Wednesday
July 23, 2014

Posts by DrBob222


Total # Posts: 43,165

college chem
Devron answered this for you below.

Physical Science
Just because this may be a little foreign don't let it intimidate you. It's a matter of plugging in the numbers. The formula is q = mass x specific heat x (Tfinal-Tinitial). The numbers are mass = 0.75g from the problem. specific heat = 0.385 J/g*C from the problem. Tf...

Science
Just remember that a force always has an equal and opposite force opposing it. If I sit on a chair the chair (and floor) must push back with the same force I exert during sitting. When I was a student in physics class I asked "but how can that be?" and the prof answe...

End of Year question
Mine would be "awesome". "Great" as a second choice. "Beautiful" as a third choice.

chemistry
I don't think so. If the 1000 has no period after it it has only 1 s.f. and the answer 1E3. If it has a period, the answer is 1056.

chemistry
I suspect that is because molecular and ionic formulas have flaws in them (or they could be typos--in fact some appear to be typos). NaHCO3 + H2SO4 ==> NaHSO4 + H2O + CO2

science
1. I know this is a poor answer but it's the best I can do. The images are reversed and inverted because that's what lenses do. 2. At high power it takes VERY LITTLE movement to take the specimen out of the field of view; therefore, you want to get it centered and you ...

Alegbra ck to see if I did it correclty please
I think you have it down cold.

chemistry
43.7 has only 3 s.f. Add that to 0.393 for an answer with 3 s.f. and divide by 4 s.f. so you may have only 2 in the answer. 1.741 has 4 which is one too many.

chemistry
I would change all of these to km. Note that with no period after the 80,000 mm. that has only one s.f. 0.000035 km 0.0083 km 75.341 km 0.08 km --------- 75.429335 which I would round to 75.43

Chemistry
post #1. Work with mols. mols NaOH in 8g = grams/molar mass = ? mols NaOH in 599 mL of 0.250M = M x L = ? Total mols NaOH = ? Now total volume is 599 mL + 1.68 gallons. Convert mL to L and convert 1.68 gallons to L. Add to find total L. Then (NaOH) in final solution is mols/L

chemistry
I'll be glad to check your work or answer questions on this topic but it does you no good for me to give you the answers.

Chemistry
Ma x Va = Mb x Vb Substitute and solve for the unknown.

Chemistry
Table salt is NaCl, an ionic compound. It dissolves in water due to the dipoles of H2O attracting the positive Na ions and the negative Cl ions. That plus the energy released when the Na ion and Cl ion form hydrates with the water is enough to break the lattice energy of the N...

chemistry
What specifically do you not understand? Basically I have two explanations. The first one I incorrectly assumed that all of the ice would melt. It doesn't and I showed how to work the problem in an earlier post. That I took your work down to the point where you get a negat...

Chemistry
1. We would expect H2O to have the higher boiling point due to hydrogen bonding. 2. We would CS2 to have the higher boiling point due to dispersion forces.

To Drbob222
You have it wrong my friend. Everyone cares but no one with expertise in physics is available to help at this moment. I usually don't help in physics because I may give the wrong answer. Most of the time you can get an answer in 2-3 hours but here it is almost midnight CDT...

To Drbob222
I'm sticking to chemistry.

chemistry
If you followed your math you ended up with Tf of 15.3. I didn't go through line by line but my explanation was that your work should have produced a negative value for Tf. When that happens we know it can't be right from the data given so we know something is wrong. T...

chemistry
All of your work is ok until here. 50*4.18*(Tf-22) 1030+8350+104.5Tf=-(209Tf-4598)( negative since heat lost) 4782=313Tf tf=15.3 Should have been 1030 + 8350 + 104.5Tf + 209Tf + 4598 = 0 Then you get xxxTf = -some number and that makes Tf = -something and you KNOW that can'...

chemistry
http://www.jiskha.com/display.cgi?id=1399943202

chemistry
That's because I assumed, incorrectly, that all of the ice would melt. It won't. How many J does it take to move T of ice at -20C to OC? That's q = (mass ice x specific heat ice x (Tf-Ti) = [25g x 2.01 J/g x (20)] = 1005 J. How much will that lower the T of the wat...

chem
The boiling point of a liquid, including water, is the temperature at which the vapor pressure equals atmospheric pressure. So at sea level atmospheric pressure is 760 mm Hg so water boils at 100. On top of Mt Whitney the pressure may be say 700 mm Hg. So the water will boil (...

Chemistry
I see only parts A and B, no C nor D. A is the oxidation at the anode of Cr. Cr(s) ==> Cr^3+(aq) + 3e B is the reduction at the cathode. 3Ag^+(aq) + 3e==> 3Ag(s)

To Tom1---Chemistry
Read what I wrote. I said 3.7E10 dps = 1 Ci, not that Ci = 1.

Chemistry
k = 0.693/t1/2 k = approx 0.09 but you should get a more accurate number. Convert 140 mg to number of atoms initially (at time = 0) Use ln(No/N) = kt to determine N = number of atoms after four hours. The difference between initial and after 4 hours is atoms that decayed in 4 ...

Chemistry
dGorxn = (n*dGoproducts) - (n*dGoreactants)

Chemistry
Look up dHo formation and dSo formation. Then dHo rxn = (n*dHo products) - (dHo reactants) dSo rxn = (n*dSo products) - (n*dSo reactants) Then dG = dH - TdS for each temperature dG = - number is spontaneous dG = + number is not spontaneous.

chemistry
1 equivalent NaOH = 40 g 0.1 equivalent NaOH = 4.0g 4.0 g in 1 L volumetric flask, dissolve in distilled H2O and make to the mark. Mix thoroughly.

chem
2.01588 g/mol

Science 3
If DC circuit, then I = E/R but you must determine Reffective and that depends upon if they are in series or parallel.

Science
If this is a DC circuit, I = E/R

Science 2
I assume this is a DC circuit.

Science 2
E = IR

Science 2
If R1 and R2 are in series, then R circuit is 12. If in parallel, then (1/R) = (1/R1) + (1/R2) = about 3 so they must be in series. Check that out to make sure.

Chemistry Who step by step
The problem does not require simultaneous equations. I would use 143.32 for molar mass AgCl and mols AgCl = 1.913/143.32 = 0.1334 mols NaCl = mols AgCl g NaCl = mols NaCl x molar mass NaCl = 0.01334 x 58.44 = 0.7800 g % = (0.7800g/0.8870g)*100 =87.94%

(2-8) Chemistry - Science (Dr. Bob222)
work = 0 http://physics.bu.edu/~duffy/semester1/c27_process_expansion_sim.html

(2-8) Chemistry - Science (Dr. Bob222)
Copied from Wikipedia. "When no heat flows into or out of the gas because its container is at the same temperature, then there is no work done. Thus, work=0 which means external pressure on any moving surface is zero. This is called free expansion." So when the term ...

(2-8) Chemistry - Science (Dr. Bob222)
In the first question, D says that dE cannot change if T doesn't change and I was answering that it certainly can because pdV changes work and that changes dE and no T is necessarily involved. The point in the first one is that changing T changes q and changing T CAN chan...

(2-8) Chemistry - Science (Dr. Bob222)
dE = q + w q changes with T. w, though, is pdV and you can change w willy nilly which will always change dE but T is not necessarily involved in changing volume.

Chemistry
5.7 what? from what reaction? what conditions? I'll assume that is 5.7L H2O, then assume rxn is 2H2 + O2 ==> 2H2O and assume this is at STP. 5.7 L H2O x (1 mol O2/2 mols H2O) = 5.7 x 1/2 = ? L O2

Chemistry
Look up reduction potentials for Cd^2+ + 2e==> Cd and Co2^+ + 2e ==> Co. Look at which one of the two will give a positive voltage. That is the one that will proceed spontaneously.

Chemistry
I don't understand the question. Is that between Na and K? Any water involved?

chemistry
Instead of me guessing what you did why not show your work and let me find the error.

chem
Yes, and remember to substitute dHvap in J/mol, not kJ/mol. Also remember T must be in kelvin

oops---chemistry
The correct answer is d. As long as some carbon is present, adding or removing carbon will not affect the equilibrium.

chemistry
To avoid oxidation by oxygen.

science
I disagree. Think about it. A(l) + B(l) --> gas Say A has a mass of 2 g and B has a mass of 2 grams (and they are liquids), what does the gas weigh? And how did you weigh it?

chemistry
All are ok except 2. 2 is an ether.

Chemistry
First, determine the M of the HCl. That will be 25*0.2/20 = 0.25M Where is the equivalence point. That is at 25.0 mL, NaOH, of course. The questions divide the titration curve up nicely into a. at the beginning. b. before the eq point. c. at eq pt d. just after eq pt It's ...

Chemistry - Science (Dr. Bob222)
That's an interesting proposition but I don't think Le Chatelier's principle is quite the one to use here. However, if you look at it as an equilibrium (which it is), then H2O(l) --> H2O(g) So Kp = pH2O(g). When pH2O(g) has reached equilibrium with the liquid, t...

Chemistry
None of these is balanced. 5a. Mn^2+ + H2O2 ==> MnO2 + H2O b. unclear to me c. Mn^2+ + BiO3^- ==> MnO4^- + Bi^3+ 6. a & b. Fe^3+ + NH3 + H2O ==> Fe(OH)3(s) Cu + NH3(aq) ==> Cu(NH3)4]^2+(aq) c & d. Zn^2+ + NH3(aq) ==> Zn(NH3)4]^2+(aq) Al + NH3 + H2O ==> Al(OH)...

Chemistry
Convert oz to mass in grams. Then volume = mass/density

chemistry
I believe this must be to produce a ketone.

chemistry
coulombs = amperes x seconds. C = 2.3E-5 x 1200 d x (24 hr/d) x (60 m/hr) x(60 s/min) = ? 96,485 coulombs will produce (200.6/2)g Hg; therefore, g Hg = (200.6/2) x (?coulombs/96,485)

chemistry
I agree with your answer.

Organic Chemistry
Ask yourself, 79% of what = 135 or 0.79*x = 135, then 135/0.79 = x

(1-22)Chemistry - Science
However, following up on what Writeacher wrote, it is a huge help to us if you post what you think is the way to fo, post the process, explain what you don't understand, etc. That way we can focus on helping with the specific part of the problem that is causing concern rat...

(1-22)Chemistry - Science
.......C(s) + H2O(g) ⇌ CO(g) + H2(g) I.............1.00......0.......0 C..............-x.......x.......x E............1-x........x.......x Substitute the E line into Kp expressin and solve for x = pH2 = pCO pH2O = 1-x. The correct answer is D.

(1-17)Chemistry - Science
Isn't this done the same way except you know the reaction must shift to the left to reach equilibrium?

(1-16)Chemistry - Science
First you must determine which way the reaction will shift to reach equilibrium. Q = (SO3)(NO)/(NO2)(SO2) = (0.5*0.5/0.5*0.5) = 1. With K = 9 that means products are too small and reactants too large so the rxn must shift to the right to reach equilibrium. .....SO2(g) + NO2(g)...

(1-15) Chemistry - Science
Is this a comparison of KE to KE?

(1-13) Chemistry - Science
I think most of this covered in discussions of the "imperfect gas" and the van der Waals equation.

1-12. Chemistry - Science
D2 + E = product mols D2 = 3/22.4 = ? mols E = 3/22.4 = ? mols product = 1.5/22.4 However, when working with gases one can dispense with the 22.4 since that is a constant in all of the numbers; i.e., use L as if L = mols. I would think the formula of the product is D4E2. Try t...

(1-11) Chemistry - Science (Dr. Bob222)
Yes, the answer is C. Any liquid placed in a closed system will come to equilibrium with its vapor at a particular temperature. The vapor pressure then is say x. Adding more liquid will NOT make the liquid evaporate more which would, of course, increase the vapor. The vapor pr...

chemistry
https://answers.yahoo.com/question/index?qid=20100630090838AAcJFUB

To Ana
I saw you post 4-5 pages down about K for the disproportionation problem. I calculated K by RTlnK = nFEo

Chemistry
mols acid = grams/molar mass m acid = mols/kg solvent delta T = Kf*m Solve for T and add to normal freezing point of benzene to find the new f.p. Do the same for b.p. mols acid is same m acid is same delta T = Kb*m Add delta T to normal b.p. to find new b.p.

chemistry
Same as your post on benzoic acid/benzene EXCEPT delta T = i*Kf or Kb*m i = 2 for NaCl.

chemistry
a. 0.125M x 20/50 = ? b. 0.025 x 20/50 = ? c. mass = 0.1g/L x 0.010 L = ? Then mols = grams/molar mass d. mols I2 = M I2 x L I2 = ? e. I2 + 2S2O3^2- ==> 2I^- + S4O6^2- Therefore, delta mols I2 = 1/2 mols S2O3^2-

DR.bOBB
OK. Further down the list I note a bunch of question by deepa and they deal with biology. Yes, I skipped all of them. I am not a biologist. I am a chemist and most questions in biology are simply out of my field. I don't want to give any wrong answers. I do answer an occas...

DR.bOBB
I skipped a (meaning one) question yesterday because I wasn't sure of the answer. To answer your question, no I'm not skipping a massive number of questions that deal with chemistry. If you posted a question I don't remember it. Did you use chemistry as the subject...

chemistry
http://www.conserve-energy-future.com/Advantages_Disadvantages_HydrogenEnergy.php

CHEMISTRY HELP !!!! CHECK !!!
I didn't work it that way and I don't see anything wrong with the way you did it. I agree with the answer.

CHEMISTRY HELP ! Check Please!
I don't agree with a I agree with b although I'm not sure of "what a small fraction" is. .

chemistry
%alcohol = (weight alcohol/total weight)*100 = ?

chemistry
See your other post.

Chem
a. What's the original volume? P1V1 = P2V2 b. What's the original volume? (V1/T1) = (V2/T2) Remember T must be in kelvin

Chem
PV = nRT Watch the units

Chem
Use PV = nRT

Chem
PV = nRT

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

Chem
Intuitively you see that the pressure has decreased which means the volume must have increased; therefore, the volume of the old flask is v and the volume of the combined flasks is 32+v Since p1v1 = p2v2, then 389*v = 154(32+v) and solve for v.

Algebra ( benchmark)
do you mean, "and NO more than 3200"?

Science
No, the atomic number of Pb is 82 (that's number of protons in the nucleus). The atomic weight Pb is 207.2.

Science
Why not type in the 14 questions; preferably only one or two per post. And show your answers and why you answered that way.

no link--Science
And you will not be able to leave a link on this forum unless you are one of the tutors. And not all tutors have this privilege.

chemistry
Below are four stages: 1. heat needed to raise T ice @ 20C to zero C. 2. heat needed to melt ice at zero to liquid water at zero. 3. heat needed to raise T ice at zero C to final T. 4. heat lost by 20 degree water to final T. [mass ice @ 20 x specific heat solid ice x (Tfinal-...

Chemistry
I worked this just a few post below but the Ecell was 11 mv. Same process though. Ecell = Eo - (0059/2)log(0.1/x) and solve for x.

Chemistry 104
This has been posted numerous times today. See those answers.

Chemistry
Look at it this way. The dipoles from the H2O molecules attract the Na^+ and Cl^- and pull on them. That's the pull to disrupt the crystal lattice energy. And it isn't a one step here to disrupt the crystal lattice and then another step to form the hydrates. It's t...

Chemistry
One major correction. It is true that the intermolecular forces (the water molecules pulling at the lattice energy) but those are ion-dipole forces and not ionic. Charged yes but not ionic). The answer to your question is that youmust take into account the energy gained when t...

Chemistry 104
Ecell = Eocell - (0.0592/2)log(x)/(Zn^2+) 0.011 = 0 -(0.0592/2)log(0.1/x) Solve for x.

chemistry
heat to melt ice + heat to raise T of melted ice to Tfinal + heat lost by warm water = 0 [mass ice x heat fusion] + [mass melted ice x specific heat H2o x (Tfinal-Tinitial)] + [mass warm water x specific heat H2O x (Tfinal-Tinitial)] = 0 Substitute and solve. The only unknown ...

Chemistry 104
Instead of us guessing, why don't you show your work so we can find the error.

Chemistry
See your earlier post.

Chemistry
See your others posts. And please stop changing screen names. It won't help and in fact keeps us from helping as much as we might if you used the same name.

Chemistry
Eo is zero, right? :-) The SHE under standard condition is always 0.

Chemistry
I assume that's 3.8 atm. 2H^+ + 2e ==> H2 E = Eo - (0.0592/2)log[(pH2/(H^+)^2]

Chemistry
Ecell = Eocell - (0.0592/n)log[(Cr^2+)/(Ni^2+)] and you get Eocell by adding the OXIDATION for Cr to the REDUCTION of Ni^2+. I would do it here but the values in your text won't agree with the values in my OLD text.

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