Saturday
April 19, 2014

Posts by drbob222


Total # Posts: 41,801

CHEMISTRY HELP !!!!
The concentrations of the "ingredients" changes with time because one is being depleted and the other is being increased. E = Eo - (0.05916/n)log(1/M^x+) for each half cell.

incomplete---chemistry

Chemistry
I must be missing something. If you had 1.75g initially and 45.02% remains, then you have 1.75 x 0.4502 = ? g remaining after 85 days. Isn't that right?

Chemistry
k = .693/t1/2 t1/2 should be in days. Solve for k and substitute in the equation below. ln(No/N) = kt No = solve for this N = 45.02 k from above t = 85 days Solve for No which will be 100%.

Chemistry
There are 3.7E10 dps/Ci 1 Bq = 1 dps. So 18.9 uCi will be 18.9E-6 Ci. (3.7E10 dps/1 Ci) x 18.9E-6 Ci = ? dps Since 1 Bq = 1 dps, then ? dps = ? Bq Check out my thinking.

CHEMISTRY HELP !!!!
In #1, formation of Pb to Pb^+ should be smaller than Pb ==> PbSO4 because the formation of PbSO4 drives the reaction to the right. #2. dG = -nFEocell

chemistry first year
This is a limiting reagent (LR) problem. You can tell because amounts are give for both reactants. V is voltage, value, volume. Volume maybe. ........N2 + 3H2 ==> 2NH3 begin volume = 20 + 100 = 120 L. What volume NH3 will be produced if we use all of the N2 and and excess o...

chemistry first yera
HA + NaOH ==> NaA + H2O mols NaOH = M x L = ? mols HA = mols NaOH (look at the 1:1 coefficients) mols HA = grams/molar mass You know mols HA and grams, solve for molar mass.

Chemistry
[350g H2O x specific heat H2O x (70-25)]+[mass steam x (heat vap)] + [mass H2O from steam x specific heat H2O x (70-100)] = 0 Solve for x = mass steam The only unknown in that equation is mass steam and mass H2O from steam. I would let them = y and plug in the other numbers an...

Chem
If the density of the solution is 1.00 g/mL (and it may not be) it has a mass of 4200 grams. That x 0.031 = g Ag in the solution.

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

chemtry 1
Use PV = nRT

chemistry
You just need to set what you have equal to Kb for CN^- which isn't in any table but can be calculated this way. Kb for CN^- = (Kw/Ka for HCN) so (Kw/Ka for HCN) = (x)(x)/(0.8-x) and solve for x.

TO ANY SCIENCE HELPER
You know the half life for carbon 14 is 5,730 years. If you aren't told that in the problem you can look it up. You can calculate the rate constant (which you will need later) this way. k = 0.693/t1/2 k = 0.693/5730 = 1.21E-4 Substitute this k into the equation below. ln(N...

Chemistry
I don't think so. Pdry gas = 754mm - 18 mm = 736 mm and P gas in atm is 736/760 = ? Then PV = nRT or n = PV/RT = 736*0.0885/(760*0.08206*293) = ? Then mols = g/atomic mass or atomic mass = g/mols. Atomic mass Mg is about 24 and I obtained more than twice that.

chemistry
Do you mean 0.890 m or 0.890 M?

TO ANY SCIENCE HELPER
Why don't you post a problem and explain what you don't understand about it.

chemistry
2Al2O3 ==> 4Al + 3O2 mols Al2O3 = 742.5 g/molar mass Al2O3. Now use the coefficients in the balanced equation to convert mols Al2O3 to mols Al. Finally, g Al = mols Al x atomic mass Al.

Chemistry
I believe it has 4 non-bonding electrons. The two (paired) in the 2s and the two (paired) in the 2p.

Chemistry
I would go wth b. The C-O bond length is 112.8 pm according to wikipedia. The covalent radius for C is 0.77 and that of O is 0.73 according to my home periodic table.

Chemistry
.....Ag2CO3 ==< 2Ag^+ + CO3^2- I.....solid......0.....0.0001 C.....solid......2x.......x E.....solid......2x...0.0001+x Subsitute the E line into the Ksp epxression and solve for x = solubility in M. Then grams = mols x molar mass

Chemistry
I don't see any correction to go from pure O2 to air (21% O2 in air). A minor point. Since T is given as 26.4 I would have added that to 273.2. But if 882.6 is the correct answer I don't know how you came that close when not using the 21%. Perhaps you just didn't s...

Radioactivity
a. The rate of decay = 26,880 dpm (decays/min) b. k = 0.693/t1/2 Solve for k and substitute into the below equation. ln(No/N) = kt No = 26880 N = ? k from above t = 265 days c. 1 Bq = 1 dps Your sample is 26,880 dpm so 26,880 decays/min x (1 min/60 sec) = about 448 dps. ln(No/...

Radioactivity
The half live of C14 is only about 6,000 years and this is not suitable to a rock sample of that age. There is a section is the link below that talks about which methods are best for various ages. http://en.wikipedia.org/wiki/Radiometric_dating 2. k = 0.693/t1/2 Look up t1/2 i...

chemistry
q = mass H2O x specific heat H2O x (Tfinal-Tinitial)

Chemistry
right.

Chemistry pH
pH = -log(H^+) pH = 3.72; (H^+) = approx 2E-4 but that's an approximation. You should do this more accurately as well as all of the calculations that follow. %ion = [(H^+)/Msample]*100 ...........HA ==> H^+ + A^- I.........0.6.....0......0 C...........-x....x......x E.....

Chemistry
This forum is not designed for graphing, drawings, spacings, etc etc. What the problem wants you to do is to graph P vs 1/V So the first point will be 1 atm for P and 1/150 mL for volume The second point will be 1.15 atm for P and 1/130 mL for V etc

Chem
In ==> In^3+ + 3e tough eh! Cd^2+ + 2e ==> Cd

Chemistry
Your set up is right (except for calling torr psi). So your error must be in the math part.

Chemistry
No, 519 cc isn't correct either. Post your work and I'll find the error.

Chemistry
I didn't work 1 but 2 can't be right. 775 is Ptotal so how can it be pO2?

Chemistry
1. (P1V1/T1) = (P2V2/T2) Remember T must be in kelvin. 2. Ptotal = pO2 + pH2O Substitute and solve for pO2.

Honors chemistry
q = mass x heat fusion

CHEM- need help ASAP
I worked this for Jon earlier. Post any follow up questions here. http://www.jiskha.com/display.cgi?id=1397681371

Chemistry
mols Na = grams/molar mass Using the coefficients in the balanced equation, convert mols Na to mols Cl2. Now convert mols Cl2 to liters remembering that mols x 22.4L/mol = ?L

Chemistry
Let's write ethylamine as BNH2. If the pH is 11.87 the pOH is 14-11.87 = pOH of 2.13 and 2.13 = -log(OH^-) so (OH^- is approx 7E-3M but you need to that more accurately as well as all of the other calculations that follow. Then .......BNH2 + HOH ==> BNH3^+ + OH^- I........

Chemistry
See your Kb ethylamine post. Same procedure. Post your work if you get stuck.

chemistry
The solution is acidic at the equivalence point due to the hydrolysis of the cation of the weak base.

Chemistry
The CN^- is hydrolyzed. ...........CN^- + HOH ==> HCN + OH^- I.........0.8..............0.....0 C..........-x..............x.....x E.........0.8-x............x.....x Kb for CN^- = (Kw/Ka for HCN) = (x)(x)/(0.8-x) and solve for x = (OH^-) = (HCN) This give you the HCN. Conve...

chemistry
I'm not exactly sure what you want but I would do this for the balanced chemial equation. For the thermo equation you want this without the 2 coefficient and you want to add the dH = -129 kJ/mol 2NaHCO3 ==> Na2CO3 + CO2 + H2O NaHCO3 ==> 1/2 Na2CO3 + 1/2 CO2 + 1/2 H2O...

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...

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...

chemistry
pN2 = XN2*Ptotal

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.

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 ...

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

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

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?

Chemistry - Science (Dr. Bob222)
See your other post above.

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

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.

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 ad...

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...........

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 cha...

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

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.

Chemistry
Why can't you simply substitute into the formula given in the problem?

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.

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 ask...

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., clock...

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 valu...

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.

Chemistry
http://en.wikipedia.org/wiki/Template:Periodic_table_%28electron_affinities%29

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

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.

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

Chem
mass = volume x density

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...

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.

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.

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 K...

CHEM
What is Ag? What's the other number for?

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)

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 nutri...

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

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 fo...

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 S...

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

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).

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

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

science
Generally days are shorter in the winter than in the winter.

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 ...

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

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.

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. ...

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 ...

chem
Ptotal = pO2 + pH2O

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 syste...

CHEMISTRY HELP !!!!
dGsystem < 0 for any spontaneous process.

Chemistry
pH = -log(H^+) Substitute and solve for pH.

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

chemistry
mols glyc = grams/molar mass mols H2O = grams/molar mass Xgly = mols gly/total mols XH2O = mols H2O/total mols.

chemistry
PV = nRT

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.

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 co...

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.

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.

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.

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