Saturday
November 22, 2014

Posts by DrBob222


Total # Posts: 45,542

chemistry
Use dG = -RT*lnK and calculate dG. Then dG = dH - TdS.
November 19, 2014

chemistry
See your other post.
November 19, 2014

chemistry
Use delta T = K*m and solve for m. In dilute solutions the m and the M are very close to the same, then pi = osmotic pressure = MRT Post your work if you get stuck.
November 19, 2014

Chemistry
I didn't put units on my answers and I should have done so. They are (H3O^+) = 1.58E-7 M (OH^-) = 1.58E-7 M. And just to make things a little more interesting let me point out that this is a NEUTRAL solution with a pH = 6.80. We always talk about pH = 7.0 as being neutral ...
November 19, 2014

Chemistry
I saw only this one extra question whereas your post said "additional" questions. If there are more than this please just post everything again at the top of the page. You don't do anything with the 37C temperature. That's the temperature of the water at body...
November 19, 2014

Chemistry
I expect you meant H3O^+ and not H2O. (H3O^+)(OH^-) = Kw (H3O^+)=(OH^-) = sqrt Kw.
November 19, 2014

Chemistry
Some is correct. I don't know how your calculator works (calculators aren't standard) but I can tell you how to proceed. First, where did you get the pKa for formic acid? I looked it up on the web and found 3.77. You can get slightly different numbers depending upon ...
November 19, 2014

Chemistry
pKa = -log Ka
November 19, 2014

Chemistry
Use the Henderson-Hasselbalch equation. pH = pKa + log (base)/(acid) pH = ? pKa = look up (base) = 0.07 (acid) = 0.07
November 19, 2014

Chemistry
I can't confirm those dH formation values but I'll assume you have them right. In calculating, however, when you finish isn't that 3344.1 kJ that many kJ for the reaction as shown and not kJ/mol. It appears you used dHrxn = (n*dHformation products) - (n*dH ...
November 19, 2014

Chemistry
2. I've been thinking about this and I can't see a good reason why it isn't zero. It absorbs heat on the way up to vapor and releases heat on the way back down to the crystalline state. Think about that, is that right? If that is true it sure would save a lot of ...
November 18, 2014

Chemistry
3. How much heat (q) is needed to heat the water. q = mass H2O x specific heat H2O x (Tfinal-Tinitial) = approx 250,000 but that is an estimate as are all of the other numbers that follow. Look up the heat combustion for ethane, probably given in kJ/mol Convert that to the ...
November 18, 2014

Chemistry
1. mass H2O = 85 g + 85 g = ? (mass H2O x specific heat H2O x (Tfinal-Tinitial) + Ccal*(Tfinal-Tinitial) = 0 Substitute and solve for Tf.
November 18, 2014

chemistry
CH4 + 2O2 --> CO2 + 2H2O mols CH4 = 10.4 Using the coefficients in the balanced equation, convert mols CH4 to mols CO2. Then use PV = nRT and convert mols CO2 at the conditions listed to volume in L.
November 18, 2014

Chemistry
2. If 114.6 kJ are produced per 1 mol NO then 2*114.6 or 229.2 kJ will be produced for 2 mols(2*30 = 60 g). You may want to check this out in the problem because it always leaves one in doubt exactly what is meant. I'll assume the above is correct. Then 229.2 kJ x (1.16E4g...
November 18, 2014

Chemistry
1. q = Ccal*(Tfinal-Tinitial) for the rxn. q/0.1375 = q/gram q/gram x atomic mass mg = q/mol. Change those to kJ/g and kJ/mol
November 18, 2014

Chemistry
Don't hog the space. Post 1 question at a time. Show your work and/or explain what you don't understand about the problem. And don't change screen names;i.e., Vince and Tim.
November 18, 2014

Chemistry
The data you gave for #1 shows delta H as +483.6 and that makes it an endothermic reaction so there will be no heat given off. You may want to re-reread/re-type the question. 2. heat lost by Fe + heat gained by Au = 0 (mass Fe x specific heat Fe x (Tfinal-Tinitial) + (mass Au ...
November 18, 2014

chem
Always remember, think in terms of mols. How many mols do you want? That's gram/molar mass. Then M = mols/L solution. You know M and mol, solve for L and convert to mL.
November 18, 2014

Chemistry
After thinking about this for 5-6 hours I don't think it simplifies the problem and I don't think the process is the same.
November 18, 2014

Chemistry
I think that simplifies the problem somewhat but the process is the same.
November 18, 2014

Chemistry
I would do this. Since the SrSO4 is relatively more soluble than BaSO4 (Ksp about 3,500 times) I would calculate the solubility of SrSO4 in a saturated solution ignoring the solubility of BaSO4 and figure the small solubility of BaSO4 makes very little difference. So Ksp = (Sr...
November 18, 2014

chemistry
I would do it this way. pOH = -log(OH^-) = 8 pH + pOH = pKw = 14 pH = 14- pOH = 14-8 = 6 So what's wrong with 6? Your problem is that you failed to realize that since 7 is neutral where (H^+) = (OH^-) = 10^-7M each, so when OH^- is 1E-8 (NOTE THIS IS LESS THAN 10^-7) SO IT...
November 18, 2014

chemistry
mols EDTA = M x L = ? mols Ca = same since EDTA complexes 1:1 You titrated only 10 mL aliquot of a 250 mL sample so mols in the original sample is mols from above x 250/10 and that is mols Ca in the initial sample. grams Ca = mols Ca x atomic mass Ca and % in sample is (gCa/...
November 18, 2014

chem
H-C is a sigma bond C-Cl is a sigma bond C=O is a double bond which consists of 1 sigma bond and one pi bond. So I would count them as 3 sigma and 1 pi.
November 18, 2014

Chemistry Lab
I won't be much help. It may make a difference but it all depends upon what the instructor will be checking and how much work you completed the first day vs the next two days. If you heated the Mg ribbon and crucible the first day but continued heating the second day it ...
November 18, 2014

chemistry
Here is a site that may be interesting to you and may shed some light on your problem. http://en.wikipedia.org/wiki/Molar_ionization_energies_of_the_elements This shows ionization energy = 1312 kJ/mol H ATOMS.
November 18, 2014

chemistry
There may be an equation but if there is one I don't know it. I've always just counted them.
November 18, 2014

Chemistry
I don' see anything wrong with this. I calculated OH using 0.6 x 0.002/1.002 and came up with a slightly smaller number but it rounds to your value and if I square that and multiply by Ca (I used 0.850 x 1/1.002) = 0.848 but no matter how I slice it the answer always ...
November 18, 2014

Chemistry
Why don't you post your work and let us find the error.
November 18, 2014

chem
Reverse equation 1 and add to equation and that gives you 4PCl3 + 4Cl2 ==> 4PCl5 which is just 4x what yu want so divide everything by 4.
November 18, 2014

physical science
?cal = mass Al x specific heat Al x (Tfinal-Tinitial)
November 18, 2014

chemistry
q = mass H2O x specific heat H2O x (Tfinal-Tinitial) is the heat absorbed. Then q/1.375 is heat absorbed per gram CaO and that x molar mass CaO is heat absorbed per mol CaO. I think those questions would follow although you didn't post them yet.
November 18, 2014

Chemistry 11
I've looked at your data again. %H2O appears to be done correctly. I disagree with the answer to the question about getting results similar to your neighbors results. If everyone is on the same page and everyone has good lab technique then the results should be comparable...
November 18, 2014

Chemistry 11
Bob Pursley answered this for you just a few minutes ago and you've hardly let the ink dry before re-posting as if you had heard nothing. No, the amount of material you took makes no difference in the formula nor the percent. If I have 5g out of 10 g sample, that's 50...
November 18, 2014

chem
mols Mg = mass Mg/atomic mass Mg. Wouldn't mass Mg be (mass xble+Mg) - (mass empty xble)? Now think about the MgO. Now that you see how easy it is to get mass Mg, wouldn't a very similar tactic obtain mass MgO.
November 18, 2014

chemistry
The problem tells you that you obtain 2511 kJ heat for burning 2*26 or 52 g C2H2. Instead of using 52g the problem is using 85g so the heat produced must be 2511 kJ x (85/52) = ?
November 18, 2014

chemistry
No table included. Take the sum of the B.E for bonds broken on the reactants side subtract the sum of the B. E, formed on the product side to calculate dHrxn
November 18, 2014

Chemistry
I posted a response to this two/three days ago and I asked, "What's the question?" No response from you.
November 18, 2014

Chemistry, HELP!
Sam, I'm not an agronomist, therefore, I don't know the rules for testing pH in that field. I've looked on the web and I know the definition of pH. If you could give me some of the rules for this I may be able to help. A pH of 5.5 means (H^+) = 3.16E-6 M and that ...
November 18, 2014

chemistry
http://healthyeating.sfgate.com/can-taking-much-vitamin-b12-harmful-7189.html http://healthyeating.sfgate.com/can-much-vitamin-b6-vitamin-b12-6060.html http://www.drweil.com/drw/u/ART02810/facts-about-vitamin-b
November 18, 2014

Chemistry
P1V1 = P2V2
November 18, 2014

Chemistry
I would do this. ...........CaCO3 ==> CaO(s) + CO2 I.........0.1 mol...0.1 mol...0 C...........-x.......+x.......+x E..........0.1-x....01+x......+x You know x is 0.220 atm. Use PV = nRT and solve for n = number of mols. x = approx 0.07 mols and (CO2) = approx 0.07/10L = ...
November 18, 2014

Chemistry
Probably yes but I can't think of one at the minute.
November 18, 2014

Chemistry
1. Then heat can move from the surroundings to the calorimeter and the reverse. For the specific heat capacity are you talking about that of the calorimeter or the material being measured. 2. The coffee cup calorimeter is at best a device for estimation because heat can move ...
November 18, 2014

Verifying-Chemistry related-Dr.Bob222
http://en.wikipedia.org/wiki/Perlite
November 18, 2014

chemistry
Change 18.3 g Al to mols. mols = grams/atomic mass. Then heat lost by Al + heat gained by water = 0 [mols Al x specific heat Al x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0 Solve for mass H2O after substitution.
November 18, 2014

chemistry
q = mass C x specific heat x (Tfinal-Tinitial) q is 815.1 J
November 18, 2014

chemistry
Just remember the definition. M = mols solute/L solution or molarity = mols solute/L solution and I shorten that to M = mols/L solution That's the only one I remember and any time I have two of those three the other one can be calculated. So mols = M x L L = mols/M When I ...
November 18, 2014

chemistry
You can do this one of two way. #1. (g sucrose/g solution)*100 = 36.0% and solve for g sucrose. #2. 36.0% means 36 g sucrose/100 g solution. So how much will it take for 655 mL instead of 100. That will be 36.0g sucrose x (655/100) = ? g sucrose Check out both and see if you ...
November 17, 2014

chemistry
some? maybe a lot? perhaps nothing? I don't know what concentrated Pb(ClO3)2 means. The problem can't be worked unless the concentration is known.
November 17, 2014

Chemistry
ln(No/N) = kt No = 100 N = 100-24 = 76 k from the problem Solve for t in seconds. #2 Same equation. Different substitutions and solve for N Post your work if you get stuck.
November 17, 2014

Chemistry- URGENT please HELP
It must not have been all that urgent.
November 17, 2014

Chemistry- URGENT please HELP
Instead of me guessing what you did wrong why don't you post your work and let me find the error?
November 17, 2014

pharmaceutical calculations
What units do you want it. 15 g/2L is one way and it is w/v. More than likely you want g/100 mL. So 15g/2L is 7.5g/1 L = 0.75g/100 mL
November 17, 2014

chem please help drbob222
I should have noticed I was calculating KE and the question related to PE. If KE goes up PE of the system goes down so it WAS in the right direction. I sometimes read these things too fast. Sorry about that. Thanks for setting me straight.
November 17, 2014

chem please help drbob222
I agree with c. KE = 1/2*m*v^2 So if v increases, KE MUST increase so dE increases so A ins't right. B says it decreases and that's the wrong way so cross B.
November 17, 2014

chemistry
How many mols does she need? That's M x L = ? Plug that mols (n) into PV = nRT at the conditions listed and solve for V in L.
November 17, 2014

Chemistry
Use (H^+)(OH^-) = Kw = 1E-14
November 17, 2014

Chem please help
You're not interpreting the choices correctly. What do you have for KE of A and KE of B and what numbers did you use to get KE?
November 17, 2014

Chem please help
I find that when these problems start that 1/2 of this and twice something of that the easy way to keep things straight is to simply assign arbitrary numbers to one of the objects. For example, say A has a mass of 2 kg and a velocity of 2 m/s. Usinsg that as a starting point ...
November 17, 2014

Chemistry
What's the question. And put an arrow in the equation. With no arrow we don't know left side from right side.
November 17, 2014

chem please help
You're right. It isn't a or b. The SI unit for work is the joule. So ......
November 17, 2014

chem
Each tablet contains 5.26E-3 mol Ca. How many g Ca? That's 5.26E-3 mols x atomic mass Ca = approx 0.2 g (but you need to do that more accurately) or 200 mg. Then 200 mg/tablet x # tablets = 700 for the minimum. Solve for # tablets and if you get a fraction round to the ...
November 17, 2014

Science
Would it make sense that if a herbicide kills the meadow flower that such spraying might also kill the caterpillar which lives on and eats the flower (and probably also gets sprayed in the process)?
November 17, 2014

Science
I don't know the question. I didn't ask the question; you did.
November 17, 2014

Science
What other meadow species are mentioned? Remember we don't see what you're copying.
November 17, 2014

Chemistry
Didn't I do this for you last night? I think I did. Look at your posts of yesterday.
November 17, 2014

science
yes. If you think it should change because the volume changes, it is true V changes but so does mass. density = grams/cc cc gets smaller, grams gets smaller, density stays same because g and cc change in the same ratio.
November 17, 2014

oops--typo--Chemistry Physics
q2 = mass water x specific heat H2O x (Tfinal-Tinitial) q2 = 33 x 2.0 x (72-32) = ? btu. That's the amount of heat that must be added to liquid water at 32F to raise the temperature from 32F to 72F. Then qtotal btu = q1 + q2 That should be a 1.0 and not a 2.0 above. I ...
November 17, 2014

Chemistry Physics
No. Look back at my original response. q1 for changing phase of ice from solid at 32 F to liquid at 32 F is q1 = mass ice x heat fusion. q1 = 33 lb x 144 btu/lb = ? btu You don't need specific heat ice, only the heat fusion at the melting point. I looked up specific heat ...
November 17, 2014

Chemistry Physics
You can use Google to convert but you want q in btu so why not look up heat fusion in btu/lb for metling and specific heat in btu/lb*F for raising the T from 32 to 72. I looked up the heat fusion and came away with 144 btu/lb but you should confirm that. I also looked up the ...
November 17, 2014

Chemistry Physics
I don't think so. What's 3.35E5? Usually I don't work in BTU/lb but that isn't the number I see for heat fusion in the tables. Then for q2 what is 2.26E6?
November 17, 2014

Chemistry Physics
q1 = heat to change phase ice from solid at 32 F to liquid at 32F. q1 = mass ice x heat fusion q2 = heat to raise T from 32 F to 72 F q2 = mass H2O x specific heat x (Tfinal-Tinitial) Then total btu = q1 + q2
November 17, 2014

chemistry
(P1V1/T1) = (P2V2/T1) Remember T must be in kelvin.
November 17, 2014

chemistry
Look up the vapor pressure of H2O at 20 C. That is pH2O. Ptotal = PCO2 + PH2O You know Ptotal = 715.8 You know pH2O is what you looked up. Solve for pCO2
November 17, 2014

chemistry
I have no idea what version A is. I have no idea what the "experiment" is.
November 17, 2014

chemistry
Use PV = nRT and solve for V.
November 17, 2014

chemistry
This is a limiting reagent (LR) problem and you know that because amounts are given for BOTH reactants. Convert g rhodium sulfate to mols with mols = grams/molar mass Convert g NaOH to mols the same way. Using the coefficients in the balanced equation, convert mols of the ...
November 17, 2014

chemistry
Use the same process as in the KMnO4/Na2C2O4 problem to find mols. Then use PV = nRT, plug in the conditions listed in the problem and solve for V
November 17, 2014

chemistry
You didn't provide the molarity of KMnO4. Step 1. You have the equation. I assume it is balanced. Step 2. mols KMnO4 = M x L = ? Step 3. Covert mols KMnO4 to mols Na2C2O4 using the coefficients in the balanced equation. Step 4. Convert mols Na2C2O4 to grams. g =mols x ...
November 17, 2014

hello!
It may be here but I see two or three things they recommend. http://www.cnpp.usda.gov/dietary-guidelines-2010
November 17, 2014

chem
molar mass/22.4 = g/L = density at stp
November 17, 2014

chemistry
Sketch the energy level diagram for atomic orbitals from 1s to 2s etc up to 5d. Then delta l can be +/-1 ONLY. Is 4f the next energy level down. If so then delta l (where l is 2 with a 5d) can go to 4f where the delta l is +1 or from 5d to 4p where delta l is -1. The series ...
November 17, 2014

chem
The easy way to do this is to remember the gas laws. Pressure increases with increasing temperature. Therefore, if T is going from 82C to -28C you know it is being cooled which means the pressure will decrease. So make the factor so you get a smaller number. Remember T must be...
November 17, 2014

Chem please help
I agree with Sarah
November 17, 2014

analytical chemistry
millimols CH3COOH = 100 millimols CH3COO- = 100 millimols HCl = 0.5M x 10 mL = 5 mn. ----------------------------- The added HCl will add to the base (acetatae ion) to make CH3COOH. ........CH3COO- + H+ ==> CH3COOH I.........100......0..........100 add...............5 C...
November 17, 2014

Chem please help
Thermal energy gives rise to a lot of molecular motion and since the velocity of all of the molecules is increased that increases the kinetic energy which is KE = 1/2 mv^2. Increasing v increases KE. right?
November 17, 2014

AP Chemistry
Good. I don't understand the question.
November 17, 2014

AP Chemistry
I think you're right. The larger object holds more heat than the smaller object but if both are at the same temperature there is no reason for heat to be transferred.
November 17, 2014

Science Help - Please
I don't know. Actually I don't understand the question. What choices do you have? That might give me a clue.
November 17, 2014

Science Help - Please
Zn is; copper is not a compound. I don't know how to answer the question. Single replacement reactions occur between metals high in the activity series and ions of metals lower in the activity series. For example, Zn metal and Cu(NO3)2 or Zn metal and AgNO3 and hundreds of...
November 17, 2014

little better--Science Help - Please
See if the spacing for Zn2+ and CH3COO-2 is a little better. Zn(s) + 2CH3COOH(aq)-->Zn^2+(aq) + (CH3COO)-2(aq) + H2(g)
November 17, 2014

Science Help - Please
Almost but not quite. If you are to write the MOLECULAR equation it should be Zn(s) + 2CH3COOH(aq)-->Zn(CH3COO)2(aq) + H2(g) If it is to be an ionic equation it should be Zn(s) + 2CH3COOH(aq)-->Zn^2+(aq) + (CH3COO)-2(aq) + H2(g)
November 17, 2014

Thermodynamics
I wonder if you're talking about different types of diffusers in the context of the following: 1. heat 2. air 3. aromatic (for aromatherapy) 4. aeration (for sewage) I wonder if you really looked on Google. I Googled "types diffusers" and they are all over the ...
November 17, 2014

Chemistry
Two questions but I may have more later. 1. Which initial T HCl is right? I used BOTH and NEITHER gives your answer of 4679 J. 2. Why do you think NaOH is the limiting reagent? 150 mL x 1.052M HCl = 157.8 millimoles HCl. 10.2g NaOH is 10.2/0.040 = 252 millimols. On a 1:1 basis...
November 17, 2014

P.E. help please
I don't think A or D is correct. I'm not a biologist so perhaps you should get a second opinion; however, USUALLY when you gt an immunization, the "shot" or whatever is something to make the body make antibodies but it doesn't contain antibodies. I think ...
November 16, 2014

Chemistry
0.166 M x (5.00/250.0) = ?
November 16, 2014

Chemistry Buffers
I'll let you balance the equation and add the phases. HF and NaF. Added HCl(an acid) will react with the base (F^-) to form HF. F^- + H^+ ==> HF Why wouldn't you expect the same kind of thing with the acetate/acetic acid buffer? It should be the same. H^+ + base ==&...
November 16, 2014

Chemistry
If you will type in your work I'll find the error. Femember dGrxn = (n*dGf products) - (n*dGf reactants). Then dG = -RT*ln*K
November 16, 2014

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