Thursday
November 27, 2014

Posts by DrBob222


Total # Posts: 45,633

chemistry due soon
Yes, c is correct.
November 22, 2014

Chem
I looked up the neutral atom and ionic species and this is what I found from smallest to largest. It isn't what I expected. Ar < Cl^- < Ca^2+ < K^+ I thought in an isoelectronic series (which this is since all atoms/ions have 18 electrons) that Cl^- would be ...
November 22, 2014

chemistry Thank a lot help
I solved this for you twice last week.
November 22, 2014

chemistry
dG = dH - TdS Max value for dG is 0. Then TdS = dH dS = dH/T = 19,000/(273+72) dS = ?
November 22, 2014

chemistry
Write the hydrolysis equations. For x it will be ........X^- + HOH ==>HX + OH^- I......0.1...........0.....0 C......-x............x.....x E.....0.1-x..........x.....x Kb for X^- = (Kw/Ka for HX) = (x)(x)/).1-x Since pH = 7 that makes pOH = 7 and (OH^-) = x = 1E-7. Solve for...
November 22, 2014

chemistry
.............PbCl2 ==> Pb^2+ + 2Cl^- I............solid......0......0.15 C............solid......x........x E............solid......x......0.15+x Ksp = (Pb2+)(Cl^-)^2 Ksp = (x)(x+0.15) Solve for x.
November 22, 2014

Chemistry
Yes, dS for the system is 79.0 J/K*mol but I would use T at boiling point of 98C (371K) to solve for this because you're using dHvap and it makes sense to use T at the vapor point. I note the problem asks for dSuniv at 298. I think you can get that by dG = -dH/T = (dSuniv...
November 22, 2014

Chemistry
dSsys = dH/T I think you should look at your dH value. Isn't 21.6 kJ/mol = 21600 J/mol
November 22, 2014

Chemistry
No. You don't have 2.10 mols HCl. Did you read my response? mols HCl = M x L = 2.10 x 0.035 = ? Then convert to mols H2 and from thre to L.
November 22, 2014

Chemistry
Do you mean delta Hf? If dHf<0 doesn't that mean dHf = negative and doesn't that mean it is exothermic and wouldn't that mean it gets hotter?
November 22, 2014

chemistry
mols HCl = M x L = ? Using the coefficients in the balanced equation, convert mols HCl to mols H2 gas. Now convert mols H2 gas to L. L H2 = mols H2 x 22.4 L/mol = ? L.
November 21, 2014

Ratio - proportion - unit rate
$71.88 doesn't appear to be a question to me. Answer Ms. Sue's question.
November 21, 2014

Chemistry
Here is my response to your earlier question. Although you didn't explain what you didn't understand, I think you must understand it ok for the equation is balanced. Read my response and redo this one and see if that doesn't help. If it doesn't, repost and this...
November 21, 2014

Chemistry
C2H5OH + 3O2 ==> 2CO2 + 3H2O heat of combustion ethanol = 3600 kJ/mol x (3.78/molar mass ethanol) = ? ? = Ccal(Tfinal-Tinitial)
November 21, 2014

Chemistry
I answered under Sam. Re-post with a follow up if the "mole" isn't clear.
November 21, 2014

Chemistry
Look at your post under Sam. These are worked almost the same way but if you don't understand please show what you know and tell me exactly what you don't understand about the question. As for mols of benzene, the answer is none although your teacher may count that ...
November 21, 2014

Chemistry
That is a constant. It's just another unit like a dozen of something (12) or a gross of sometihig (144 or 12 dozen) or a ream (500 sheets paper). In this case there are 6.022E23 molecules in a mole of molecules, 6.022E23 atoms in a mole of atoms, 6.022E23 bananas in a mole...
November 21, 2014

Chemistry
You made a typo wring sodium sulfate but typing Li2SO4. I assume you meant Li2SO4. 1 mol contains 6.022E23 molecules so 6.78E23 molecules x (1 mol/6.022E23 molecules) = mols Li2SO4. There are two Li^+ per 1 molecule Li2SO4; therefore, there must be twice mols Li&+ must 2x mols...
November 21, 2014

Science- Skin
I see measurements here. Perhaps this will help. http://dermatology.about.com/cs/skinanatomy/a/anatomy.htm
November 21, 2014

Chemistry
Instead of me guessing what you know (or don't know) about this why don't you tell me exactly what your problem is in redox equations and let me help you through it?
November 21, 2014

oops--Chemistry
I used 22.4 L/mol for O2 and that is true for 273 C but for 298 I should have used 24.45 L/mol. That is, mols O2 x 24.45 L/mol = ? L O2 and that's the theoretical yield.
November 21, 2014

Chemistry
You need to calculate the theoretical yield. 2H2O ==> 2H2 + O2 mols H2O = grams/molar mass = 10,000/18 = ? Using the coefficients in the balanced equation, convert mols H2O to mols O2. That's ? mols H2O x (1 mol O2/2 mols H2O) = ? mols H2O x 1/2 = ? Then convert mols O2...
November 21, 2014

mixture problems
Let x = gallons 45% 45x + (500*3) = (500+x)*5
November 21, 2014

thermodynamics
What transformation? where?
November 21, 2014

Int.science/Laws of Thermodynamics
See your other post above.
November 21, 2014

chem
It's hard to do subscripts and superscripts here so here is what I will do. A is the atomic number, M is the mass number, X is the element. so AX^M ==> 2He^4 + 83Bi^211 Now you want the subscripts to add up on both sides as well as the superscripts to add up on both ...
November 21, 2014

DON VASCO PATNA
Or use the reliable c1v1 = c2v2 20%*15L = 15%*L L =?
November 21, 2014

chemistry
2KClO3 ==> 2KCl + 3O2 mass O2 released = 39.8-28.7 = 11.10g mols O2 released = grams/molar mass Using the coefficients in the balanced equation, convert mols O2 to mols KClO3. Now convert mols KClO3 to grams KClO3. That's g KClO3 = mols KClO3 x molar mass KClO3. grams ...
November 21, 2014

Science
I suppose the answer your teacher wants is 50+40 = 90 on the basis that 50 parts one liquid + 40 parts of another makes 90 total. But let me let you in on the real world. Volumes, in almost all cases are NOT additive. Sometimes volumes add to give more than the total of the ...
November 20, 2014

Chemistry/Physics
Both are negative. Why did you subtract? dE = -2.43-5.00 = -7.43 kJ
November 20, 2014

Chemistry/Physics
Re-read your post. Did you omit calculating dE? 2430 J and it is exothermic. q = -2430J so dH is -2430 J. It does 5,000 J work so work - 5000 J. dE = q + w. dE will be in J. Convert to kJ and convert the other so to kJ.
November 20, 2014

Chemistry
Look up the bond energies for each bond. Then bond energies broken - bond energies formed = dH rxn Here is a tutorial + bond energies listed. http://www.kentchemistry.com/links/Kinetics/BondEnergy.htm
November 20, 2014

chemistry
You need to find the caps key on your computr and use it. While you are at it, find the period also. 2H2 + O2 ==> 2H2O When working with gases one can use volume interchangeably as moles. Therefore, If you have 250 mL H2 you will need 250 x 1 mol (O2/2 mols H2) = 125 mL O2 ...
November 20, 2014

college chem
Yes, that's what you do and when you get there there is nowhere else to go. You're subtracting kJ/mol from kJ/mol and the answer is in kJ/mol. (1*-285.8)-(-229.9+0) = ?
November 20, 2014

College Chem
This looks obvious to me. Exothermic reactions release heat so the heat to the calorimeter increases and the temperature goes up inside. T rises. Endothermic reactions absorb heat (where does the heat come from) so the calorimeter loses heat and the temperature goes down ...
November 20, 2014

chemistry
% w/w = (g solute/g solution)*100 = ? DON'T make the mistake that g solution is 250 g.
November 20, 2014

Chemistry
Isn't that all you need? Plot A vs C. You get concentrations from the volume of the stock solution diluted to x mL.
November 20, 2014

Chemistry
I would have measured the absorbance. Did you have a working curve; e.g., absorbance measurements of several solutions of different concentrations. They look like this. https://www.google.com/search?q=graph+beer%27s+law&client=firefox-a&hs=bnu&rls=org.mozilla:en-US:official&...
November 20, 2014

Chemistry
I'm confused by the language of "Can you tell if". Did you run any experiments specifically for this? If the dilute solutions follow Beer's Law and the stock solutions are not too concentrated, they may follow Beer's Law also. Generally, however, ...
November 20, 2014

Math Help
yes
November 20, 2014

int.science gtg in 8 min.
q = mass H2O x heat capacity
November 20, 2014

Int.Science
q1 = heat needed to raise T Cu from 83 C to it's melting point (you will look that up) is q1 = mass Cu x specific heat Cu x (Tfinal-Tinitial) where Tf is the melting point and Ti is 83C. q2 = heat needed to melt Cu at its melting point is q2 = mass Cu x heat fusion You ...
November 20, 2014

chem
I can't make sense of your post but here is how you work the problem. 1. Write and balanced equation. You've done that. 2. Convert grams HgO (whatever that is) to mols. mols = grams/molar mass 3. Using the coefficients in the balanced equation, convert mols HgO to mols...
November 20, 2014

chemistry
Is this at STP? If not what is the volume or total pressure? mols H2 = grams/molar mass mols SO2 = grams/molar mass total mols = mols H2 + mols SO2 XH2 = mols H2/total mols XSO2 = mols SO2/total mols pH2 = XH2*Ptotal XSO2 = XSO2*Ptotal
November 20, 2014

chemistry
1 ppm is 1 mg/L; therefore, 45 mg/L = 45 ppm.
November 20, 2014

chemistry
I don't know. Few of us have the solubility tables memorized. Do you have a graph or a table that lists the solubility at various temperatures. Post that and we can help.
November 20, 2014

Chemistry Numerical
You need k. k = 0.693/t1/2</su> Then ln(No/N) = kt Set No = 100 Set N = 100*1/8 =? k from above. Solve for t in days.
November 20, 2014

Chemistry
See your other post above.
November 20, 2014

chemistry
heat lost by hot metal + heat gained by water = 0 [(mass metal x specific heat metal x (Tfinal-Tinitial)] + [(mass H2O x specific heat H2O x (Tfinal-Tinitial)]=0 Substitute the numbers and solve for the only unknown in the equation.
November 20, 2014

Chemistry
Done
November 20, 2014

Chemistry
Use the dilution formula.
November 20, 2014

Chemistry
Sorry, but I don't see a 12:04 posting and no pH questions from you.
November 20, 2014

Chemistry
I'll give you some hints but it is up to you to put all of it together to make a coherent answer. For AuCl3 ==> Ag^3+ + 3Cl^- Write out Ksp expression and solve for (Cl^-). Plug in Ksp, (Au^3+) = 0.5M and calculate (Cl^-) Do the same for AgCl AgCl --> Ag^+ + Cl^- ...
November 19, 2014

Chemistry
Here is what I found. http://www.jiskha.com/display.cgi?id=1416382196
November 19, 2014

college chem
The electrode reactions are Zn ==> Zn^2+ + 2e Fe^2+ + 2e ==> Fe The anode is where oxidation occurs; therefore, Zn is the anode and it is the negative electrode. Electrons flow from Zn to Fe. Zn is more "active" than Fe.
November 19, 2014

Chemistry
HClO3 is a strong acid and ionizes 100%; therefore, (H3O^+) and (ClO3^-) = 0.28M.
November 19, 2014

Chemistry
You need to put some units on the numbers. Where does Qrxn come from? What kind of reaction?
November 19, 2014

Chemistry
C2H5NO2 + 2H2O → 2CO2 + NH3 + 3H2 a. That will be zero unless you want to count the vapor pressure of water at 27C. I assume that is to be neglected. b. You have 0.0125 mols glycine. You get 0.0125 mol NH3, 3*0.0125 mols H2 and 2*0.0125 mols CO2. c. PV = nRT d. PV = nRT
November 19, 2014

chemistry
(2*molar mass H2O)/(molar mass Na2CO3.2H2O)*100 =
November 19, 2014

chemistry
%Mg = (grams Mg/total mass)*100 = ? Note: total mass is 9.03 + 3.48 = ? %N = (3.48/total mass)*100 = ?
November 19, 2014

AP chemistry
In three words, not very easily. You don't need the O2. ZnCO3 + heat --> ZnO + CO2
November 19, 2014

chemistry
mols ethylene glycol = grams/molar mass = ? Then m = molality = mols/kg solvent (kg solvent is 0.0854 in the problem) The formula are similar for f.p. and b.p. f.p. delta T = Kf*m. Substitute and solve for delta T, then subtract from the normal f.p. of O C to find the new f.p...
November 19, 2014

chemistry
No. In trying to avoid confusing you because I didn't know what other compounds you had (and some may have been ionic), I ended up confusing you by including the i. Just forget the i or if yu want to keep it there, note that I TOLD you it was 1 for this problem. delta T = ...
November 19, 2014

chemistry
delta T = i*Kf*m and I assume all of the solutions you have are non-electrolytes and i = 1. You know Kf (the freezing point constant) and if you don't it will be in your text and it's all over the web. m is the molality and that's in the problem (in this case 1.40...
November 19, 2014

Chemistry
This is an excess of OH^-; therefore, (OH^-)= 1.96E-4M Then pOH = -log(OH^-) = ? Then pH + pOH = pKw = 14. You know pKw and pOH, solve for pH.
November 19, 2014

Chemistry
I don't think so. Count those zeros. I think you have one too many. Now you know what I don't like about those pesky things. 0.01 mmols/51 mL = 1.96E-4M 0.026L x 0.01M = 0.00026 mols NaOH 0.025L x 0.01M = 0.00025 mols HCl 0.00001 mols/0.051 L = 1.96E-4 Or you can let ...
November 19, 2014

Chemistry
Yes, I would say the missing information is important (at least to the problem). I like millimoles (you can change to mols if you like by dividing millimoles by 1000). I like millimoles because it keeps all of those zeros on the left from showing up. millimols NaOH = 26.0 x 0....
November 19, 2014

Chemistry
Mollie, I know all of the tutors on this site are good but we don't have ESP or any of those extraordinary powers. In other words, what solution are you talking about?
November 19, 2014

Science Technology
This site will provide more than you every wanted to know about the camera. http://en.wikipedia.org/wiki/History_of_the_camera
November 19, 2014

science
I believe O2 is generated by the electrolysis of H2O. I don't think it is generated as needed on a space suit but in the space ship, stored in canisters, and the canisters and contents are attached to the space suit with astronaut inside. If they don't wear a space ...
November 19, 2014

science
You've left me out in the wild; give me something to get my bearings
November 19, 2014

Chemistry: Sigma & Pi bonds
You know we don't do all of your homework. But we'll be happy to check your answers. For CH2Cl2 there are 2 sigma CH and CH bonds and 2 C-Cl bonds to make a total of 4 sigma bonds.
November 19, 2014

Chem
I think you're having trouble with the CH2O, too. I think by your formula and the way I do it that the formal charge on C is 0 and the formal charge on O is 0. (and the formal charge on each H is 0). Here is the dot structure. http://www.thegeoexchange.org/chemistry/...
November 19, 2014

chemistry
2Cu^2+ + 4I^- ==> 2CuI + I2 Then I2 + 2S2O3^2- ==> S4O6^2- + 2I^- mols S2O3^2- = M x L = ? Mols I2 = 1/2 that from the equation that 2 mol S2O3^2- = 1 mol I2. mols Cu = 2x mols I2 from the first equation = ? Then M Cu^2+ solution is mols Cu/volume = mols Cu/0.010 L
November 19, 2014

chemistry
mols Zn = grams/atomic mass = ? mols Zn = mols ZnCl2 since the equation shows 1 mols Zn produces 1 mol ZnCl2. Then M ZnCl2 = mols/L solution.
November 19, 2014

chemistry
(g solute/g solution)*100 = 3.1E-5 (0.225/g soln)*100 = 3.1E-5 Solve for g solution (in mL) and convert to L.
November 19, 2014

chemistry
Nope but close. 1 Al + 3N + 9O = ? NO3 = nitrate ion is not an atom. There are 4 atoms in 1 NO3^- and 3x that is 12 + the 1 Al = ?
November 19, 2014

Chemistry
I see a number of posts today. A couple of days ago I answered most if not all and suggested you give some indication of how to solve the problem or at least tell us what you don't understand or what you do understand about the problem. I will go through all of these again...
November 19, 2014

Chemistry
These usually are confusing for students; the secret is to follow the rules. 4Be is 1s2 2s2. For the 1s2 n = 1, s means l = 0 and there is 1electron with +1/2 and the other with -1/2. You simply go down the choices and pick any that has n = 1, l = 0, ml = 0 and ms = +/- 1/2. ...
November 19, 2014

Chemistry
How much heat do we need to raise T 112 g sample of water from 25 to 100? That's mass H2O x specific heat H2O x delta T = 112 x 4.184 x 75 = 35, 146 J. E 1 photon = hc/wavelenth E 1 photon = 6.626E-34*3E8^2/3.28E-3 E/photon x #photons = 3,146 J And solve for # photons.
November 19, 2014

chemistry
You've posted this before but provided no more information than the last time. I responded last time that I had no idea what version A is/was or what you're doing. We aren't clairvoyant and my crystal ball is hazy today. I can't help without knowing what the ...
November 19, 2014

chemistry
(P1V1/T1) = (P2V2/T2)
November 19, 2014

General
I don't know what you mean by "and field 100 bottles.." I suppose the answer is zero mm since mm is a length of measurement and not volume.
November 19, 2014

Chemistry
I agree with your thoughts about #1. For #2, I would look at it this way. If C combines with O2 we get C + O2 ==> CO2 and that is, indeed, a combination reaction. However, if we use a hydrocarbon, such as CH4 and combine that with O2 we get CH4 + O2 ==> CO2 + H2O and ...
November 19, 2014

chemistry
mass = volume x density You know mass and density, substitute and solve for volume in mL. Convert to L.
November 19, 2014

Chemistry
You have calculated the accuracy and not the % error. %error is 100-94.7 = 5.3% Or to do it another way, this is what you do. [(6.02-5.70)/6.02]*100 = same number above.
November 19, 2014

Chemistry
If you need further assistance you need to provide a few more details about exactly what you've done. To convert your answer of 352.49 J/g to kJ/mol, multiply that figures by the molar mass of H2O which gets you to J/mol and divide by 1000 to convert to kJ/mol. Your ...
November 19, 2014

chemistry
You may have made a typo but mass Mg from your data is -0.01 which is impossible. To answer your question, mols Mg = mass Mg/atomic mass mg. # molecules MgO (I wonder if you don't want mols of this, too) = (mass MgO/molar mass MgO)* 6.022E23 = ?
November 19, 2014

chemistry
dE = dm*c^2 E = (0.00650/1000)*3E8^2 =? The 1000 converts g to kg.
November 19, 2014

chemistry
volume H2O is 55.0 + 55.0 = 110.0 and that is 110.0g q = mass H2O x specific heat H2O x (Tfinal-Tinitial) mols Ba(OH)2 = M x L = approx 0.017 but you need a better number than that and that produces twice that number of mols or approx 0.034. Ba(OH)2 + 2HCl ==> BaCl2 + 2H2O ...
November 19, 2014

chemistry
mols H2SO4 in the solution is M x L = 0.400 x 0.1 = 0.04 grams = mols x molar mass = 0.04 x 98 = 3.92g
November 19, 2014

chemistry
Use dG = -RT*lnK and calculate dG. Then dG = dH - TdS.
November 19, 2014

chemistry
See your other post.
November 19, 2014

chemistry
Use delta T = K*m and solve for m. In dilute solutions the m and the M are very close to the same, then pi = osmotic pressure = MRT Post your work if you get stuck.
November 19, 2014

Chemistry
I didn't put units on my answers and I should have done so. They are (H3O^+) = 1.58E-7 M (OH^-) = 1.58E-7 M. And just to make things a little more interesting let me point out that this is a NEUTRAL solution with a pH = 6.80. We always talk about pH = 7.0 as being neutral ...
November 19, 2014

Chemistry
I saw only this one extra question whereas your post said "additional" questions. If there are more than this please just post everything again at the top of the page. You don't do anything with the 37C temperature. That's the temperature of the water at body...
November 19, 2014

Chemistry
I expect you meant H3O^+ and not H2O. (H3O^+)(OH^-) = Kw (H3O^+)=(OH^-) = sqrt Kw.
November 19, 2014

Chemistry
Some is correct. I don't know how your calculator works (calculators aren't standard) but I can tell you how to proceed. First, where did you get the pKa for formic acid? I looked it up on the web and found 3.77. You can get slightly different numbers depending upon ...
November 19, 2014

Chemistry
pKa = -log Ka
November 19, 2014

Chemistry
Use the Henderson-Hasselbalch equation. pH = pKa + log (base)/(acid) pH = ? pKa = look up (base) = 0.07 (acid) = 0.07
November 19, 2014

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