Friday
September 4, 2015

Posts by DrBob222


Total # Posts: 49,899

chemistry
Didn't I do this a couple days ago for you. Instead of reposting, tell me what you didn't understand about the answer and we can get through it. t is the only unknown in the equation.
May 10, 2015

Chemistry
Do this. dHrxn = (n*dHformation products) - (n*dHformation reactants) You can look up the dH formation, usually labeled as delta Hfo in your text/notes/on the web. Post your work if you get stuck.
May 10, 2015

chemistry
You can read this site. http://chemistry.oregonstate.edu/courses/ch361-464/ch362/irinstrs.htm Part way down the first page you see the following: All of the source energy gets to the sample, improving the inherent signal-to-noise ratio. The digitization and computer interface ...
May 10, 2015

analytical chemistry
I don't know the answer to your first question since I don't know what your prof had in mind. The information and questions after that is out of my league. I've never done any work with synchronous spectra; in fact, I don't know what it is. Sorry about that.
May 10, 2015

Chemistry
There may be shorter ways to do this but here is what I would do. PbxOy + C ==> yCO2 + xPb Use PV = nRT and solve for mols CO2 at rtp. Convert mols CO2 to g oxygen. g Pb = 13.70-g O = g Pb Then mols Pb = grams pb/atomic mass Pb = ? mols O atoms = grams O/atomc mass O = ? ...
May 10, 2015

Chemistry
Convert 5 g CuO to grams CuSO4.5H2O. That s 5 g CuO x (molar mass CuSO4.5H2O/molar mass CuO) = ?g CuSO4.5H2O equivalent. This is the theoretical yield (TY). The actual yield (AY) from the problemn is 10g. %yield = (AY/TY)*100 = ?
May 10, 2015

chemistry
I don't know that this will answer the question but it's interesting, anyway. https://www.google.com/search?q=can+FT+be+used+for+UV-vis+spectra&ie=utf-8&oe=utf-8
May 10, 2015

Chemistry
CH3CH2CH2CH2CH2-OH + CH3-COOH ==> CH3CH2CH2CH2CH2OOCCH3 + H2O
May 10, 2015

wave optics
sound waves
May 10, 2015

ap chemistry
negative S means -entropy and negative means minus. So the sign is the opposite of +.
May 9, 2015

ap chemistry
What does negative S mean to you?
May 9, 2015

ap chemistry
I believe all three are negative S.
May 9, 2015

Science
Scroll down to Basic Concepts. http://en.wikipedia.org/wiki/Global_Positioning_System
May 9, 2015

Science
From what I have been able to read, four are required unless the receiver clock is synchronized with the satellite clocks in which case only three are required. I think the key part of this question is "pinpoint.......on EARTH'S SURFACE". Knowing on earth's ...
May 9, 2015

chemistry
2HCl + Ba(OH)2 ==> 2H2O + BaCl2 mols HCl = M x L = ? mols Ba(OH)2 = M x L = ? Determine the limiting reagent and go from there. Post your work if you get stuck and I can help you through.
May 9, 2015

chemistry
I would use dG = 0 = dGo + RTlnQ but that doesn't give me 775 atm.
May 9, 2015

Chemistry - Acids/Bases
I think it is time that someone clarified the definition of strong/weak acids/bases and/or examples of those that are insoluble. Of course I could be mixed up; in that case, perhaps I could be clarified. :-)
May 9, 2015

Chemistry - Acids/Bases
Most of us have classified strong and weak acids/bases as all or nothing; i.e., strong has to do with does it ionize 100%(or close to 100%) or not. If yes we say it is strong, if not we say it is weak. If you read much on the internet, especially about strong/weak bases you ...
May 9, 2015

ELECTROCHEMISTRY
What Eo values are you using for Cd and H.
May 9, 2015

chem 100 electrochemisty
If you had shown your work I could find the error. You're right, the Cl doesn't change oxidation state; however, it enters the reaction (formation PbCl2) so it should be included in the equation.And I assume you meant to say USE Eo to calculate Ereaction.
May 9, 2015

chemistry
q1 = heat needed to raise T of ice from -18 C to zero C. q1 = mass ice x specific heat ice x (Tfinal-Tinitial) q2 = heat needed to melt ice at zero C to liquid H2O at zero C. q2 = mass ice x heat fusion q3 = heat needed to raise T liquid H2O from zero C to 25 C. q3 = mass ...
May 9, 2015

chem 100 electrochemisty
Add -nFEo for Cu^3+ + 2e ==> Cu^+ to -nFEo for Cu^+ ==> Cu^2+ + e Then total = -nFEo. Solve for Eo I ran through it quickly and if I didn't punch in the wrong numbers it's about +2.5 v for Cu^3+ + e ==> Cu^2+
May 9, 2015

Chem 100
What about Cl2 + H2O2 ==> 2Cl^- + O2 + 2H^+ I don't know if this is the spontaneous direction or the reverse but you can look up the Eo potentials and decide which direction to write it.
May 9, 2015

college chemistry
dG = dH - TdS At the melting point of zero C the system is in equilibrium; therefore, dG = 0. Substitute and solve for dS.
May 9, 2015

college chemistry
Thomas, it wouldn't hurt to read over your posts before you push that submit button. No caps and no periods and typos to boot leave a post that's difficult to interpret. For this one I've guessed at half of the question; assuming I've guessed right you do the ...
May 9, 2015

college chemistry
I don't know what you're supposed to use (what are you studying in the chapter) but one way to do it is this. Look up dHvap and dSvap, then dG = dH - TdS Since dG = 0 at the boiling point, then T = dHvap/dSvap
May 9, 2015

chemistry
Any pH? Any concentration of sodium acetate? Any buffer strength? 25 drops acetic acid + 15 (split the difference) sodium acetate, add water, and viola! However, you don't have much of a buffer with all of that other information dangling.
May 9, 2015

Analytical Chemistry
ok. good. Now you understand that "standard 1" really isn't a standard. That's the unknown. If you were doing this on graph paper (I don't know how you do it on Excel), you would extrapolate that straight line starting at the 9.990 point and moving to the...
May 8, 2015

Analytical Chemistry
I commented in my first response that your concentrations were calculated correctly. However, I don't know what the 19.979; 29.986, etc are. These may be the intensity. Also, I note you have a b of 4.7499 which I didn't see in the first post. At least I don't ...
May 8, 2015

Pre-Ap Chemistry
2KClO3(s)->2KCl(s) + 3O2(g) mols KClO3 = grams molar mass = ? Using the coefficients in the balanced equation, convert mols KClO3 to mols O2 gas. Then substitute n into PV = nRT and solve for V in liters at the conditions listed. Use P = 0.683 atm, R is 0.08206 L*atm/mol*K...
May 8, 2015

Pre-Ap Chemistry
You need to rethink this. K = 273 + 34 which is NOT 315.4.
May 8, 2015

Pre-Ap Chemistry
mols Na = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols Na to mols H2. Then convert mols H2 to L H2 by L H2 = mols H2 x 22.4 L/mol = ? Approx 2 L if I didn't punch in something wrong on the calculator.
May 8, 2015

chemistry
(1/[A]) - (1/[Ao]) = akt You know a, k, and can calculate (Ao). Solve for A.
May 8, 2015

chemistry
The dilution formula is mL1 x M1 = mL2 x M2 mL1 x 6 = ....
May 8, 2015

CHEMISTRY
OK but you are not allowed that many significant figures.
May 8, 2015

CHEMISTRY
When working with gases one may use volume as if L were mols. 794L NO2 x (1 mol NO/3 mol NO2) = ?
May 8, 2015

Chemistry
M HCl = mols/L solution = ? M H^+ = M HCl since HCl is a strong acid and ionizes 100%. pH = -log (H^+) pH + pOH = pKw = 14 allows you to calculate pOH after you know pH then pOH = -log(OH^-) gives you OH^- Alternatively, after you know (H^+), you can use (H^+)(OH^-) = Kw = 1E-...
May 8, 2015

Chemistry Help, Please!!!
(H^+)(OH^-) = Kw. You know Kw. You know from the ionization of H2O that (H^+) = (OH^-) from H2O ==> H^+ + OH^- Solve for (H^+) and convert to pH. I suspect you've already done this and didn't get pH = 7 so you think something is wrong. It isn't. The pH will not ...
May 8, 2015

THIS IS DUE BY 10PM
T is wrong. What's the 22.4? It doesn't belong there. Where is n? It belongs there. No surprise the data base gave you a thumbs down.
May 8, 2015

chemistry
I would do this. %C in H2C2O4 is approx 27% but you should get a more accurate answer. %C = (2*atomic mass C/molar mass)*1000. 1005g of 27% C gave a reading of 102540. So the % C in the soil is 27% times two correction factors. One factor converts for the difference in IR ...
May 8, 2015

chemistry
Another calculation site. http://www.piketech.com/skin/fashion_mosaic_blue/application-pdfs/CalculatingPathlength-LiquidCells.pdf
May 8, 2015

chemistry
http://www.smarteam.com.tw/calcell.pdf
May 8, 2015

analytical chemistry
You're right. It requires something and absorbance is ok to use. You may not have absorbance but you plotted something to get the equation you posted. What did you use; ? vs concentration. What's the ? If you want to pursue this further I recommend you start a new ...
May 8, 2015

analytical chemistry
From what you've described you must have plotted a "standard addition" plot. Your straight line equation does not include the b of y = mx + b. You will tell be it's zero but it isn't. Those concentrations you plotted are not 1.5 ppm, 3 ppm, etc but unk+1....
May 8, 2015

analytical chemistry
What you've done so far appears to be ok. You must be plotting with data not posted. As for R, that looks pretty close to 1 to me.
May 8, 2015

Chemistry
Pb goes from +2 on the left to +2 on the right; no change. O2 on the left goes to O on PbO with -2 and to SO2 at -2 EACH.
May 8, 2015

Chemistry
If you want more help the only thing we can do is to work the problem and present it to you on a platter. And whatever it is that you don't understand gets put off until another day. I have an alternative. Why not explain what you don't understand. The steps are there...
May 8, 2015

Chemistry
First determine the constant, k, for the reaction. k = 0.693/t1/2 Then ln(No/N) = kt Let No be 100 (but you may use any number you want as long as N is 25% of No. Then N = 25 k from above. Solve for t in days.
May 8, 2015

Physical Science
f = ma
May 8, 2015

chemistry
I had no idea there was a traditional and a non-traditional method for balancing redox equation. So tell me what you don't understand about this and we can get it done.
May 8, 2015

Chemistry
What's 6000m. Did you mean 6000 mL? That is the TOTAL volume needed; the question wants to know how much must be ADDED so you must add 6000 mL - 500 you already had = 5500 mL to be added.
May 8, 2015

Science, check answers please
Thanks for letting me know.
May 8, 2015

Science, check answers please
I think A is ok for 3. For 8, the thing that bothers me about a conductor as an answer is that adding a conductor to a wire when the wire is already a conductor makes no sense to me. A magnetic field is established around a conducting wire when a current flows through the wire...
May 8, 2015

Science, check answers please
3 and 10 are wrong. 8 I don't know. I don't like any of the choices on 8. Increasing current would do the job. A solenoid IS an electromagnet. That may be the best choice of those listed.
May 8, 2015

chemistry
Can't draw images on Jiskha but here is a good one on Google. https://www.google.com/search?q=heating+curve+for+water&tbm=isch&imgil=AqCbHF3FgK9F1M%253A%253BXTumgatoZfQ0JM%253Bhttps%25253A%25252F%25252Fwww.boundless.com%25252Fchemistry%25252Ftextbooks%25252Fboundless-...
May 8, 2015

chemistry
I know it's cool to use lower case for everything; however, CO, Co and co mean different things in chemistry. When you type chemistry questions you should find the caps key and use it. CaCO3 ==> CaO + CO2 mols CaCO3 = grams/molar mass = ? Use the coefficients in the ...
May 7, 2015

chemistry
What mass of solute is contained in 250 mL of 0.895 M NH4Cl? I think that this is a molarity question. Molarity = mass of solute/volume of solution in L. You're right. It is a M question and M = mols/L. 1 mL = 0.001 L so 250 mL * 0.001 L = 0.25 L Right again. 250 mL = 0....
May 7, 2015

Chemistry
Another (P1V1/T1) = (P2V2/T2)
May 7, 2015

Chemistry
Use (P1V1/T1) = (P2V2/T2) P is in atm, T in kelvin, V will be in L and convert to mL. R is 0.08205 L*atm/mol*k For a you will need to convert mm Hg to atm. atm = 658/760 = ? For b you have atm, you will need to convert C to K. 273 + C = K For c same conversions as b. Post your...
May 7, 2015

chemistry
You're right about [(g solute/g solution)]*100 = Wt %. There are a number of points to clear up with what you've written. 1. No, I don't think you assume 100 g for the mass of the solution. The problems tells you in the last sentence the the mass of the solution is...
May 7, 2015

science
salamander
May 7, 2015

Chemisty
No. It has to do with the common ion effect in which Cl is the common ion. That decreases the solubility of AgCl from what it would normally be. But I can tell you the answer is NOT 1.60E-10 for that is Ksp and not the solubility. ........AgCl ==> Ag^+ + Cl^- I.......solid...
May 7, 2015

Chemistry
P1V1 = P2V2
May 7, 2015

Chemistry
What don't you get? Dalton's law of partial pressures tells us that the total pressure of a system is the sum of the partial pressures of each gas. You have two gases in this system; i.e., N2 gas and water (as a vapor which is a gas). So according to Dalton's Law, ...
May 7, 2015

Chem
I worked this for you yesterday. I can find it for you if you can't or you can tell be what you didn't understand about my explanation.
May 7, 2015

chem
dHrxn = (n*dHf products) - (n*dHf reactants) Set dHrxn to -15.1 kJ and solve for dHf for nitroglycerin.
May 7, 2015

chem
q1 = heat needed to raise T from -20 to zero. q1 = mass ice x specific heat ice x (Tfinal-Tinitial) q2 = heat needed to melt ice at zero to liquid water at zero C. q2 = mass ice x heat fusion q3 = heat needed to raise T of liquid water at zero C to 100 C. q3 = mass H2O x ...
May 7, 2015

chem
[mass steel x specific heat steel x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] \ 0 Subsitute and solve for the unknown.
May 7, 2015

chemistry
What problems do you have in understand this?
May 6, 2015

Chem
This is a limiting reagent problem and combustion problem rolled into one. First determine the limiting reagent. I do them the long way. 2H2 + O2 --> 2H2O mols H2 = 90/2 = 45 mols mols O2 = 90/32 = about 3 but you need a better answer than that. Convert mols H2 to mols H2O...
May 6, 2015

Chemistry
Is that 5.0 L flask? (H2) = mols/L = approx 0.15 (CO2) = 0.8/5 = about 0.15 but you need a more accurate answer for both. ..........H2 + CO2 ==> H2O + CO I.......0.15..0.15......0.....0 C........-x....-x.......x.....x E.....0.15-x..0.15-x....x.....x Substitute the E line ...
May 6, 2015

Chemistry
mols Zn = grams/atomic mass Zn = ? mols H2 formed = same as mols Zn (look at the 1 mol Zn forming 1 mol H2) Substitute mols H2 into PV = nRT at the conditions listed and solve for volume in L. Remember T must be in kelvin and P in atmospheres for V to come out in L. Use 0....
May 6, 2015

Quant Reasoning
a. $80/month x 12mo/yr x 3yr = ? ? + 300 = total cost.
May 6, 2015

General Chemistry 132
I'm a retired chemistry professor from a university in Louisiana (but not living in Louisiana now). Taught chemistry for 40 years.
May 6, 2015

General Chemistry 132
Yes, but first, note the correct spelling of celsius. By definition, delta H (enthalpy) is - if heat is emitted from a reaction and + if heat is absorbed by a reaction. Since the temperature of the water decreases that means the solvation of NH4NO3 absorbed energy and it told ...
May 6, 2015

Chemistry
Use the HH equatiion. (acid) = 2*1.8 and x = (base)
May 6, 2015

chemistry
a is not right. You are adding an acid to a buffer. The base will be the one reacting with the acid and the base is A^-. b. In chemistry the first two thoughts about working a problem are as follows: 1. mols 2. ICE table In a buffer solutiion, I usually do these by millimoles ...
May 6, 2015

Chemistry
Find mols of each, do an ICE chart, use the HH equation.
May 6, 2015

chemistry
I don't know exactly how you're using the term neutrality but I don't think it does. pH is tied inexorably to (H^+) and (OH^-) and when you change any of the three the others dance and change accordingly.
May 6, 2015

chemistry
How would you like for us to help you with this assignment short of writing it for you?
May 6, 2015

chemistry
# equivalents NaOH = grams/equivalent weight (eq wt NaOH is 40 which is the same as the molar mass because it has 1 OH group) N = equivalents/L solution = ?
May 6, 2015

chemistry
See your post above.
May 6, 2015

College Chemistry
Ecell=E0-(.0592/n)logQ Eo is 0 0.3 = -0.0592*log Q Solve for Q. Then Q = (dilution solution)/(concentrated solution) You have no way of knowing which the the more dilute but you can try it both ways; i.e. substitute Q and 0.1 and try it. Q = 0.1/x and Q = x/0.1. One of the ...
May 6, 2015

chemistry
You can read about it here. http://www.chemteam.info/Redox/Redox-Rules.html Please read the above but here is how you do this one. All compounds are zero. Al is in group III (or 13 depending onh the system used) so the oxidation state is 3. You have 12 O at -2 each for -24. ...
May 6, 2015

chemistry
Is that 0.5 mol or 0.5M? What's the concentration of the HNO3.
May 6, 2015

Chemistry
I think I've done this for you before. Is there something about the process you don't understand?
May 6, 2015

Chemistry
Instead of me guessing what you wrote why not show your work and let me find the error (if there is one)?
May 6, 2015

Chemistry
mols NaOH = grams/molar mass = ? a. 0.871 is correct for M. b. 1.016 g/mL x 1000 mL x (?%/100) x (1/36.5) = 0.871 Solve for ?
May 6, 2015

Chemistry
10.6-5.95 = g H2O = 4.65 mols H2O = 4.65/18 = ? mols ZnSO4 = 5.95/molar mass ZnSO4. Find the ratio of water to 1 mol ZnSO4. The easy way to do that is to divide the mols H2O by mols ZnSO4 and round to a whole number. If I punched in the right numbers on my calculator that ...
May 6, 2015

chemistry
I think you are on the right track. You just have another step or two to go. And you're right, this is a limiting reagent problem; I usually work these the long way. mols Pb(NO3)2 = M x L = approx 0.00121 mols Na2SO4 = approx 0.00130 Pb(NO3)2 x Na2SO4 ==> PbSO4 + 2NaNO3...
May 6, 2015

Chemistry
mols HCl = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols HCl to mols CaCl2. Now convert mols CaCl2 to grams CaCl2. g = mols x molar mass
May 6, 2015

chemistry
I presume you have [H2CO3] and [H2O^+]. You can use [H3O^+]{OH^-] = Kw = 1E-14 to solve for (OH^-). (HCO3^-) = essentially the same as (H3O^+) (CO3^2-) = Ka2
May 6, 2015

chemistry
I don't believe the answer by anonymous will get it. Use P1V1 = P2V2 226 x 1.7 = 2.7V2. Solve for V2.
May 6, 2015

chemistry
The following determines the M and N. If you really want molality repost but m = mols/kg solvent and probably you can do that yourself. 1.10 g/mL x 1000 mL x 0.15 x (1/98) = ?M Technically one cannot determine the N without knowing the reaction; however, USUALLY, it is M*#H ...
May 6, 2015

Chemistry
Why didn't you show what you had? But thanks for telling us your next problem. How many mols vit C do you have. That's 1/molar mass = ? and I'll make up a number say 0.1 but of course you know that isn't right. Then you can convert mols of vit C to mols of ...
May 6, 2015

Chemistry
mols urea = grams/molar mass = ? mols H2O = grams/molar mass = ? Total mols = sum mol fraction = XH2O = mos H2O/total mols pH2O = XH2O*PoH2O. If you want it at 25 C, use Po at 25 C.
May 6, 2015

Chemistry
I would do this. pHe + pH2O = 1.16 atm. Calculate pHe alone but be careful that you use the same units. Then use PV = nRT and solve for V for the dry He. Using that number for n dry He, solve PV = nRT for n for H2O at 17.5 torr. Add n H2O + n He for total mols, then PV = nRT ...
May 5, 2015

chemistry
I'm sure I worked this earlier. Let me know if there is something you don't understand about the process.
May 5, 2015

chemistry
pKa = -log Ka or Ka = 10^-pKa. Solve for Ka.
May 5, 2015

Chemistry
I assume the heat capacity of the calorimeter is zero. heat lost by metal + heat gained by waer = 0 [mass metal x specific heat metal x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0. Substitute and solve for specific heat metal.
May 5, 2015

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