CHEMISTRY COMMUNITY

AKatukota

For the take home final, will we have to take it during the time slot the closed book final would have been or could we take it any time in the next week?

AKatukota

I believe that they just converted the units differently in the answer key

AKatukota

Thank you! I was wondering this also and I see the relation in why you would subtract.

AKatukota

Is molecularity then just the amount of reactants that interact?

AKatukota

Should we also know to derive it?

AKatukota

You just add up the individual orders. So if you have A + B --> C and reactant A is order 1 and reactant B is order 2, the overall order would be 3

AKatukota

So catalysts are in the reactants then products side. And intermediates are in the product then reactant side?

AKatukota

So the higher the negative potential the more reducing power it has? This would make it oxidized though right?

AKatukota

How you know which has the highest reducing power? Will we be given the gradient table to determine this? I know the the more negative the standard potential the more reducing power the metal has. But where are we getting these numbers from?

AKatukota

Does anyone know when you would flip the sign in a half relation? I know that if you flip the equation the sign flips, but then do you not do this when calculating E(cell)? like if they give you the E value in the problem and the equation has to be flipped do you flip the sign?

AKatukota

Yeah for example for 6M.1, they give the half reactions and Cu^2+|Cu is written, but then in the full diagram it is written M(s)|M+(aq)||Cu^2+(aq)|Cu(s), and they say that the Cu^2+ is the anode, but how is that? On the full cell diagram it is on the right so is that not the cathode? This is the ful...

AKatukota

So for 6M.3 for example, how would I use this strategy here? Some of these half reactions are not on the equations sheet we were given on the test so how would we know. For example for part b, how do we know AgI is the anode and AgCl is the cathode? Im still confused on applying this concept.

AKatukota

This makes sense. I was wondering why in the equation we not change the sign. Thank you!

AKatukota

Also, for part b of this question, how would you right out the reduction half reaction? I am confused on how to figure out what it is and how to write it out.

AKatukota

Ohhh so in order to get n, you have to balance the half reactions and then subtract the electrons?

AKatukota

So why exactly is the delta G = delta H - T delta S needed just because there are two different temperatures?

AKatukota

Also can you use Barr in calculating Q? I thought it had to be atm

AKatukota

I also don't know how to do this? Like how would we incorporate the pressures given into this? Do we use delta G = -RTlnK?

AKatukota

So for example question 5G.13 in the textbook, how would you find Gibbs free energy when given K, temperature, and there pressures of the products and reactants?

AKatukota

Im also a bit confused as to why we are calculating Q again?

AKatukota

How do you know delta G is 0 again?

AKatukota

I believe a salt bridge can be used and I think he showed a diagram in lecture on this in the concentration cell

AKatukota

This makes sense thank you! I was also confused on this part but it makes sense that it is the voltage that is measured when the current is flowing.

AKatukota

I believe in an electrolytic cell, a process called electrolysis takes place. The anode in this case is labeled + and the cathode -. Unlike a galvanic cell, a current must be supplied by an external electrical power source. This is how you would drive a process in a non spontaneous direction.

AKatukota

As reactants are consumed in a working electrochemical cell, the cell potential will also decrease until it reaches zero. The Nernst equation is used to establish the relationship between how cell potential depends on concentration

AKatukota

A galvanic cell is an electrochemical cell in which a spontaneous reaction is used to generate an electric current. So an example would be a battery

AKatukota

So if the temperature goes up, the reaction is releasing energy and is negative?

AKatukota

I am very confused on this question: (a) Calculate the heat that must be supplied to a copper kettle of mass 400.0 g containing 300.0 g of water to raise its tem- perature from 20.0 8C to the boiling point of water, 100.0 8C. (b) What percentage of the heat is used to raise the temperature of the wa...

AKatukota

So for the first one, why does the volume remain 1.20L?

AKatukota

Thank you!! This really helped because I was having trouble figuring out the internal energy.

AKatukota

What should we know about the activity of a reaction?

AKatukota

sorry there should be a division symbol between 1.09 x 10^-4 and .0073

AKatukota

On his website, under textbook errors 6D.5 is listed so you are good!
It says % protonation = (1.09 x 10^-4)(.0073) x 100% which should equal 1.5%.

AKatukota

Why is the concentration of H3O+ in the equation 0.15? I know the first equation completely ionized, but that carries over?

AKatukota

What would CH3NH3Cl dissociate to produce?

AKatukota

The K wasn't given in the problem directly, are we supposed to look at some kind of table?

AKatukota

Is it that it is 5% of less than 5% OF the initial concentration?

AKatukota

How do you determine how many significant figures to write when determining pH?

AKatukota

In this homework problem, how would you write the chemical equilibrium equation for 0.055M AlCl3? In the solutions manual, it is written very differently than I've seen? Thanks!

AKatukota

It will be more thermodynamically stable if it has a smaller K.

AKatukota

The reaction quotient , Q, is pretty much used and compared to K to determine the direction the reaction will proceed in. If Q<K, then products favored. If Q>K then the reactants favored.

AKatukota

SO basically when a stress is applied to a system, the system will counteract those changes by favoring either the reverse or forward reaction.

AKatukota

How would we do part b? Im confused on the different temperature. DO the same rules apply?

AKatukota

Would someone be able to help me with 6B.3? How are we supposed to incorporate the different volumes to get pH?

AKatukota

Yes if there is a higher concentration of reactants, then products will be favored according to Le Chatlier's Principle.

AKatukota

mmol is millimole so you would convert that into moles and then for concentration divided by liters.

AKatukota

Q refers to the direction that the reaction will proceed in. You use Q in comparison to K. For example, if Q<K, then the reaction favors reactant production. If Q>K then it favors products. If Q=K, then the reaction is at equilibrium.

AKatukota

You would put P in front when there are gases involved in the reaction.

AKatukota

For this homework problem, what are we supposed to do when the amounts are given in mmol to find the reaction quotient, Q?

AKatukota

For this question, what do we do when there is a solid or liquid in the reaction? What if there is (aq)? I remember him saying something becomes 1.

AKatukota

Merging of two atomic orbitals means that the orbitals overlap. So the greater the extent of the orbital overlap, the stronger the bond. A mixing of s, px, py, pz orbitals would create four hybridized orbitals = tetrahedral sp3.

AKatukota

How would you draw the hybridization orbitals for N2 to show the 2 pi bonds?

AKatukota

I had a question on this too. In the textbook solutions, it says that the answer for (ii) is 1.50M for [OH-], the pH = 13.824, and the pOH = 0.176?

AKatukota

For HClO vs HClO2, how would you reason that HClO2 is the stronger acid? In the textbook it said it was based on the greater number of O atoms in HClO2, but why?

Thank you!

AKatukota

How do you know that formic acid is stronger than acetic acid? What would be the reasoning?

AKatukota

For 6A.13, how would you know if the ion is an acid or base?

For example, for F- and H-, how do you know F- is a Lewis base and H- is a Lewis base?
And why would BF3 be a Lewis acid?

AKatukota

Ok got it thanks!

AKatukota

This really helped thanks! For EDTA do we just memorize that it is 6 as per the example in class? What would be the formula for it? Thanks.

AKatukota

A chelate is basically just a complex containing one or more ligands that forma ring of atoms including the central metal atom.

Chelate formation lies behind the body's strategy of producing fever when infected by bacteria for example.

AKatukota

Which of the following ligands can be polydentate? If the ligand can be polydentate, give the maximum number of places on the ligand that can bind simultaneously to a single metal center: (a) HN(CH2CH2NH2)2; (b) CO322; (c) H2O; (d) oxalate. For this question, how exactly do you know if a ligand is p...

AKatukota

So it is always the neutral atom first got it thank you! Also, for this same question why would there be a bis there?

AKatukota

When would you put an overall charge on the coordination compound?

AKatukota

Great!

AKatukota

It should be on everything after the midterm up to Friday's lecture. So studying all the lecture notes and homework problems would be beneficial.

AKatukota

Thanks this helped me as well!

AKatukota

Thank you this was helpful!

AKatukota

Thank you!

AKatukota

I think it's good to know!

AKatukota

Drawing the lewis structure is helpful, but it is not required.

AKatukota

It should be on all material covered after the midterm.

AKatukota

dipole moments are based on partial positive and negative ends of a molecule. You can determine through the electronegativity differences in the molecule. Since O is more electronegative than S, O has a partial negative charge and S has a partial positive charge. There is a dipole moment within the ...

AKatukota

It is helpful to remember the shape names as well as bond angles.

AKatukota

Ok, makes sense!

AKatukota

The formal charge equation we were taught is

FC = V - (L + S/2)
where
FC = formal charge
V = valence e-
L = Long pair e-
S = shared e-

AKatukota

This helped thank you!

AKatukota

Expanded valence shells means that the element can accommodate more than 8 valence electrons (i.e P, S, Cl)
This is because atoms in Period 3 or higher have d-orbitals in valence shell that accommodate additional electrons.

The octet guideline : 8e- --> s^2 p^6

AKatukota

Resonance is basically the blending of structures. It is multiple bonds that can be in different locations. Electrons involved in resonance structures are delocalized. For example, Benzene, C6H6, has 3 localized double bonds (2 possible structures).

AKatukota

Hi! Yes so the two exceptions are Cu and Cr. So in these cases the s level is actually higher than the d. So for Cu, the configuration would be [Ar] 4s^2 3d^9. However, it must be rewritten in numerical order: [Ar] 3d^9 4s^2. Now if we were to write the configuration of Cu^2+, the two electrons must...

AKatukota

Basically it is subscript x because since l=1, ml can = -1,0,1. Since they are specifying that ml=-1 that gives you the subscript x. If ml=0, the subscript would be y. If ml=1, the subscript would be z.

AKatukota

Anions gained an electron, therefore the radius is larger than that of the parent atom. If an atom loses an electron, it is a cation, and has a smaller radius. Hope this helps! :)

AKatukota

1D.19 How many orbitals are present in the (a) 4p-subshell; (b) 3d-subshell; (c) 1s-subshell; (d) 4f-subshell of an atom?

How would I go about doing this?

AKatukota

When n=6, why are the possible values for l = 0,1,2,3,4,5,6? I thought it would just be 0-5, since it's n-1? I am trying to answer all parts of this question: (a) How many values of the quantum number l are possible when n = 6? (b) How many values of ml are allowed for an electron in a 5f-subshell? ...

AKatukota

How do we know that for orbital 6p for example, that the principle and angular momentum quantum numbers are n=6 and l = 1? I know that for l, the quantum numbers can be 0,1,2,3,4,5 right, but for orbital 6p, how is it just l=1?

AKatukota

Thank you! This question really helped me as well.

AKatukota

It seems that we would probably be given these values or they would be found on some sort of reference table. But it also would not be a bad idea to know their general values.

AKatukota

Yeah I am unsure about when this equation would be used or calculations associated with it?

AKatukota

h represents Plank's constant. So when you graph E vs the frequency of light, the slope of that line is Planck's constant.

AKatukota

So when it asks for the De Broglie Wavelength, you would find the wavelength through h=mvl or l = h/mv

AKatukota

Work function is basically the energy required to remove an electron from the metal surface. If the energy of the photon is not greater than or equal to the energy to remove an electron (work function), then no electrons will be emitted.

AKatukota

Unless the E(Photon) is greater than or equal to the E(Energy to remove an electron), an electron will not be emitted even for HIGH INTENSITY light, which was quite unexpected in the photoelectric effect experiment. Light sources with long wavelength (low frequency) light does not eject electrons ev...

AKatukota

So when plotting the frequency of light vs Energy, the slope of that line produces the proportionality constant, or Planck's constant. Energy is proportional to hv.

AKatukota

For the Lyman series, the lower energy level is n=1. For the Balmer series it is n=2.

AKatukota

Frequency is proportional to the Energy. So, as the frequency (Hz) increases, so does the Energy (J).

AKatukota

So formula units just means atoms?

AKatukota

Usually it is better to convert back to meters.

AKatukota

Great, thank you! And then I would divide by the 0.5L correct? I got .0458M potassium ions and .009M sulfide ions.

AKatukota

All stoichiometric coefficients must be the lowest whole number, and multiplying by 2 would give the lowest whole number coefficients for that equation!

AKatukota

You would get Avogadro's number, which is 6.022x10^23 atoms / mol then multiply by 288 ppm (which is the diameter), and then convert back to meters by dividing by 10^12 pm.

AKatukota

I don't believe that there can be more than one limiting reactant. In a reaction, there is ONE limiting reaction and the others are in excess. Once the limiting reactant is used up, the reaction can no longer occur, because the amount of product being produced is limited.

AKatukota

How would I start this problem?

A solution is prepared by dissolving 0.500 g of KCl, 0.500 g of K2S, and 0.500 g of K3PO4 in 500. mL of water. What is the concentration in the final solution of (a) potassium ions; (b) sulfide ions?

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