the temperature is raised the reaction favors the products since it shifts to the right due to the reaction using up the heat to produce more products.

VioletKo3F

Test 1 starts in discussion sections next week. It will cover the first two units: chemical equilibrium and acids and bases.

VioletKo3F

The c in Kc stands for concentration while the p in Kp stands for pressure. It just depends on which you are using to determine the K.

VioletKo3F

P is pressure, v is volume, n is the number of moles, R is the Ideal Gas Constant (8.314 J / mol·K), and T is the temperature in K.

VioletKo3F

You would have to take into consideration all the numbers you used in the calculation of the k value. Just use the numbers given to you in the question to determine your sig figs.

VioletKo3F

Volume has a direct relationship with pressure, so if one increased, the other would also increase and vise versa.

VioletKo3F

In a mixture of gas, each gas is responsible for a partial pressure. In comparison, the total pressure is just the sum of these partial pressures.

VioletKo3F

Is a molecule polydentate as long as it has a lone pair to bind?

VioletKo3F

What do we need to know about Hemoglobin and Myoglobin? How would they be tested?

VioletKo3F

How can you tell if a compound is a lewis acid or base by looking at their lewis structure?

VioletKo3F

How are some molecules Lewis acids but not Bronsted acids?

VioletKo3F

A amphiprotic molecule can both act as a proton acceptor and donator. It has both the characteristics of an acid and a base.

VioletKo3F

Based on the Brønsted–Lowry acid–base theory, a conjugate acid is formed by a base receiving a proton. A conjugate base is the opposite - it is the base formed when the acid donates a proton.

VioletKo3F

Simply put, organic compounds that acts as a base are called organic bases. They are usually proton acceptors and contain nitrogen since it can be easily protonated.

VioletKo3F

Sigma bonds are significantly stronger than pi bonds because of an overlap in orbitals.

VioletKo3F

A t-shaped molecular geometry has 3 ligands attached to a central atom. The bonds form a 90 degrees and the attachments form a t-shape.

VioletKo3F

It is relevant in describing conjugate acids or bases that define a Brønsted-Lowry acid-base reaction.

VioletKo3F

To give an example, sp hybridization has a bond angle of 180 while sp2 has a bond angle of 120. The s-characteristic of the sp hybridization is larger and has a larger bond angle.

VioletKo3F

Does anyone know if there's discussion on Wednesday?

VioletKo3F

There are two nitrogen atoms with a lone pair each, so it makes sense for there to be two hydrogen bonding sites.

VioletKo3F

The orbitals that form sigma bonds overlap more than the orbitals forming the pi bonds so they are much stronger.

VioletKo3F

What does it mean to "explain why lone pairs are more likely to found in certain locations around a central atom and
how and why they affect the bond angles in a molecule, cation, or anion"?

VioletKo3F

Look up the electronegativity on the table and subtract the smaller electronegativity from the larger one.

VioletKo3F

Valence-shell electron-pair repulsion (VSEPR) is a model used to predict the 3d geometry of molecules based on the electron pairs and bonds.

VioletKo3F

Resonance structures do not affect vsepr structures - they only explain molecular shape.

VioletKo3F

Are there any review worksheets being posted?

VioletKo3F

Are we allowed to do 3F questions as well?

VioletKo3F

What's the equation for the formal charge?

VioletKo3F

Does anyone know if we'll get the actual midterm back? Or is it only our grades?

VioletKo3F

No, it should only cover new topics covered after the midterm.

VioletKo3F

Does anyone know the answer to 11a?

VioletKo3F

Are acids and bases on the midterm? I went over the homework questions and there was nothing on it, but the outline for bonding includes it. If so, what do you need to know?

VioletKo3F

We finished the quantum world last week and started on chemical bonding so I also think it should be only chemical bonding for week 5.

VioletKo3F

What do we need to know about the wave vs particle model of electromagnetic radiation? How would it be covered on a midterm if it did show up?

VioletKo3F

The expanded octet needs open spots on the d orbital, which has a total of 10 electrons max. So I believe at most there would be 10 electrons added.

VioletKo3F

Resonance hybrids have a structure written as the average of two+ structural formulas separated by a double-headed arrow. It is also defined as "the net sum of valid resonance structures."

VioletKo3F

I heard the midterm covers the fundamentals, quantum world, and chemical bonds, but try to focus more on quantum world.

VioletKo3F

Partial charges are for polar covalent bonds and dipole moments, so I believe your TA mixed it up.

VioletKo3F

I don't really know what you mean by lowest energy level, but the noble gases are the least reactive and have the lowest electronegativity.

VioletKo3F

The post above pretty much sums it all up so here's a link if you want extra information: https://chem.libretexts.org/Bookshelves ... rown_et_al.)/11%3A_Liquids_and_Intermolecular_Forces/11.2%3A_Intermolecular_Forces

VioletKo3F

I usually do all the homework problems per each section after the lectures so that it'll help me study for the midterm. But technically, you only have to do 5 just to get the points for homework.

VioletKo3F

A lot of the workshops offer worksheets and extra practice with certain topics. If you need help with a certain section, I would also try going to the step-ups. There are review sessions just for the midterm as well so I would definitely recommend attending these.

VioletKo3F

Does anyone know that actual length of double and triple bonds? Will we need to know this on the tests?

VioletKo3F

There are many review sessions posted on the website so you should look at the schedule and plan out which ones you want to make.

VioletKo3F

In a ground state, the electrons are in the lowest energy levels and cannot be lowered any further by transferring them to different orbitals.

VioletKo3F

I would try to go over all the homework problems and take notes on parts of the textbook that were a little more challenging conceptually. Also, I think it's really helpful to go to the workshops since they give out worksheets with more challenging questions that may come up on tests.

VioletKo3F

I would use whatever value is given on the equation sheet to be safe. Rounding should always come at the end so don't be lazy when doing the calculations.

VioletKo3F

I think you might need to know ranges for visible light wavelengths (others that are longer/ shorter than visible) and maybe the different series (lyman, balmer, etc)

VioletKo3F

Cassandra_1K wrote:For limiting reactants on the test do we have to explain how we know one is a limiting reactant or can we just specify which one?

You should show the work for how you found the limiting reactant. Even if you're wrong, you would be able to get partial credit for explaining.

VioletKo3F

Since Angstroms are 1*10^-10m and nm are 1*10^-9m, the nm is 10 times larger than the Angstrom. To convert from nm to Angstrom, you would just multiply by 10.

VioletKo3F

Personally I don't quite understand the correspondence between energy and "The extent of the change in the electrical field at a given point". Could someone explain this aspect please? Thank you! To clarify, "the extent of change" can be seen as slope. Try drawing it out: one wa...

VioletKo3F

Does anyone know what the number in parenthesis next to the standard atomic weight stands for?
Ex.
H
hydrogen
1.00794(7)
What's the 7?

VioletKo3F

I don't think the unit prefixes will be tested directly on the test, but it might come up in the questions (ex. How many molecules are there in 56 mg of...) I would recommend finding a mnemonic that corresponds with each prefix. There's a lot of them online so try finding one that's easy for you to ...

VioletKo3F

I went to the workshop today but had to leave early, so if anyone can explain this problem for me, I would be really grateful :') The following two-step reactions produces hydrogen: Step 1: CH4 +H2O - > CO + 3H2 Step 2: CO + H2O -> CO2 +H2 Given 0.036g of methane (CH4) and 0.108g of water, how much ...

VioletKo3F

Also, make sure to pay attention for the sig figs in the questions. Although they're small points, he still looks for them in final answers.

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