CHEMISTRY COMMUNITY

Saachi_Kotia_4E

I have a different version of the test but I got the problem right. Could you post the full equation for the problem? What is the pH of a 0.020 M solution of sodium propionate? the pKa of c3h6o2 is 4.88 C3H5o2-(aq) + H20(l) --> C3H6O2(aq) + OH-(aq) I know how to do the problem I just want to make s...

Saachi_Kotia_4E

I know its a little late but can someone tell me what the answer for number 5 on test 1? I want to make sure I got it right. I had my test on Wednesday and the problem asked about a 0.02 M solution with a pKa of 4.88. Thanks!

Saachi_Kotia_4E

When we are arranging different atoms in order of increasing/decreasing strength as reducing agents, how do we know which cell potential to use? some elements have several cell potentials depending on how many electrons are added (for example, Fe+ to Fe has a different cell potential than Fe2+ or Fe...

Saachi_Kotia_4E

how do you do this? and does someone know the equivalent problem in the 6th edition?

Saachi_Kotia_4E

I have no idea how to do this lol. I dont know the equivalent problem in the fact 6th edition so if someone knows can you put it in the replies so other people can look at it? Thanks!

Saachi_Kotia_4E

Can someone explain why n=1? When I write out the half reactions, 2 electrons are being transferred from the 2 H+ atoms to the H2 molecule.

Saachi_Kotia_4E

when finding the rate constant from elementary reactions, do we ignore the slow reaction or the fast reaction and why?

Saachi_Kotia_4E

Is there a quick way to assume the sign of the Ecell? if I understand your question correctly, you can determine the sign of Ecell depending on whether or not the reaction is spontaneous. so if G for the reaction is negative, Ecell is positive and vice versa. and if the reaction favors the products...

Saachi_Kotia_4E

how do you find the time it takes for the second order reactions to take place in 7B.13? what formula do we need to use?

Saachi_Kotia_4E

what are the basic units for rates and rate constants? are they different for different orders?

Saachi_Kotia_4E

if the E cell for a half reaction in Appendix 2B has a positive value, but the half reaction used in the problem is the other way around, do we flip that value of Ecell?

Saachi_Kotia_4E

what are the periodic trends for standard potential? specifically, can someone explain 7th edition 6M.7?

Saachi_Kotia_4E

does the order of the molecules on the left or right side matter when writing the ruction using cell notation? for example, if the anode half reaction has Fe2+ going to Fe3+, should we write Fe2+, Fe3+ or Fe3+, Fe2+? I know Lavelle said something about that but I can't remember what it was. also, ho...

Saachi_Kotia_4E

can someone show me their work or explain how to do this problem? I'm confused on all three parts. it's 6L.7 from the 7th edition, and 15 from the 6th edition.

Saachi_Kotia_4E

how do you know when you need to add Pt in the cell diagram? I thought it was when everything on one side of the diagram was in the same phase, but there was one example in the textbook that had solid and aqueous iodine which still had platinum. so how do you know if it needs platinum?

Saachi_Kotia_4E

Aidan Ryan 1B wrote:What are things we have learned that are not state functions?

work and heat are the only things we've learned about that aren't state functions

Saachi_Kotia_4E

I dont think it matters, as long as it makes sense. For example, using joules would be better if you get something like 57 J, because that would be 0.057 kJ and it just looks neater with J. On the same note, if you get 57000 J, it might be better to convert that to 57 kJ

Saachi_Kotia_4E

this would depend on what you get for the entropy of reaction. PCl5 is less stable at higher temperatures because the resulting entropy is negative. HCN is more stable at higher temperature because the entropy is positive.

Saachi_Kotia_4E

I would assume that we would have to convert it to joules. since U is the internal energy, and energy is measured in joules, they would probably expect us to give the answer i joules. but the conversion from L*atm to joules is given on the formula sheet, so you don't have to memorize it, just rememb...

Saachi_Kotia_4E

What types of problems would we be using 3/2 R, 5/2 R, 3R, 7/2 R, and 4R? what exactly do those values indicate, and what part of a word problem would indicate that our calculations require us to use those values?

Saachi_Kotia_4E

for 4C.13, I tried calculating q(water)=-q(ice) using the mass of the ice and the specific heat of the ice, however, I wasn't getting the right answer. the solutions manual uses the molar heat of ice instead of the specific heat of ice. is there a reason why using the specific heat of ice would be w...

Saachi_Kotia_4E

the changes in pressure and volume have a minimal effect on solids and liquids because of how tightly packed the atoms are compared to gases. liquids and solids can not change volume if they are compressed, however atoms in gases are far enough apart that they are affected by compressions. the same ...

Saachi_Kotia_4E

what is the enthalpy of combustion, and how is it different from the enthalpy of formation? how does it affect the calculation of reaction enthalpy? for example, in exercise 4D.15?

Saachi_Kotia_4E

can someone explain why we use 5/2 R and 3/2 R in the calculation of entropy for problem 7? I dont quite understand what those values indicate.

Saachi_Kotia_4E

can someone explain how calorimeters and bomb calorimeters work? I dont really understand the explanation in the textbook. what do they do and what are we trying to calculate when doing problems?

Saachi_Kotia_4E

I think it depends on the surroundings of the reaction, for example certain containers allow it to be reversible, while others restrict it. I may be wrong, but this is what I understood from the homework problems. regardless, the homework seems to tell you whether or not its reversible, so I dont th...

Saachi_Kotia_4E

what is the value of the constant R? in one of the homework problems, we used R=0.08206 in the n=PV/RT formula, but then we used R=8.314 in the w=-nRTlnV1/V2 formula. why is the value of R different?

Saachi_Kotia_4E

does anyone understand how to do 5.35? thats the one with the graph

Saachi_Kotia_4E

when we calculate x for weak acid/base problems, we can disregard x in the denominator when Ka is less than 10^-3, because it doesn't add any significant change to the concentration of the reactants. does this same logic apply to the problems we solved for the chemical equilibrium section?

Saachi_Kotia_4E

what is the difference between the pH and the pKa? what does each one calculate? and the same with pOH and pKb?

Saachi_Kotia_4E

if Q is less than K, that means that there are currently more reactants than products, which means that products will continue to form until the solution reaches K, which is equilibrium. if Q is greater than K, it means that the concentrations of the products are higher than the equilibrium concentr...

Saachi_Kotia_4E

can someone explain how to do this problem?

Saachi_Kotia_4E

for this problem, in the solutions manual, it says "because the equilibrium constant is small, assume that x<<0.22"

what does this mean?

Saachi_Kotia_4E

I believe that the format of (P^x) is for partial pressures of gases, while the format of [C]^x is for concentrations of solute. I'm not sure if they can be interchanged however, can someone clarify that?

Saachi_Kotia_4E

what does it mean when the reaction is leaning to the left or the right? or when a reaction is shifted to the left/right? there were some questions about it in the first video module, but I dont really understand the concept.

Saachi_Kotia_4E

I am working through the homework for this section and I dont understand how to do 5G.5, especially part c. Can someone explain the logic behind solving this problem?

Saachi_Kotia_4E

can someone explain why salts of weak bases produce acidic solutions and salts of weak acids produce basic solutions?

Saachi_Kotia_4E

what do we need to know about acid rain and respiratory acidosis for the final?

Saachi_Kotia_4E

How do you determine how acidic an acid is? for example, if you had to put HClO3, HClO, HClO2, and HClO4 in order from least to most acidic, how would you go about doing that? how would you do it for bases?

Saachi_Kotia_4E

I was looking at an old final and saw a question about the C2+ bond and the C2- bond. What would the lewis structures of C2+ and C2- look like? and which has a stronger bond? How do you calculate bond order?

Saachi_Kotia_4E

From what I understand, this is correct. Lewis bases have lone pairs that they are able to donate to a bond, while the acids have room to accept that electron pair. I found this online: "A Lewis acid is a chemical species that contains an empty orbital which is capable of accepting an electron ...

Saachi_Kotia_4E

I think its less than both 90 and 120 but I might be wrong

Saachi_Kotia_4E

for 7th edition 2E.13b, which is N2O, how can we assume that N is the central atom, and not O?

Saachi_Kotia_4E

for molecules with an AX3E2 shape, why do the electron pairs take equatorial positions and not axial positions? since the lone pair-lone pair repulsion is the strongest, wouldn't it make sense that the two lone pairs would distance themselves as much as possible, and therefore take axial positions? ...

Saachi_Kotia_4E

hybridized orbitals have energy that is between unhybridized orbitals, it can be seen as a blend of different orbitals. such as the sp3 hybridized orbital, which is a blend of the s orbital and the 3 p orbitals, and has an energy that is between the s and p orbitals. this also results in a different...

Saachi_Kotia_4E

sigma bonds involve a single overlap, such as when two s orbitals overlap, or one s overlaps with a p orbital. pi bonds involve a double overlap, such as when two p orbitals overlap side by side, so that they are inflexible. this is why pi bonds are stronger

Saachi_Kotia_4E

either is fine although im not sure if one is preferred over the other

Saachi_Kotia_4E

Can someone explain how to do this problem? what does the lewis structure look like and how can we determine the bond angle based off of that?

Saachi_Kotia_4E

a general rule of them that I use for polarity is whether or not the molecule is symmetrical. for examples, something like CH4 would not be polar because it is symmetrical. also, polarity has to do with the electronegativity charges of the atoms in the bond. if a molecule consists of a very electron...

Saachi_Kotia_4E

how do you know what the bond angles between atoms are from just knowing the structure? for example for 7th edition 2E.7 part c, how do you know that there is a 109.5 degree angle?

Saachi_Kotia_4E

because the larger number of shared electrons draw the atoms in closer together

Saachi_Kotia_4E

yes since the most electronegative atom is the central atom, it is bonded to most of the other atoms on the compound. in order for it to be the most stable, the central atom should have a formal charge as close to 0 as possible

Saachi_Kotia_4E

electron affinity is the energy it takes for an atom to gain an electron. ionization energy is the energy needed for an atom to lose an electron. the trend for both is the same, it increases across a group and decreases down a period.

Saachi_Kotia_4E

The exceptions are the first few atoms because they usually lose electrons to fill just the 1s orbital. I think other exceptions are like the example from class with SO4, where sulfur had more than 8 electrons because they went into the 3d orbital of sulfur.

Saachi_Kotia_4E

When drawing Lewis structures, how do you know where the atoms are? Like what angles the atoms are? Sometimes they're all in a straight line, but other times they're at 90 degree angles.

Saachi_Kotia_4E

What does it mean when the bonds of the resonance structures are all the same length? How does that compare to a molecule with bonds that have different lengths? And how do we know which of the resonance structures exist in real life?

Saachi_Kotia_4E

On the study guide summary it says we need to knowhow to: Describe the interpretation of atomic orbitals in terms of probability.

What does this mean?

Saachi_Kotia_4E

Instead of using this: En = - h R / n^2
Can we use this: frequency = R(1/n1^2 - 1/n2^2)

What's the difference? Prof Lavelle uses the first one but the textbook uses the second.

Saachi_Kotia_4E

This is what it says on the list of things we need to know for the upcoming test: Understand the relationship between Schrodinger's equation (H ψ = E ψ), wave functions, and orbitals. I know we don't need to know any calculations, but what do we need to know about schrodingers equation? Can someone ...

Saachi_Kotia_4E

For 1D 13 part d, how do you know that there are 4 sub shells for a shell with n=6?

Saachi_Kotia_4E

How do you do 1D 23? Can someone explain the concepts behind it as well as explain the answers?

Saachi_Kotia_4E

How do you determine how many orbitals an atom has based on whether its s, p, d, or f? For example, problem 1D 19?

Saachi_Kotia_4E

So far, I have just been repeating problems from the textbook in order to see what areas I'm weak in. I personally didn't like the audio visual modules because the answers were multiple choice, which isn't what we're going to have on the test. I will also do more problems from the book that aren't a...

Saachi_Kotia_4E

Can someone explain what the photoelectric experiment and effect are in simpler terms? I had a hard time following the lecture.

Saachi_Kotia_4E

I am taking Test 1 this Thursday. What is the best study plan? Should I focus on Test 1 topics until the test, and start Ch 1 homework after the test, or should I start working on Ch 1 at the same time as reviewing for Test 1? What are you all doing?

Saachi_Kotia_4E

If you first find the mass %, you can then easily assume that there is 100g of sample in order to determine the empirical formula. Then, you can use the mass percentages to find the number of moles of Co and F. After that, divide both values by the smaller of the two values in order to determine the...

Saachi_Kotia_4E

The coefficient is showing the ratio of each molecule in a chemical equation. It's easier to understand if you think of it like the number of atoms or molecules in an equation, but if you are doing any calculations, it would be considered the number of moles. It technically is the number of moles fo...

Saachi_Kotia_4E

The way I understand it is: formula units can mean atoms or molecules, depending on what the question is asking for. For example, if you need to find the number of formula units in a a certain mass of H2O, you calculate the number of H2O molecules. But if it asks you to find the number of hydrogen a...

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