Friday
April 18, 2014

Posts by DrBob222


Total # Posts: 41,788

chemistry
Use the Henderson-Hasselbalch equation

Chemistry
Let's call benzoic acid HBz and the benzoate ion then is Bz^- With HNO3, the added acid (HNO3) reacts with the base, Bz^-. Bz^- + H^+ ==> HBz With KOH, the added base (KOH) reacts with the acid, HBz. HBz + OH^- ==> Bz^- + H2O

Chemistry
H2C2O4 + 2NaOH ==> Na2C2O4 + 2H2O mols H2C2O4 = grams/molar mass Using the coefficients in the balanced equation, convert mols H2C2O4 to mols NaOH. Then mols NaOH = M x L. You know mols and M, solve for L and convert to mL.

Chemistry
You need to decipher this post for us.

chemistry
Second try. My first one was deleted. 32.9150g = mass dish + Fe -30.7310g = mass empty dish ------------- +2.1840g = mass Fe %Fe = (mass Fe/mass Fe sample) = 2.1840/5.000)*100 = ? = approx 43.68% Note: I feel compelled to point out that this is a lousy procedure BECAUSE when t...

Chemistry
I expect LR stands for limiting reagent. Your calculation of 560 J for q is correct. You added 100 x 0.1M = 10 millimols (0.01 mols) to 0.01 mols So your answer is 560 J/0.01 mol = 56000 J/mol or 56 kJ/mol

Chemistry
Sorry about that. I got carried away with calculating the mass Ca3(PO4)2. mols ? mols Ca^2+ x (2 mol Na3PO4/3 mol Ca^2+) = ? mols Ca^2+ x 2/3 = ? mols Na3PO4. Does that look familar from above. g Na3PO4 = mols Na3PO4 x molar mass Na3PO4. And that should look familiar from abov...

Chemistry
Is this unknown sample Ca^2+. Then 3Ca^2+ + 2PO4^3- --> Ca3(PO4)2(s) You must know mols Ca^2+ from your unknown. Then mols Ca^2+ x (2 mols PO4^3-/3 mols Ca^2+) = mols Ca^2+ x 2/3 = ? mols Ca3(PO4)2. Then g = mols x molar mass.

chemistry
IF your equation is correct (and I don't think it is) then 150 ppm is 150 mg/L or 0.150 g/L = (0.150/atomic mass Ca) mols/L = approx 0.00375M. Then M standard soln x mL = ? millimoles. mmols EDTA = twice that M EDTA = mmols/mL. I was under the impression that EDTA complexe...

chemistry
Just to be sure we're on the same page my post could be misinterpreted. You are SUPPOSED to convert kJ/mol to J/mol. Using kJ/mol won't work.

chemistry
In fact, a rule of thumb in the kinetics business is that reaction rate can be doubled for every 10 degrees T. Since this ratio k2/k1 = about 2.05 I would guess T2 would be close to 365 or something like that.

chemistry
I don't think so. 273 + C = K 273 + C = 17 C = ? not 290?? Second think I notice is that your calculated temperature decreased. k2 is about double k1 so wouldn't you think T would be higher. Did you convert kJ/mol to J/mol? That's a common error.

chemistry
Use the Arrhenius equation.

chemistry
You can look up the exact numbers but C = about 12 = 36 H = 1 = 5 O = 16 = 32 Then add 36 + 5 + 32 = 73 I don't know where the 292 came from.

Science asap thankies :)
Was it a ferromagnet? They exhibit ferromagnetism which in Fe, Ni, and Co are examples.

Chemistry
molecules is not M. I would convert molecules to mol which will be mols/cc and convert that to mols/L which is M.

Chemistry
rate = k(CF3CH2F)(OH)

chemistry
Convert 20m, 12.5m and 3.85m to cm, then pool L x W x depth = volume in cc mass H2O is volume in cc x 1.00 g/cc. Then q = mass H2O x specific heat H2O x (Tfinal-Tinitial). Substitute and solve for q.

chemistry
What is your problem with this bekah? For a you must have worked a hundred of weak acids problems with a known starting molarity. At first glance it looks like 2 is a buffer problem that can be solved with the Henderson-Hasselbalch equation.

chemistry
With what reaction? 2H2 + O2 ==> 2H2O 5.00 mols O2 x (2 mol H2O/1 mol O2) = 5.00 x 2/1 = 10 mols H2O produced.

chemistry
I would go with 2 as true. Use pH = pKa + log (acid)/(base) to evaluate the other statements.

chemistry help
You remember two things. a. Reactions go to completion for one of three reasons. 1. a ppt is formed. For this you need to know the solubility rules. In this case PbS is formed which is a ppt. 2. a gas is formed. For this you need to know what is a gas and what isn't. In th...

Chemistry - Science (Dr. Bob222)
I've worked this below.

Chemistry - Science
Ag^+ + Cl^- ==> AgCl mols AgCl = grams/molar mass =? ? mol AgCl = mols Cl^- = mols Ag^+ = mols AgNO3. g AgNO3 = mols AgNO3 x molar mass AgNO3 %AgNO3 = (g AgNO3/mass sample)*100 = ?

chemistry
I agree with both of you.

chemistry
No. Barium is Ba. BaO is barium oxide. Ba + H2O ==> Ba(OH)2 + H2. You balance.

chemistry
You are being asked to transform a word equation into a chemical equation. You do this for every problem you work in chemistry. sulfur dioxide + water = sulfurous acid SO2 + H2O ==> H2SO3 SO2 is the anhydride of sulfurous acid.

College Chemistry (DrBob222)
If I didn't mess up somewhere the pKa = 5.20. Interesting problem. mmols NaOH added = 36.12 x 0.1 = 3.612 ...........HA + NaOH ==> NaA + H2O So at the equivalence point you have 3.612 mmols NaA in solution. Now you add 18.06 mL x 0.1M = 1.806 mmols ..........A^- + H^+ =...

College Gen.Chemistry
The straight line of y = 3,256x + 0.007 is the calibration curve of Absorbance on the y axis vs concn on the x axis. So insert 0.545 for y (that's the absorbance) and solve for x (that's the concn). I assume that is concn in grams/250 mL although nowhere is that inform...

Chemistry
Isn't dG = dGo + RTlnQ?

Chemistry
1.58e-4 what? mL? L? Does it sound reasonable that you can dissolve almost 61 g Mg(OH)2 in less than 1 mL (even less than 1 L)? If you had shown your work I could tell instantly what you did wrong. As it is I sit here and type all this out and let you look and see if you can f...

College Chemistry (DrBob222)
See your post below.

College Gen. Chemistry - Science
So how many mols did you have to start? That's mols = M x L = 0.120 x 0.245 = 0.0294. When some of the water has evaporated you know you still have 0.0294 mols there. And the molarity now is 0.348M and not 0.245M. So M = mols/L. M = 0.348; mols = 0.0294. Solve for L of sol...

chemistry
Ag^+ + Cl^- ==> AgCl mols NaCl = 0.05g/molar mass = ? mols AgNO3 = mols NaCl M AgNO3 = mols AgNO3/L AgNO3 You know M and mols, solve for L AgNO3 and convert to mL.

chemistry
You can't without knowing how much of the oxalate you have; however, you may find the ratio of oxalate to permanganate from the below. 2MnO4^- + 5C2O4^2- + H^+ ==> 10CO2 + 2Mn^2+ The above equation isn't completely balanced but you may complete it if you wish; howev...

CHEM
mols LiI = grams/molar mass. Substitute and solve for mols. Then M = mols/L solution. You know mols and L (after converting from mL), solve for M.

CHEM
8.0 what? 8.0 % w/v? 8.0 % w/v means 8 g NaOH/100 mL solution or 80g/1000mL = 80g/L. mols NaOH in 80g is 80/40 = about 2 so this is 2M. Then mols = M x L = 2M x 0.009L = ? mols NaOH

chemical
and you want to know what?

Chemistry
a) mols = grams/molar mass b) q = mass H2O x specific heat H2O x delta T That gives you delta H/10.1 and delta H/mol = delta H/10.1 g x ( molar mass/1 mol) and convert that to kJ/mol

incomplete--Chemistry

Chemistry 2
...CuBr(s) + 4NH3 ==> Cu(NH3)4^2+ + Br^- I....solid....0.69.....0............0 C....solid.....-4x.....x............x E....solic....0.69-x...x............x What we usually do is to say that this reaction goes essentially to completion since Kf for the complex is such a large...

Chemistry 2
...........Ag2CrO4 ==> 2Ag^+ + CrO4^2- I..........solid......0.......0 C..........solid......2x.......x E..........solid......2x.......x Substitute the E line into the Ksp expression and solve for x

Chemistry
See your post on Ag2CrO4.Worked the same way with solubility in M. Convert that to grams.

Chemistry
...........Al(OH)3 ==> Al^3+ + 3OH^- I.........solid.........0.......0 C.........solid.........x.......3x E.........solid.........x.......3x Substitute the E line into the Ksp expression for Al(OH)3 and solve for x = (Al^3+). Convert that to OH^-, change to H^+ and convert ...

Chemistry
a. 3.67 mg/mL = 3.67 g/L 3.67 x (1 mol/461.01) = 7.96E-3 = (PbI2) ..........PbI2 --> Pb^2+ + 2I^- I.........solid....0........0 C.........solid....x........2x E.........solid....x........x Ksp PbI2 = (Pb^2+)(I^-)^2 Ksp = (7.96E-3)(2*7.96E-3)^2 = ? NOTE: (I^-) = twice (Pb^2+...

Chemistry
5g/100 = (K2CrO4) mols K2CrO4 = grams/molar mass = approx 0.026 but you should do it more accurately. K2CrO4 --> 2K^+ + CrO4^2- So (K2CrO4) = 0.026 mol/0.1L = 0.26 M (K^+) = 2*0.26 = ?M (CrO4^2-) = 0.26M

chemistry
delta T = Kf*m Substitute and solve for m = molality m = mols/kg solvent Substitute and solve for mols. mols = grams/molar mass. You know grams and mols, solve for molar mass.

Chemistry
How much heat, q, is evolved ? That's q = 3.76 kJ/mol x (3.0g NaCl/58.46 g NaCl) = ?. Then q = mass H2O x specific heat H2O x delta T. Substitute and solve for mass H2O

Chemistry
Convert 2.0 L acetylene to grams using density. q = heat evolved = 1299.5 x (g C2H2/26) = ?

Chemistry
The reaction is exothermic because heat is evolved. mols Zn = grams/atomic mass = ? mols acid = M x L = ? Zn + HCl ==> ZnCl2 + H2 You balance. The reagent in excess is not the limiting reagent. q = mass H2O x specific heat H2O x delta T. h) dH = q Note that this is in J/rxn...

Redox Titration questions!
Did you put the Fe in solution and reduce it to Fe^2+ for titration with KMnO4. If so, then MnO4^- + 5Fe^2+ + H^+ ==> Mn^2+ + 5Fe^3+ Note: This is not the entire equation; therefore, it isn't balanced. However, the part that matters (the redox part) IS balanced. You may...

chemistry
q = mass H2O x heat fusion

chemistry
Use PV = nRT and solve for n N2. Use PV = nRT and solve for n O2 Add n = mols to find total mols. Then use PV = nRT and solve for P in the new container at the new conditions.

Chemistry: Check my answers?
Those look ok to me to let me put a bug in your ear. By typing your answers AT THE END we must scroll down the page to find the answer. Why not write the equation and write yes out to the right or just underneath. That way we can see immediately if all is ok without scrolling ...

chemistry
N2 + 3H2 ==> 2NH3 mols NH3 = grams/molar mass = approx 6 mols but that's an estimate and you should get a better number than that. Now convert mols NH3 to mols N2. That's approx 6 mols NH3 x (1 mol N2/2 mol NH3) = approx 6*1/2 = approx 3. Then g N2 used = mols x mol...

College Chemistry
NaI will ppt. Gases are more soluble at lower temperatures. MOST, but not all, ionic solids are more soluble at higher T.

Chemistry
http://www.science.uwaterloo.ca/~cchieh/cact/c120/bondel.html

chemistry
KOH + HOCl => H2O + KCl On these problems it helps to know where the equivalence point is located. mL HOCl x M HOCl = mL KOH x M KOH Substitute and solve for mL KOH. I get 50 mL NaOH needed. Therefore, you know this 150 is well past the equivalence point so the pH is determ...

chemistry
% by mass = [(mass solute)/(mass solute+mass solvent)]*100 = ?

chemistry
You need to know the solubility rules. Here is a simplified set. I shall be happy to check your answer. http://www.csudh.edu/oliver/chemdata/solrules.htm

AP Chemistry
dG = dH - TdS at equilibrium dG = 0; therefore, dH = TdS Substitute and solve for dS.

Chemistry
I don't think so. P ok but probably not T. If the glass of ice water is at equilibrium I assume that means some ice and some water are in the glass. If they are at equilibrium (meaning ice is not disappearing(melting) and water is not freezing, wouldn't that mean the g...

Chemistry
The same as the environmental temperature of its surroundings..

Chemistry
dG = dGo + RTlnQ where Q is set up the same way as Keq.

Chemistry
H has 1e and needs 2. Se has 6e and needs 8 So formula is H2Se I don't know what the last part of your post means.

Chemistry
It's tough to make it very much simpler but here are the same steps with some extra comments thrown in to help make the transition from bit to bit. But you won't learn by my doing the work for you; therefore, I don't intend to work the problem. Why didn't you c...

Chemistry
The same way you calculated it for rxn 1. dGo = -RTlnK2. You get the dGo from the dG formation for CO2.

Chemistry
MO2(s) ==> M(s) + O2(g) C(s) + O2(g) --> CO2(g) --------------------------- MO2(s) + C(s) ==> M(s) + CO2(g) Calculate k for rxn 1. dGo = -RTlnK1 Look up dGoformation CO2 and calculate k for that reaction as k2. Then for the sum of rxn 1 + rxn 2 (which gives the final ...

chemistry
I think the easiest way to work these "too small, too large, neither" problems is to go through the formula used to calculate the end result. I have summarized them here for problem #1. My comments are included with each in bold face. KHP standardization with NaOH. m...

Chemistry for health science
FeCO3 + 2HNO3 ==> Fe(NO3)2 + H2O + CO2 1.06 kg Fe = 1060 grams. mols FeCO3 = grams/molar mass. Using the coefficients in the balanced equation, convert mols FeCO3 to mols HNO3. Then mols HNO3 = M x L. You know mols and M, solve for L and convert to whatever unit (mL for exa...

Biochem
From 0.1 mL to (0.1+5+4.9) = 0.1 to 10 or the dilution factor is 10/0.1 = 100

Chemistry
I don't think you can assume either. And q = mcdelta T IS q(p); i.e., q at constant p. Also, I don't think this problem can be solved without knowing the volume or mass of the saturated solution. Obviously a 200 g sample will evolve more heat than a 100 g sample.

Chemistry
2Mg + O2 ==> 2MgO You must mean if 40 g magnesium OXIDE are produced and you must be using 24 for the atomic mass Mg and 40 as molar mass MgO. In those circumstances. mols Mg = 24/24 = 1 mol and that will produce 40 g MgO. mols O2 consumed = 40g MgO x (1 mol O2/2 mol MgO) =...

Chemistry - check answers
Yes, but you show know this is correct from F-F = 4.0-4.0 = 0 O-F = 4.0-3.5 = 0.5 H-F = 4.0-2.1 = 1.9 F-F is least polar H-F is most polar.

Chemistry - check answers
All of these look ok except 3. C is not right for 3. Look up the electronegativity of each element and subtract to find the relative polarity of each compound.

Chemistry
A = Ao - kt

Chemistry
See your post below.

Chemistry
A = Ao - kt

Chemistry
To be at equilibrium the solution must have dissolved all it can dissolve and some solid must be present.

Chemistry
No it is not at equilibrium because there is no solid present. Note the correct spelling of soluble.

chemistry
mols glucose = grams/molar mass = ? Then m = mols glucose/kg solvent Then delta T = Kf*m New freezing point = zero C - delta T.

chemistry
Use the Henderson-Hasselbalch equation.

Chemistry
I don't do it that way. That way is the quickest and easiest, so I'm told, and the way I do it long and the hardest way BUT I do it. Perhaps this will help you. 1. Divide into the two half equations. 2. Preliminarily balance the atoms that are changing; i.e., for Cr2O7...

Chemistry
This problem is confusing. Is that second titration a 25 mL aliquot of the original or has the solution been boiled so that the new volume is only 25 mL. If the latter, then MCO3 + 2HCl ==> MCl2 + CO2 + H2O mols HCl initially = 0.250 L x 0.203 M = 50.75/1000 = ? mols NaOH a...

chemistry
Add E1 to 2*E2 and divide by 3.

Chemisty - Unsure how to proceed- Combustion rxn
No. You find the heat of combustion which is in tables (or you can calculate it), then q = dHcombustion x (23g/molar mass ethanol) If you don't have heat combustion tables you can calculate it this way. From your equation above, use dHfrxn = dH combustion = (n*dHf products...

Chemistry-Repost for DrBob222
Well, it's this way. If you read the problem, as I did, the first line says you want to prepare 500 mL of a buffer. When I read that I quit reading and wrote instructions for preparing 500 mL of said buffer. You read the whole problem, which I should have done, and saw the...

Chemistry
I'm at a distinct disadvantage since I can't see the titration curve but I think this is what you do. The equivalence point is 7 (which I really don't understand since weak acids and strong bases are supposed to be somewhere in the 8.3 range for the eq pt but this ...

Chemistry-Repost for DrBob222
You can use the mg directly in the ratge equation. And I made a typo. That first line should have read, "Is that C60O3

Chemistry
Use the Henderson-Hasselbalch equation.

Chemistry-Repost for DrBob222
Six of one but all roads lead to the same answer. You start with 0.01M NaOH and you dilute it from 50 to 100 which is a factor of 2. 0.01/2 = 0.005M OR 0.01M x (100/200) = 0.005 OR mols NaOH = M x L = 0.01M x 0.05L = 0.0005 mols and M = mols/L = 0.0005/0.1L = 0.005M (50 mL + 5...

Chemistry-Repost for DrBob222
You said you understood part a. That's the initial amount of MgF2 dissolved in the 1L of water. You should have done this for part a. ............MgF2 ==> Mg^2+ + 2F^- I...........solid.....0.......0 C...........solid.....x.......2x E...........solid.....x.......2x Ksp ...

Chemistry
dG = dH- TdS Set dG to zero and solve for T. That gives you the T for equilibrium, any move less than that moves in the non-spontaneous direction.

chemistry
I don't know if that 1.85 atm is absolute or not; I assume this is to be worked the "easier" way. Use (p1/t1) = (p2/t2) Don't forget T must be in kelvin.

SCIENCE
1. I don't know that I believe it is uncommon to draw Lewis diagrams of ionic compounds. If we go with that assumption, however, I would go with d. 2. food? oil? 3. Doesn't it all depend upon what kind of mixture we have? For example, we separate oil (petroleum) at ref...

Chemistry
For the reaction A + B ==> C + D Q = (C)(D)/(A)(B) which looks like Keq but isn't. I suppose the simple answer is yes. You have two components of equal magnitude on the right and those are the products.

Chemistry
Two comments. Shouldn't that Q be (5.69E-5)^2/(1.34)? Can you add dGo (in kJ) and RTlnQ (which I believe is in J) without convert one or the other?

Chemisty
a. (Ca^2+) = 0.05 x (100/200) = ? b. (SO4^2-) = 0.10M x (100/200) = ? c. You can't do this? d. Calculate Krxn quotient. A ppt will form if Krxn quot > Ksp.

Chemistry HELP PLEASE!!
Mg^2+ + 2e ==> Mg(s) 2Cl^- ==> Cl2 + 2e Oxidation is the loss of electrons so which half rxn is that? Then oxidation occurs at the anode. Reduction occurs at the cathode (which is the gain of electrons).

Chem Check Please!!!
This looks ok to me.

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