Wednesday
July 1, 2015

Posts by DrBob222


Total # Posts: 49,367

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

Chemistry
My assumption is that you are to use bar as the standard pressure and not atm. If you want atm change bar to atm and recalculate accordingly. 2NaHCO3(s) ==> Na2CO3(s) + H2O(g) + CO2(g) a. Ptotal = 7.68 bar = pH2O + pCO2 pH2O = pCO2 = 7.68/2 = ?bar b. Substitute the pH2O and...
May 5, 2015

Chemistry
You need to re-write the equations as such. PbI2(s) ==> Pb^2+ + 2I^- Pb^2+ + 4I^- --> [PbI4]^2- -------------------------- add the two equation to get this. PbI2(s) + 2I^- ==? [PbI4]^2- for which Keq = Ksp*Kf You can plug in Ksp and Kf and see that Keq is what it should ...
May 5, 2015

chemistry 121
...........HOAc + H2O ==> H3O^+ + OAc^- I..........0.5M............0.......0 C..........-x..............x.......x E.........0.5-x............x.......x Substitute the E line into Ka expression and solve for x = (H3O^+) then convert to pH. If you know Ka (and you do) then ...
May 5, 2015

Equilibrium constant
..........SO2Cl2 ==> SO2 + Cl2 I.........0.022......0......0 C.........-x.........x......x E.......0.022-x......x......x The problems tell you that (Cl2) = x = 1.7E-2. Substitute into Kc expression and calculate Kc
May 5, 2015

Equilibrium
Keq = (I)^2/(I2) = 0.015 You know I2 at equilibrium and you know keq, solve for I.
May 5, 2015

chemistry
volume to start = 2.29 volume added = 15.75 total volume = ? 0.723M x (2.29/total volume) = ? Note: This assumes volumes are additive; technically they are not but in dilute solutions like this the are for all practical purposes (still not technically)
May 5, 2015

chemistry
Would you believe I have no idea what IL-23 power is (although I assume you mean powder). Let's see. If I had 10 ug/0.1 mL wouldn't that be 100 ug/mL
May 5, 2015

chemistry
We're still giving you freebies. Somewhere down the line you need to start telling us what you think and why or at least tell us what you don't understand about the problem. CH4 + 2O2 ==> CO2 + 2H2O The problem isn't clear about which gases to separate. I assume...
May 5, 2015

chemistry
PV = nRT If you use kPa for P, use 8.314 for R. Remember T must be in kelvin.
May 5, 2015

chemistry
Responded above. Good luck on the exam.
May 5, 2015

chemistry
right. Note that Cu is below hydrogen in the activity series; therefore, it will not displace hydrogen from the acid. What you get is an oxidiation/reduction reaction in which the Cu is oxidized to Cu^2+ and the H2SO4 is reduced to SO2. But that only happens if the H2SO4 is ...
May 5, 2015

chemistry
I have news for you. Copper will not dissolve in H2SO4 unless it is heated. If heated it will react but it does not produce H2 gas. It produces SO2. So which equation is right?
May 5, 2015

science
specific heat has units of J/g*K or joules/gram/degree kelvin. Typically, specific heat is the heat required to raise the temperature of 1 gram of some material by 1 degree K. Heat capacity has units of J/K; i.e., note no "specificity" in amount as in grams. There is...
May 5, 2015

chemistry
It is a unit like a loaf of bread(so many slices), a dozen eggs (12 of anything), a gross of pencils(144 of anything), a ream of paper(500 sheets). A mole is 6.022E23 of anything.
May 5, 2015

chemistry
1. Write and balance the equation. 2Al + 6HCl ==> 2AlCl3 + 3H2 2. Convert 5.8 g Al to mols. mol = grams/atomic mass = 5.8/27 = approx 0.2 but you need a more accurate answer than that estimate. 3. Using the coefficients in the balanced equation, convert mols Al to mols HCl...
May 5, 2015

chemistry
0.997 g/mL x 500 mL x (1 kg/1000 g) = ?
May 4, 2015

Chemistry Help - Check Please
That sounds good to me although I'm not an organic chemist.
May 4, 2015

Chemistry help
It would help if you told us what you don't understand about these. For #1, pH = -log(H^+). Substitute and solve for pH. For #2. Same formula. I assume this is the TOTAL H^+ and there is no need to add in any contribution due to the ionization of H2O.
May 4, 2015

Chemistry
mols AlCl3 = grams/molar mass. You know molar mass and grams, solve for mols. Then m = molality = mols/kg solvent. You know kg solvent and mols, solve for m. Then delta T = i*Kf*m You know Kf and m; i for AlCl3 is 4. Solve for delta T. Then subtract delta T from the normal ...
May 4, 2015

Science
f = ma f is same mass greater a must be
May 4, 2015

chemistry
Is that m or M? I assume you know there is a difference but since you don't use the caps key we never know.
May 4, 2015

CHEMISTRY
(V1/T1) = (V2/T2) Remember T must be in kelvin.
May 4, 2015

Chemistry
96,485 coulombs will form approx 87/2 = approx 44 g MnO2. These are estimates and you need to redo them with more accurate numbers. How many coulombs do you need to produce 1000 g? That's approx 96,485 x (44/1000) = ? = Q Then Q = amperes x seconds. Substitute and solve ...
May 4, 2015

Chemistry
Ecell = Eocell - (0.05916/n)*log(dilute/concd) Eocell = 0 Substitute and solve for Ecell.
May 4, 2015

Chemistry
What values are you using for Ered.
May 4, 2015

science
KE = 1/2*m*v^2 If v is 2x as much then KE is 4x as much.
May 4, 2015

Chemistry
It would have helped if you had shown you work. I get K = 1.36 and your equation looks ok to me. Anything else that might shed some light on the problem? The only possibility I have is that you and I may not be using the same E value.
May 4, 2015

Chemistry
What are you using for the Ered Sn and Pb? Do you have any concentrations given or are you to assume 1 M concns?
May 4, 2015

chemistry
1 orange costs $1.00; what's the cost of 2 oranges? 1 mol occupies 22.4 L; what's the volume occupied by 2 mols?
May 4, 2015

Chemistry
You have the wrong formula and wrong data. Hf is heat fusion; you want Hvap. Hf is 80 cal/g; Hvap is 540 cal/g Q = m*Hvap Hvap = 540 cal/g
May 4, 2015

Chemistry
The reaction is exothermic and you know that because the temperature of the water increased. q = 6795 J for 0.85 mol; therefore, q = 6795/0.85 = dH = ? Remember to add a - sign since this is exothermic. Also remember to convert from J to kJ.
May 4, 2015

Chemistry
PV = nRT Make sure P, V, R units are consistent.
May 4, 2015

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