Thursday
July 24, 2014

Posts by DrBob222


Total # Posts: 43,169

Chemistry
pEtBr = XEtBr*PoEtBr 319.7 = X*400 XEtBr = about 0.8 (estimated) see last post. Xunk = 1-about 0.8 = about 0.2 mols unk = 23.71/molar mass or 23.71/Y. mols EtBr = 30.64/109 = about 0.281 Then Xunk = mols unk/total mols. 0.2 = [(23.71g/Y)/(23.71Y)+(0.281)] and solve for Y = mol...

Chemistry
0.218M means 0.218 mols CH3COOH/L solution. g CH3COOH = 0.218 x molar mass = approx 13g but you should redo this and all of the other calculations that follow. I've estimated everything. From density, mass = volume x density = 1000 mL x 1 g/mL = 1000 grams. So 1000g = mass...

CHEMISTRY
delta H is - according to the rxn as written. delta S is - according to the rxn as written If dG is +, then TdS is more + than dH. I guess that means dS is more negative than dH but it's the TdS TERM that counts.

CHEMISTRY
When you ask which direction the rxn will shift I think you must say "if T is added" or "if P is increased" or some other variable is changed. Perhaps you are asking which direction is spontaneous?

CHEMISTRY
See the above about my trouble with the word shift. 1. products higher S than reactants. dS = + 2. reactants higher S than products. dS = - 3. products higher S than reactants. dS = + 4. reactants higher S than products. dS = -

CHEMISTRY
All of this looks good to me except for the last part. Since the number of significant digits is 4 (at least I'm calling 3900 as 4 because I assume it is 3900.) then that 2.99 is really 2.997 ( or if not 4 s.f. for 3900 then it would be 2.997 and round to 3) which makes th...

CHEMISTRY
How much of this do you know how to do. Show your work and let me go through it.

chemistry
The ammonium ion (NH4^+) is hydrolyzed according to this equation. NH4^+ + H2O ==> H3O^+ + NH3 (H3O^+) = acidic

CHEMISTRY
Why do you have the problem identifying the conjugate pairs? The pair consists of the one with more H and the one with less H. And for CO3^2- it should be obvious not to pick H2O as its conjugate pair.

CHEMISTRY
How are we going to do that? Then we have B::N and there are too many electrons around the central atom.

CHEMISTRY
pi = iMRT i is 1 for the four listed so it all depends upon M. Which M gives the largest pi?

chem
heat produced by burning 9.69g C6H6 is 5.69 mJ/mol x (9.69/molar mass C6H6) = ? MJ. Convert to J. Then J = mass H2O in g x specific heat H2O x (Tfinal-Tintial) and solve for Tf.

chem
How much heat was evolved in the combustion? That's 3209.0 kJ/mol x (1.829/159.29) = q = ? Then q = Ccal*delta T. Solve for Ccal.

Chemistry
Assuming you are using an indicator, you stop when the indicator changes color from its acid color to its base color.

Chemistry
That 5.67% m/v means 5.67 g glucose/100 mL blood; therefore, 5.67g glucose x (5,200 mL/100 mL) = ?

Fun time
1.55 g/mL x 3000 mL = ? The mass of the H2SO$ in that 3.0L is 1.55 g/mL x 3000 mL x 0.65 = ?

Chemistry
I agree

Chem 1120
Yes and no. You have Kc given in the problem. All you need to do is to substitute Kc into the Kp = Kc*(RT)^delta n and solve for Kp and you're done. The only thing changing I2 from solid to gas changes is delta n. For I2(g) ==>2I^-(g) delta n will be 2-1 = 1

Chem 1120
Kp = Kc(RT)^delta n. BTW, isn't I2 a solid. Then does I2 go in the denominator.

Chemistry
1___________ 2__________ 3_________ 1__________ Mix the two and you have 3_________ 1___________ 2__________

Chemistry
Yes. If that 1.1 is 1.1 and not 1.10 atm, then 0.71 is right. If it is 1.10 you should have one more place in your answer.

Chemistry
Two points. If T is to 4 places I would use R as 0.08205 although that won't make much difference. The other one makes more difference. P is 1.1 atm in the problem and not 1.

Chemistry
no. If you obtained two different answers why did you pick that one? You know something must be wrong. How did you get V = 24.7 L. If I plug those numbers into V =nRT/P I don't get that. But I do obtain a number that agrees with the formula I gave you.

Chemistry
The general gas formula of PV = nRT can be modified to P*molar mass = density*R*T

Chemistry
n = mols gas = 0.155/22.4 = ? n = grams/molar mass. You know n and grams, solve for molar mass.

Chem
1170.0 kJ/42.75 x #g = 191.9 kJ

Science
Probably not D.

Chemistry
This question makes no sense.

chemistry
and your answer?

Science
And your answer is?

Science
And your answer?

science
When you cut a bar magnet in two you end up with two smaller bar magnets. You don't get a monopole.

science
To get a sonic boom in air the "jet" must travel faster than the speed of sound in air. For air that is about 343 m/s. The "jet" fish would need to travel faster than the speed of sound in water. At 25C the speed of sound in fresh water is about 1497 m/s or...

science
In general, the speed of sound with wind is speed in still air + speed of wind. So shouting with the wind at your back means the speed is increased; shouting with the wind in your face means sound to your front is decreased speed.

babysitting
It doesn't sound like that to me but I'll take your word for it. However, you still listed no choices.

no choices--babysitting
This is baby sitting?

chemestry
E = R(1/n^2 - 1/n^2) R = 1.097E7*(1/4 - 1/25)

exam
CH4 + 2O2 ==> CO2 + 2H2O dHfrxn = (n*dHf products) - (n*dHf reactants) dHf rxn = -780 kJ/mol Substitute the others and solve for dHf CO2

CHEMISTRY
Did I miss something here? If the solubility of KClO3 is 10g/100g H2O and you add 15 g KClO3 to 100 g H2O, then it will dissolve 10 g KClO3 and the other 5g KClO3 will be unaffected. Of course the solution is saturated after the water has dissolved all it can.

CHEMISTRY
What do you mean by embedded. Do you mean you dissolved 15g or you added 15g KClO3.

CHEMISTRY
1. 1% means 1g I2/100 g solution = 10g I2/1000g solution = 10g I2/(10g I2+ 990g ethanol) 2. mol I2 = grams/molar mass 3. m = mols/kg solvent = ? You can convert to M if you know the density of the solution.

chemistry
Will alter the enthalpy of what?

science
http://en.wikipedia.org/wiki/Reflection_%28physics%29

Surds
(a+b)^2 = a^2 + ab + b^2

CHEISTRY
Do you know the order of the reaction?

Chemistry
LiOH(s) + H2O(l) ==> Li^+(aq) + OH^-(aq) dimeNH(l) + H2O(l) ==> dimeNH2^+(aq) + OH^-(aq)

science
What's the Law of Inertia say? That an object in motion tends to stay in motion until acted upon by an outside forcew. The car is traveling at 50 km/hr so the dummy, the car seats, the belts, the steering wheel and everything in the car is also traveling at 50 km/hr. When ...

science
You can read all about "clocks in rocks" here. http://www.sciencecourseware.com/virtualdating/files/1.0_ClocksInRocks.html I shall be happy to critique your summary explanation.

chemistry
C6H12O6 ==> 2C2H5OH + 2CO2 mols glucose = grams/molar mass = estimated 0.5 Using the coefficients in the balanced equation, convert mols glucose to mols ethanol. That is 0.5 x (2 mols ethanol/1 mol glucose) = 0.5 x 2 = 1 mol ethanol produced. Then g ethanol = mols x molar m...

science
mols H2SO4 = grams/molar mass Then M = mols H2SO4/L solution. Note: 100 mL = 0.100 L.

electric circuit
Probably 6 cells in series to give 12 v, then 6 sets of those (36 cells total) in parallel.

Clincal
I don't see a question here.

chemistry
Please read and rephrase. It makes no sense as is.

chemistry
See your other post above.

no image---science

Chemistry
mL1 x M1 = mL2 x M2 mL1 x 17.8 = 250 x 2.00M Add some distilled H2O to the 250 mL volumetric flask, then pipet the value of mL1 of the 17.8M H2SO4 into the 250 mL flask adding concentrated H2SO4 cautiously. Add distilled H2O to the mark and mix thoroughly.

chemistry
1 in^3 = 16.38 cc 13.4 in^3 to cc = ? 1 lb = 453.59 grams 5.14 lb to grams = ? Then d = mass/volume

CHEMISTRY
How much voltage do you need? How much can you get from these two materials? Look up the Eo values and calculate.

CHEMISTRY
Here is a simplified activity series table. A metal will displace any metal ION BELOW it in the activity series; i.e., Al will displace Cu^2+ but Cu will not displace Al^3+. 2Al + 3Cu^2+ ==> 3Cu(s) + 2Al^3+ Cu^2+ + Al^3+ ==> no reaction. http://www.cod.edu/people/faculty...

CHEMISTRY
Look up the standard reduction potentials for I2, Br2, and Al^3+. Then set them up on a sheet of paper something like this, along with H2. ..........................Eo vs SHE Br2 + 2e --> 2Br^-..........1.07 I2 + 2e --> 2I^- ...........0.54 2H^+ + 2e --> H2..............

CHEMISTRY
See the activity series question.

CHEMISTRY
By definition, reduction occurs at the cathode.

CHEMISTRY
You obtain the electrolysis products of H2O and not Al.

CHEMISTRY
It's an arbitrary standard and an arbitrary number.

CHEMISTRY
I wouldn't say they contained H2O but I agree they are moist. Compared to a wet cell; however, relatively speaking the dry cells are dry.

CHEMISTRY
You repeated my line but didn't answer if this was a made up problem or not. I don't like that answer until I have more information about the question.

CHEMISTRY
I wonder if this is a made up problem? Sn^2+ + 2e ==> Sn E = -0.14 Cr --> Cr^3+ + 3e E = ? ---------------------- Ecell = -0.60 then Cr must be -0.46 written as an oxidation so as a reduction it would be +0.46 but that isn't what it gives in the tables.

chemistry
What numbers do you have?

Chemistry
Some picky points. n N2 I obtained 0.007279 so I rounded to 0.00728. For n O2 I obtained 0.00436 I obtained 0.0029 for mols N2 just as you did; however, it is done by 0.0036 x 2/3 and not 3/2. Finally,(this is not so picky) the problem asks for mL so you should convert your 0....

Chemistry
almost. n = 0.0079? Why did you throw away the 1 on 0.00791. You have three places in yur other numbers; you should keep three for the answers. Then if I multiply 0.00791 x 16 I get 0.1265678 which rounded to 3 s.f. is 0.127grams CH4.

Chemistry
Change -15F to degrees C. That's approximately -26 Then delta T = Kf*m approx 26 = 1.86*m solve for molality. m = mols/kg solvent = mols/1kg You have m and kg, solve for mols. Then mol = g/molar mass. You have molar mass and mols, solve for g

CHEMISTRY
H2 gas at a pressure of 1 atmosphere bubbled over "black platinum" in a 1 M solution of H^+ is arbitrarily set at zero. Black platinum is platinum with a fine coating of extremely small particles (granules) of Pt. That surface apparently gives better reproducibility ...

CHEMISTRY
3 M+1...M+2...M+3 Then the two half reactions are M^2+ ==> M^+3 + e M^2+ + e ==> M^1+ then add the two half rxns --------------- 2M^2+ ==> M^3+ + M^+

CHEMISTRY
Just think of an example of an element in a compound with the element at its max oxidation state. For example take SO3 where S is +6. It CAN'T be oxidized any further (if this is the max) to go to S7 or S8 or higher) but it can go down to something like SO2 or S or H2S. So...

CHEMISTRY
You don't think so or you don't know so. Did you check it? I checked it and all atoms appear to balance. I even found a site in which someone did a lot of work to do it with half reactions. Here it is if you are interested. The numbers match those from another site whi...

CHEMISTRY
It's not simple but here is what I found on the internet. I don't vouch for its authenticity. 10[Cr(N2H4CO)6]4[Cr(CN)6]3 + 1176KMnO4 + 1399H2SO4 = 35K2Cr2O7 + 420CO2 + 660KNO3 + 1176MnSO4 + 223K2SO4 + 1879H2O

CHEMISTRY
I'm confused by your use of the terms reactant/products side. From the original question I thought that was a compound and if it is a compound there is no reason why you can't have an element exhibiting two different oxidation states. In coordination compounds that is ...

CHEMISTRY
I would start this way. This is a zero charged compound so the cation must be +3 and the anion part must be -4. We know CN is -1. I always go with +1 for H and -2 for O unless I know better. A value of +4 for C is always a good choice (unless it interferes with my +1 for H ato...

CHEMISTRY
right. 3KIO3 + 2KMnO4 + H2O ==> 3KIO4 + 2K^+ + 2OH^- + 2MnO2 but that is not the usual way of doing it. Usually we have an ionic equation or a molecular equation but a mixed is not wrong (unless your prof says to write a molecular equation in which case you will have points...

CHEMISTRY
Actually, there is nothing wrong with having a "mixed" equation in which you have both molecules and ions. However, in your case you added 5K^+ on the left and you added only 3K^+ on the right. So in changing from the ionic to the molecular equation your molecular eq...

CHEMISTRY
I think the answer is no but you just didn't finish. You added 5K^+ on the left. 3 of those on the right go with 3KIO4 and the other two go with 2KOH

CHEMISTRY
Here is a step by step of what I do for half reactions. This is the LONG way of doing it but I use it for two reasons: 1. It requires the student to know oxidations states. 2. The same procedure is used for acid OR basic solution. And I'm going to omit the spectator ions; ...

chemistry
You don't give the density of the solution so I have no way of knowing what the final volume. You also don't give any units for the 190^3 for water. If we assume units are cc If we assume the volumes are additive (and you can make that assumption since the volume of wa...

chemistry
You must have a reaction in mind. You can't get PbCl2 from MgCl2 without some reaction.

chemistry
HNO3 + KOH ==. KNO3 + H2O mols HNO3 = M x L = 2.5 x 0.1 = 0.25 mols KOH = 2.55 x 0.1 = 0.255 Since the reaction is a 1:1 ratio, the HNO3 is the limiting reagent and 0.25 mols H2O will be produced. g H2O = mols H2O x molar mass H2O = ?

pharmacy calculations
I answered this for you earlier.

ph
I'm not a pharmacist but if that means take 250 mg every 8 hours for 7 days, the total dose is 250 mg/dose x 3 doses/24 hrs x 24 hours/1 day) x 7 days = ?

questions
So you want 15 tablets for 1/2 the month (30/2 = 15 days) and another 15/2 day supply so that is 15 + 7.5. You dispense 15 + 8 = 23 tablets unless you want to cut one of the tablets into two. I don't know if you are allowed to cut tablets or not. If so then you want 22.5 t...

Chemic
mL1 x %1 = mL2 x %2 mL1 x 98% = 50 mL x 5% Solve for mL 1. Add that amount to 50 mL volumetric flask and make to the mark with distilled H2O.

CHEMISTRY
You're right. I turned it around. Sorry about. Just reverse everything and you will have that half reacted. For KPb(OH)3 the cation is K^+ and the anion is Pb(OH)3^- So I would write PbO2 ==> Pb(OH)3^- I assume this is a basic solution. Pb is +4 on the left and +2 on th...

CHEMISTRY
In acid solution.? 2H^+ + ClO^- + 2e ==> Cl^- + H2O In basic solution? H2O + ClO^- + 2e --> Cl^- + 2OH^- The way to learn this is to do them. Looking at what someone else has done won't get it. If you will share what your problem(s) is/are in doing these perhaps I ca...

Chemistry
Yes, and if your prof is picky about the number of significant figures you whould round that to 514 mL. You are limited to 3 from the 325 to start.

Chemistry
When it's an all gas sample and the T and P don't change, you may use a shortcut and use volume directly as if they were mols. 2C6H14(g) + 19O2(g) -> 12CO2(g) + 14H2O(g) 325 mL CO2 x (19 mols O2/12 mols CO2) = 325 mL x (19/12) = mL O2 consumed.

Chemistry
Use PV =nRT and convert NH3 and O2 (each) to mols = n. Find the limiting regent Convert to mols N2 formed, the use PV = nRT and convert to mL at the conditions listed.

Chemistry
I don't think you did anything wrong. v1 = 683 mL p1 = 0.792 atm t1 = 19C = 273+19 = 292K v2 = 733 mL p2 = ? in atm. t2 = 76C = 273+76 = 349K (0.792*683/292) = (p2*733/349) If I used 292.15 and 349.15 the answer is 0.8819 which rounds to 0.882 atm. Usually when something l...

Chemistry
(P1V1/T1) = (P2V2/T2)

Chemistry
Since they threw that T as 27.2 then I would add to 273.2 to convert to K (I missed that above) so I would use 300.4 and not 300.2. That gives you n = number of mols. The problem asks for grams methane. g methane = mols x molar mass CH4 = mols methane x 16 = ? Note: Check your...

Chemistry
P in atm (741/760) = ? atm V in L. 200 mL = 0.200 L T in kelvin. K = 273 + 27.2 = ? With all of those, R = 0.08205.

Chemistry
If P is changed to atm [(741/760) = ?] then R is 0.08205 L*atm/mol*K

Chemistry
Use PV = nRT and solve for n = number of mols CH4. Then n = grams/molar mass. You have molar mass and n, solve for grams.

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