Tuesday
September 2, 2014

Posts by DrBob222


Total # Posts: 43,445

Chemistry
It really helps us help you if you use the same screen name. Tom, Tyler, help ASAP etc is not helpful at all. You know from your previous post how to calculate the standard Zn/Ag^+ cell potential. That is Eocell and that is for standard concentrations of 1M Zn^2+ and Ag^+. ...
May 13, 2014

Chemistry ASAP
yes
May 13, 2014

Chemistry ASAP
Look up the reduction potential for Zn^2+ + 2e ==> Zn(s) in your text. Reverse the sign. Add that to the reduction potential for Ag^+ + e ==> Ag(s) That potential will be for the reaction of Zn(s) + 2Ag^+(aq) ==> 2Ag(s) + Zn^2+(aq)
May 13, 2014

Chem 130
E= 2.180E-19 J x (1/n^2)
May 13, 2014

Chem 130
[Kr]4d25s2 http://www.webelements.com/zirconium/atoms.html
May 13, 2014

Math 6th Grade
Do you honestly think -15 = -21? How can that be. 2 = 2 and 6 = 6 and -2 = -2 but -15 = -21?
May 13, 2014

chemistry
You have two typos in your equation. The correct equation, balanced, is CaCO3 + 2HCl ==> CaCl2 + H2O + CO2 mols CaCO3 = grams/molar mass mols CO2 = mols CaCO3 from the coefficients in the balanced equation. Now g CO2 = mols CO2 x molar mass CO2.
May 13, 2014

Chemistry
I would first convert 40% HCl into molarity. 40% (I guess that's w/w) HCl means 40g HCl/100 g solution. 40g/36.5 = approx 1.10 mols HCl mass = volume x density so volume = mass/density. That 100 g soln = 100/1.2 = approx 80 mL or 0.08 L; therefore, the molarity is 1.1/0....
May 13, 2014

science
You can add the phases. You have it partly balanced but I am removing the 2 and 3 and start over. First you write the products (and that isn't considered part of the balancing). H3PO4(aq) + CaCl2(aq) ==> Ca3(PO4)2 + HCl You do these by trial and error; basically that ...
May 13, 2014

SIG FIGS
1.75E2
May 13, 2014

college chemistry
To melt ice requires q1 = mass ice x heat fusion. To raise T of melted ice at zero C to Tfinal requires q2 = mass melted ice x specific heat liquid H2O x (Tfinal-Tinitial) To cool the water from 75C to Tfinal requires q3 = mass liquid water x specific heat x (Tfinal-Tinitial...
May 13, 2014

chemisty
q1 = heat needed to raise temperature of liquid water from 15 C to 100 C. q1 = mass x specific heat H2O x (Tfinal-Tinitial) q2 = heat need to convert H2O at 100 C to steam at 100 C. q2 = mass H2O x heat vaporization.
May 13, 2014

college chem
Devron answered this for you below.
May 13, 2014

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...
May 13, 2014

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 ...
May 13, 2014

End of Year question
Mine would be "awesome". "Great" as a second choice. "Beautiful" as a third choice.
May 13, 2014

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.
May 13, 2014

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
May 13, 2014

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 ...
May 13, 2014

Alegbra ck to see if I did it correclty please
I think you have it down cold.
May 13, 2014

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.
May 13, 2014

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
May 13, 2014

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
May 13, 2014

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.
May 13, 2014

Chemistry
Ma x Va = Mb x Vb Substitute and solve for the unknown.
May 13, 2014

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 ...
May 13, 2014

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 ...
May 12, 2014

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.
May 12, 2014

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...
May 12, 2014

To Drbob222
I'm sticking to chemistry.
May 12, 2014

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. ...
May 12, 2014

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'...
May 12, 2014

chemistry
http://www.jiskha.com/display.cgi?id=1399943202
May 12, 2014

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 ...
May 12, 2014

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 (...
May 12, 2014

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)
May 12, 2014

To Tom1---Chemistry
Read what I wrote. I said 3.7E10 dps = 1 Ci, not that Ci = 1.
May 12, 2014

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 ...
May 12, 2014

Chemistry
dGorxn = (n*dGoproducts) - (n*dGoreactants)
May 12, 2014

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.
May 12, 2014

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.
May 12, 2014

chem
2.01588 g/mol
May 12, 2014

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.
May 12, 2014

Science
If this is a DC circuit, I = E/R
May 12, 2014

Science 2
I assume this is a DC circuit.
May 12, 2014

Science 2
E = IR
May 12, 2014

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.
May 12, 2014

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%
May 11, 2014

(2-8) Chemistry - Science (Dr. Bob222)
work = 0 http://physics.bu.edu/~duffy/semester1/c27_process_expansion_sim.html
May 11, 2014

(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 ...
May 11, 2014

(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 ...
May 11, 2014

(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.
May 11, 2014

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
May 11, 2014

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.
May 11, 2014

Chemistry
I don't understand the question. Is that between Na and K? Any water involved?
May 11, 2014

chemistry
Instead of me guessing what you did why not show your work and let me find the error.
May 11, 2014

chem
Yes, and remember to substitute dHvap in J/mol, not kJ/mol. Also remember T must be in kelvin
May 11, 2014

oops---chemistry
The correct answer is d. As long as some carbon is present, adding or removing carbon will not affect the equilibrium.
May 11, 2014

chemistry
To avoid oxidation by oxygen.
May 11, 2014

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?
May 10, 2014

chemistry
All are ok except 2. 2 is an ether.
May 10, 2014

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 ...
May 10, 2014

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, ...
May 10, 2014

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)...
May 10, 2014

Chemistry
Convert oz to mass in grams. Then volume = mass/density
May 10, 2014

chemistry
I believe this must be to produce a ketone.
May 10, 2014

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)
May 10, 2014

chemistry
I agree with your answer.
May 10, 2014

Organic Chemistry
Ask yourself, 79% of what = 135 or 0.79*x = 135, then 135/0.79 = x
May 10, 2014

(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 ...
May 10, 2014

(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.
May 10, 2014

(1-17)Chemistry - Science
Isn't this done the same way except you know the reaction must shift to the left to reach equilibrium?
May 10, 2014

(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...
May 10, 2014

(1-15) Chemistry - Science
Is this a comparison of KE to KE?
May 10, 2014

(1-13) Chemistry - Science
I think most of this covered in discussions of the "imperfect gas" and the van der Waals equation.
May 10, 2014

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 ...
May 10, 2014

(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 ...
May 10, 2014

chemistry
https://answers.yahoo.com/question/index?qid=20100630090838AAcJFUB
May 9, 2014

To Ana
I saw you post 4-5 pages down about K for the disproportionation problem. I calculated K by RTlnK = nFEo
May 9, 2014

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.
May 9, 2014

chemistry
Same as your post on benzoic acid/benzene EXCEPT delta T = i*Kf or Kb*m i = 2 for NaCl.
May 9, 2014

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-
May 9, 2014

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 ...
May 9, 2014

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...
May 9, 2014

chemistry
http://www.conserve-energy-future.com/Advantages_Disadvantages_HydrogenEnergy.php
May 9, 2014

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.
May 8, 2014

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. .
May 8, 2014

chemistry
%alcohol = (weight alcohol/total weight)*100 = ?
May 8, 2014

chemistry
See your other post.
May 8, 2014

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
May 8, 2014

Chem
PV = nRT Watch the units
May 8, 2014

Chem
Use PV = nRT
May 8, 2014

Chem
PV = nRT
May 8, 2014

Chem
(P1V1/T1) = (P2V2/T2)
May 8, 2014

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.
May 8, 2014

Algebra ( benchmark)
do you mean, "and NO more than 3200"?
May 8, 2014

Science
No, the atomic number of Pb is 82 (that's number of protons in the nucleus). The atomic weight Pb is 207.2.
May 8, 2014

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.
May 8, 2014

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.
May 8, 2014

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-...
May 8, 2014

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