Wednesday
July 30, 2014

Posts by DrBob222


Total # Posts: 43,219

check---chemistry
Please read and correct so it makes sense.

Chemistry
You do these by noting that the formation constant is huge so that the complex essentially forms at 100%, then turn the reaction around as if it were a weak acid and calculate the (M^2+). ..........M^2+ + 6CN^- ==> M(CN)6^4- I.....0.170M....1.31M........0 C....-0.170...-6*0...

Chemistry
(P1V1/T1) = (P2V2/T2)

(5) Chemistry - Science (Dr. Bob222)
First thanks for sharing that Zn/Cu answer. I was sure that was right and as I posted last night, I might be missing something but if so I didn't see it. My equation for the buffer was 4.99 = 4.74 + log (130+x)/(100-x) 0.25 = log (130+x)/(100-x)see below 1.78 = (130-x)/(10...

(5) Chemistry - Science (Dr. Bob222)
Let HA = CH3COOH millimols HA = mL x M = 1000 x 0.1 = 100 mmols A^- = 1000 x 0.13 = 130 First determine what the pH of the solution is initially using the Henderson-Hasselbalch equation. I obtained 4.85 but you should ocnfirm that. Then you want to increase that by 0.14 by add...

Chemistry - Science (Dr. Bob222)
millimols NH3 = mL x M = 100 x 0.1 = 13 mmols HCl = 87 x 0.15 = 13.05 My best guess is that these are to be considered the same since the 87 has two s.f. and 13 does too. ........NH3 + HCl ---> NH4Cl I.......13....13........0 C......-13...-13.......+13 E........0.....0........

science check answer
I think your first choice was right.

Chemistry - Science (Dr. Bob222)
mmols CH3NH2 - 0.40 x 130 mL = 52 ..........CH3NH2 + HCl ==> CH3NH3^+ I..........52.......0........0 add.................x............. C.........-x.......-x........x E.........52-x......0........x 11.59 = 10.64 + log (52-x)/(x) 8.91 = (52-x)/x 8.91x = 52-x 9.91x = 52 x = 5...

Chemistry - Science (Dr. Bob222)
Did you convert pKb given to pKa?

Chemistry - Science (Dr. Bob222)
This looks almost like the KOH/acetic acid above. If you still have trouble show what you've done and where you're stuck as well as what you don't understand and I can help you through it.

Chem Check Please!!!
I think when the cell is set up as written above (with the diagram) it means Ag + Cl^- ==> AgCl + e E = -0.222 Cu^2+ + 2e --> Cu E = 0.337 So the sum is +0.115 or c.

Chem Check Please!!!
1 is right. 2. I am not familiar with this particular series but you can read about it here. http://en.wikipedia.org/wiki/Spectrochemical_series

Chem Check Please!!!
I don't think the answer is either c or d. If the complex is diamagnetic doesn't that mean all of the electrons are paired. Doesn't that make it low spin. And if they are paired doesn't that make the delta oct difference between t2g and eg large? So I would thi...

Chem Check Please!!!
I agree

CHEMISTRY HELP !!!!
Isn't that e. I think I answered this a day or so ago and for some inexplicable reason I thought it was Cr(IV) but of course Cr(II) is right.

chemistry
29.6% (w/w) is 29.6 g KCl/100 g solution. That is 29.6g KCl in (29.6g KCl + 70.4 g H2O. mols KCl = grams/molar mass = ? kg H2O = 0.0704 molality of the solution is mols/kg solvent Then delta T = i*Kb*m i = 2 for KCl. Solve for delta T and add to 100 C to find new boiling point.

Science
work is -pdV work is -0*dV = 0

chemistry
This problem is a bit confusing to me. If you've collected the H2 over water and you calculate V H2 from PV = nRT why won't the volume of the H2O be the same as the volume of H2 gas? I plugged in the numbers and obtained abou4 31 L for volume H2. Seems to me any other ...

chemistry
.....CH3NH2 + HOH ==> CH3NH3^+ + OH^- I...0.1003............0.........0.1204 C.....-x..............x..........x E...0.1003-x..........x........0.1204+x Kb = (CH3NH3^+)(OH^-)/[CH3NH3^+] Look up Kb and plug in the numbers. Solve for x = (CH3NH3^+)

chemistry
Those formula don't mean anything to me. If you write them in acid/base notation, which I suspect they are, it would be easier. At any rate, look at your post above and see if it isn't worked the same way.

chemistry
If the volume decreases (by say a factor of 2) that will double the (PH3) and double (BCl3). For a factor of 1.774 concn will be increased for EACH by 1.774. Remember the solid doesn't appear in Kc. Kc = 1/(PH3)(BCl3) So Kc > Q = 534.8/(1.774)(1.774)

chemistry
Do you mean for this reaction be be written as N2 + O2 ==> 2NO with Kc = 2400. That's the way you have your arrows.

chemistry
Substitute the equilibrium concentrations given in the problem into the Kc expression and solve for K.

chemistry
q = mols H2O x molar heat capacity x (Tfinal-Tinitial)

Chem 130
You need to find the arrow key and use it. mols CaCO3 = grams/molar mass Using the coefficients in the balanced equation, convert mols CaCO3 to mols CO2. Now convert mols CO2 to grams CO2. g = mols x molar mass

Chem 130
You have a 100 L tank and you want to fill it with He to a pressure of 155 atm at 22 C. This problem is two problems in one. One for He and the other for H2. Here is the He one done for you. It's just a matter of substituting into PV = nRT and using n for solve for grams. ...

Chem 130
Use PV = nRT and solve for n in each tank. Then n = grams/molar mass. You know molar mass and n, solve for grams in each tank.

chemistry
Ptotal = pO2 + pH2O You know Ptotal and pH2O, solve for pO2. Note Ptotal and pH2O are not in the same units.

Chem 130
Ptotal = pO2 + pH2O You know Ptotal and pH2O, solve for pO2.

Chemistry
%Z(w/w) = (g Z/total grams)*100 = ? where total grams = gX + gY + gZ

Chemistry
dHsurr = -dH/T

Chemistry
Is that 2.6M HCl? I will assume so. Zn + 2HCl ==> ZnCl2 + H2 How many mols H2 is that? Ptotal = 845 torr pH2O at 65C = approx 190 torr. You need to look up this value in your text/notes because I've estimated it from some tables I have. pH2 = 845-190 = about 655 mm or 6...

Chemistry
See your other post.

Chem 130
mols He = 2.03/molar mass He = n1 mols He = 6.19/molar mass He = n2 (n1/12L) = (n2/xL) Solve for x L.

Chemistry
............MgF2 ==> Mg^2+ + 2F^- I...........solid.....0.......0 C...........solid.....x.......2x E...........solid.....x.......2x Ksp = (x)(2x)^2 You know x = 2.3E-3M.Substitute and solve for Ksp.

Chemistry
Let's call aniline BNH2 ...........BNH2 + HOH ==> BNH3^+ + OH^- I..........0.201...........0........0 C...........-x.............x........x E.........0.201-x..........x........x Kb = (BNH3^+)(OH^-)/(BNH2) You know x. Substitute into Kb expression and solve for Kb.

Chemistry - Science (Dr. Bob222)
I worked through it and came up with 1.09v also. 1.13 seems to be the closest ad I would go with that. Sometimes answer sheets give approximate answers and this could be one of them. If I'm missing something I don't see it.

chemistry
Use PV = nRT and solve for P (in atmospheres) and convert to mm Hg. 1 atm = 760 mm Hg. Don't forget T must be in kelvin.

Organic CHM II
http://lipidlibrary.aocs.org/Lipids/tag2/index.htm

chemistry: please check work
I agree with the procedure as well as the value and the number of significant figures.

Chemistry
http://en.wikipedia.org/wiki/Delocalized_electron

chemistry
What do you need help with? The lower concn will be the increasing and the higher concn will be decreasing until both have the same concn. So you know the lower concn will be oxidized and the higher concn will be reduced.

Chemistry
No, of course you don't know the final T. That's what you're trying to find. It ways that in the problem, "What is the final T if ..." heat lost by Ni + heat gained by H2O = 0 [mass Ni x specific heat Ni x (Tfinal-Tinitial)] + [mass H2O x specific heat H2...

Chemistry
You can but that's the hard way to do it. It is much easier to substitute the individual numbers and work it out by pieces.

Chemistry
heat lost by Ni + heat gained by H2O = 0 [mass Ni x specific heat Ni x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0

Chemistry
You want 1 mol SO3 and not 2 so divide by 2. You want the reverse so change the sign.

Chem Check Please!!!
I disagree with 1. I agree with 2,3,4. I con't see all of the name typed on 5 but e is right if that is chromium IV.

Chemistry
It's twice dHof

Chemistry
zero or very low

Chemistry
Take equation 1 and add it to the reverse of equation 2 and add that to the reverse of 1/2 equation 3. When reversing dH, change the sign. When taking 1/2 equation, also take 1/2 dH.

chemistry
Q = coulombs = amperes x seconds Q = 0.680A x 20m x (60s/m) = ? = about 816 96,485 coulombs will deposit (63.54/2)g Cu. You have 816 coulombs; therefore, 63.54/2 x (816/96,485) = about 0.3g if I punched the right buttons.

Underwater explosion
Other tutors may wish to weigh in on this question but I think the answer is yes IF the timing is just right and the compressed air force can be sustained long enough.

Chem
This is an example of a back titration; i.e., the KI/KIO3 produces I2, the I2 reacts with some of the vit C, the excess I2 is titrated with thiosulfate. 6H^+ + I^- + IO3^- ==> 3I2 + 3H2O Then vitC + I2 ==> 2I^- + vitCx mols IO3 added initially = M x L = 0.025 x 0.01988 =...

chemistry
The question isn't exactly clear; it isn't clear that it is the greatest amount of acid per grams antacid or per mol antacid. H^+ + OH^- ==> H2O So the one with the largest OH per mol will neutralize the most acid. That is Al(OH)3. And you don't capitalize every...

chemistry
Wouldn't that be 100g/5 dm^3 = 20g/dm^3

Chemistry
No, the problem says to write the equilibrium constant expression. Nothing about finding the value of K.

Chemistry
What is your problem with these. Keq expressions are the same. K = (products)^x/(reactants)^y and raise each substance to the power indicated by the coefficient.

chemistry
How many mols do you want? That's M x L = ? Then mols = grams/molar mass. You know molar mass and mols, solve for grams.

chemistry
mols acetic acid = grams/molar mass, then M acetic acid = mols/L

chemistry
M = mols/L

chemistry
See your post above.

Chemistry
Yes you do exactly what you have outlined. I would look at change in C and change in O for n. If we see ethanol as C2H6O and assign oxiatioin states of -2 for O and +6 for 6H, that makes 2 C in ethanol as -4. On the right the 2C are +8 so the change in e is 12. We can check th...

chemestry
I suggest you google these terms.

Chemistry
Same process. Write the balanced equation. Convert g CO2 to mols with mols = grams/molar mass. Use the coefficients to convert mols CO2 to mols HCl. Then M HCl = mols HCl/L HCl.

Chemistry
Na2CO3 + 2HCl ==> 2NaCl + H2O + CO2 mols Na2CO3 = M x L = ? Using the coefficients in the balanced equation, convert mols Na2CO3 to mols HCl. Then the defintion of M HCl = mols HCl/L HCl. You know M and mols, solve for L.

science
L1 x %1 = L2 x %2 ?L x 0.8% = 0.5L x 9% ?L = ?

what is the answer
Set up a ratio and proportion. (feet/shadow) = (feet/shadow) (8.1/24.3) = 20.1/x) Solve for x.

chemistry
The temperature at which water boils at high altitudes is lower than the temperature it boils at lower altitudes. Therefore, when cooking on a high mountain the water may boil 98 instead of 100 C so you should boil it (less, more). 2. Water boils when water boils. Turning up t...

Chemistry
NOPE. You changed SO4^2- on the right to S2O4^2- and you can't do that. Also you have the e on the wrong side. Other than that it is ok. 2OH^- + SO3^2- ==> SO4^2- + 2e + H2O

Chemistry
I shall be glad to help you through this but you need to learn to do these yourself. I do these the looong way. The first step is to determine the oxidation step of each element. I will help you here. S on the left is +4 and on the right is +6. Add electrons to the appropriate...

chemistry
It will take mass H2O x heat vaporization to turn the 30g into steam at 100 C.

Chemistry
This one is right. If you haven't already do so go back and look at the sulfite ==> sulfate because the one is not right.

Chemistry
I think the trouble you are having is caused by not putting the charges in. That H on the right should be 4H^+. The MnO4 on the right should be MnO4^-. When you do that the e need on the right is not 8 but 3 so the charge on the left is zero and on the right is (-1+4-3) = zero...

Chemistry
Again you need to learn to do these. Mn on the left is +4 and on the right is +7. Cu on the left is 2+ and on the right is zero. Balance the electron change first. Mn on the left goes to Mn on the right with ? change of e. Cu on the left goes to Cu on the right with ? change i...

CHEMISTRY
I worked this for you yesterday.

Chemistry
mols malic acid = grams/molar mass M = mols/L solution.

Chemistry
I worked it using the numbers you provided and came up with the same answer you did of 0.963 so there is nothing wrong with your math. The problem is that the reduction potential of Ni is not 0.26. It is -0.26.

chemistry
I don't believe you didn't know how to do any of this. 1. delta Tb = impure b.p.- pure b.p. 2. delta T = Kb*m Substitute and solve for m. 3. Isn't the mass given in the problem. Convert to kg. 4. m = mols/kg solvent. You know m and kg solvent, solve for mols

chemistry
See your post above.

chemistry
I suggest you read these things before you post them. You provided absolutely no information other than it is in the introductory information. But I don't see any introductory information.

Chemistry
You say you've looked up these values. My values won't be the same as yours because I'm using an old book but they will be close. Here is how you do the first one. Cr==> Cr^3+ + 3e You look in your table and find this potential. It will be listed "backwards...

chemistry
(H3O^+) = (A^-)

chemistry
pH = -log(H3O^+) 4.95 = -log(H3O^+) -4.95 = log(H3O^+) Another way of writing this is (H3O^+) = 10^-4.95 Solve for (H3O^+)

chemistry
An interesting problem. Three equation and three unknowns but we can work it around with just two since these are related. Let X = mass BaO and Y = mass CaO and mm stand for molar mass. ---------------- eqn 1 is X + Y = mass whatever that may be. Convert to sulfates and you ha...

chemistry
Mg + 2HCl ==> MgCl2 + H2 mols Mg = X mols H2 produced = X (look at the coefficients; 1 mol H2 produced for 1 mol Mg used) Volume = mols*22.4L/mol volume 22.4X liters.

to Bob P--Chemistry
I've gone cross eyed with these large numbers but I don't believe H and O balance in your equation.

Chemistry
2C60H87O23N12P +173O2 ==>120CO2 + 72H2O + 24HNO3 + 2H3PO4 Check this carefully. mols biomass = grams/molar mass Using the coefficients in the balanced equation, convert mols biomass to mols CO2. Now convert mols CO2 to grams. g = mols CO2 x molar mass CO2

chemistry
pH = -log(H^+)

Chemistry
The easiest way to do these problems is in parts and you need three formulas to do it. q at a phase change; i.e., solid to liquid or liquid to gas. For solid to liquid (melting point) it is q = mass solid x heat fusion. For liquid to gas (boiling point) it is q = mass liquid x...

CHEMISTRY
I worked this for you last night. Did you look at that?

chemistry
I believe you forgot the coefficients (e.g. 8). 8CH4 ==> C8H8+ 12H2 dGfrxn = (n*dGfC8H8 + n*dGfH2)-(n*dGfCH4) 620.735 = [(1*214.417) + (12*0)] - (8*dGfCH4) 620.735 = 214.417 + 0 - 8x Solve for x.

Chemistry
dH = mass H2O x specific heat H2O x (Tfinal-Tinitial) This will give you the enthalpy change for the reaction as stated in the problem and that is for 0.05g P. Generally these problems don't want that; they want the enthalpy change per mol but this problem doesn't ask ...

chemistry
I suppose you are to use M and m as the same. 0.121g/100 gH2O = solubility. mol N2O = 0.121/60 = approx o.002 and 0.002/0.1kg solvent = 0.02m p = KcC 1 atm = Kc*0.02 Kc = 1 atm/0.02 = 50 atm/m p = KcC 1.600 = Kc from above *C Solve for C in molality and convert to g/100 if des...

Science
In warmer climates the winters are warmer. The moisture from a hot shower is in the form of vapor (gas); however, it could be a liquid if it hasn't had time to completely vaporize and the water droplets are still visible (and you can feel those droplets on the skin).

Chemistry
mols H2SO4 = M x L = approx 0.1 mols NaHCO3 = M x L = approx 0.05 2NaHCO3(aq) + H2SO4(aq) ==>Na2SO4(aq) + 2H2O(l) + 2CO2(g) This should get you started. Post your work if you get stuck and clearly explain what you don't understand.

Chemistry
m = mols/kg solvent 2.0 = mols/3.5 Solve for mols, then mol = grams/molar mass. You know m and molar mass, solve for grams.

Chem Check Please!!!
I don't agree with 4. I agree with 5 and 6.

Chem Check Please!!!
I don't agree with 2. I agree with 3.

Chem Check Please!!!
I don't agree with #1.

Chemistry
I think Ni is initial N. and Nf is final N so the electron is making the transition from N = 1 to N = 2 so this is an absorption but the formula I list is for emission. That won't change frequency or wavelength but it will change the sign of E. delta E = R(1/1 - 1/4) where...

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