Tuesday
March 3, 2015

Posts by DrBob222


Total # Posts: 47,384

Chemistry
1. Balance the equation. 2. This is a limiting reagent (LR) problem. Determine the LR. 3. Convert mols reactants to heat produced. This is the theoretical yield.
December 12, 2014

Chemistry
12% m/v (w/v) means 12g solute/100 mL solution. How many mols is 12 g Na2SO4? That's mols = grams/molar mass = approx 0.08 but you need a more accurate answer than that. What volume? That's 100 mL or 0.1L M = mols/L. I don't think the density is needed.
December 12, 2014

chemistry
As for the Na question. I've not made a secret that I think some of the questions are not very good, some of the answers are not very good, but mostly, as this one, there is no clear answer or the answers are muddled. At any rate, here is my take on this one. A is true. ...
December 12, 2014

chemistry
Thanks!. One more. Are these questions you post test questions? I'm working on the answer to the Na question.
December 12, 2014

chemistry
OK, so I'll repeat some of them. What do you have as resource material for study? Is the material explained thoroughly? Where do these questions come from? Are they test questions?
December 12, 2014

chemistry
You answered one question but not the others. Please fill me in on the others.
December 12, 2014

chemistry
Did you see my note from last night? Here is a link. I would like some answers please. http://www.jiskha.com/display.cgi?id=1418364644
December 12, 2014

Equations and Inequalities
Links do a better job of explaining than I can ever do. Here is another link. Read it and put it in your own words. his isn't purple math although I think that web site is very good. http://www.ehow.com/info_8382315_difference-between-inequality-equation.html
December 12, 2014

Chemistry
0.557 mol x atomic mass Ag = mass Ag (mass Ag/mass sample)*100 = % Ag Substitute and solve fo mass samle.
December 12, 2014

Chemistry
Use PV = nRT Remember T must be in kelvin
December 12, 2014

Chemistry
If I read this problem correctly it provides numbers that are entirely unrealistic and I don't want to tackle it. For example, 0.365 mol H2O = approx 6.6 grams. If the density is 1.0 g/mL that is about 0.0066 liters which makes the HCl about 0.250/0.0066 = approx 38 M and ...
December 12, 2014

Chemistry
A solubility of 36.0 g NaCl/100 g H2O is 36.0/58.44 = 0.616 mol NaCl. 100 g H2O is 100/18 = about 5.55 mols H2O so the solubility in terms of mols/mols is 0.616 mols NaCl/5.55 mols H2O. 5.55 mols H2O x (0.263/0.616) = ? mols H2O to prepare a saturated solution.
December 12, 2014

To Morgan
Where are you getting all of this stuff? What university/college? Where do the exercises(questions) come from? What sources to you have for study? What percentage are you getting from Jiskha? Thanks. I'm just curious.
December 12, 2014

Chemistry
Na2SO4 + BaCl2 ==> BaSO4 + 2NaCl mols Na2SO4 = M x L = ? mols BaCl2 needed = same as mols Na2SO4 since the reaction coefficients are 1 mol Na2SO4 to 1 mol BaCl2. Then M BaCl2 = mols BaCl2/L BaCl2. You know M and mols, solve for L and convert to mL.
December 12, 2014

chemistry
q = heat = mass x specific heat x (Tfinal-Tinitial)
December 12, 2014

chemistry
Nope. You have it backwards (actually you want the reciprocal of what you wrote). Its grams/molar mass = mols Then mols/2.5 = m
December 12, 2014

Chemistry
The one electron in the H atom is in the n = 1 shell in its ground state. It can be moved from the n = 1 shell to n = 2 or n = 3 or n= 4 etc by absorbing energy. Thus we can expose H atoms to energy and cause the electron to move to higher levels BUT not just any amount of ...
December 12, 2014

chemistry
The ppt is Ca3(PO4)2. You have 8.16E25 atom Ca ions. That's 8.16E25 x (1 mol/6.02E23) = ? mols Ca and divided by 3 = mols Ca3(PO4)2. From there you know you have twice that mols P atoms (mols P x 6.02E23 = atoms P) and 8x that number of mols O atoms (atoms O = mols O x 6....
December 11, 2014

chemistry
OK but I disagree. b can be right in certain cases, as in the case of the H atom, but for other atoms the orbitals(s,p,d,f) determine the energy of the electrons. The answer d is correct for n of any element. Here is a graph of such a function. http://en.wikipedia.org/wiki/...
December 11, 2014

chemistry
I would go with d.
December 11, 2014

chemistry
d It is quantized.
December 11, 2014

chemistry
What do you not understand about this? Anytime you are within a phase it is q = mass x specific heat x (Tfinal-Tinitial) Phase changaes are different. At the melting point it is q = mass x heat fusion. At the boiling point it is q = mass x heat vaporization. Those three ...
December 11, 2014

Science
This is a limiting reagent problem and you know that because amounts are given for BOTH reactants. I worked a problem just a few minutes ago and here is a link. Just follow the same steps. http://www.jiskha.com/display.cgi?id=1418356094
December 11, 2014

Chemistry
See your other post.
December 11, 2014

Chemistry
I have rewritten the equation without phases to save space. This is a limiting reagent (LR) problem and you know that because amounts are given for BOTH reactants. 2NaCl + H2SO4 --> 2HCl + Na2SO4 Usint 2.00 mols H2SO4 and all of the NaCl needed will give you 2.00 x (2 mols ...
December 11, 2014

Chemistry
.......H2C2O4 + H2O --> H3O^+ + HC2O4^- I......0.175.............0.......0 C........-x..............x.......x E.....0.175-x............x.......x Substitute the E line into Ka1 expression and solve for x = (H3O^+) = (HC2O4^-). That gives you H3O^+ and HCO4^- and note they ...
December 11, 2014

Chemistry
All waves have same speed in a vacuum of 3E8 m/s. All have a wavelenth although each is different. All have a frequency although each is different. All have energy although each is different. They all have amplitude that depends upon intensity. In short all could be true. I ...
December 11, 2014

chemistry
Exactly. The only difference is the definition. M = mols/L solution m = mols/kg solvent At very low concentrations M is about equal to m.
December 11, 2014

chemistry
q1 = heat to raise T from -20 to zero. q1 = mass ice x specific heat ice x (Tfinal-Tinitial) where Tf is 0 and Ti is -20. q2 = heat to convert solid ice at zero to liquid water at zero C. q2 = mass ice x heat fusion q3 = heat to raise T of liquid water at zero C to 90 C. q3 = ...
December 11, 2014

chemistry
Experimentally you can try dissolving polar and non-polar solids in the solvent. Since like dissolves like polar solids are soluble in polar solvent and vice versa. Remember, however, that advice sometimes fails. Theoretically, you compare the electronegativity of the elements...
December 11, 2014

chemistry
I worked this problem just below just a short time ago. The formula for obtaining mols hasn't changed since then. mols = M x L = ? http://www.jiskha.com/display.cgi?id=1418348915
December 11, 2014

chemistry
mols NaNO3 = grams/molar mass Then m = mols/kg solvent. 2.5 L is 2.5 kg if the density of H2O is 1.00 g/mL.
December 11, 2014

chemistry
Theoretically I would do it this way. You want how many mols? That's M x L = mols. Then mols = grams/molar mass. You have molar mass and mols, solve for grams. Place that many grams in a 1L volumetric flask, add some water, swirl until dissolved, then make to the mark with...
December 11, 2014

chemistry
jim, dd, et al. We prefer you keep the same screen name. We can help you better if you do that. q = heat absorbed = mass H2O x specific heat H2O x (Tfinal-Tinitial)
December 11, 2014

chemistry
Here it is by FF but with you using so many screen names one never knows. As I said above, using the same screen name helps us help you and changing names helps no one. http://www.jiskha.com/display.cgi?id=1417667658
December 11, 2014

chemistry
I think I worked this problem for you about a week or so ago.
December 11, 2014

chemistry
Increasing P has little effect on the solubility of solids but it increases the solubility of gases. Increasing surface area of solids increases solubility and increased agitation helps also. Increasing temperature increases the solubility of most solids but decreases some. ...
December 11, 2014

vy? in Physics
I suggest you repost your COMPLETE problem under the title of physics. I think it will be easier for a physics prof to answer a real rather than a hypothetical question.
December 11, 2014

Chemistry
yes. Do you have an answer you know is correct for the delta G problem?
December 11, 2014

Chemistry
CH4(g)+ 2O2(g) → CO2(g) + 2H2O(g) + 802 kJ You obtain 802 kJ for every 16 g CH4 so 802 kJ/mol x (g/16) = 150 kJ. Solve for g
December 11, 2014

Chemistry, Vapor Pressure
Use the molar mass; the lower molar mass should have the higher vp. That doesn't work for c because of H bonding in H2O. And 4 has the same molar mass the the OH on the alcohol has H bonding also. H bonding makes the boiling point higher and the vp lower.
December 11, 2014

Chemistry
heat lost by T + heat gained by water = 0 [mass Ti x specific heat Ti x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0 You have all of the numbers to substitute except for mass Ti. You solve for that from the density. The volume is 100 cc (400 ...
December 11, 2014

chemistry
I've looked at this problem for the last few days you've posted it and I still don't like any of the answers. A isn't right and I knew B wasn't right which makes the choice between C and D. I don't like either of those answers and here is why. If you ...
December 11, 2014

chemistry
That was not for this problem. I was remembering d as the correct answer for the Ni/H2O problem you worked on earlier, posted your work, and I pointed at the error you made was not substituting correctly for Tf and Ti for the Ni. As I remember Tf was 95.0 and Ti was 25.4 for a...
December 11, 2014

chemistry
That's what I would do.
December 11, 2014

chemistry
Exactly. And the unit is J. Now, that's for 0.0599 mols which you have in your first post. Convert that to J/1 mol and convert that to kJ/mol 0.84645 kJ/0.0599 mol = ? kJ/mol
December 11, 2014

chemistry
The best way to say it is that you didn't follow the script. Let's do this in two steps. Step 1 is to calculate the heat of solution (actually cooling of the solution). q = mass H2O x specific heat H2O x (Tfinal-Tintial) What is q?
December 11, 2014

chemistry
Yes I can but I would rather you show your work and let me find the error. And please explain why you have a problem in substituting the numbers.
December 11, 2014

Chemsitry
This is not a specific answer to your question but you need courses in math (algebra I and algebra II), chemistry, biology/physiology, English, any other science, communication courses (speech etc). Most four-year institutions offer a prepharmacy curriculum and I suggest you ...
December 11, 2014

Chemistry
Note: Don't forget the van't Hoff factor of 4 for FeCl3.
December 11, 2014

chemistry
k = 0.693/t1/2 Substitute and solve for k and use k in the equation below. ln(No/N) = kt No = 28 N = ? k from above t = 84 days.
December 11, 2014

cem
FeBr3
December 11, 2014

soran univresity
This is a chemistry question but it is so garbled I have no idea how to respond. It appears to have two mixed questions. The Volhard method has nothing to do with KMnO4.
December 11, 2014

chemistry
Cu3(PO4)2(s) + H2O==> 3Cu^2+(aq) + 2PO4^3-(aq) Ksp = (Cu^2+)^3(PO4^3-)^2
December 11, 2014

chemistry
1 mol H2 = 2.0g; 3 mols H2 = 6.0g = 0.006 kg. ? kJ = 210 kJ x (1000 kg/0.006 kg) = ?
December 11, 2014

science: question
Specifically, autoclaving is a method for sterilizing equipment under pressure at 121 degrees C for 15-20 minutes. You can Google "autoclaving" for more information. I have seen this done by dentists for natural teeth that are to be re-inserted as part of the dental ...
December 11, 2014

Chemistry
This may not help much but it's all I could find. http://en.wikipedia.org/wiki/Benzene#mediaviewer/File:Benzene_Representations.svg
December 11, 2014

Chemistry
Use PV = nRT and solve for n = number of moles at the conditions listed. For p you must use ptotal = pH2 + pH2O ptotal = 745 mm pH2O = 19.8 mm from the problem. Solve for pH2 (which is dry H2), then remember to convert to atm. 760 mm = 1 atm. When you have n, that's mols ...
December 11, 2014

Chemistry
Dissolving NH4Cl in H2O is an endothermic solution process. You measure how much it cools the solution by the temperature of the H2O. q = mass H2O x specific heat H2O x (Tfinal-Tinitial) The q you measure is for 3.2g/53.4g or q/0.0599 mol. You want to convert that to q/1 mol. ...
December 10, 2014

Science tech
https://ph.answers.yahoo.com/question/index;_ylt=A0LEViROColURaEA7u0PxQt.;_ylu=X3oDMTByNW1iMWN2BHNlYwNzcgRwb3MDNwRjb2xvA2JmMQR2dGlkAw--?qid=20070917042651AAuHwBT
December 10, 2014

Chemistry
1 mol contains 6.022E23 molecules so 0.923 mol will contain ........?
December 10, 2014

Urgent chemistry help
I don't understand these. The answer to the last one is that the subscripts change as the valences change.
December 10, 2014

Chemistry
The easy way to do this is not the easy way to explain it. I will do it both ways. The easy way to explain first. The density under the conditions listed is g/L = 0.371/1.97L = 0.188 g/L. The general gas equation can be modified for density as PM = dRT where M is molar mass ...
December 10, 2014

science
I think you're on target. http://en.wikipedia.org/wiki/Shale
December 10, 2014

science
or here. https://answers.yahoo.com/question/index;_ylt=A0LEVoCV3ohUHlYAbeAPxQt.?qid=20080801225715AA1BAq2
December 10, 2014

pharmaceutical math
You want to dilute the 30% cream by a factor of 3 so if you take 60 g of the 30% stuff and add cream base (120g) you should have it. c1v1 = c2v2 180*10 = 30*v2 v2 = 180*10/30 = 60 g of the 30%.
December 10, 2014

Science
You need balance and something to measure the volume.
December 10, 2014

Science
Floating is easier in the ocean because that is salt water and it has a higher density than fresh water.
December 10, 2014

Chemistry
I don't think this is exactly an isotonic solution but the answer to your question is that a 5.00 (mass/mass) solution of glucose contains 5.00 g glucose/100 g solution. Note: I don't know the density and it may be that the density of the solution may correct it to be ...
December 10, 2014

chemistry
1. Cu + 2Ag^+ ==> 2Ag + Cu^2+ 2. mols Cu = grams/molar mass = approx 0.03 BUT that's an estimate and you should do it more accurately. mols Ag = twice mols Cu = approx 0.06 ........CH3COOAg ==> CH3COO^- + Ag^+ I.........solid.......0..........0 C.........solid..........
December 10, 2014

pharmaceutical calculations
I don't see a question here.
December 10, 2014

chemistry
Your problem is delta T. That's Tfinal-Tinitial. For the water your 3.1 is correct. Tf is 25.4 and Ti is 22.3 and dT is 3.10. But that isn't right for the Ni. Tf is 25.4 and Ti is 95.0. dT is not 3.10.
December 10, 2014

chemistry
No, I don't obtain that. If you post your work I will find the error.
December 10, 2014

Chemistry
(n1/v1) = (n2/v2)
December 10, 2014

Chem
See your other post.
December 10, 2014

Chem
PV = nRT
December 10, 2014

Science~!
1 is b 2 density = mass/volume 3 melting point, boiling point, solubility in water are all physical properties.
December 10, 2014

chemistry
1. I don't see a molar absorptivity constant nor any information to calculate same. 2. Please clarity if that A = 0.540(you have 0.549 in your calculation) is the amount in 0.5 mL or the amount in the 2mL. The way the problem reads to me is confusing; i.e., I don't ...
December 10, 2014

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 Substitute and solve for the only unknown, mass Ni.
December 10, 2014

Chem.
It does not produce OH^- in solution.
December 10, 2014

Chemistry 2!
Kc = (C2H5OH)/(H2O)(C2H4)
December 10, 2014

Chemistry 2!
Substitute (C2H4) and (C2H5OH) and Kc into the Kc expression and solve for (H2O)
December 10, 2014

chemistry
Here is the way this works. At the beginning of the titration you have a mixture of CO3^2- + HCO3^-. When you titrated with the first 17 mL you don't touch the HCO3^-; you titrate all of CO3^- halfway. That is CO3^2- + H^+ ==> HCO3^-. With that information you can ...
December 9, 2014

chemistry
Why guess? Work it out. dHrxn = (n*dHf products) - (n*dHf reactants)
December 9, 2014

chem
Please note that you didn't get too different answers here. My response gives rate of fastest = 1.05 x slowest. Bob P gave rate slowest = 0.949 x rate fastest. Also note that 1/1.05(4) = 0.949
December 9, 2014

chem
The fastest will be Ar36; the slowest will be Ar40. (rate 36/rate 40) = sqrt(40/36)
December 9, 2014

chemistry
2C + 3H2 + 1/2 O2 --> C2H5OH dH = -238.7 kJ/mol. Doesn't - tell you that heat is released. That makes the answer D.
December 9, 2014

Chemistry
Yes, I think you're making it tougher than it is. You have an error in mols of NaHCO3. grams NaHCO3 = 1.5/2 = 0.75 mols NaHCO3 = 0.75/84 = 0.0089 Then M = mols/L. You know M = 1E-4 and you know mols = 0.0089 so L = 0.0089/1E-4 = 89 L. If you carry all of the digits that is...
December 9, 2014

Chemistry
In all of my years in the field of chemistry I have never heard of electrons having addresses. However, I would think the answer to your question is 3S1/2
December 9, 2014

Chemistry
pros and cons: https://answers.yahoo.com/question/index;_ylt=A0LEV7oydYdU_igAYh0PxQt.;_ylu=X3oDMTByMG04Z2o2BHNlYwNzcgRwb3MDMQRjb2xvA2JmMQR2dGlkAw--?qid=20080615210840AAKraO2 cons: https://answers.yahoo.com/question/index;_ylt=A0LEVvGcdYdURlIA5pcPxQt.?qid=20080531154353AARHrVw
December 9, 2014

chemistry
The modified gas formula is P*molar mass = density*RT. Solve for M (to determine the molar mass), and using that number substitute back into PM = dRT with the new conditions and calculate the new density. There are others ways to do this but this is the easiest way to explain ...
December 9, 2014

Chemistry
There are three equations that handle all of these situations. Equation 1 is for WITHIN a phase, q = mass x specific heat x (Tfinal-Tinitial). Example. For the liquid phase of water from zero C to 25 C, then q for that part is q = (48g x 4.184 J/g*C x (25-0) = ? Equations 2 ...
December 9, 2014

chemistry
(P1V1/T1) = (P2V2/T2)
December 9, 2014

chemistry
You have two equations. pH = pKa + log(base)/(acid) Substitute and solve fr base/acid. Calling base = b and acid = a, you will get a ratio of b/a = ?, This is equation 1. equation 2 is a + b = 3.0E-3 Solve the two equations simultaneously for a and b = (acid) and (base) note:(...
December 9, 2014

science
Yes, C is the correct answer and it's because c = freq*wavelength. So if frequency goes up, wavelength goes down.
December 9, 2014

Analytical Chemistry
One factor worth remembering is 1 ppm = 1 mg/L. Convert 2.91g Na3PO4 to g Na. That is 2.91 g Na3PO4 x (3*atomic mass Na/molar mass Na3PO4) = ?. You have ? g Na^+ in 2.33 L. That is (? g Na^+/2.33 L solution) = ? g Na/L; now convert ?g/L to ?mg/L.
December 9, 2014

Chemistry
t1/2 = 1/ak[A]o Substitute 0.27 for [A]o. The reaction is not given; usually in those circumstances a is assumed to be 1.
December 9, 2014

chemistry
Your post contains too many strange symbols. See if you can correct the post.
December 9, 2014

Organic Chemistry
How many mols of the tetraphenylporphin do you have? That's mols = M x L = ? Since the ratio is 1:1 you have that same number of mols Cu^2+ and the same number of mols of CuCl2. Then mass CuCl2 = mols CuCl2 x molar mass CuCl2.
December 9, 2014

Chemistry
You have some strange symbols which I assume was supposed to be an arrow. I've corrected it. Do you mean [N2O4] = 0.800M at equilibrium? or initially? I'll assume at equilibrium. ...........N2O4(g) ==> 2NO2(g) Kc = (NO2)^2/(N2O4 0.200 = (NO2)^2/(0.800. Solve for (NO2).
December 9, 2014

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