Friday
September 19, 2014

Posts by DrBob222


Total # Posts: 43,868

chem
7.42E-5 kg x (1000g/1 kg) x (1000 mg/g) = ?
May 15, 2014

chemistry
yes. You reversed the sign because the reaction is reversed. So that makes it positive. Then double that for e.
May 15, 2014

chemistry
You have the reaction as shown. You want the reverse reaction and double that. So take dH that you have, change the sign (because of the reversal) and double it.
May 15, 2014

Math 2
I would ask 1/4 what of fabric?
May 15, 2014

chemistry
Read and correct your post. Clarify. It makes no sense as is. delta T in kJ?
May 14, 2014

chemistry
You can see from your previous ost how this is done. I'll be glad to check your numbers.
May 14, 2014

chemistry
Calculate mg morphine in each of the choices. a. 20% w/v means 20 g morphine/100 mL. I wouldn't recommend this choice (if you want the patient to live). b. 2M solution. How many mols is that. mols = M x L = 2M x 0.050 L = 0.1. g = mols x molar mass = 0.1 x 283 = 28.3 g or ...
May 14, 2014

Chemistry
The two half reactions are 2Al ==> 2Al^3+ + 6e Eo = 1.66 3Fe^2+ + 6e ==> 3Fe Eo = -0.44 -------------------- Add half cells to obtain rxn. Add Eo to obtain Eocell.
May 14, 2014

Chem
dGorxn = (n*dGo products) - (n*dGo reactants)
May 14, 2014

Chemistry
n stands for number of mols. It is 1 for CaO, 1 for CaCO3, and 1 for CO2. Look up dHo formation CO2, CaO, and CaCO3. Calculate dHo reaction. Look up dSo for CO2, CaO, and CaCO3. Calculate dSo reaction. Then dGorxn = dHorxn - TdSorxn
May 14, 2014

Chemistry
dHorxn = (n*dHoformation producs) - (n*dHoreactants) dSo rxn = (n*dSo formation products( - (n*dSo formation reactants) dGrxn = dHrxn - TdSrxn dG<0 spontaneous dG=0 equilibrium dG>0 not spontaneous.
May 14, 2014

NO SCHOOL
I presume this is a tax, probably Goods and Services Tax in Canada. Your post isn't clear. If you have 100 to spend on an item it will cost you 100 + 10% of 100. Or you may mean that the total cost of an item, including GST, is 100.00. And you want to know the cost without...
May 14, 2014

chemistry
Surely it's in your text. You're right. Bases are proton acceptors according to the Bronsted-Lowry theory of acids/bases.
May 14, 2014

chemistry
This isn't in your text/notes. The first half is According to this theory, acids are proton donors. So bases must be proton ........?
May 14, 2014

chemistry
Metals with a small heat capacity heat faster and cool quicker than metals with a higher heat capacity.
May 14, 2014

chemistry
That's right. % = (mass solute/total mass)*100 = ?
May 14, 2014

chemistry
You have half of it right. The other half you have ignored. q1 = heat needed to raise T of water from 15C to 100 C is what you have calculated. q2 = heat needed to change T of water at 100 C to steam at 100 C. That is q2 = mass H2O x heat vaporization.
May 14, 2014

math
Change meters to cm. 1 meter x (100 cm/1m) = 100 cm 100 cm + 5 cm = ?
May 14, 2014

Chemistry
I would say an oxidizing agent, a reducing agent, and a salt bridge/porous barrier. If you want to get technical I suppose you might add a cell (something to hold the oxidizing agent/reducing agent and the salt bridge).
May 14, 2014

chemistry
H3PO4 + 3NaOH ==> Na3PO4 + 3H2O
May 14, 2014

Chemistry
What does the equation tell you? That 89.3 kJ are absorbed when 1 mol (76.1g CS2) are formed. You have 6.33 g; therefore, 89.3 kJ x (6.33/76.1) = ? kJ
May 14, 2014

science
60 meters in 34 seconds. That is avg velocity of 60m/34s = ? m/s.
May 14, 2014

chemistry
20L propane = 20L x (1 mol/22.4L) = about 0.892 mols propane. You get 2220 kJ for 1 mol; therefore, you will get 2220 x (0.892 mol/1 mol) = ? kJ released.
May 14, 2014

Chemistry
1. Write the equation. 2. Balance it. 3. dHrxn = (n*dHo formation products) - (dHo formation reactants)
May 14, 2014

Chemistry
You're cluttering the board now. Spend your time solving problems instead of typing.
May 13, 2014

Chemistry
Same 'ol same 'ol. See your other posts.
May 13, 2014

Chemistry
I don't see anything new here. See your other posts.
May 13, 2014

Chemistry
See your other posts.
May 13, 2014

Chemistry
Zn^2+ + 2e ==> Zn from the table is -0.76v. Your half cell reaction is Zn ==> Zn^2+ + 2e E = +0.76v Ag^+ + e ==> Ag E = 0.80 v. --------------------------- Add rxnx; add half cell oxidation half to reduction half. Cell rxn is Zn + 2Ag^+ ==> Zn^2+ + 2Ag Ecell = 0....
May 13, 2014

Chemistry
n = 2 and you know that from the equation I wrote earlier of Zn + 2Ag^+ ==> Zn^2+ + 2Ag The term you are talking about is (RT/nF)ln[(Zn^2+)/(Ag^+)] and if you want to substitute R, T, n, and F in there you may. However, if you do all of that AND multiply by 2.303 to convert...
May 13, 2014

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

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