Friday
October 24, 2014

Posts by DrBob222


Total # Posts: 44,711

Analytical Chem
Yes but there is an easier way to do it. Let S = solubility Zn(CN)2==> Zn^2+ + 2CN^-,then + H^+ =>HCN ..solid....S.......2S Ksp = (Zn^2+)(CN^-)^2 For HCN ==> H^+ + CN^- You should confirm all of this. Ka = 6.2E-10 = (H^+)(CN^-)/(HCN) If pH 2.39 then (H^+) = about 4E-3...
September 16, 2014

Chemistry 400/ Chem 1A
excess mol ethanol x molar mass ethanol = grams ethanol in excess
September 15, 2014

Chemistry 400/ Chem 1A
mols KMnO4 = grams/molar mass = approx 0.033 but you need to this and all of the calculations that follow more accurately. mols ethanol = approx 0.05 Convert mols KMnO4 to mols H2SO4. That's 0.033 x 6/4 = 0.05 Convert mols ethanol to mols H2SO4. That's 0.05 x 6/5 = 0....
September 15, 2014

chem
Calculate the neutron:proton ratio. For 48K it has 29N and 19P N/P = 1.5 79Br has 44N and 35P with N/P = 1.26 32Ar has 14N and 18 P with N/P = 0.77 Here is a graph of #neutrons vs #protons. 32Ar is far below the band of stability. 48K is above 79Br look relatively close; I ...
September 15, 2014

Chemistry
mols Al = g/atomic mass = approx 3.06 but you should do this more accurately (as well as all of the other calculations below. I estimate.) Convert to mols O2 using the coefficients in the balanced equation. That's 3.05 x (3 mols O2/4 mol Al) = 2.29 Do you have that much O2...
September 15, 2014

chemistry
mols = M x L Only KCl has Cl^- so that has been diluted from 57.0 mL to 57.0+57.0 + 56.0 = 170 mL. New concn is 0.325 x (56.0/170) = ? Another way is to find mols Cl^-. That is M x L = 0.325 x 0.057L = ? Then M KCl = mols KCl/L solution = (0.325*0.057)/(0.056+0.057+0.057)
September 15, 2014

chemistry
I've been waiting on you to show some work and that hasn't happened yet. Please indicate your answers and why you think that is the answer.
September 15, 2014

chemistry
q = mass x specific heat x (Tfinal-Tinitial)
September 15, 2014

chemistry
17% is h1 35% is 83 Then 48% is 84 (0.17)*81 + (0.35)*83 + (0.48)*84 = ?
September 15, 2014

chemistry
See above.
September 15, 2014

Organic Chemistry
http://www.youtube.com/watch?v=vheqX9W8bf4
September 15, 2014

chemistry
b
September 15, 2014

chemistry
Don't run the numbers together. 1s2 2s2 2p6 3s2 3p2 = ? Add the electrons and that must the be atomic number of the element on the periodic table.
September 15, 2014

chemistry
Wouldn't the answer be obvious if you took the different between F and F; i.e., the electronegativity of F is 4.0 so 4.0-4.0 = 0 and that's < 0.5, right? You can calculate, just for the fun of it, the others. EN H is 2.1 EN K is about 0.8 or 0.9 (you can look it up...
September 15, 2014

chemistry
According to the Arrhenius theory: The acid is the one with the H^+. The base is the one with the OH^-. OR Accoarding to the Bronsted-Lowry theory: The acid is the one that donates a proton. The base is the one accepting a proton
September 15, 2014

Chem
41. q = mass H2O x specific heat H2O x (Tfinal-Tinitial) 42. 100 C is the boiling point for H2O. If you add more heat to water at 100 C it will start to boil. It will continue to boil until all of the water has evaporated. The temperature of the pot will not go above 100 C ...
September 15, 2014

chemistry
I shall be happy to critique what you write.
September 15, 2014

Chemistry
Thanks for showing your work. I think your error is in the last step. If I divide 100/4E-19 I get an answer like 25E+19 or 2.5E20 Check that out.
September 15, 2014

Chemistry
E of 1 photon = hc/wavelength E of 1 photon x # photons = 100 J
September 15, 2014

Chemistry
I don't know what you're doing wrong with your calculator but you need to find out and get it under control. 162/4.53E20 = approx 40E-20 or 4E-19 (I think the actual number is 3.57E-19). (both numbers wrong). My final answer comes out to be about 5.6E-7 m which is ...
September 15, 2014

Chemistry
I think the error is in the exponent.
September 15, 2014

Chemistry
If you will show your work perhaps I can find it as in the other laser problem.
September 15, 2014

Chemistry
1 watt = 1 J/s 15 watt = 15 J/s 15 milliwatts = 15 millijoules/s =0.015 J/s 0.015 J/s x (60 s/min) x (60 m/hr) x (3 hrs) = ? total Joules This E is for 4.53E20 photons so total J/4.53E20 = energy in J/1 photon. Then E in J/photon = hc/wavelength. Solve for wavelength.
September 15, 2014

Chemistry
Go to Google, type in mass proton. Or look in your text/notes.
September 15, 2014

Chemistry
wavelength in m = h/mv h is Plancks constant m is mass proton in kg v is velocity in m/s
September 15, 2014

Chemistry
Go to Google and type in mass electron. I think it is 9.08E-31 kg but you should confirm that.
September 15, 2014

Chemistry
dX*dp = h/4*pi dp is change momentum = m*v; therefore, 4*pi*dX*m*V = h Substitute 4, pi, dx = 611E-12, m is mass electron in kg, h is Planck's Constant, solve for V
September 15, 2014

Organich Lab Help Please!!!!!!!!
I think you're ok if the assumption that the volumes are additive is ok but I don't know about that. Having said that, I don't know of any other way of approaching the problem. If I were making up the problem I would have made the aq layer the top on a and the ...
September 15, 2014

Organich Lab Help Please!!!!!!!!
I went through this last night and you've corrected at least one of the problems. What is your trouble now? Explain in detail. Based on my calculations I would think the aqueous layer would be on the bottom for a. How can you test it. You have the mixture in a sep funnal, ...
September 15, 2014

Chemistry: Please Help!!
39. KE = 1/2*m*v^2. As the more energetic molecules of water (from the sweat) leave due to evaporation, the average energy of the remaining molecules is decreased and lower energy means lower T. Another way of saying the same thing is that energy to help the molecules escape (...
September 15, 2014

Chemistry: Please Help!!
37. Look up the density of H2O versus temperature. I believe the maximum density is at 4 C; therefore, 4C should be the temperature of water at the bottom. right? 38. I might take issue with the statement. The water flows from the outside of the root to the inside of the plant...
September 15, 2014

Chemistry
B is not likely. There is no driving force for N2 and H2O to react but I don't base that prediction upon the polarity of the molecules themselves. Diving forces for reactions are 1. formation of a precipitate (insoluble material). 2. formation of a gas (one is already a ...
September 15, 2014

Chemistry
P1V1 = P2V2 Substitute and solve for the unknown.
September 15, 2014

Pure Chemistry
P1V1 = P2V2
September 15, 2014

chemistry
mass = volume x density mass = 10 mL x 2.5 g/mL = ?
September 15, 2014

chemistry
There are 10^9 nm in 1 m. 0.002 m x (1 m/10^9 nm) = ?
September 15, 2014

Chemistry
yes
September 15, 2014

Analytical CHM
I did this for you yesterday, in detail. KHP + NaOH ==> KNaP + H2O mols KHP = grams/molar mass = 0.8/molar mass KHP = approx 0.0039 but you need to do this step as all that follow more accurately as I've estimated. Step 2. Convert mols KHP to mols NaOH using the ...
September 15, 2014

Chemistry
All you ever wanted to know about charge balance: http://ramsey1.chem.uic.edu/audrey/chem222/assign_docs/fall_12/mass_charge_ANS.pdf All you ever wanted to know about mass balance. http://mimoza.marmara.edu.tr/~zehra.can/CHEM209/6.%20Mass%20Balance%20Charge%20Balance.pdf both...
September 15, 2014

Chemistry
566 kJ/2 mol x 0.750 mols = ?
September 15, 2014

Organich Lab Help Please!!!!!!!!
You have posted this for the last day or two. One reason you don't have an answer is that you don't say what the ethylene bromohydrin is mixed with. You say mixed with 100 mL OF WHAT? Second reason is when I look up ethylene bromohydrin on google I find the density is ...
September 15, 2014

chemistry
(3.92/gallon)x (13.5 gallons/week) x (1.5 weeks) = ?
September 14, 2014

chemistry
mols Ag in 6.00g = grams/atomic mass mols Cu = 1/2 mols Ag (from the coefficients in the balanced equation) Then g Cu = mols Cu x atomic mass Cu
September 14, 2014

Chem 1
What's the temperature of the water when the bottle is first filled. Let's say it is such that the density of the watrer is 1.0 g/mL. If the problem doesn't tell you it can't be solved exactly. If density i8s 1.0 g/mL, then the mass of the water is 1,700 grams...
September 14, 2014

CHM
mols KHP = grams/molar mass mols NaOH = mols KHP M NaOH = mols NaOH/L NaOH. You know M and mol NaOH, solve for L NaOH. Both 0.8 and 0.9 are done the same way.
September 14, 2014

Chemistry
3.13 A = 3.13E-8 cm volume = (3.13E-8)^3 = ? m = volume x density = ? bcc is 2 atoms/unit cell. 2 atoms/unit cell*atomic mass/6.02E23 = mass from above. Solve for atomic mass.
September 14, 2014

chemistry
You omitted the units for the rate constant. It's a first order reaction. ln(No/N) = kt No = 2.45 mol N = ? k from above t = 5 min but since k is per second, 5 minutes must be converted to seconds.
September 14, 2014

College Chemistry
Look up the density of ethanol, then mass = volume x density
September 14, 2014

chemistry
This can be solve without an equilibrium constant and none is listed. If one were this is what you do. ..............2HI--> H2 + I2 Kc = (H2)(I2)/(HI)^2 You know (I2) from the problem. (H2) = (I2) Plug in those values and solve for (HI) at equilibrium.
September 14, 2014

chm
Answered way way above.
September 14, 2014

CHEM
CH4 is symmetrical; CH3Cl is not. Look up the 3D shape of each. CH4 is tetrahedral in shape so each of the polarities of each of the C-H bonds cancel each other. With CH3Cl; however, You have 3 C-H bond at tetrahedral angles but the C-Cl bond, more polar than the C-H bond, ...
September 14, 2014

Chemistry
ice water.
September 14, 2014

chemistry
c1v1 = c2v2 concn x volume = concn x volume But first, a question. How will you DILUTE 21.4 M to make it 51.5M. You DILUTE something to make it less concentrated, not more concentrated.
September 14, 2014

chemistry
I'm not into writing discussion questions. I shall be happy to critique your discussion, though.
September 14, 2014

chemistry
You can't add these up? Look on your periodic table and add the atomic masses.
September 14, 2014

chemistry
See your other post.
September 14, 2014

chemistry
Sorry, I answered one question twice. Ignore the first part.
September 14, 2014

chemistry
You can't add these up? Look on your periodic table and add the atomic masses. S + O2 ==> SO2 How many mols SO2 do you want? Use PV = nRT and solve for n. Using the coefficients in the balanced equation, convert mols SO2 to mols S, then grams S = mols S x molar mass S.
September 14, 2014

CHM
How can I suggest an alternative when I don't know what you used. And the indicator changes with the kind of titration you do. If you used KHP, I assume that was to standardize something like NaOH. In that titration, the pH at the equivalence point is about 8.3 and ...
September 14, 2014

Chemistry
% yield = (actual/theoretical)*100 = ? with mols: mols H2O in 64g is 64/18 = 3.555 %yield = (3.55/4.04)*100 = 88.0% with grams: %yield = (64.0/72.8)*100 = 87.91; however, if I remember this problem right the number was 72.7 g H2O (g = mols x molar mass = 4.04 x 18 = 72.7) and...
September 14, 2014

Chemical
mols NH4Cl = 20 g/53.5 = about 0.37 but you need to do this and all other calculations here more accurately. 14.8 kJ/mol x 0.37 mol = 5.5 kJ = 5500 J. Then -5500 J = mass H2O x specific heat H2O x (Tfinal-Tinitial) Solve for Tf.
September 14, 2014

Science
See your other post.
September 14, 2014

Chemistry
It is now 1/12 of atom C12 = 1/12 x 12 = 1.0 and 1.0/6.02E23 = 1.66E-24 grams for 1 amu. If 1/10 P31 then 1/10 x 31 = 31/10 and 31/10 x 1/6.02E23 = 5.15E-24 g = 1 amu. Check my thinking.
September 14, 2014

Chemistry Urgent Help Please!
https://answers.yahoo.com/question/index?qid=20120310230538AAx93Yk
September 14, 2014

Chem help
https://answers.yahoo.com/question/index?qid=20120310230538AAx93Yk
September 14, 2014

Chem !!!!!!!!!!!!!!!!
It's tough to provide an answer when I don't know the question. What impurities? What compounds? But in the absence of all of that I would think you're looking at V, Fe, Mn, Ti, Cr, Cu, Co, Ni salts. Most of those compounds are colored and I think all of the Na ...
September 14, 2014

Chem !!!!!!!!!!!!!!!!
You want the material to be extracted to be relatively soluble in the solvent. advantage solvent more dense than water: The solvent will be the bottom layer and can be drained "from the bottom" of a separatory funnel. The "leavings" will be at the top and ...
September 14, 2014

Chemistry
wavelength = h/mv w = 2.5E-10m h = Planck's constant m = mass of electron. I think this is 9.11E-31 kg but you should confirm that. v = ?
September 13, 2014

Organic Chem Help :(
See the three links below. Select each and scroll down the page to the table on the right side of the screen. Find the density. If it is greater than 1.05 it will be on the bottom. If it is smaller than 1.05 it will float. http://en.wikipedia.org/wiki/Chloroform http://en....
September 13, 2014

chemistry
So what did you choose/use. I can't list an alternative if I don't know what you used. And it's the standardization of what? with what?
September 13, 2014

chm
It depends upon the indicator used for the titration. If methyl orange or methyl red is used there is no effect. 2NaOH + CO2 --> Na2CO3 + H2O 2NaOH makes one Na2CO3 and in using m.o. or m.r. you titrate all of the carbonate as CO3^2- + 2H^+ --> H2O + CO2 If ...
September 13, 2014

Analytical CHM Lab
Because it is next to impossible to secure a sample of NaOH free of impurities. The most prominent impurity is that solid NaOH pellets absorb CO2 and H2O from the air almost as fast as you can weigh it. You CAN prepare some CO2 free NaOH in SOLUTION form but that still must be...
September 13, 2014

Organich Lab Help Please!!!!!!!!
I'm sorry but most of us here don't have the time to write a chapter. If you will tell us how we can help you get started we can help with that but I don't think any one will write your paper for you.
September 13, 2014

Chemistry
I just answered your question WAAAAY down below at your first post.
September 13, 2014

Chemistry
I prefer to do limiting reagent problems (LR) another way but I'll stick to this way for this problem. You have 8.08/2 = 4.04 mols H2 and that will use 4.04 x 1/2 = 2.02 mols O2. Do you have that many mols O2? Yes, you have 72/32 = 2.25 so H2 is the LR and O2 is the ...
September 13, 2014

chemistry
What do you mean by "most"? That's a relative term. Do you want the most in absolute terms or in percent?
September 13, 2014

chemistry
Wouldn't you expect the difference to be zero if F bonds with itself? And that's < 0.5
September 13, 2014

chemistry
See your other posts.
September 13, 2014

chemistry
If the radius Na^+ is 1A and Cl^- is 1.8A then we can assume the bond is 2.8A long and that is the length of one side of the cube of NaCl. We assume there is no space between the ions. So the volume of the cube will be (2.8E-8 cm)^3 = 2.195E-24 cc. How much does one molecule ...
September 13, 2014

chemistry
2000 x 0.25 = 500 calories from fat. 2000 x 0.75 = 1500 calories from sugar. g fat x 9.0 cal/g = 500 g fat = about 55.6 g fat for 25%. g sugar x 4.5 cal/g = 1500 g sugar = 333.3 g sugar for 75%. g O2 needed for fat consumption is 2C57H114O6 x 165O2 = 114CO2 + 114H2O mols fat...
September 13, 2014

Chemistry
q lost by metal = mass metal x specific heat metal x (Tfinal-Tinitial) = ?
September 13, 2014

Help please, :)
http://en.wikipedia.org/wiki/French_and_Indian_War
September 13, 2014

science
wavelength = h/mv Remember to change v to m/s
September 13, 2014

chemistry
mols H2 = grams/molar mass = 8.08/2 = 4.04. (I rounded for the molar mass H2; you may want to do it more accurately.) Convert mols H2 to mols O2 using the coefficients in the balanced equation. 4.04 mols H2 x (1 mol O2/2 mols H2) = 4.04 x 1/2 = 2.02 mols O2 needed to react ...
September 13, 2014

Chemistry
I made a typo.The question mark key is next to the > key and I hit both at the same time.
September 13, 2014

Chemistry
Your post says to rewrite the following using a thermochemical equation but you don't give anything to rewrite. Sorry. Now I see the combustion of propane. C3H8 + 5O2 ==> 3CO2 + 4H2O dH = -2220 kJ I have also seen these written as C3H8 + 5O2 ==>? 3CO2 + 4H2O + 2220 kJ
September 13, 2014

Chemistry
The digits are right but the number of s.f. is not. If I read the question properly when you take 1/2 of 10 to find radius that leaves you just one s.f. and one is all you can have in the answer. If that is 10.0 things would be different. If the 10 is correct I think the ...
September 13, 2014

Chemistry
I don't think so. I believe you multiplied by 2.4m and not 240 cm. Also I don't think you rounded off to the right number of significant figures.
September 13, 2014

Chemistry
Surely you have a table or graph in your text/notes to do this. I don't know of anyone who have all of these solubility tables memorized.
September 13, 2014

Chemistry
mols = M x L - ? Then mol = grams/molar mass
September 13, 2014

Analytical Chemistry
Principles behind the procedure? I guess I never thought about it. You pipet with an accurately measured sample and make to the final dilution in an accurately labeled final volume.
September 13, 2014

Organic-Chem Lab Question Need Help!!!
Do you have the K for the extraction using propanol. If so that should tell you. For part b it is ALWAYS better (f better is better yield) to extract with 3 portions of a solvent over 1 extraction with a single amount (even though 15*3 = 45). You can run through and calculate ...
September 13, 2014

Still confused
You have one equation. Solve for x and 14,000-x. The x will be the amount invested at 4% and 14,000-x will be the amount invested at 2.5%. Solve the equation and you'll get. If you have trouble with the equation post (respond here and not with a different post) exactly ...
September 12, 2014

-Math-Desperate
Let X = amount invested at 4%, then (14,000-X) = amount invested at 2.5%. The equation is 0.04X + 0.025(14,000-X) = 458.00 Solve for X and 14,000-X.
September 12, 2014

Correction Please
I assume someone worked the problem for you and gave you instructions for the width. But if you know the width, use the equations to substitute and solve for the length. It can't be that bad. L is 2*w-3
September 12, 2014

chemistry
Did you give up on me? a + b = 0.02 b/a = 0.158 or b = 0158a So a + b = 0.02 and we substitute 0.158 for b to read a + 0.158a = 0.02 1a + 0.158a = 0.02 1.158a = 0.02 a = 0.02/1.158 = about 0.0173 M. Substitute this value for a into a + b = 0.02 and b = 0.02-0.0173 = 0.00273 M ...
September 12, 2014

chemistry
close. I don't know where you got the 1. 10^-0.8 = 0.158. Now, that's equation 1. We can save some typing if we just call (acid) as a and (base) as b. So b/a - 0.158 and b = 0.158a Now equation 2 I gave you in my original response as a + b = 0.02 M (that's 20 mM). ...
September 12, 2014

chemistry
For whatever it's worth, the pKa of acetic acid is 4.76 according to a text I have so I suspect the author of your problem just rounded it to 4.8. And acetic acid has only one pKa value, not two.
September 12, 2014

chemistry
OK. Forget about the video and follow my instructions. There are only 5 or 6 steps. One equation you need is that last one I wrote. 4.0 is the pH you want the buffer to be. 4.8 is the pKa given to you in the problem. Substitute into the HH equation to obtain 4.0 = 4.8 + log(...
September 12, 2014

chemistry
Saraly, I think you have misread the problem. The pH is 4.0 and the pKa (there is only one listed) is 4.8 So 4.0 = 4.8 + log base/acid and base/acid = ?
September 12, 2014

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