Monday
September 1, 2014

Posts by DrBob222


Total # Posts: 43,437

Chemistry 1
I don't see a question here. I assume you want to calculate the heat of neutralization (in what units?)
July 1, 2014

Chem
I thought I worked this a couple of days ago. 4H ==> 2H2 So 435 kJ/mol x 2 mol = 870 kJ. 870,000J = mass H2O x specific heat H2O x (Tfinal-Tinitial) Plug and chug. Solve for mass H2O
July 1, 2014

Chemistry
Balance the redox part first. You don't need to write the entire equation, just the redox part. C2O4^2- + Cr2O7^2- ==> 2Cr^3+ + 2CO2 C in C2O4 changes from +6 (for 2C) to +8 (for 2C) which is a change of 2e. Cr in Cr2O7^2- changes from +12 (for 2Cr) to +6(for 2 Cr) ...
July 1, 2014

Chemistry
mols KOH = M x L = ? Since aspirin is a monoprotic acid then mols aspirin = mols KOH. g aspirin = mols aspirin x molar mass aspirin. % aspirin = (mass aspirin/0.534)*100 =
July 1, 2014

Chemistry
(35.9675*0.003365) + (37.9627*0.000632) + (39.9624*0.99600) = ?
July 1, 2014

Chemistry
1 ton = 2000 lbs. 261 tons x (2000 lbs/1 ton) x 0.014 x (molar mass (CH3)2Hg/atomic mass Hg) =
July 1, 2014

Chemistry
If that is 7.04% N (and not N2), you have 7.04g N in 100 g of the fertilizer. To convert to g urea just multiply by the chemical factor (which usually isn't taught in schools now). 7.04 x (molar mass urea/2*atomic mass N) = ?
July 1, 2014

chemistry
Did you make typo? If Kp is at 160 C then it will be different at 100 C. Assuming you mean Ptotal at 160 C... ....2NaHCO3(s)=>Na2CO3(S)+CO2(g)+H2O(g) I...solid.......solid......0......0 C...solid.......solid......p......p E...solid.......solid......p......p Kp = pCO2 * pH2O...
July 1, 2014

Soil Chemistry
Yes you are, STP means standard temperature and pressure. So P is 1 atm standard, T is 273 K standard and you are to calculate standard V.
July 1, 2014

Soil Chemistry
(P1V1/T1) = (P2V2/T2) Whatever units you use for the left side use the same units for the right side.
July 1, 2014

Soil Chemistry
I don't see a question here.
July 1, 2014

Chemistry
Two rules to follow in chemistry problems. 1. Work in mols. You get mols two ways. The first is when you have grams; that's mols = grams/molar mass. The second is when you have a solution; then mols = M x L. 2. When you have mols you can convert mols of anything in the ...
June 30, 2014

Chemistry
Ba(NO3)2 + 2NaIO3 + H2O ==> Ba(IO3)2*H2O + 2NaNO3 Ba(NO3)2 is the limiting reagent with either number. mols Ba(NO3)2 = M x L = 0.4912 x 0.030 = 0.014736 = mols Ba(IO3)2.H2O g Ba(IO3)2 = mols x molar mass = theoretical yield (TY). Actual yield (AY) = 6.895g in the problem...
June 30, 2014

Chemistry
See you other post.
June 30, 2014

Chemistry
See your post below. Same procedure.
June 30, 2014

Chemistry
See your post below. You calculate mols to calculate grams.
June 30, 2014

Chemistry
See your post below. BTW, you would get faster responses if you didn't change screen names. Joe, Steve, Chris, ?
June 30, 2014

Chemistry
This is a limiting reagent (LR) problem. 2NH4F + Ca(NO3)2 ==> CaF2 + 2NH4NO3 1. Write and balance the equation as above. 2. Convert numbers to mols. mols = M x L = ? mols Ca(NO3)2 = M x L = ? mols NH4F = M x L = ? 3a. Using the coefficients in the balanced equation, convert...
June 30, 2014

chemistry
2AgNO3 + CaCl2 ==> Ca(NO3)2 + 2AgCl mols CaCl2 = grams/molar mass = ? Use the coefficients in the balanced equation to convert mols CaCl2 to mols Ca(NO3)2 (That should be mols CaCl2 x 2 = ?). Then g Ca(NO3)2 = mols Ca(NO3)2 x molar mass Ca(NO3)2 = ?
June 30, 2014

Soil Chemistry
You must pay attention to units no matter what problem you are working. Here, use PV = nRT and solve for n P must be in atm and 755/760 = ? atm. V in L n = number of mols. Solve for this. R = 0.08205 L*atm/mol*K T = 24C + 273 = ?K. T must be in kelvin. Then n = mols = grams/...
June 30, 2014

Soil Chemistry
No big problem. Just remember the definitions. Oxidation is the loss of electrons. Reduction is the gain of electrons. In the problem Mn goes to Mn^2+, so Mn ==> Mn^2+ + 2e is the loss of electrons and is oxidation. A is the only answer that fits for Mn. I don't see the...
June 30, 2014

Chemistry
You need three things: a. What is the change in oxidations state? b. Were electrons lost of gained. c. the definitions: oxidation is the loss of electrons. Reductions is the gain of electrons. Here is a. Zn has an oxidation state of zero on the left and +2 on the right. Loss ...
June 29, 2014

chemistry
http://en.wikipedia.org/wiki/Hard_water
June 29, 2014

Chemistry
q = 4 mol x 435 kJ/mol = ? kJ = ? x 1000 J. q = mass x specific heat x (Tfinal-Tinitial). YOu know Tfinal, Tinitial, specific heat, and q, solve for mass
June 29, 2014

Chemistry
Convert 1 L to gallons. Convert Canadian $ to U. S. $. 0.771 CD/L x (1 USD/1.401 CD) x (1 L/0.264 gallons) = ? USD/gallon.
June 29, 2014

Chemistry
Explain your trouble. You set up Ca(s) --> Ca(g) dH = +192 kJ Ca(g) --> Ca^+ + e dH = + 589.5 kJ Ca^+(g) --> Ca^2+ + e dH = + 1146 kJ Cl2(g)--> 2Cl(g) dH = 242.6 kJ 2*Cl(g) + 2e -->2*Cl^-(g) dH =2*-348 kJ Ca^2+(g) + 2Cl^-(g) --> CaCl2 dH = lattice...
June 29, 2014

Chemistry
1/wavelength = R(1/4 - 1/n^2) 1/4 is 1/2^2
June 29, 2014

Chemistry
E for 3.00 mm is E = hc/wavelength. Convert wavelength in mm to m. That gives E for 1 photon which is q/photon q needed to raise T H2O is q = mass H2O x specific heat H2O x delta T = 1.45g x 4.184 x 1 = estimated 6 J Then q/photon x # photons = estimated 6 and solve for # ...
June 29, 2014

Chemistry
You have a typo in the equation. 6HCl + Fe2O3 -> 2FeCl3 + 3H2O g Fe2O3 reacted = 37.5-5.5 = 32.0g mols Fe2O3 = grams/molar mass = estimated 0.2 a. mols HCl used = 0.2 x (6 mol HCl/1 mol Fe2O3) = estimated 1.2. M HCl = mols/L = estd 1.2/0.240 = ? b. mols FeCl3 = mols Fe2O3 x...
June 28, 2014

Chemistry 12
KOH ==> K^+ + OH^- mols KOH = grams/molar mass = ? M KOH = mols KOH/L solution = ? pOH = -log(KOH) Then pH + pOH = pKw = 14. You know pKw and pOH, calculate pH.
June 27, 2014

Chemistry
pi = MRT pi = 0.138 atm M = ? R = 9.08205 L*atm/mol*K T = 273.15 + 28 = ? Solve for M. Then M = mols/L. You know L and M, solve for mols. Then mols = grams/molar mass. You know mols and grams, solve for molar mass.
June 27, 2014

Chemistry 108
mass benzene = volume x density = ? mols benzene = grams/molar mass = ? m benzene = mols benzene/kg solvent For f.p.: delta T = Kf*m, then subtract delta T from 0C to find new f.p. For b.p.: delat T = Kb*m, the add delta T to 100 C to find new b.p.
June 27, 2014

science
I don't see a question here.
June 26, 2014

Chem
CH4 + 2O2 ==> CO2 + 2H2O 16g CH4 releases 802 kJ so 16 x 542 kJ/802 kJ = ?
June 26, 2014

Chem
2Mg + O2 ==> 2MgO + 1203 kJ (although I can't tell if you meant that to be a + or a -). You know from the equation that 2 mol Mg (which is 2*24.3 g Mg) liberates 1203 kJ/ So 1203 kJ x 7.01/(2*24.3) = ? and you place the right sign on it.
June 26, 2014

Chemistry
I looked up the enthalpy of solvation for NH4Cl and CaCl2. I can work this problem for you now. If you still need help, please repost as a new question and I will get to it.
June 26, 2014

Chemistry
Do you have any other data given such as heat solvation etc?
June 26, 2014

Chemistry
Not balanced. MnO4^- + C2O4^2- + H^+ ==> 10CO2 + H2O + Mn^2+
June 26, 2014

chemistry
It depends upon what 1:2 means. There is confusion among even experienced on this. If 1:2 means 1 part NaHCO3 + 2 parts water, then the concn is 0.6M x (1/3) = ? If you mean 1 part NaHCO3 + 1 part (to make 2), then the concn is 0.6M x (1/2) = ? The following is a good web site...
June 26, 2014

math
I think "would be produced" is superfluous wording. I read it as what is the greatest odd number after rounding 660 to the nearest hundreds. 660 rounds to 700 and that's an odd number
June 25, 2014

Chemistry
No idea what the set up was. max P = 1.4094 what? initial P = what unit? atmosphere probably. Did the system gain weight? If so due to what?
June 24, 2014

analytical question
I would call this the near infrared although this is the upper end of that region. E = hc/wavelength in meters. E is J/photon. Multiply by 6.02E23 to convert to J/mol photons and change that to kJ/mol.
June 24, 2014

Analytical chem
If I read this right, you have 3 mg Cu initially, you place it in 250 mL, withdraw 15, add 15 more of something else and take 25 of that 30. So you should have 0.003/63.55 mol = ? initially and at the end it will be (0.003/63.55) x (15/250) x (25/30) = ? and that is in 30 mL ...
June 24, 2014

Chemistry
a 9% by mass means 9g ethanol in 100 g solution or 9g ethanol/(9g ethanol + 91g H2O). m = mols/kg solvent convert 9g ethanol to mols. mol = grams/molar mass. Then m = mols/0.091 = ? b delta T = Kf*m c You don't have but one solution here; what are you comparing?
June 24, 2014

Chemistry
what reaction?
June 24, 2014

Chemistry
2Al + 6HCl ==> 2AlCl3 + 3H2 mols Al = grams/molar mass Using the coefficients in the balanced equation, convert mols Al to mols H2. Then use PV = nRT and convert mols H2 to L at the conditions listed. Change L to mL.
June 24, 2014

chem school
Find your caps key and use it. m stands for molality; M stands for molarity. I assume M is what you want? And I doubt you mean 880 m or M. 3H2SO4 + 2Al(OH)3 ==> Al2(SO4)3 + 6H2O mols H2SO4 = M x L = ? Convert mols H2SO4 to mols Al using the coefficients in the balanced ...
June 24, 2014

Chemistry
S + O2 ==> SO2 SO2 + Cl2 ==> SO4^2- mols S = grams/atomic mass = ? 1 mol S = 1 mol SO4^2- 1 mol SO4^2- = 1 mol BaSO4 I believe that is D
June 24, 2014

Chemistry
We can't draw diagrams/graphs on this forum. Plot the data, as the problem asks, zero, first, second order reactions look different. Here are some images. https://www.google.com/search?q=graphically+order+reactions&client=firefox-a&hs=LiV&rls=org.mozilla:en-US:official&...
June 24, 2014

chemistry
Did I miss something here? According to the first part of your post the volume of the unknown liquid is exactly 25 mL. According to the last part it is 50-3.25 = 46.75 mL. d = m/v but I don't know which volume to use.
June 24, 2014

chemistry
E = hc/wavelength Plug in E in J, h is Planck's constant, c is speed of light in m/s. Answer for wavelength is in meters, change to nm.
June 24, 2014

chemistry
Pb(NO3)2 + 2NH4I ==> PbI2 + 2NH4NO3 mols Pb(NO3)2 = M x L = estimated 0.16 mols NH4I needed = estd 2*0.16 = about 0.32 M NH4I = mols NH4I/L NH4I. You know mols and M, solve for L.
June 23, 2014

college chem
Here is the hint you should need to work the problem. You have two equations and you solve them simultaneously (which I think is the easier way) but there are other ways to do it. pH = pKa + log (base)/(acid) Take the Ka of k1, k2, and k3. The closes one to 6.9 is the one you ...
June 23, 2014

Chemistry
PV = nRT Remember T must be in kelvin. R is 8.314 if you use P in kPa.
June 23, 2014

Science
What acid/base? What indicator? You should be able to look up the pH range of the indicator but if you give me the name of the indicator perhaps I can find a place on the web that will gives the color changes vs pH.
June 23, 2014

chemistry
q = mass x specific heat x (Tfinal-Tinitial) q = 120g x 4.184 J/g*C x (29.2-20) q = ?
June 23, 2014

science
The mirror is a piece of glass with a silver backing on it(for back surface mirrors) that reflects light. The wall doesn't reflect enough light to "see yourself in a wall".
June 22, 2014

chemistry
a However, I think it plays a role in some cases.
June 22, 2014

chemistry
which do you think and why?
June 22, 2014

Chemistry
And how can I help you with this? How much do you already know how to do?
June 22, 2014

Chemistry
Where is your hang up on this?
June 22, 2014

finite math
That's the problem. That's the end of it. You've multiplied P*r*t, what else is left to do?
June 22, 2014

Chemistry
I think the easiest (but the long) way is to say volume N2 = 0.8 x 1 L = 0.8 L volume O2 = 0.2 x 1L = 0.2 L. Then use PV = nRT and solve for n = mols N2 and mols O2. Then mols N2 = grams/molar mass and mols O2 = grams/molar mass. You know molar mass and mols, solve for grams ...
June 22, 2014

chemistry
Too much typing. Do this (%)(au) + (%)(au) + (%)(au) ........ = au (0.158*91.91) + (0.009*93.90) + ..... = au.
June 22, 2014

chemistry
We can't draw diagrams, Sara/john/robert/et al/ If you can explain what you don't understand about it perhaps I can help you draw it.
June 22, 2014

chemistry
John/Sara/Robert/et al. You must know the rules which are n may be any whole number >1. l may be a whole number from 0 to n-1; i.e., 0, 1, 2, 3, etc. m may be any whole number from -l to +l including zero s may be either +1/2 or -1/2. For example, 1 is allowed but 2 is not...
June 22, 2014

chemistry
mols Mg = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols Mg to mols H2SO4. Then M H2SO4 = mols H2SO4/L H2SO4. You know mols and M, solve for L. Using mols Mg, convert to mols H2 for part 2.
June 22, 2014

chemistry
heat gained by ethanol + heat lost by water = 0 heat gained by ethanol = mass x specific heat x (Tfinal-Tinitial). Use density to convert mL to mass. heat lost by water = mass x specific heat x (Tfinal-Tinitial). Use density to convert mL to mass. Tfinal is the only unknown.
June 22, 2014

oops--chemistry who step by step for me
I made a typo so I've erased my entire response and posted the correct answer. You know your answer can't be right because you have 4 g K2CO3 but the entire sample is only 1.2 g and 4 g is more than the you started with My calculation 20cm3/100cm3 = 0.2 Yes, 0.2 is the...
June 22, 2014

chemistry step by step for me
Do you mean LiCl and BaI2. There is no BaI.
June 22, 2014

Org Chem
Ko/a = amt org layer/amt H2O layer. K is 8 MeCl2 is 30 mL H2O is 30 mL Caffeine is 10g Let X = amount extracted with org layer, then 10-x = amount left in H2O layer. 8 = (x/30)/(10-x)/30 You can cancel the 30 in the denominator. Solve for x. You can do it three times for three...
June 22, 2014

Columbus State
I would have answered much faster if I had seen "chemistry" posted. Instead Writeacher did you a favor and corrected the heading or I never would have looked at "columbus State". The easy way to do this is to change Kc to Kp. Kp = Kc(RT)^delta n. Then run a...
June 22, 2014

chemistry
It works the same way as stoichiometry. rate Cr(SO$)3 x (3 mol C2H6O/2 mol Cr(SO4)3) = 1.24 x 3/2 = ? Note that Cr(SO4)3 cancels but C2H6O stays to change the units to that specie.The coefficients do the job. Same for the other problem. 3.7E-5 x (4/2) = ?
June 21, 2014

Chemistry pls clearly step step for me
And I can't calculate to obtain that answer either. I don't think the problem is worded correctly. Here is why I think that. If the sample is 56.7% NaHCO3 then it is 43.3% Na2CO3. g Na2CO3 = 2 x 0.433 = 0.866g Na2CO3 g NaHCO3 = 2 x 0.567 = 1.134g NaHCO3 total = 1.134+0...
June 21, 2014

chemistry--NCCU
I would have answered this much quicker if you had typed in the subject instead of something obscure like NCCU.
June 21, 2014

chemistry---NCCU
millimols benzoic acid = mL x M = about 27 but that's an estimate and you should redo the math. Then pH = pKa + log (base)/(acid) 4.30 = pKa benzoic acid + log benzoate/27 Look up the value of pKa for benzoic acid, substitute, solve for base. That will be millimols sodium ...
June 21, 2014

intro to chem
q = mass Au x specific heat Au x (Tfinal-Tinitial) q = 3000 g x 0.128 J/g*c x 37C = 1.4 E4 J to two s.f. If you multiply 3 x 0.128 x 37 you don't get 3.6. You get 14.2 BUT that 3 is not right. It is in kg and your specific heat unit is in J/g*c so you must change the 3 kg ...
June 21, 2014

intro to chem
I don't understand how you get 3.6 anything. 3000 x 0.128 x 37 = ?
June 21, 2014

intro to chem
I'm guessing here since I don't know what you used for specific heat Au and what units you want the answer. But my guess is you used specific heat in cal/g*C and that's about 0.032. delta T is 60-23 = 37. Then I think you failed to convert 3 kg Au to g Au so 3 x 0....
June 21, 2014

intro to chem
What did you use for specific heat Au? with units?
June 21, 2014

intro to chem
q needed = mass Au x specific heat Au x (Tfinal-Tinitial)
June 21, 2014

chemistry Please who helps me stpe by step
mass sample titrated = 2 g x (25/250) = 0.2 g. You have two unknowns which will require two equations and you solve those simultaneously. Let X = mass Na2CO3 and Y = mass NaHCO3 ------------------------ Equation 1 is : X + Y = 0.2 Then # milliequivalents = grams/...
June 21, 2014

chemistry
pH of the original solution before NaOH is added is pH = pKa + log (base)/(acid) pH = 9.26 + log (0.1/0.1) = 9.26 millimols NH3 = 0.1 x 1000 = 100 mmols NH4Cl = 0.1 x 1000 = 100 mols NaOH added = 1.8/40 = 0.045 mols or 45 millimols. .............NH4^+ + OH^- = NH3 + H2O I...
June 21, 2014

Chemistry
%by mass = (mass solute)/(mass solution) % w/w = 19.7g NaOH in 100 g solution. % w/w = 19.7 g NaOH in [19.7g NaOH + (100-19.7)g H2O].
June 21, 2014

CHEMISTRY
W = nRT*ln(Vfinal/Vinitial) If you want W in joules use R = 8.314
June 21, 2014

Chemistry
That's probably right. If I use 4.76 for pKa for acetic acid and plug in 1.82 for mols base and 1 for mols acid, I get pH 5.02. Using pKa 4.74 gives 5.00.
June 20, 2014

Chemistry 10As
16% w/v means 16 g ethanol in 100 mL solution. So add 5*16 = 80 g ethanol, place in a 500 mL volumetric flask, and make to the mark with distilled water.
June 20, 2014

chemistry
Look up refrigeration or air conditioning on google.
June 20, 2014

Chemistry
11=4+2+m+2 Solve for m
June 19, 2014

Chemistry
I don't think any of us memorized all of the solubility tables for all of the salts in the universe. If you have a graph or a table that gives you the solubility at various temperatures, post them and I can help. If you don't have that information I may be able to find...
June 19, 2014

chemistry
b although I don't like the way it is stated.
June 19, 2014

Chemistry
(H^+)(OH^-) = 1E-14 So smaller H^+ means higher OH^- or higher H^+ means lower OH^-
June 19, 2014

chemistry
mols HCl = grams/molar mass mols C6H6 = grams/molar mass total mols = mols HCl + mols C6H6 Xbenzene = mols benzene/total mols.
June 19, 2014

algebra
g/9 = ?
June 18, 2014

Chemistry
I would classify these as a redox reaction.
June 18, 2014

Chemistry
(V1/T1) = (V2/T2) Remember T must be in kelvin.
June 18, 2014

Chemistry
Multiply equation 1 by 2 and reverse it. Add to equation 2. That will give you the equation you want but you need to go through the steps to confirm that. When you multiply an equation, do the same to delta H. When you reverse and equation change the sign of delta H.
June 18, 2014

chemistry
What water has hydrated the H2SO4, the reaction is exothermic so heat is evolved.
June 18, 2014

chemisrty
So you reacted 1.2M x 0.050L = 0.06 mols HCl with 0.06 mols NaOH in 100 mL solution. mass solution = 100 mL x 1.05 g/mL = 105 grams. delta T = dT = 29.8-24.1 = 5.7 degrees. q = (mass soln x specific heat x dT) + (Ccal x dT) q = (105 x 4.184 x 5.7) + (32.5 x 5.7) = ? J for 0.06...
June 18, 2014

algibra
y1-y2/x1-x2 -10-(-2)/1-(-7) -8/8 = -1 = m
June 18, 2014

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