Tuesday
August 4, 2015

Posts by DrBob222


Total # Posts: 49,640

chemistry
When I was in school and I got a problem like this I changed up the problem a little to see if I couldn't figure it out. So let's change the problem. We have 250 g sample that is 50% water. How much water is there. We know almost instantly that is 125 g H2O available. ...
May 19, 2015

science
NaHCO3 + CH3COOH=>CH3COONa + H2O + CO2 8.4........20g.........x......y....4.4 So you start with 20+8.4 = 28.4 You lose 4.4 which should leave you with 24.0 grams. (In case you're interested, that's the CH3COONa(that's x = 8.2 g) + H2O(that's y=1.8 g) + ...
May 19, 2015

Chemistry
H2SO4 + 2NaOH ==> Na2SO4 + 2H2O millimols H2SO4 = 21 x 0.54 = approx 11 but you need a better answer than that. mmols NaOH = 39 x 0.12 = estimated 5. Which is the limiting reagent. 5 mmols NaOH will require 2.5 mmols H2SO4. You have that much; therefore, NaOH is the ...
May 19, 2015

chemistry
How many equivalents do you want? That's L x N = equivalents = 60 x 0.5 = 30 How many grams is that? That's # equivalents x equivalent weight = 30 x 40 = ? grams if it were pure NaOH. But it is only 88% pure so you need ? grams/0.88 = ? The reasoning goes like this. I ...
May 19, 2015

math help please!!!
100^12/100^8 = 100^12-8 = 100^? When you move the 100^8 from the denominator to the numerator, you change the sign of the exponent and 12-8 = 4.
May 19, 2015

Chemistry
none.
May 18, 2015

Chemistry
Ah, I see. You figures it out while I was typing. Good work. Note that for a redox equation to balance it must balance three things. 1. atoms must balance (yours did) 2. charge must balance (yours did) 3. e lost must = e gained. (yours didn't. Yours had 5e gained and 2 ...
May 18, 2015

Chemistry
I think your MnO4^- is right for acid solution. Br2 is also. Perhaps it the electrons. Let's check. MnO4^- + 8H^+ + 5e ==> Mn^2+ + 4H2O 2Br- ==> Br2 + 2e So multiply eqn 1 by 2 and eqn 2 by 5. Apparently you used some other numbers. This is what you should get. 2MnO4...
May 18, 2015

Chemistry
It may appear to be correct but it isn't. The atoms balance and the charge balances BUT there are two things wrong. 1. A balanced equation never has electrons on either side amd you have 3e on the left side. 2. The electrons lost do not balance the electrons gained. How ...
May 18, 2015

Chemistry
Note the correct spelling of celsius. The easy way to do these is to assume an initial volume, any number that is convenient will do. Then the new volume is 0.04 x that initial volume. {P1V1/T1) = (P2V2/T2) Remember T must be in kelvin.
May 18, 2015

Science (Chemistry)
First, I think you made a typo. I assume you meant to write H2S ==> 2H2 + S2 Second, you need to explain to me how you obtained a,b,c without any numbers. You need numbers to calculate a reaction quotient. Why didn't you provide your answer and what you did. That way I ...
May 18, 2015

Chemistry
q = mass Fe x specific heat Fe x (Tfinal-Tinitial) Substitute and solve for Tfinal
May 18, 2015

Chemistry
Do you have anything (a graph, table, etc) that tells you (or allows you to obtain) the solubility of KNO3 at 70 C and 45 C?
May 18, 2015

science
This is similar to the problem I worked for you two days ago with the 100 g iron producing rust. http://www.jiskha.com/display.cgi?id=1431803547
May 18, 2015

science
Balance the equation. Then mols AgNO3 = grams/molar mass = ? Use the coefficients in the balanced equation to convert mols AgNO3 to mols NO2 and do the same to convert to mols O2. Add mols NO2 + mols O2 Convert total mols of the gas to volume in liters by L gas = mols gas x (...
May 18, 2015

chemistry
I like to do these in millimoles. Although technically they are to be done with concentration in molarity, mmols works just as well and I think it is easier. You have two equations. Let a = acid and b = base. eqn 1 is a + b = 500 x 0.75 mmols. eqn 2 is 7.5 = pKa2 + log (b/a) ...
May 18, 2015

Biochemistry
I have no idea what this question means. My best suggestion is that if you understand the question that you use the same kind of process I used for that phosphate buffer I did last night.
May 18, 2015

Chimistry
heat lost by metal + heat gained by water = 0 [mass metal x specific heat metal x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial) = 0 Solve for specific heat metal Note that you have calculated the specific heat capacity of the metal. The problems asks ...
May 18, 2015

Biochemistry
I didn't answer this last yesterday when you first posted because the post was screwed up. It looks ok now. You want 100 mL of 200 mM phosphate buffer. That is 100 mL x 0.2 M = 20 millimols phosphate. So you know base(b) + acid (a) = 20. That is equation 1. You obtain ...
May 17, 2015

Chemistry-Decay
You didn't type in the initial rate of decay but I THINK it is 15 dps. Check that out and use the correct value. Also you didn't include the half life but I think that is 5730 years. Again, check that out and use the correct value. First, determine k. k = 0.693/t1/2 ...
May 17, 2015

Analytic Chemistry
I think you need to redo the ICE table and I don't understand what (or why) you did with the NaI. The (AgNO3) for the first addition is 0.0260 x (15.00/15.50) = 0.02516 M. The NaI is reduced likewise as 0.0130 x (0.5/15.5) = 0.0004194 and you should check these numbers and...
May 17, 2015

Science 8
Light travels with different speeds in different materials. It travels at 3E8 m/s in a vacuum but slower in air and slower still in glass. Because it travels with different speeds it is refracted when moving from one medium to another. I think you can get at least two ...
May 17, 2015

physics
momentum before = momentum after 4*10 = 4*5 + 10*x
May 17, 2015

chemistry
dG = dH - TdS Substitute and solve for dG. Then dG = -RTlnK Substitute and solve for K.
May 17, 2015

College Chemistry
I don't mind helping you through it but tell me what you know about this. Just working the problem won't help you. I assume part a means the equation for the SPONTANEOUS REACTION or is it the reaction for the way the cell is set up (and that could be spontaneous). So ...
May 17, 2015

Chemistry - PLEASE HELP!!!
M = mols/L (that's the definition--start with that). Then mols = grams/molar mass = ? and I'll estimate that at approx 25/40 = about 0.5 mol (remember this is only close so yo need to redo the math to obtain a more accurate answer). M = mols/L. You know mols and you ...
May 17, 2015

Chemistry - Equilibrium
I tried to find some graphs; here is the best I could do.http://en.wikipedia.org/wiki/Reaction_coordinate You're right with your statement about catalysts and I agree that the last two change. I am ambivalent about c because of the wording. Adding a catalyst certainly ...
May 17, 2015

Chemistry
The approximate concentration of the HCl solution that you have on hand is 0.5M. Therefore, if you transfer 10.00 mL of that HCl solution to an Erlenmeyer flask, the concentration of the HCl still is approximately 0.5M. Since HCl is a strong acid and ionizes 100%, the ...
May 17, 2015

Math (Solving Equations)
I think what "you do from here" is to expand and factor the terms; however, can you subtract 2x/3 from X^2/6. Those are not like terms. I don't believe you can do that, at least not legally. Therefore, I don't agree with the "getting here" part. ...
May 17, 2015

Chemistry
Look up the redox potential of each and note that the problem SHOULD have specified acid or basic conditions.
May 17, 2015

science
q = 1000 g x heat vaporization at 37 C in cal/g. Convert to kcal.
May 17, 2015

chemistry
(P1V1/T1) = (P2V2/T2) Remember BOTH temperatures must be in kelvin
May 16, 2015

chemistry help
Can you describe the diagram. Is there a way of reading the diagram for concentration, mols, mL, etc.
May 16, 2015

chemistry help
Can't be done with no concentrations listed. If you have the concentrations use the Henderson-Hasselbalch equation. Post your work if you get stuck but show what the the concentrations you are using.
May 16, 2015

chemistry help
I don't know the rest of the problem but a Zn/Al galvanic cell the Al is the anode and Zn is the cathode.
May 16, 2015

To Mahlako---biology
You need to do this right. Co2 is not CO2 and the equation is not balanced. It's 6CO2 + 6H2O ==> C6H12O6 + 6O2 An equation not balanced is correct only when noted that it is unbalanced.
May 16, 2015

science (percentage yield)
OK. You know how to get mols. mols = grams Fe/atomic mass Fe = 100 g Fe/55.85 = ?. That is estimated 1.9. To convert mols use the coefficients in the balanced equation. To convert from mols Fe to mols Fe2O3 that's 1.9 mols Fe x (2 mol Fe2O3/4 mols Fe) = 1.9 mols x (2/4) = ...
May 16, 2015

science (percentage yield)
Rust is a number of oxides of iron(III); technically, we can't calculate how much rust will form since it can take more than one form. If we call rust Fe2O3 it is done as follows. 4Fe + 3O2 --> 2Fe2O3 mols Fe = grams/atomic mass = ? Use the coefficients in the balanced ...
May 16, 2015

Science
I agree.
May 15, 2015

Science
I agree.
May 15, 2015

Science
I agree, at least part of the sound wave is absorbed. What is left over still can be transmitted or reflected.
May 15, 2015

Chemistry
You want it balanced? You want it corrected? You have a question? Corrected as as follows: 2Li + Cu(NO3)2 > 2LiNO3 + Cu If you really meant CuNO3, then Li + CuNO3 ==> LiNO3 + Cu but copper(I) nitrate is not that common.
May 15, 2015

Chem
If you're worked this several times with no luck I assume that means you are checking with a database. Why not show your work and let us find the error? It's much easier that way instead of us guessing what you have done right and what you have done wrong.
May 15, 2015

Science 8th Grade
start, stop, change direction, compression/decompression, etc.
May 15, 2015

chemistry- Check please
I think you need to find a way to clarify the question. As an example of what is missing, Zn ==> Zn^2+ + 2e Eocell = +0.76 Cu^2+ + 2e ==> Cu Eocell = +0.34 -------------------------------- Zn + Cu^2+ ==> Zn^2+ + Cu and Ecell = about 1.1 v BUT it isn't clear that ...
May 15, 2015

chemistry- Check please
I know we've talked about this before. Do you have some reason for knowing your answers are not right. Also, I'm still a little confused about how this is to be done; for example, if I use H2 and Ag (as opposed to Ag and H2) the voltage is -0.8 and that would be lower ...
May 15, 2015

Science
http://en.wikipedia.org/wiki/Evolution
May 14, 2015

chemistry
So it has a mass of 53.0 grams and volume of 51.5 cc (volume of the water = mass/1.00 = 51.5 cc. Density of the saline is ?
May 14, 2015

chemistry
delta T = Kb*molality Substitute and solve for m m = mols/kg solvent Substitute and solve for mols. mols = grams/molar mass. You know grams and mols, solve for molar mass.
May 14, 2015

Chemistry
4.41E-3/11 sec is rate of consumption S2O3^2-. Rate of production I^- is same.
May 14, 2015

Chemistry
To calculate dS for each reaction, it is dSrxn = (n*dSo products) - (n*dSo reactants) You look up the dSo values in your text or notes.
May 14, 2015

Math
I don't believe +2 is right. You should do (y2-y1)/(x2-x1) and see if you obtain 2.
May 14, 2015

For my future, I'm 13.
You were 21 just a few posts below. Are you going back in time?
May 14, 2015

Science
It's density = grams/volume Substitute and solve.
May 14, 2015

Science
find volume of tank in cubic feet. 11 x 18 x 12 = ? cubic feet. Then (62.4 lbs/ft^3) x ? cubic feet = weight water in lbs.
May 14, 2015

Science
See your other fish tank problem. Same formula, Substitute and solve for the only unknown.
May 14, 2015

Chemisty
Bob Pursley is right. More explicitly, it comes from this. If we start with 100 counts and drop to 50 counts (which is 1 half life or t1/2), then ln(No/N) = kt ln(100/50) = kt1/2 ln 2 = kt1/2 0.693 = kt1/2 and k = 0.693/t1/2
May 14, 2015

Chemisty
ln(No/N) = kt No = 3000 N = 2736 k = ? t = 48 hrs. Solve for k. Then k = 0.693/t1/2 Substitute k from above and solve to t1/2
May 14, 2015

Chemistry
How many mols do you want? That's mols = M x L = ? Then mol = g/molar mass. You have mols and molar mass, solve for grams.
May 13, 2015

chemistry
Yea! Go to the top of the class.
May 13, 2015

chemistry
You must read and follow step by step. I'll get you started. Following are my step by step instructions and I'll do the first few steps to show you how it's done. 1. Write and balance the equation. You have that. 4Al(s)+3O2(g)->2Al2O3(s) 2. Convert what you have...
May 13, 2015

chemistry
Your 0.09259 is mols Al. That's the first step. Now you do mols O2 and follows steps 2,3,4.
May 13, 2015

chemistry
I don't get that answer. Post your work and I'll find the error. Follow the steps above.
May 13, 2015

chemistry
2a and 2b above. mols = grams/molar mass For Al that is grams/atomic mass = 2.5 g/ 27 = ?
May 13, 2015

chemistry
This procedure will work almost all of the stoichiometry problems. This one is a limiting reagent problem (LR); you know that because amounts are given for BOTH rectants. I work these the long way. 1. Write and balance the equation. You have that. 4Al(s)+3O2(g)->2Al2O3(s) 2...
May 13, 2015

chemistry
Yes, I can.
May 13, 2015

Organic chemistry
The hydrolysis of phthalic anhydride yields phthalic acid.
May 13, 2015

chemistry
When you blow into the solution you are adding CO2 to the solution. The CO2 reacts with water to form H2CO3 and that ionizes to produce H^+. That lowers the pH of the solution and the phenolphthalein turns the acid color which is colorless. You write the equations.
May 13, 2015

chem
Didn't you ask recently if this is an outer or inner complex? That ALMOST tells you that it is d2sp3. And the fact that oxalate is a bidentate and there are three of them makes the coordination number of six. That almost surely makes it octahedral. And octahedral is d2sp3.
May 13, 2015

chemistry
Single bonds are sigma (s-s or s-p bonds). Pi bonds are double & triple (sp AND p-p).
May 13, 2015

Chemistry
2. You had 5 mL in the tube initially (of KSCN but that's still 5 mL). You add 5 mL of 0.2 M Fe(NO3)3 so the iron nitrate has been diluted from to 10 mL; therefore, its concentration has been halved. That is 0.2 M x (5/10) = ? I'm assuming that the last sentence about ...
May 13, 2015

Chemistry
I assume you mean boiling point as in solutions and not boiling point of the pure material. i is the van't Hoff factor and is the number of particles MnSO4 ==> Mn^2+ + SO4^2- so i = 2
May 13, 2015

Chemistry
Hydrogen is flammable; therefore, no open flames
May 12, 2015

Chemistry Gas Law
Mg + 2HCl ==> H2 + MgCl2 Use PV = nRT and solve for n = mols H2 gas at the conditions of the problem. Use the coefficients in the balanced equation to convert mols H2 to mols Mg. Then g Mg = mols Mg x atomic mass Mg (in grams). Convert to mg. Finally, length of Mg is 1.83 ...
May 12, 2015

chem
I don't know what they are considered to be but they are dimagnetic.
May 12, 2015

science
I don't understand the question. There are all kinds of molecules. Are you talking about air molecules, water molecules, dust molecules, or some other kind? About move, do you mean do they move up, down, horizontally one way or the other?
May 12, 2015

To Kelsey
Your buffer problem has moved down quite a bit but I've responded to your last response with my own response.
May 12, 2015

chem
http://en.wikipedia.org/wiki/Potassium_ferrioxalate See the site above. This is a high spin complex which I believe means it is an outer orbital complex.
May 12, 2015

chem
My crystal ball is hazy today. What are you doing? Which reagents are you using? I assume it's a typo but I'm sure you meant "dihydrate">
May 12, 2015

Chemistry-check answer please
I may have misunderstood the question but I don't agree with your answer. Did you work out the voltage generated by each possible pair? And do you want the highest or lowest voltage, period, or do you that only for cells that are spontaneous? For the low voltage, for ...
May 12, 2015

Chemistry
q = mass oil x specific heat oil x (Tfinal-Tinitial)
May 12, 2015

Chemistry
You are making it far too complicated. pH = pKa + log (base)/(acid) millimols base = 150 x 0.75 = ? millimols acid = 250 x 0.50 = ? Substitute the millimols into acid/base and solve for pH. Tehcnically, one can't substitute millimols; i.e., it is supposed to be ...
May 12, 2015

Chemistry
What's the problem. Use the HH equation. If you want me to check it let me know what you're using for pKa for HF.
May 12, 2015

chemistry
See your other post.
May 12, 2015

chemistry
You CANNOT continue in chemistry and not use the caps key. I will get you started. Cr goes from +6 for each on the left to +3 on the right for each. I on the let is -1 and on the right is zero. Make things easy by making that 2KI on the left. You may need to change it later ...
May 12, 2015

Chemistry
H2CO3 has two ionization constants; i.e., ka1 and ka2. Generally the Ka values for diprotic acids is far apart and you simply treat these as two separate ionizations; the second one contributes little so you ignore it. ..........H2CO3 ==> H^+ + HCO3^- I........0.23.......0...
May 12, 2015

science(check answers)
I don't see anything to check. (No answer)
May 12, 2015

Chemistry
7.2 is right for pK2. And I obtained 6.0g NaH2PO4 which is quite close to your number. The difference is that I used 43.15 mL of 1M NaOH to do that and that's the difference. Do you want to work on that a little or want me to show you what I did.
May 12, 2015

Chemistry
I don't think so. pH = 7.21 + log (0.007/0.007) pH = 7.21 which isn't 8.00 7 mL x 1 M = 7 millmols NaOH = 0.007 mols.
May 12, 2015

Chemistry
If we are to try for the same number I need to know what you used for pK2.
May 12, 2015

Chemistry
I obtained 0.038 for x. So Y is 2x isn't it? ...........XY2 ==> X^2+ + 2Y^- I........solid.....0.......0 C........solid.....z......2z E........solid.....z......2z Note that Y is just twice X. I tried, with different manipulations, to obtain 0.0318 but couldn't do it...
May 12, 2015

Chemistry
No, the answer is 2.0E-5. I've looked at the problem again and it appears not to have any "tricks of the trade" attached to it so I believe if you have a database version or an answer sheet that those are incorrect.
May 12, 2015

Chemistry
.......X2Y(s)<-->2X^+(aq)+Y^(2-)(aq). Ksp = (X^2+)^2(Y^2-) X = 0.02 Y = 0.05 Ksp = (0.02)^2(0.05) = ?
May 12, 2015

chem
N2 + O2 --> 2NO mols N2 = grams/molar mass = 10/28 = approx 0.3 but you need a more accurate answer than that estimate. Use the balanced equation to convert mols N2 to mols NO. That's 0.3 x (2 mols NO/1 mol N2) = approx 0.3 x 2/1 = approx 0.6 mol NO. Then grams NO = ...
May 12, 2015

Chemistry
See your post above.
May 12, 2015

Electronics, Physics
The parallel group has an equivalent resistance of 1/R = 1/R1 + 1/R2 1/R = 1/60 + 1/5 R = ? which I will call Rp Then the total for the circuit is Rtotal = 10 + Rp = ?
May 12, 2015

Math to hard please help
The 4x^2 and 3x^2 are like terms. You can add or subtract like terms but not unlike terms. The 15x is a different terms than x^2 and has no other like term. So 4x^2 - 3x^2 = x^2 +15x has nothing to add or subtract so it remains 15x. -3 and -5 = -8
May 11, 2015

Chemistry
I don't intend to work this problem for you under any name. You take those numbers I gave you earlier and substitute them. Telling me you don't know how to solve for t doesn't help. Substitute the numbers, show me your work, go as far as you can, then tell me what ...
May 11, 2015

Science
http://www.enviropedia.org.uk/Weather/Movement_of_Air.php
May 11, 2015

chemistry B-11
P1V1 = P2V2
May 11, 2015

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