CHEMISTRY COMMUNITY

Leyla Anwar 3B

Additionally, in order to balance a redox reaction in a basic solution, you add H2O molecules to whatever side of the equation is lacking Oxygen molecules, and then add double that amount of H2Os to the opposite side of the reaction, and then finally, add that same doubled amount of OH- molecules to...

Leyla Anwar 3B

You were a wonderful teacher with great ability to keep lectures lighthearted and fun. I really admired how much you cared for us as students although we could not really meet face to face. You are a passionate teacher with a lot of [censored] and while this class required dedication, you made it al...

Leyla Anwar 3B

For this problem, how do you calculate the n? The solutions says that it is 1 but I'm unsure of how that was derived.

Leyla Anwar 3B

The strongest reducing metal will be the one that is most likely to be oxidized, as it must cause the reduction of another molecule. Based on this, the metal with the most negative reduction potential will be the strongest reducing metal since it itself is the least likely to be reduced. Hope this ...

Leyla Anwar 3B

You can think about it like: 0.015 mol of Sn(NO3)2 has 0.015 mol Sn2+ and 0.03 mol NO3 Where did you get the 0.03 from? Additionally, the Ecell* for this problem is 0.14V but I don't know where that came from. It was just in the solutions. Is that specific for the equation or did we have to solve f...

Leyla Anwar 3B

In reviewing this problem, I had the same trouble because the solutions manual jumped around! I broke it up like so: 1) subtract 0.27 V from 0.33 V 2) divide 0.06 from the previous step by -0.0129 V 3) take the inverse of ln, meaning calculate e^ 4) take the -log of your answer in step 3 You should...

Leyla Anwar 3B

Hi! On sapling week 9/10 #8, #9, and #10 used special equations to solve for time for zero, first, and second order reactions. The equations were as follows: Zero order: [A]t = -kt + [A]0 First order: ln([A]t/[A]0) = -kt Second order: 1/[A]t = 1[A]0 - kt I was just wondering what these equations are...

Leyla Anwar 3B

Guys! Thank you so much! These responses were so clear and helpful!
Just to check, the k in the equation does not do anything for solving this problem because the rate given includes that already?

Leyla Anwar 3B

Can someone please help me with this problem. I don't even no where to start : ( The reaction... A+B⟶C+D rate=k[A][B]2 ...has an initial rate of 0.0480 M/s. What will the initial rate be if [A] is halved and [B] is tripled? and What will the initial rate be if [A] is tripled and [B] is halved? Thank...

Leyla Anwar 3B

The easiest way for me to remember the units is to think about the graphs Dr. Lavelle would draw in class. For first order you plot ln[A] vs. time so the units will be 1/s. For second order you plot 1/[A] vs. time so the units are 1/M*s. For 0 order you plot [A] vs. time so the units are M/s. For th...

Leyla Anwar 3B

I am confused as to when the negatives are included in the equation:
rate = −1/a(d[A]/dt) = 1/b(d[B]/dt) = 1/c(d[C]/dt)
Sometimes there is a negative in front of the [B] component and sometimes not, I just don't know when its necessary. Thanks!

Leyla Anwar 3B

I keep trying this problem and I thought that this was balanced:
4Fe+3O2+3H2O⟶2Fe2O3∙3H2O
but it is incorrect and I am unsure what I am doing wrong, could someone please help explain?

Leyla Anwar 3B

I am also trying to do this problem right now, I think that the H2O has to be on the product side to balance with the Hs already on the reactant side, I think you add 2H20 and 2OH- to the product side to balance this.

Leyla Anwar 3B

I am also stuck on this problem, the hint says to balance the half reactions but I am confused how to do that with compounds, how do you know what goes into each half reaction?

Leyla Anwar 3B

Why did you add 2H2O to the product side instead of one? Sorry, I don't understand, is it because you don't want to cancel out one of the H2Os in the end?

Leyla Anwar 3B

Hi! I solved this problem but I don't understand the concept of "Monoatomic ions have oxidation states equal to their ionic charges." For this problem, KClO4 -> KCl + 2O2, why is K in the reactants in its monoatomic form and why is Cl in its monoatomic form in the products? I suppose I jus...

Leyla Anwar 3B

The R's are actually the same just calculated with differnt units, typically you use R=0.0821 for PV=nRT but if you want J then you would use R=8.314. It's all about units.

Leyla Anwar 3B

If K is in the units it is Kelvin and if K is a variable you are solving for, such as within the deltaG equation, then it is the equilibrium constant!

Leyla Anwar 3B

Does combustion require any type of circumstance then, such as constant P or V. It would seem that it doesn't but I am unsure.

Leyla Anwar 3B

Understanding this problem is understanding the deltaG naught equation where deltaG = deltaH - TdeltaS. If you use the tables of information they give you, you can see if each compound has a positive or negative deltaG and also be able to see the deltaH and deltaS for each, from here I think you can...

Leyla Anwar 3B

The oxidation numbers are specific to the atom/molecule you are working with, not with the entire reaction. However, you do have to keep in mind that the charges in a chemical equation must also be balanced (although this is unrelated to the oxidation number in terms of the reaction). Does this mea...

Leyla Anwar 3B

You have done this problem correctly! I think it is important to just remember that when you have endothermic reactions you will have a positive delH and for exothermic reactions you will have a negative delH. As for delS, when moving up the phase changes, in order from solid --> gas, the more movem...

Leyla Anwar 3B

In this case, water vapor is going from moving as a gas to settling on a solid, therefore losing mobility. This process is happening spontaneously which means that deltaG is negative. Because it is going from gas to solid it is an exothermic reaction, which tells you your deltaH. Again, because it i...

Leyla Anwar 3B

For this problem you have to solve for K. In order to do that you need to use one of the two deltaG equations. there is: deltaG= detlaH - T(deltaS) and there is: deltaG = -RTlnK so for this problem, use the bottom equation to solve for K, the problem provides you with all of the missing variables ex...

Leyla Anwar 3B

During a phase change the delta G will be 0 (because there is equilibrium between the phases)! Make sure your units are in order and then solve for T.

Leyla Anwar 3B

The deltaS equation for change in temperature is nCpln(T2/T1) but you are not directly given any moles. We did a problem like this in my discussion and we divided the n to the deltaS side and included (mol^-1) in the units. However, this problem includes the mol^-1 in the C values given to us. Could...

Leyla Anwar 3B

Could someone please explain what reversible and irreversible are and when each are relevant to a problem? I think they have different equations but I don't know which belongs to which or when to use them. Thank you in advance!

Leyla Anwar 3B

Is the equation to calculate between them Cp=Cv+R? I'm specifying this because someone mentioned this above but I don't fully understand.

Leyla Anwar 3B

I can't seem to get this question right. The feedback for my incorrect answer says: Calculate the number of moles of N2 produced from the mass of NaN3 using the stoichiometry in the balanced chemical reaction. Calculate the volume of N2 using the ideal gas equation and the number of moles, pressure,...

Leyla Anwar 3B

I figured out how to solve this problem. The easiest way to look at this problem is from the point of view of the units. After figuring out the problem that way I was able to see how to do it. For the first question, q must only be in kJ so that means you need to divide it by the moles of sample A. ...

Leyla Anwar 3B

I agree with the other response. In this sapling question we could also tell that we're expected to use q=c∆T by looking at the units. For the heat capacity (calorimeter constant) of the calorimeter, the unit is kJ/°C. This means that we do not consider its mass (which also makes sense since mass o...

Leyla Anwar 3B

Closed systems have a fixed amount of matter and allow the transfer of energy as heat. Volume can actually be changed in such a system but it would most likely be as a result of a change by the experimenter such as moving a piston up or down to change volume and pressure. So, does the transfer of e...

Leyla Anwar 3B

5I.23) A reaction mixture consisting of 2.00 mol CO and 3.00 mol H2 is placed in a reaction vessel of volume 10.0 L and heated to 1200. K. At equilibrium, 0.478 mol CH4 was present in the system. Determine the value of Kc for the reaction CO(g) + 3H2(g)⇌CH4(g)+H2O(g) at 1200. K. 5I.33) A sample of a...

Leyla Anwar 3B

I initially tried this problem using the correct Cs for ice, not water, when solving for qice and it was not the correct method. Can someone please explain why you use Cs=4.184 for both qice and qwater? I would think you need to use the specific one for each of them but to get the correct answer you...

Leyla Anwar 3B

Hey! So this problem needs to follow this equation: Hfus + q(ice) = -q(water), which is really this: heat required to melt ice + heat required to bring the 50.6 g of melted ice to the final temperature = heat released that cools 421g of water to the final temp To find Hfus you have to convert the gr...

Leyla Anwar 3B

There is no reason to use the deltaH = nCpdeltaT equation for this problem since the reaction enthalpy is given and you are simply asked for how much heat is absorbed (or in part c, given the amount of heat absorbed and asked to find the amount of CO2 produced). To calculate part a, simply multiply...

Leyla Anwar 3B

The ones I can remember he saying in class were graphite, O2, and H2. Were there any others he explicitly mention? He also mentioned C and I think N2. Hopefully he will supply all bond enthalpies with any question requiring it and if it is not on the list then you can most likely assume it is 0 and...

Leyla Anwar 3B

Does polyprotic mean that it can donate more than one proton? And therefore make monoprotic mean there can only be a subtraction of one proton? (or addition of many/one electron)

Leyla Anwar 3B

What is an inert gas and could someone please give an example?

Leyla Anwar 3B

Basically all you have to do is compare the pKa and the pH. If you are dealing with an acid: pH > pKa then it is charged because there is more A- (which is charged) pH < pKa then it is neutral because there is more HA (which has no charge) If you are dealing with a base: pH > pKa then it is neutral ...

Leyla Anwar 3B

Hey! I was able to solve this problem: "The Kb for an amine is 9.254×10−5. What percentage of the amine is protonated if the pH of a solution of the amine is 9.204 ? Assume that all OH− came from the reaction of B with H2O" but had one question. The feedback of the problem said "To de...

Leyla Anwar 3B

Here is a list of the strong bases:
LiOH - lithium hydroxide
NaOH - sodium hydroxide
KOH - potassium hydroxide
RbOH - rubidium hydroxide
CsOH - cesium hydroxide
*Ca(OH)2 - calcium hydroxide
*Sr(OH)2 - strontium hydroxide
*Ba(OH)2 - barium hydroxide

Leyla Anwar 3B

Yes, Q is any time. You would measure Q at that moment to determine the direction of the reaction. If Q<K, the reaction is going right; more products are made If Q>K, the reaction is going left; more reactants are made Does this mean there can be multiple Q values for different times during the rea...

Leyla Anwar 3B

This problem can be solved in the way we solve simultaneous linear equations in algebra. So in this particular question, you will have to add the first reaction equation and the REVERSE of the third reaction equation. Also you might have multiply one of the equations by a constant and don't forget ...

Leyla Anwar 3B

I have tried this problem and I believe I am setting up my ICE table correctly. When you are setting up the Kp equation, are Ppcl5, Ppcl3 and Pcl2 the same thing as the equilibrium values for PCl5, PCl3, and Cl2? I guess I'm wondering if their partial pressures are the same as their equilibrium val...

Leyla Anwar 3B

I have tried this problem and I believe I am setting up my ICE table correctly. When you are setting up the Kp equation, are Ppcl5, Ppcl3 and Pcl2 the same thing as the equilibrium values for PCl5, PCl3, and Cl2? I guess I'm wondering if their partial pressures are the same as their equilibrium valu...

Leyla Anwar 3B

Something to remember here is that, yes while temperature causes a change in K, if the pressure is changed by a change in volume, then K would change as well (because concentration is changing). That is not the case for C but just to remind you. And for D, like others have stated, because of Le Chat...

Leyla Anwar 3B

They are essentially the same, you use the same equation to solve for both so with that they are interchangeable. Like they have said above, you can use the ideal gas law for that conversion. The equation is PV=nRT and since you would be changing from concentration to pressure or vice versa, you can...

Leyla Anwar 3B

For this question how do you solve for P? I don't really understand what P is when you are using the K equation?

Leyla Anwar 3B

When using an ICE chart do you always do "-x" for the products and "+x" for the reactants? That was a pattern I noticed but I don't know for sure.

Leyla Anwar 3B

I'm struggling to get the right answer for this question. I know you have to use Hess's Law, but I think I'm uncertain on how to manipulate the separate K values for the different equations when you have to, say, flip the reaction or multiply it by 3. Can someone please explain. What is Hess's Law?...

Leyla Anwar 3B

What does it mean when a hybridization is something like 2sp3? Someone told me it meant a higher n state but I don't know to figure that out when looking at the lewis structure of a compound. If anyone understands that and could explain, I would be grateful : )

Leyla Anwar 3B

For strong acids and bases is the only way to know by memorizing them? How do we figure it out without memorization?

Leyla Anwar 3B

Is this still true? Do we need to know how to calculate with acid rain formulas for the final?

Leyla Anwar 3B

To be clear, we don't really have to know tritration for the final do we? Is what we have to know basically the stoichiometric point where moles acids added = moles of base sample?

Leyla Anwar 3B

This is what the square looked like and helps if only given one value you're trying to find the other.

Leyla Anwar 3B

The oxidation state is the number of electrons gained or lost by the atom in question (usually, the question will ask about the central atom). For example, the oxidation state of Al in [AlF4]- is +3. Basically, in order to find the oxidation number, just find the charge of the other atom (multiplie...

Leyla Anwar 3B

How would you identify a monodentate and a bidentate? If you are shown a picture you would be able to see if an atom or molecule is bonded to the central TM atom one time or if it bonds multiple times. Bidentate would mean two bonds and it would look almost like a flower petal, attachments at two s...

Leyla Anwar 3B

I think it is important to remember that the final is closed book so we wont be able to use the table provided on Dr. Lavelle's website which means that you will have to memorize the names. It would be best to get a lot of naming practice beforehand :) .

Leyla Anwar 3B

Hi! I agree with the above post. I also think it's important to keep in mind the denticity of the ligands in the coordination complex. For example, if one of the ligands is bidentate, then it could form 2 coordinate covalent bonds with the central atom (it would count as 2 instead of 1 towards the ...

Leyla Anwar 3B

Can someone explain more in detail of what bidentate means in a coordination compound and how it is different from a monodentate? Bidentate ligands are able to attach/bond to the transition metal twice. (Tridentate= three times, polydentate= multiple bonds) Sorry, forgot to add this. This means tha...

Leyla Anwar 3B

Are ligands specific to transition metals/metals or can they be applied to all elements?

Leyla Anwar 3B

Does that mean that the bond order is the number of electrons between two bonded atoms?

Leyla Anwar 3B

This would be true with any bond that is more than just a single bond because a double bond and triple bond mean that a pi bond is present. You can't have a pi bond with single bonds (because those are sigma). Any structure with resonance, means there is at least one bond greater than a single bond ...

Leyla Anwar 3B

Given that Lavelle has said we don't need to really know but to have the general understanding, especially with basic angles that we see a lot, like 109.5, how did you all solve #17 on sapling (asking for the bond angles of the C3H4 diagrams)? I don't really understand how to do it.

Leyla Anwar 3B

For me, the only stuff I memorize is the names of the different shapes and how all angles in a tetrahedral shape are 109.5. For the rest of the shapes, I just go back to freshman geometry days and solve for the angles by dividing 360 by the number of bonds in each plane (x, y, z). How do you know h...

Leyla Anwar 3B

How would lone pairs affect the ability for dipole moments to cancel out? Would it at all? I know it changes the shape by repelling other bonds and pushing them down so would that make their symmetry off?

Leyla Anwar 3B

An ion by definition will have lost or gained electrons, so this can result in a change of the number of electron densities, therefore ions tend to be angular shaped. For OClO there are 3 regions of electron so the electron domain geometry will be trigonal planar, but since only 2 of the 3 position...

Leyla Anwar 3B

Although both O and F have higher electronegativities than C, the net vector would be between the F atoms because difference in electronegativity of C and F is greater than that of C and O. The easiest way to look at this problem in my opinion is through the net vector. It shows what would cancel a...

Leyla Anwar 3B

Like everyone else has stated, not all molecules with a double bond are bent. CO2 is a good example of this. When there are no lone pairs on the C then the O's want to be as far away from each other as possible because of their electronegativity (I think). CO2 is a linear molecule with two double bo...

Leyla Anwar 3B

When trying to memorize the VSEPR models, do we also need to memorize the angles since we cannot calculate them?

Leyla Anwar 3B

How would you arrange OH in order to make it a total charge 0 and a radical? I figure you just take away one electron from O (7 valence e- instead of 8)? Can you just do that?
If anyone could please explain for CH3 as well I would appreciate it so much.

Leyla Anwar 3B

To determine the difference in electronegativity, you can use a periodic table that displays electronegativity values. For a C-H bond, the difference would be: 2.55 - 2.20 = .35 (electronegativity of C minus electronegativity of H). In this case, the difference is too small for the compound to be r...

Leyla Anwar 3B

I have found the answer to be A, B, and E. I understand I2 but I don't understand C2H6 or BF3. How do C and H not have a difference in electronegativity and why would BF3 and NF3 have similar forces applied to them? They both have different electronegativity between the atoms in their molecules and ...

Leyla Anwar 3B

I have a similar question from sapling:
Which molecules exhibit only London (dispersion) forces?

a. C2H6

b. BF3

c. NF3

d. CH3Cl

e. I2

I have tried almost every combination. I thought it was just I2 (E) but it tells me I'm wrong. I really don't know the answer. Could someone please explain?

Leyla Anwar 3B

One of the sapling question asks us to list the order from strongest to weakest LDF bond. The molecules were I2, Br2, and Cl2 and placed in that order. The reasoning was that the larger and heavier the atom, the stronger the bond length. I thought it would be the opposite because the larger the atom...

Leyla Anwar 3B

If you can't get the total charge to 0 (FC=0 for all atoms) then would you want any specific atom to be the one that can get FC=0 (if possible at all)? Like, would it be the atom in the center of the lewis structure? Or the atom with the highest or lowest electronegativity?

Leyla Anwar 3B

For this problem I was confused as well. Just knowing that the O oxidation number was 2- helped because the total oxidation number should equal total charge. Count up the total oxidation number for all the Os and then subtract to what you need to reach the total charge of the molecule and that will ...

Leyla Anwar 3B

One of the Sapling questions asked us to draw the lewis structures for nitrite and nitrate but did not give us the compounds' formulas. Are we supposed to have the polyatomic ions memorized for this class? I didn't realize it was one of those for awhile and thought I was missing something. I guess i...

Leyla Anwar 3B

Does the atomic radius being smallest at the top right have anything to do with the more complete octet those elements have? Because as you move down the radius increases but it has extra valence electrons that need to be balanced. I guess I'm just wondering if the octet has anything to do with it.

Leyla Anwar 3B

Does this mean that, for example (not real)
..
H-N-H (pretend the dots are on top and below N, not the first H)
..

the equation for FC of N would be: 5 - (2/2 - 4) instead of 5 - (4/2 - 4)?
I thought that you count each line (-) as two? But you all are saying you count it as one?

Leyla Anwar 3B

In short, having the l=1 is in there places a limitation on the whole thing. So it no longer the entire n=5 shell, its the l=1 sub-shell number of electrons which is less than the entire n=1 shell.

Leyla Anwar 3B

So 5 d means there are 5 different orbitals in the d-block? Then this means there are 1 for s, 2 for p, 5 for d, and 7 for f? I have been confused on this myself. And the orbitals are the shapes that they (are 'they' electrons?) can take?

Leyla Anwar 3B

What is the difference between a shell and a sub-shell? And which is the orbital within?

Leyla Anwar 3B

I actually think I understand more clearly now. The n=3 shell can hold up to 18 electrons because: 1s = 2 electrons 2s = 2 electrons, 2p = 6 electrons 3s= 2 electrons, 3p = 6 electrons, 3d = 10 electrons since n=3 is the row of the 3s^ the amount of electrons is 18: 2+6+10 = 18 As for n=6, l=3, the ...

Leyla Anwar 3B

For a similar problem, "How many electrons in an atom could have these sets of quantum numbers?" n=3 n=4,l=3 n=6,l=3,ml=−1 I am unable to figure out how to solve this. I calculated 14 for n=4, l=3 because I counted 2 electrons per orbital up to the f-block in the 4th shell and I said 2 for...

Leyla Anwar 3B

Will ion equations be covered in Midterm 1? I realize it is part of the fundamentals so does that mean we should know how to solve these types of problems?

Leyla Anwar 3B

For this problem why would the Na be multiplied by 2. Also, do the charges of the elements affect how this problem is solved?

Leyla Anwar 3B

Why do we need to convert from g to moles here? Does the molarity equation need to have the compound in moles instead of grams? I just don't know the reasoning for needing moles. Thanks.

Leyla Anwar 3B

This answer would be 3 sig figs because in the question, the smallest number of sig figs given was 3 (144 pm and 1.00 mol both have 3 sig figs). When you do calculations with multiplication or division, to determine how may sig figs your answer has, you use the same number of sig figs as the number ...

Leyla Anwar 3B

Hi, where does the 32.05 come from? Is that how to make any metal a sulfide? Or is that specific to Ca?

Leyla Anwar 3B

A question on sapling says: "The average speed of a diatomic chlorine molecule at 25 degrees C is 323.9 m/s^-1. What is the wavelength of a chlorine molecule at this temperature? Assume that the molecule acts as a single particle." In order to solve this problem it was necessary to note th...

Leyla Anwar 3B

Personally, I always write down all the equations I know. For example, on the top of my page I would write "E=hv", "c=v(lamba)" and the same for the rest. You should also do this with constants (ex: h= 6.626 x 10^-34). Then, after reading the question, write down your known value...

Leyla Anwar 3B

In E=hv,
h = planck's constant --> 6.626 x 10^-34 ; since this is a constant it will always be this value
v = frequency (Hz)

Leyla Anwar 3B

The difference between m and nm is usually that when solving for wavelength your result would be an answer similar to (for example), (7.14 x 10^-7)m. I have noticed that it is usually 10^-7m and since nm = 10^-9, the only thing you have to do to convert is move the decimal over two more spaces to th...

Leyla Anwar 3B

Something important to keep in mind to help you remember is that increasing the intensity only increases the number of photons, not the incident energy. The electron won't be emitted without enough energy to overcome the threshold energy and to combat this issue, the frequency must be increased. The...

Leyla Anwar 3B

For this same question, how do you find how many photons of infrared radiation the lamp generates in 1.0 s? You take the total energy (11J) and divide it by the energy per photon? I'm not really sure. If someone could explain I would appreciate it. Additionally, I am not sure how to configure the &q...

Leyla Anwar 3B

So within a specific example that could be the case? I think I understand. Thank you for helping!

Leyla Anwar 3B

When asked to solve the kinetic energy of an ejected electron in a photoelectric effect centered question, if the mass of the electron is not stated do we assume it is a constant (9.11 x 10^-31 kg)? I worked on a problem where I needed to solve for the Ek but I did not know the mass of the electron....

Leyla Anwar 3B

If long wavelength light is not ejecting electrons from a metal surface, how come increasing the intensity would not help eject electrons? Why would the wavelength being "long" prevent the light from acting like a "wave"?

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