CHEMISTRY COMMUNITY

Varadhan_3G

What is the relationship between pka and ph? Which equation do we use to go between them? Thank you.

Varadhan_3G

Hemoglobin should be tetra dentate. Problem 21 on marshmallow is helpful for visualizing the structure of hemoglobin.

Varadhan_3G

Maddie wrote:does this have to do with determining the strength of the acid

Yes, if the inductive effect withdraws electron density, say from an OH- bond, the acidity of the compound will increase.

Varadhan_3G

In problem #21, why is the charge of the central Iron 2+? How do we interact with the surrounding N molecules, and what do the dotted bonds signify again? Thank you.

Varadhan_3G

Let's look at an example: HBr + H2O --> H3O+ + Br- Here, HBr is the acid and H2O acts as the base. H3O+ is the conjugate acid as it is the species that is protonated, and Br- is the conjugate base because it is the species from which a proton is donated. The formula for the conjugate base of HBr is ...

Varadhan_3G

In the textbook, look at section 3H.2 for the formation of synthetic industrial diamonds and box 4D.1 for the production of industrial hydrogen. Hope this helps :)

Varadhan_3G

Stereochemistry refers to the spatial arrangement of atoms. It involves isomerism--stereoisomerism, constitutional isomerism. If you would like I can send you a powerpoint I made on the subject! :)

Varadhan_3G

If you memorize why cisplatin is able to stop DNA replication, and by extension cell division, you should also be able to apply this information to the final. I feel like in the context of the final, the application and memorization of this information is more or less synonymous.

Varadhan_3G

I think you would leave it as amphoteric, unless the question specifies otherwise.

Varadhan_3G

A conjugate ion is the molecule/ion formed when a proton is added to a base.

A conjugate base is what remains of an acid molecule/ion when a proton is lost.

Example:

HCl + NH3 --> NH4+ + Cl-
Here, NH4+ is the conjugate acid, and Cl- is the conjugate base.

Varadhan_3G

Will we need to memorize values of electronegativity at any point?

Varadhan_3G

Benzene is non polar, as it is a hydrocarbon only containing c-c and c-h bonds, and hydrocarbons are generally non polar. The c-h bond, though, is slightly polar, as c is more electronegative than h, giving it a small dipole moment.

Varadhan_3G

Yes, the velocity of light is always a constant, as far as we are concerned.

Varadhan_3G

We will receive our tests during week 10 discussion--the time at which they are posted on MyUCLA is dependent on TA. :)

Varadhan_3G

It occurs when either an anion or cation attracts the partially negative end of a neutral polar molecule. The force becomes strong as either the ionic charge increases, or as the magnitude of the dipole of the polar molecule increases. Ex: NaCl dissociates--Na+ and Cl-, in the presence of water, due...

Varadhan_3G

Do we need to know about the relative magnitudes of intermolecular forces and hydrogen bonds.

Varadhan_3G

You will need to know intermolecular forces, sigma/pi bonds, VSPER theory, resonance hybridity, Lewis acids and bases, polarizability.

Varadhan_3G

Is there a lot of overlap between chem 14A and chem 14B; is it more learning in depth what we have previously learned or are we learning entirely new material?

Varadhan_3G

Once a class average is determined at the end, the grades will be adjusted, I think.

Varadhan_3G

London dispersion is dictated by the proximity of electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles. This force induces a dipole-dipole attraction and is what causes condensation into liquids and freezing into solids.

Varadhan_3G

You don't need to know much about black body radiation for chem 14A. I am not sure about the rest of the series though. Regardless, here is a link that explores the topic more in relation to chemistry than physics: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_M...

Varadhan_3G

In chem 14A I think we will only need to know the general shape of s, p, and d orbitals, and that too, only in order to graph them. This is a link that I found really helpful:).
https://ch301.cm.utexas.edu/section2.ph ... shape.html

Varadhan_3G

Are there any equations that use ms? Will we only ever need to know its application as we have learned it before, or will we need to apply it somehow?

Varadhan_3G

'l' value regards the shape of the orbital--as it changes from spherical to polar when an electron goes from an s to a p orbital, the 'l' value changes from 0 to 1.

Varadhan_3G

https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&ved=2ahUKEwj5gc2h1s_lAhVRtZ4KHacwACAQjRx6BAgBEAQ&url=https%3A%2F%2Fch301.cm.utexas.edu%2Fsection2.php%3Ftarget%3Dimfs%2Fpolar%2Fdipole-moment.html&psig=AOvVaw1xFoXkNQUKXNPadlW7uZNF&ust=1572926577393...

Varadhan_3G

A single bond is a sigma bond. A double bond is a sigma bond and a pi bond. A triple bond is one sigma and two pi bonds. A sigma bond is covalent and shows no resonance. A pi bond is a covalent bond between orbitals perpendicular to the bond direction. https://www.google.com/url?sa=i&rct=j&q...

Varadhan_3G

Also for salts (like NH4Cl), we can assume their complete dissociation! :)

Varadhan_3G

You have a reserve of 28 valence electrons. Once you single bond each fluorine and provide them with full octets, 2 pairs of non-bonding electrons will remain, and you would draw these around the central bromine. Each fluorine should have an octet...if the answer key is showing one fluorine to have ...

Varadhan_3G

The central atom is the one with the comparatively lower electronegativity because an atom in the central position shares more of its electrons than does a terminal atom. :)

Varadhan_3G

Atoms are not lost or created either:) It is a lot like recycling--there is more information on the conservation of matter on Professor Lavelle's website (I would recommend watching the video of his lecture on this topic).

Varadhan_3G

Will we also be provided these constant values on the midterm? Thank you.

Varadhan_3G

Work = threshold energy. First, you need to convert the work from ev to joules: 2.93eV * (1.602*10^-19J/eV) = 4.69*10^-19J Second, convert each wavelength of given into energy using E=hc/(wavelength): 2.86*10^-19 (red ruby) and 4.91*10^-19 J (GaN) Third, compare the energies you calculated to the t...

Varadhan_3G

1B.15: The velocity of an electron that is emitted from a metallic surface by a photon is 3.6 3 103 km?s21. (a) What is the wavelength of the ejected electron? (b) No electrons are emitted from the surface of the metal until the frequency of the radiation reaches 2.50 3 1016 Hz. How much energy is r...

Varadhan_3G

In addition to showing all units, it would be helpful to clearly split the limiting reaction question into 3 parts: (1) the type of amount for which you are calculating, (2) the dimensional analysis to compare amounts for compounds (3) determination of excess after determining limiting reactant.

Varadhan_3G

Atomic radius refers to the distance between the nuclei of two identical atoms. I don't think atomic radius is something you can easily calculate unless already given distance (use equation r=d/2 where r is radius and d is internuclear distance); you would need to use x-ray/spectroscopic methods oth...

Varadhan_3G

Unless the problem specifies to use mHz (megahertz), you should always be using Hz.

Varadhan_3G

Orbital filling concerns Aufbau's principle. Essentially, in their ground state electrons fill orbitals in order of increasing energy, lower first, and higher last. The energy of orbitals follows the (n+l) rule. The 4s orbital has n=4 and l=0, 4+0=4, and the 3d orbital has n=3 and l=2, 3+2=5. Thus, ...

Varadhan_3G

A lamp rated at 32 W emits violet light of wavelength 420 nm. How many photons of violet light can the lamp generate in 2.0 s? How many moles of photons are emitted in that time interval? A watt is a unit of power, 1.00 J/s; we can rewrite 32 W as 32 J/s, so in 2 seconds: (32J/s)*(2s/1), the seconds...

Varadhan_3G

I would recommend doing all of the problems assigned, even if some may seem repetitive. Even the smallest of differences in wording/calculation can make a big impact when taking the midterm. I would also suggest not only knowing the equations used by memory, but the derivations behind some of the mo...

Varadhan_3G

When writing out equations is it always necessary to include the states of matter (if not specified in the problem)? Thank you:)

Varadhan_3G

I don't think we will need to know the formula for a compound so lengthy (and relatively uncommon in textbook material), but I would recommend knowing more common chemical compounds and their respective charges. Here is a quizlet that might be helpful for remembering compounds: https://quizlet.com/4...

Varadhan_3G

You can also view your study list by visiting the MyFeatures on MyUCLA, and under each class, to the right (under class website), there is a link to grades. :)

Varadhan_3G

It is mentioned on one of the links on the website that the following four modules should be completed before week 2: Photoelectric Effect, Atomic Spectra and the Bohr Frequency Condition, Wave Properties of Electrons and the De Broglie Equation, and Heisenberg Uncertainty Equation. There is no pena...

Varadhan_3G

Does it matter if a student's post echoes another? For example, after posting an explanation we realize that another student has already posted that explanation. Does our post still count? Thank you.

Varadhan_3G

Zeroes are significant when: They are found in-between significant digits, E.g. : 405, 20,001 (3 sig figs and 5 sig figs respectively) A final/trailing '0' after a decimal point and a non-zero value, E.g. : 0.00060, 1.40 x 10^2 (2 sig figs and 3 sig figs respectively). A decimal place after zeroes i...

Varadhan_3G

I'm not sure it will always be possible to determine the states. Like Isabella said, you can look at the molecular formula for common compounds and use rules such as pure acids being liquids, and when the word 'insoluble' is used adjacent to a compound we can assume that compound to be a solid. Also...

Varadhan_3G

Problem: Copper(II) nitrate reacts with sodium hydroxide to produce a precipitate of light blue copper(II) hydroxide. (a) Write the net ionic equation for the reaction. (b) Calculate the maximum mass of copper(II) hydroxide that can be formed when 2.00 g of sodium hydroxide is added to 80.0 mL of 0....

Varadhan_3G

Hi Rosa, We are given that in a neutralization reaction, CaCO3(s) + H2SO4(aq) ---> CaSO4(s) + CO2(g) + H2O(l), 1kg of CaCO3(s) produces 'x' moles of CO2(g). To solve for moles of CO2(g), first convert 1kg CaCO3 into grams, and then convert it to moles using molar mass, so that through stoichiometric...

Varadhan_3G

Chemical Reaction: CaCO3(s) --> CaO(s) + CO2(g). Hi Jessica! Like what Sophia said, as CaCO3 is the only reactant in this reaction, we can assume this to be the limiting reactant, but I don't think that information is necessary to solve for the percentage yield. The problem tells us that the thermal...

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