Thursday
August 21, 2014

Posts by DrBob222


Total # Posts: 43,319

chemisrty
Looks like not enough information is there but it can be done. The easy way to understand it is to assume some convenient concn for the weak acid and the NaOH and work it out. The easy way to solve it is to do it by reasoning. You can go through the numbers if you wish but the...
April 16, 2014

chemistry
Use the HH equation. The way I read the problem you have a solution that is 0.2M in propionic acid and another solution 0.2M in sodium propionate. pKa = -log Ka = about 4.89 but you should confirm that and adjust the figure to your liking. 4.65 = 4.89 + log (base/acid) b/a = 0...
April 16, 2014

chemistry
pN2 = XN2*Ptotal
April 16, 2014

College Chemistry (DrBob222)
k = 0.693/t1/2 ln(No/N) = kt No = any convenient number but I would use 100 to represent 100%. Then if it decreases by 73% that leaves 27% so N = 27 k from above t = ? Solve for t in seconds if you use half life in seconds.
April 16, 2014

chemistry - (Dr. Bob222)
I obtained 1.51 which is essentially the same as your answer. Did they give a reaction? The formula actually is 1/A - 1/Ao = akt so the a could change things but usually is not a number like 2/3. Must be a wrong answer. If you find to the contrary please be sure and post so I ...
April 16, 2014

chemistry - (Dr. Bob222)
[1/(A)] - [1/(Ao)] = kt k is given in seconds; therefore, change 2.5 minutes to seconds.
April 16, 2014

CHEMISTRY HELP !!!!
What's with this "show your work"? What work? No information is furnished. You can look up the Ka value in this table. http://bilbo.chm.uri.edu/CHM112/tables/KaTable.htm
April 16, 2014

Chemistry - Science (Dr. Bob222)
Can't you simply plug in k1 and k2 along with T1 and T2 and solve for activation energy with the Arrhenius equation?
April 16, 2014

Chemistry - Science (Dr. Bob222)
See your other post above.
April 16, 2014

Chemistry
2KNO3 ==> 2KNO2 + O2 The equation above is not necessary for solution of the problem. Use PV = nRT and solve for n.
April 16, 2014

Chemistry
I obtained, using the equilibrium as 2HI ==> H2 + I2 as K = (H2)(I2)/(HI)^2 = (0.1)(0.1)/(0.7)^2 = 0.0204 which would be 1/0.0204 = 49 for the way you suggested.
April 16, 2014

Chemistry
I have made mistakes like that but in this case I didn't. It could be either way. Which ever way you do it will work out. If you assume you started with HI, then 2HI ==> H2 + I2 and the EQUILIBRIUM MIXTURE will be as given. Then you work out Kc for that reaction. You ...
April 16, 2014

Chemistry
First, convert mols to M. (HI) = 7/10 = 0.7M (I2) = 1/10 = 0.1M (H2) = 1/10 = 0.1M Next calculate the Kc. 2HI ==>H2 + I2 Kc = (H2)(I2)/(HI)^2 Kc = (0.1)(0.1)/(0.7)^2 = approx 0.02 Then do and ICE chart. ............2HI ==> H2 + I2 I...........0.7....0.1...0.1 add...
April 16, 2014

Chemistry
Actually all of these can be worked using the table of reduction potentials but I will give that process last and show shortcuts for metals vs metal ions and for halogens vs halogen ions. The metals are done by looking at the activity series of metals. Here is a simplified ...
April 16, 2014

Chemistry
I assume you performed some experiment and you are to use your observations to help answers this question. What were your observations?
April 16, 2014

Chemistry
0.9% w/w NaCl in water means 0.9g NaCl/100 g solution. So you put 0.9 g NaCl in 99.1g H2O and shake till dissolved. You want to make 200 g of this so double those numbers.
April 16, 2014

Chemistry
Why can't you simply substitute into the formula given in the problem?
April 16, 2014

Chemistry
This post has gotten pretty far down the list and I may not see it by tomorrow. If you're still confused please post a new question at the top of the page.
April 16, 2014

Chemistry
I think your part way there but I don't think you grasp the problem. And n =2 is the last shell of F. First, the electronic configuration of F is 1s2 2s2 2p5. You can see from this, and the problem restates that, that there are 9 electrons in the F atom. Thr problem is ...
April 16, 2014

Chemistry
n is the principal quantum number and in general terms is the old Bohr shell. l (ell) is the azimuthal quantum number and describes the ellipticity (how elliptical) of the orbit. ml describes how the orbit is arranged in space ms describes the spin of the electron; i.e., ...
April 16, 2014

Chemistry
You need to learn to do these. Here are the rules. n can be any whole positive number beginning with 1, 2, 3, etc. l(ell) can be any positive whole number beginning with zero but can't be larger than n-1 ml can have values from -ell to + ell. ms may have either of two ...
April 16, 2014

Chemistry
I think so although no number is placed on it in that table you looked at. Most might say iodine since there is so little At around.
April 16, 2014

Chemistry
http://en.wikipedia.org/wiki/Template:Periodic_table_%28electron_affinities%29
April 16, 2014

Chemistry
For a 1 tesla field the Larmor frequency is freq = 28.025 GHz. http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/nmr.html
April 16, 2014

CHEm
Use PV = nRT and solve for n = number of mols. Then n = grams/molar mass. You know n and molar mass, solve for grams. I would convert cubic meters to L.
April 16, 2014

Chem
PV = nRT and solve for n = number of mols. Then n = grams/molar mass and solve for molar mass.
April 16, 2014

Chem
mass = volume x density
April 16, 2014

Radioactivity
k = 0.693/t1/2 Substitute k into the equation below. ln(No/N) = kt No = 120 N = ? k from above t = 120 seconds (since the half life is given in sec you will have a seconds terms for k so you must convert 2 minutes to seconds). Solve for N. See the link below for the definition...
April 16, 2014

Chemistry
What do you mean you don't know where to start. This is just a case of substitute and solve. 7.7E24 = Kc(0.08205*298)^(4-2) Solve for Kc.
April 16, 2014

Chemistry Help
Coulombs = amperes x seconds = approx 3000. 107 g Ag will be deposited for every 96,485 coulombs. So Ag deposited is 107g Ag x (approx 3000/96,485) = ? g Ag.
April 16, 2014

Chemistry
A. The reaction for A is just the reverse of the original; therefore, the new Kp(that is K'p) for the new rxn will be 1/Kp B. B is just 1/2 the original; therefore, the new Kp (that's K"p) will be sqrt(Kp) For any reaction of A ==> B, then Kp = pB/pA. So when ...
April 16, 2014

CHEM
What is Ag? What's the other number for?
April 15, 2014

CHEM
Your post isn't very clear. Do you mean this is a concentration cell with one half cell of 1E-2M and the other 3.2E-2. If so then Ecell = -(0.05916/1)log (dilute/concd)
April 15, 2014

chemistry
mols sample = 0.05/114 = approx (but you do it for the real number) = 0.00044 q = mass H2O x specific heat H2O x delta T. q = 200g x 1 cal/g*C x 5.7 q = approx 1100 calories for 0.05g or 1100/0.05 = approx 23000 calories 23,000 calories x (1 kcal/1000 cal) = 23 kcal = 23 ...
April 15, 2014

chemistry
3,5,5 look just like 1 and 2. 6 and 7 are done by working backward. delta T = i*Kf or Kb *m You're given delta T, solve for m. Then m = mols/kg solvent. Solve for mols Then mols = grams/molar mass. You're given mols and grams; solve for molar mass. i = 1 for both 6 and 7
April 15, 2014

chemistry
2. Find the freezing point of a solution composed of 50g IBr in 120 g of water. Assume 100% ionization. KBr = k1+Br1-. I assume you made a typo and IBr really is KBr. mols KBr = grams/molar mass. Solve for mols. molality = m = mols/kg solvent Solve for m delta T = i*Kf*m i ...
April 15, 2014

chemistry
1. Find the boiling point of a solution composed of 110g of HgCl2 (a non-ionizing solute) in 175g of water. mols HgCl2 = grams/molar mass Substitute and solve for mols. molality = m = mols/Kg solvent Substitute and solve for m delta T = i*Kb*m Your post says i = 1 Kb = 1.51 ...
April 15, 2014

chemistry
dGo = -nFEo Solve for n. That will give you the change in electrons.
April 15, 2014

Chemistry
I differ slightly (84.82) probably because you rounded to 1.62 while I kept everything in the calculator until the final answer. But to three significant figures I would round the answer to 83.8 (probably krypton).
April 15, 2014

Chemistry
(rate1/rate2) = sqrt(M2/M1) Substitute and solve for molar mass.
April 15, 2014

science
Oh my! Twisted minds. I'm still smarting over carbon dioxide and water having the same physical properties.
April 15, 2014

science
Generally days are shorter in the winter than in the winter.
April 15, 2014

Science
A is the correct answer. Water is H2O and carbon dioxide is CO2. They have different physical properties (water is a liquid while CO2 is a gas at room temperature.) Both have a set ratio of atoms as shown by the formulas I've written. Water and CO2 have different chemical ...
April 15, 2014

Science
And a c'mon to Kalie, too. What are physical properties? What are chemical properties.
April 15, 2014

Science
I don't agree with that answer. Carbon dioxide is a gas; water is a liquid. And you think they have the same physical properties? C'mon.
April 15, 2014

chem
You're right about Pgas = X*Ptotal but I don't think you understand the equation I wrote. Dalton's Law of partial pressures tells us that the total pressure inside a container is the sum of the individual gas pressures. So I wrote the equation Ptotal = pO2 + pH2O. ...
April 15, 2014

chem
The temperature is used to look in a table of T vs vapor pressure. It tells you the vapor pressure of the water (in this case 25.81 mm Hg) at 26.4 C. I don't agree with your answer. And why in the world would you change mm and torr to atm if the problem didn't ask for ...
April 15, 2014

chem
Ptotal = pO2 + pH2O
April 15, 2014

chemistry
You can calculate delta S for the system and delta H for the system at 25 degrees C by using dHo formation and dSo formation and dHo rxn = (n*dH products) - (n*dH reactants) dSo rxn = (n*dH products) - (n*dH reactants). What's the temperature. dS surrounds = -dH/T dS ...
April 15, 2014

CHEMISTRY HELP !!!!
dGsystem < 0 for any spontaneous process.
April 15, 2014

Chemistry
pH = -log(H^+) Substitute and solve for pH.
April 15, 2014

chemistry
M of the diluted stuff is 1.14 g/mL x 1000 mL x 0.20 x 1/98 = 2.33M M of the strong stuff is 1.84 x 1000 x 0.98 x 1/98 = 18.4M Then use the dilution formula. mLA x MA = mLB x MB 100 x 2.33 = mLB x 18.4M Solve for mL B. I obtained approx 13 mL
April 15, 2014

chemistry
mols glyc = grams/molar mass mols H2O = grams/molar mass Xgly = mols gly/total mols XH2O = mols H2O/total mols.
April 15, 2014

chemistry
PV = nRT
April 15, 2014

Chemistry
I'm not sure what you want for #1. We can't draw structures on this forum. For #2, the Cl outside the coordination sphere is the ionic Cl, therefore Cl- + Ag^+ ==> AgNO3. The two coordinated Cl atoms within the sphere are not ionic and do not react with AgNO3.
April 15, 2014

chem
1. mols NH3 = M x L = ? Using the coefficients in the balanced eqauation, convert mols NH3 to mols H2SO4. Now M H2SO4 = mols/L, You know mols and M, solve for L and convert to mL if needed. 2. You have mols NH3. Using the coefficients convert mols NH3 to mols (NH4)2SO4. Now ...
April 15, 2014

Chemistry
Write and balance the equation. Convert 400.0g C3H8 to mols. mol = grams/molar mass Using the coefficients in the balanced equation, convert mols C3H8 to mols or the product. Now convert mols of the product to volume. mols x 22.4 L/mol = Liters.
April 15, 2014

chemistry
How many mols NaCl do you want? That's M x L = ? Then mols = grams/molar mass. You know molar mass and mols, solve for grams.
April 15, 2014

chem
Density = 1.025 g/mL; therefore, 100 mL has a mass of 1.025g/mL x 100 mL = 102.5g. 100 mL H2O should weigh 100 g; therefore, there are 2.5 g vinegar in the sample and that is 2.5%. This assumes that the volumes of vinegar and H2O are additive.
April 15, 2014

Chem
q = mass Al x heat fusion Note that mass is in grams and heat fusion is in kJ/mol; therefore, you must convert g Al to mol or heat fusion from kJ/mol to kJ/g
April 15, 2014

chemistry
What is the "mass you calculated" refer to?
April 15, 2014

chemistry
What reaction? What change in % did you calculate? I don't get the question?
April 15, 2014

chemistry
mols F^- = 0.0025g/atomic mass F and since that is is 1 L, that is the concn in mols/L. Evaluate Qsp and compare with Ksp.
April 14, 2014

chemistry
(P1V1/T1) = (P2V2/T2) P1 = 1 V1 = 0.550 T1 = 273 P2 = ? V2 = 7.50E-2L T2 = 273 + 20
April 14, 2014

Chemistry
No and partly because I may have led you astray. The numbers I gave you are for 1L of the solution at that concn. You only want 500 mL of that (which I missed on first reading) so you need only 1/2 of your final figure or 5.346/2 = ?.
April 14, 2014

Chemistry
Li3PO4. You want (Li^+) = 0.1385M You want to make this out of Li3PO4. But since Li3PO4 furnishes 3 Li ions for every molecule of Li3PO4, you only need 1/3 that number or 0.1385/3 = ? mols Li3PO4. Then g Li3PO4 = mols x molar mass.
April 14, 2014

Chemistry
CH3COOH + NaOH ==> CH3COONa + H2O mols NaOH = M x L = ? mols CH3COOH = mols NaOH (because of the 1:1 coefficients in the balanced equation.) g CH3COOH = mols CH3COOH x molar mass CH3COOH. Then % CH3COOH = (g CH3COOH/mass sample)*100 = ?
April 14, 2014

Chemistry
This is a limiting reagent (LR) problem. You know that when an amount for BOTH reactants is given. Zn + 2HCl ==> H2 + ZnCl2 mols Zn = grams/molar mass. mols HCl = M x L = ? Using the coefficients in the balanced equation, convert mols Zn to mols H2. Do the same for mols HCl...
April 14, 2014

Chemistry
The Eo voltage in tables may changes as a result of acid or basic conditions; however, there are no H or OH ions in the half reactions you've written so you need not worry about that.
April 14, 2014

Chemistry
If that is the smallest Ecell, then turn those half cells into a reaction. Arrange the half cells so they produce a positive voltage. 2Eu^2+ + Sn^2+ ==> 2Eu^3+ + Sn
April 14, 2014

Chemistry
2Fe3+(aq)+H2(g)→2Fe2+(aq)+2H+(aq). Ecell = Eocell - (0.5916/2*log Q and I know that confuses you but don't be. Plug in the numbers Eo and n and for Q plug in concns/pressures(in atm) as follows: Q = [(H^)^2*(Fe^2+)^2]/[(Fe^3+)^2*pH2] I write it this way because I'...
April 14, 2014

Chemistry
See your other post. delta e wrong at 6.
April 14, 2014

General Chemistry
3e not 6.
April 14, 2014

Chemistry
mols MgCl2 = grams/molar mass = ? M MgCl2 = mols/L solution = ? Since there are two mols Cl in 1 mol MgCl2, then M Cl = twice that of MgCl2.
April 14, 2014

Chemistry
An equation like this is confusing because I^-(on the left) is going to I2 (on the right) but it then dissolves in KI to make KI3 so let's simplify it by taking the KI out of it, balance it, then put the KI back in. 2I^- --> I2 I is -2 on left and 0 on right. Balance ...
April 14, 2014

chemistry help~~~~ Please!!!
k = 0.693/t1/2 Then ln(No/N) = kt. No = 25 N = 1 k from above. t = solve for this.
April 14, 2014

Chemistry-need help ASAP
I'll get you started but I don't believe you can't do any of it. I don't know what the problem is asking for when it says "difference in pH". Difference in pH from WHAT? 15 mL of 3M NaOH added to 500 mL. (NaOH) = 3M x (15/515) = ? (Note: This assumes ...
April 14, 2014

Chemistry-need help ASAP
How much of this do you know how to do?
April 14, 2014

Chemistry
HAc + NaOH ==> NaAc + H2O First determine the M of the HAc. mL x M = mL x M 22.5 x .21 = 50x (I worked this part for you at your original post yesterday. Apparently you never went back to look at it.) M HAc = approx 0.9 but you need to do it more accurately. Now divide the ...
April 14, 2014

Chemistry
I responded earlier with this. How much do you know how to do?
April 14, 2014

Chemistry
Here us a site that tells you the details. http://www.chemteam.info/Redox/Redox.html I don't do them that way. Here is how I do the CrO4^-. You can add the states. CrO4^2- ==> Cr^3+ Cr is +6 on left and +3 on right. Add 3e to left. CrO4^2- +3e ==> Cr^3+ Count the ...
April 14, 2014

chemistry
Did you square 1.75 or multiply it by 2. I think you did the latter; you should have squared it.
April 14, 2014

Chemistry
Mn is +7 in MnO4^-. It is +2 in Mn^2+. To balance the change in electrons we have MnO4^- + 5e ==> Mn^2+. I do it that way and make this the first step of the process of balancing. Some say there is a shorter way and you do this the LAST step and not the first. To do it that...
April 14, 2014

Chemistry
MnO4^- + 8H^+ + 5e ==> Mn^2+ + 4H2O
April 14, 2014

chemistry 2
HAc + NaOH ==> NaAc + H2O First, determine the molarity of the HAc. mL x M = mL x M 22.5 x 0.21 = 50*x x = 0.0945M Now divide the titration curve into four sections. a. at the beginning. b. between initial and eq point c. eq pt d. after eq pt Which of these do you have ...
April 14, 2014

chem090
I work these limiting reagent (LR) problems the long way. 2K3PO4 + 3BaCl2 ==> Ba3(PO4)2 + 6KCl mols K3PO4 = grams/molar mass = 100/212.26 = about 0.47 mols BaCl2 = 100/208.23 = about 0.48 Now convert mols K3PO4 to mols Ba3(PO4)2 using the coefficients in the balanced ...
April 14, 2014

Chemistry
Here is the way I write these. The atomic number goes on the left, the mass number on the right. So the Po would be 84Po212 ==> 82Pb208 + AXZ where A is atomic number, Z is mass number, X is the element. The left side must add up and the right side add up; i.e., atomic ...
April 14, 2014

Chemistry
Following my post above. atomic number on left, element in middle, mass number on right. Left numbers must add up on both side; right numbers must add up on both sides. So for Th we write 90Th234 ==> beta + ? beta is an electron which is -1e0. 90Th234 ==> -1e0 + AXZ So ...
April 14, 2014

chem 101
q = mass x heat vaporization Change 42.8g to mols. mols = grams/molar mass
April 14, 2014

Chemistry
assume the question is to determine M I2. ascorbic acid + I2 ==> 2I^= + ..... mols ascorbic acid = grams/molar mass mols I2 = mols ascorbic acid (1:1 ratio from the equation) M I2 = mols I2/L I2.
April 14, 2014

chemistry
You don't ask a question. I assume the problem is to determine the heat of neutralization in kJ/mol. Also, I assume there is no calorimeter constant so we ignore that. Please check the post to make sure you have all of it correctly. The answer should be about 55 kJ/mol and...
April 14, 2014

Chemistry - Science (Dr. Bob222)
Cr on the left is +6 each so 6*14 = 84+ and on the right is 14*3 = 42+. 84-42 = 42 e xfrd. I on the left is zero. On the right each I is 7+ and 6*7 = 42+. 42-0 = 42e xfd.
April 14, 2014

Chemistry
CoCl2 is soluble; therefore, it has no Ksp. The easiest way to do these is to note that with a Kf so extremely high you know the solution at equilibrium will be far to the right; therefore, we set up an ICE chart and make the reaction go 100% to the right. That is an ok ...
April 14, 2014

chemistry
Your equation is right. Your reasoning is wrong. Mg is more active because it replaces the Pb ions and forces the Pb out of solution. Here is how you tell which is more active. Here is the "activity series" of metals. https://www.google.com/search?q=activity+series+...
April 14, 2014

chemistry
See your post above. Pb is above Ag in the table; therefore, Pb is the more active metal and it will displace Ag^+ from solution.
April 14, 2014

chemistry
You have written it correctly.
April 14, 2014

Radioactivity
When an element loses an electron (from the nucleus) it is because one of the neutrons becomes a proton and the electron is ejected as a beta particle. The mass number doesn't change because the number of protons + number of neutrons is the same but the number of protons ...
April 14, 2014

Science radioactivity
Alpha and beta particles really are particles in that sense of the word. The alpha particle is a helium nucleus and a beta particle is an electron. A gamma is a ray; i.e., an electromagnetic wave much like a radio or TV wave (but a much shorter wavelength and much higher ...
April 14, 2014

chemistry
The general gas formula can be modified from PV = nRT to P*molar mass = density*RT Substitute and solve for density.
April 13, 2014

Chemistry
See your other post.
April 13, 2014

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