CHEMISTRY COMMUNITY

martha-1I

This should have been posted in the Alkynes section. Sorry about that.

martha-1I

When drawing the following structure, would we be marked down if we do not draw a straight line down after the triple bond as I did in the second drawing or would the second drawing be accepted as well?

martha-1I

The way I come up with the IUPAC name from common names is that I draw out the common name structure and then I use the drawing to name the structure using IUPAC. I have attached a picture with a detailed explanation of the process. Hope this helps.

martha-1I

They gave us potassium permanganate and iron (II) chloride, so I broke those apart into their own half reaction and double checked that my reactions were correct by checking appendix 2A to see if my reactions matched the ones for these molecules. The following are the unbalanced half redox reactions...

martha-1I

You compare the standard reduction potentials for each one. For example, the reaction to form Cu is Cu + + e - ----> Cu. According to Appendix 2A in the back of the book, the standard potential for the formation of Cu is E \circ Reduction = +0.34V. You follow the same pattern for the rest of the met...

martha-1I

Oh I understand now! Thank you!!

martha-1I

Just thought I'd post this as a reminder of highest to lowest priority when it comes to numbering.
1) Functional groups (ex. carboxylic acid, alcohol, amine, aldehyde, ketone)
2) Double or triple bonds
3) Substituents

martha-1I

the Di- in front of the -ene states that there are two double bonds in the structure. Their locations should be stated when naming the molecule.

martha-1I

In 1.31 it asks us to draw (E)-3,7-Diethylocta-1,3,7-triene. Can someone walk me through how to draw this structure. I drew something, but it does not match the answer in the back of the book. One main thing I am confused about is why there seems to be a 9 C-C chain as the the backbone of the struct...

martha-1I

This is the numbering for the longest carbon chain. It goes from left to right because we want to give the double bond the lowest possible number. There are two methyls so it's dimethyl and they are on the 3rd and 4th carbon, so it is (Z) 3,4-dimethyl-3-heptene. You are correct about it being cis/(Z),

martha-1I

I was just about to post that the way I previously described how to number the carbon chain is incorrect, so dismiss it because it does not always work. Thank you Chem_mod for clearing that up.

martha-1I

Oh yes! I was taking into account the carbon that was connecting it to the ring, which is not the right way to count the carbons on the substituent . Thank you for the clarification.

martha-1I

Since Neo only applies to alkyl substituents, would it be incorrect to name this substituent neopentane since the substituent has 5 carbons in it?

martha-1I

For the second part of 1B, it is comparing a covalent bond( C-C is covalent because it shares its electrons) and a phase change ( such as melting ice which is solid ->liquid). Breaking a covalent bond would require more heat because you would need to break the chemical bond. A phase change does requ...

martha-1I

It takes more heat to heat up one mole of butane gas than one mole of H2 gas because butane has more atoms (C4H10) and therefore requires more heat to be heated up.

martha-1I

I made a video explaining how to distinguish certain c=o structures. The file was too large so I had to upload it to YouTube. The link is below.
http://youtu.be/OfDqHCzB-uc

martha-1I

Attached is a picture explaining why the unfavorable interactions in this question are steric and torsional.

martha-1I

You can see that there is steric and torsional strain once you draw the lewis structure for molecules given. You will notice that the hydrogens in the H2C-CH2 are eclipsed and the carbon atoms are adjacent each other which gives it a torsional strain. When you move up on the molecule you will see th...

martha-1I

I attached a picture explaining why the structure is named the way it is.

martha-1I

When it comes to naming, are we required to know both the common names and IUPAC names for molecules and structures or can we chose our preference and just name using our preferred system of naming?

martha-1I

In this case, we start counting at the dimethyl site because we want the overall lowest count thus we get 2-isopropyl-1,1-dimethylcyclopentane. If we start counting at the isopropyl site, we get 1-isopropyl-2,2-dimethylcyclopentane which gives us an overall count of 5 instead of 4 (from the first ex...

martha-1I

Oh I understand. Thank you for the clarification!

martha-1I

We use it for first order reactions (ln[A] = -kt + ln[A]_initial)
Since it was stated at the beginning of the problem that all the following are first order, we use it in this case.

martha-1I

NO is a catalyst because it is consumed (in step 1) and then formed (in step 2). A nice way to think of what is happening is to envision what is happening when a catalyst is introduced into a reaction. Key word being introduce, which implies that the catalyst is not formed first but just appears. Ca...

martha-1I

Once we have converted [B] to [A], we can plug what we calculated into the equation and solve for k. The equation set up should look like this ln[0.085] =-k(115s) + ln[0.153] 0.085 - This was calculated by converting [B] to [A] and subtraction [A] initial 115s for t - we can use the time given for d...

martha-1I

23c gives us different information, so it does not require the same steps as what was described in the course reader. What makes 23c different is that we are given the amount of concentration that B rises to in 115s and given A initial . Since we start off with A we need to end with A, so we need to...

martha-1I

Rate constants (k) are always positive.
Rates can be negative or positive depending on whether it's for formation or decomposition. This is so the rates of formation and rates of decomposition could cancel out.

martha-1I

I remember the distinction like this. A catalyst is consumed and then formed. Since catalysts are put into a reaction to speed it up, it makes sense that they are consumed first (because they are used to speed up the reaction) and then formed again later. An intermediate is formed and then consumed....

martha-1I

Does the Stoichiometric Coefficient have an impact on how I should approach a first order reaction problem asking me to solve for k given that the concentration of A decreases to 1/4 its initial concentration in 61 minutes?
Reaction: 2A ---> B + C
this is from question 14.24

martha-1I

I got 107 as well for this question.

martha-1I

In 13.13 b, why is it that I 2 - (s) is not used as the anode? I wrote it as the Anode in the cell diagram because I thought that since it was a solid in the oxidization 1/2 reaction that it would be the anode, but the solutions manual has Pt (s) as the anode. It says that "an i...

martha-1I

8.206L.atm/mol.k will usually be used when using the equation PV=NRT because the units will cancel out nicely since pressure will be in atm, volume will be in L, n=mol, and T will be in kelvin.

martha-1I

I think the reason for why they used constant volume is because they compressed the engine which caused the pressure to change but the volume from that point on to stay the same. Since it is not stated that it decompressed or compressed more, we can assume the volume stayed the same after it had bee...

martha-1I

The left side of the salt bridge in the cell diagram should be the Anode that is being oxidized and the right side of the salt bridge should be the Cathode that is being reduced. I am not entirely sure about the order myself so I will leave that for someone else to answer.

martha-1I

We put inert metals in a cell diagram when there is no solid stated in the reaction given. This is so because in order for the Galvanic Cell to work properly you would need a solid metal to be either the anode or cathode.

martha-1I

I had this same question and it was answered in a forum I started The easiest way to find out n is to look how many electrons are transferred in your balanced HALF-reactions. For example, in the Copper/Zinc cell, n=2 In the Silver/Zinc cell, silver transfers 1 electron and zinc transfers 2. Since th...

martha-1I

for part b) we write the oxidation half-reaction (we established from part a that Te is being oxidized so we will write the half reaction for it) 1. Write down the half reaction Te --> H 6 TeO 6 2. balance all elements except for hydrogen and oxygen Te is already balanced 3. balance oxygen by adding...

martha-1I

For part a) you figure out the individual charges for i) Te as Te --> H 6 TeO and ii)Cl as ClO 3 - --> Cl 2 . For i) Te = 0 charge since there is no stated charge in the equation. H 6 TeO will have to be broken down in order to find the individual charge for Te. H 6 = 6(+1)=+6 Te= ? O 6 = 6(-2)=-12 ...

martha-1I

Yes you do add the H⁺ even when it is in a basic solution because the OH^- are added later, which will contribute to the formation of H₂O. In the steps I wrote above, you would stop after step 6 if it were in an acidic solution. However, since it is in a basic solution, you keep going.

martha-1I

I understand that the n in \Delta G =-nFE \circ is the moles of the reaction, but I don't understand how it is distinguished. For example in 13.9, we are asked to calculate the Gibbs Free Energy for 2Ce 4+ (aq) +3I - (aq) ----->2Ce 3+ (aq) +I 3 - (aq) with an E cell \...

martha-1I

In order to balance this and any other half-reactions in a basic solution follow these steps: 1. Write down the half reactions 2. balance all elements except for hydrogen and oxygen 3. balance oxygen by adding H 2 O 4. Balance hydrogen by adding H + 5. Balance charges by adding e - 6. Multiply in or...

martha-1I

When we are given an equation and asked to calculate change in entropy, we do so by adding up all the entropies on the product side and subtracting them from the sum of the entropies from the reactant side.
The equation is $\Delta S$ = $\sum \Delta$ S_products - $\sum \Delta$ S_reactants

martha-1I

Yes. You got it!

martha-1I

I would think answers in Joules or in KJ would be accepted since they are basically the same answer either divided by 1000 or multiplied by 1000. For example, 5kJ = 5000J, so whether you choose to express that in kJ or J either way should be correct.

martha-1I

Specific heat capacity is used for water as a liquid and not a solid because the ice cube (water in solid form) is melting so therefore we would need to compute the heat from fusion and heat once it is a liquid. First, we compute heat as the ice cube melts by using q=n \Delta H fus and once it is me...

martha-1I

Yes. Thank you for making that clear, Justin. What I described is specifically for monoatomic gases.

martha-1I

You do not need to calculate the work with respect to pressure because the equation w=-nRTln(v 2 /v 1 ) is derived from w=-P \Delta V. In the derivation we substituted nRT/v for P because P is related to PV=nRT. We then integrated and ended up with the equation w=-nRTln(v 2 /v 1 ). This derivation l...

martha-1I

q=-q is mostly used for thermal equilibrium problems. An example would be if you were to put a certain amount of warm water into a certain amount of cold water. In this case, you would use the equation to solve for the final temperature since the masses and the initial temperatures of the samples of...

martha-1I

The pressure and volume constants for heat capacity are only used when the gas in context is an ideal gas or a noble gas. If it is stated that the ideal gas is at constant volume then we use 3/2R and if it is stated that the ideal gas is at constant pressure then we use 5/2R.

martha-1I

no change in internal energy since no temperature or heat can be added or removed to the system since it is isolated. So the heat it has at the beginning is the same it will have at the end.

martha-1I

I would say it would be 2 sig figs, but usually the temperature ratio isn't the answer so you wouldn't need to consider sig figs for it. Just plug in as much of the ratio as you can to get you an accurate answer.

martha-1I

I believe we can apply the same methods to calculate \bigtriangleup S as we do to find \bigtriangleup H as long as we use the \bigtriangleup S values instead of \bigtriangleup H. For example, when using the first method to find entropy for a balanced equation, we would need to find/obtain the \bigtr...

martha-1I

In Quiz 1 preparation (winter 2013) number 2 asks us to calculate \bigtriangleup H of the reaction Al(s) + NH 4 ClO 4 (s) ---> Al 2 O 3 (s) + AlCl 3 (s) + NO(g) + 6H 2 O(g). I was going to use the enthalpy of formation method to calculate \bigtriangleup H, but I could not find the \bigtriangleup H f...

martha-1I

oh yes I did. Sorry about that. I will go back and edit it. Thank you!

martha-1I

I think it is because the element in the diatomic molecules need to be broken apart first by a high temperature in order to react spontaneously with other elements. For example, N 2 would need to be broken apart as separate N elements in order for a spontaneous reaction to occur with another element...

martha-1I

I would assume a process is reversible if it was stated to be isothermal since I have noticed from doing the homework problems that they can be interchangeable.

martha-1I

if you're referring to when we want to find work, then you are using the wrong equation for the reversible process. You are thinking of the equation for the irreversible process which is w=-P ex \bigtriangleup V. For reversible processes, we use w=-nRTln(v 2 /v 1 ) since we are assuming that all hea...

martha-1I

8.314 JK^-1mol^-1 because we want the final answer to be in units of Joules since the units of work is Joules or KJ. In general, we use 0.08206 L.atm.K^-1mol^-1 when using PV=nRT because the units will cancel out and leave us with whatever it is that we are looking for.

martha-1I

I think of it in terms of whether the system lost or gained energy. In a, the system is melting from a solid to a liquid. This mean that it is gaining energy as heat (therefore q is positive).To visualize it you can imagine the particles going from being very rigid in a tight space (solid) to flowin...

martha-1I

When asked to solve for the final temperature of "A 50g ice cube at 0 \circ C [when] added to a glass containing 400g of water at 45 \circ C" (7.39), I plugged in mC \bigtriangleup T=-mC \bigtriangleup T to find T f . I ended up with the answer 42.4 \circ C, but the back of the book has th...

martha-1I

http://youtu.be/Aw_0kz6Pb2E"onclick="window.open(this.href);return false; This video reviews how to draw Lewis Structures, resonances, and exceptions to the octet rule. Lecture and Narration - Martha Romero (Me) Directed and Filmed - Lauro Pilar (Chem 14A Student) Edited - Cresencio Tano (UCLA Commu...

martha-1I

Why is it that CH 3 COOH(aq) + NH 3 (aq) ---> CH 3 CONH 2 (aq) + H 2 O(l) is not classified as a reaction between bronsted acids and bases, but NH 4 I(am) + KNH 2 (am) ---> KI(am) + 2NH 3 (l) is? Does it have to do with the fact that the second one has liquid ammonia as its solvent? This is from hw ...

martha-1I

Thank you for the explanation!

martha-1I

Is saying that HCl dissociated, the same as saying that it deprotonated? The course reader uses dissociated and the book uses deprotonated. Do these both mean that the acid or base are fully broken apart as products?

martha-1I

How would I calculate the value of K when given that the initial pressure of X₂ was 0.10 bar? I was thinking of using ICE but I'm not quite sure how or if that is the right way to approach this problem. This is the question for part C of 10.5.

martha-1I

I'm sorry. I did not see your post until now, but I will introduce myself at the beginning of next Monday's lecture.

martha-1I

Since K 3 [CoF 6 ] does not indicate a charge, we know that the metal must cancel out any of the charges that the other elements have in order to give us a total charge of zero. In this example the total charge, excluding the metal Co, is +3 (for K) -6 (for F). These add up to a -3 charge. Since the...

martha-1I

I have attached a video showing how to draw the compound.
Hope it helps!

martha-1I

Ill post a video shortly

martha-1I

Yes the demo did help me visualize it, but I was still a bit confused after it. Thanks for the clarification here!

martha-1I

Why is it that K does not change when there is a change in pressure or volume, but does change when there is a change in temperature? I know that when the concentration of reactants and products does not change the reaction has reached equilibrium and that K is the relationship between the concentra...

martha-1I

I need some clarification on what a Dipole Moment is. I understand that it is the measure of a charge difference, but how exactly does this connect to covalent bonds and how do we calculate or find it?

martha-1I

I am not familiar with a way to figure out what type of bond Oxygen will have before starting the Lewis Structure. When drawing the Lewis Structure I recommend to 1) first count the valence electrons of the molecule, 2) then determine what is the central atom for that molecule by determining which a...

martha-1I

Oxygen tends to like to have double bonds because when drawing the lewis structure we want to form the most stable structure. This means that although it is not wrong for it to have a single bond, in some cases, a single bonds gives the overall structure a positive or negative charge and we want the...

martha-1I

Thank you so much for the clearly writen response!

martha-1I

I understand that once we know n, the orbital number of an electron, we can find L by subtracting one to n and the next quantum number can be found with the parameters of L to -L, but how do we find the next quantum number m(little s) and what does that quantum number tell us about the electron?

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