Sunday
May 24, 2015

Posts by DrBob222


Total # Posts: 49,010

Chem
2FeCl3 + 3Na2S ==> Fe2S3 + 6NaCl mols Fe2S3 = grams/molar mass = ? That's the mols you want if the reaction were 100% but it is only 65%; therefore, you want ? mol/0.65 = mols needed at 65% yield. Using the coefficients in the balanced equation, convert mols Fe2S3 to ...
March 8, 2015

chem1B
If the molarity is the same then the volume will be the same; however, the M is not the same. You want mols acetic acid = mols NaoH. That will be the equivalence point. mols acetic acid = M x L = ? Then mols NaOH = mols acetic acid. Finally M NaOH = mols NaOH/L NaOH. You know ...
March 8, 2015

Chrmistry
Instead of posting the same kind of problem under different screen names (Kelsey, Lucy, Kristen), why don't you tell us what you don't understand and get it straight so you can do these yourself.
March 8, 2015

chemistry - PLEASE HELP
You can start by making the equation easier to read. In these situations it is easier to write the atomic number FIRST, then the symbol, then write the mass number SECOND so the equation would look like this. 4 1H1 + 2 -1e0 ==> 2He4 + heat + 0n0 4*mass 1H1 + 2*mass e - mass...
March 8, 2015

chemistry
I don't know how you did it but the answer you have is exactly twice what it should be. How many mols do you want? That's M x L = ? Then grams = mols x molar mass
March 8, 2015

chemistry
2PbS + 3O2 ==> 2PbO + 2SO2 This is a limiting reagent (LR) problem and I work these the long way. mols Pb S = 6270 g/molar mass = ? mols O2. Use PV = nRT and solve for mols = n = ? Using the coefficients in the balanced equation, convert mols PbS to mols SO2 Do the same and...
March 8, 2015

chemistry
This is a limiting reagent (LR) problem and you know that because amounts are given for both reactants. 6.27 kg what?
March 8, 2015

Chemistry
This is the same kind of problem I worked earlier (P and O2). The only difference is you must go through PV = nRT to solve for mols O2. And how you type in the numbers? Do you understand that not all calculators look the same, punch the same, or work the same.
March 8, 2015

Chemistry
w = h/mv multiply both sides by mv wmv = mv*h/mv wmv = h Divide both sides by wv wmv/wv = h/wv m = h/wv
March 8, 2015

Chemistry
A). M = mols/L. You took g/L. Convert 3.60 g H2SO4 to mols. mol = grams/molar mass; then mols/L solution. B) I believe you are over thinking these problems. Just remember the definition. molarity = M = mols/L You have mols in B already. You have volume in mL, convert to L, ...
March 8, 2015

Chemistry
[(actual yield/theoretical yield)]*100 = ? = % yield
March 8, 2015

Chemistry
4P + 5O2 --> 2P2O5 Convert g P205 to mol. 195g P2O5 x (1 mol P2O5/molar mass P2O5) = ? Convert mols P2O5 to mols O2. ?mols P2O5 x (5 mol O2/2 mol P2O5) = ? volume O2 produced = mols O2 x (22.4L/mol) = ?
March 8, 2015

Biochem 12
Write and balance the equation. Then dHrxn = (n*dHf products) - (n*dHf rreactants). You can look up the values for delta H formation in your text/notes. The answer you get for dHrxn will be in kJ/mol. Convert to kJ/gram.
March 8, 2015

chemistry
I'm not understanding what you mean "ratios in the end" but if you want to post your work/answers I can check it. I went through mole fractions and calculated partial pressure of each gas, substituted that into the Kp expression and solve for Kp.
March 8, 2015

Chemistry
Are you titrating bleach directly with thiosulfate or are you going through an I2 step which you haven't mentioned.
March 8, 2015

Chemistry
If you had shown your work instead of "but I guess the numbers were wrong" we could tell instantly what was wrong. a. mols Li3N = grams/molar mass = ? Then ?mol Li3N x (6 mol Li/2 mol Li3N) = ? grams Li = mols Li x atomic mass Li = ? Also I suggest you find th arrow ...
March 8, 2015

heat transfer
How would you like for us to help you with this assignment? You're talking about a paper here and we don't write papers.
March 8, 2015

chemistry
This is a limiting reagent (LR) problem and I do these the long way. Write and balance the equation. 2C6H14 + 19O2 ==>12CO2 + 14H2O Convert 57 g O2 to mols. mol = grams/molar mass = ? Do the same to convert 43.9 g hexane to mols. Using the coefficients in the balanced ...
March 7, 2015

chemistry
dHrxn = (n*dHf products) - (n*dHf reactants) You know dHrxn and you can look up dHf O2 (it is zero) and SO3, calculate the only unknown of dHf SO2.
March 7, 2015

chemistry
-543 = mass Sn x specific heat Sn x (Tf-Ti) Substitute and solve mass Sn.
March 7, 2015

chemistry
I disagree with the way Kyle has worked the problem. I've posted by answer at your first query. Kyle's solution will give you the correct answer but it is based on his assumption (Kyle may not have assumed that in his mind but his solution does that automatically) that...
March 6, 2015

Chemistry
Take a 100 g sample and that gives you 35.51 g C 4.77 g H 37.85 g O 8.29 g N 13.60 g Na Convert g to mols. mol = g/molar mass Then you want to find the ratio of these elements to each other with the smallest being no less than 1.00. The easy way to do that is to divide the ...
March 6, 2015

SCIENCE
q needed = [mass gasoline x specific heat gasoline x (Tfinal-Tinitial) Substitute and solve for q.
March 6, 2015

organic chemistry
Sorry but I can't help.
March 6, 2015

chemistry
Draw the lewis structure of NF3 and not the lone pair. Draw the NF4^+ and note the absence of a lone pair. You may be more familiar with drawing NH3 vs NH4^+.
March 6, 2015

chemistry--Tulane University
A = ebc A= 4700*1*1.oE-4 A = ?
March 6, 2015

Science
Basically one object has excess electrons. You can read more about it here. http://en.wikipedia.org/wiki/Static_electricity
March 6, 2015

Chemistry
Use the Henderson-Hasselbalch equation. This is a buffer solution.
March 6, 2015

Chemistry
Use the Henderson-Hasselbalch equation
March 6, 2015

chemistry
I don't understand the trouble you're having. Qsp is just the ion product as if it were Ksp; then you can compare with Ksp and see if the Ksp is exceeded. If so a ppt forms, if not there is no ppt.
March 6, 2015

Chemistry
The point of this problem is to illustrate that when all are gases one may use a shortcut in which L is used as if L were mols. So using the coefficients in the balanced equation to convert L of one substance to L of any other. I assume you can balance the equation.
March 6, 2015

Chemistry
mols LiClO4 = grams/molar mass = ? Use the coefficients in the balanced equation to convert mols LiClO4 to mols O2. Now convert mols O2 to L at the conditions listed. Use PV = nRT for that. Beware of units. If you use P in kPa, you must use R = 8.314. If you use P in ...
March 6, 2015

chemistry
..........Ag3PO4 ==> 3Ag^+ + PO4^3- I.........solid.......0.......0 C.........solid.......3x......x E.........solid.......3x.......x Substitute the E line into Ksp expression and solve for x = molar solubility
March 6, 2015

Chemistry
C shortest B longer A none
March 6, 2015

chemistry
I don't understand the problem. Please rephrase it and if you have an equation include that. That phrase "of 7.00 g NH3 of 9.00g of NO" is the confusing part. It doesn't make sense.
March 5, 2015

Chemistry
All three are based on the fact that 1 grams equivalent weight is deposited with 96,485 coulombs a). You can deposit 107.9 g Ag metal with 96,485 coulombs, Coulombs = amperes x seconds
March 5, 2015

a note:--Chemistry
Ka1 is relatively large; probably you will need to solve the quadratic for Ka1.
March 5, 2015

Chemistry
What about looking at the three Ka values seprately? You notice that they are about 10^5 from each other. That means that the (H^+) is determined primarily by the first ionization. The second and third ionization produce little H^+. So do the first calculation as you would a ...
March 5, 2015

Chemistry
Tell me what you don't understand about this.
March 5, 2015

Science
It was Po.
March 5, 2015

Science
yes. Do you know what that element was?
March 5, 2015

Science
I don't agree with A.
March 5, 2015

chemistry
Use PV = nRT to calculate pressure of each gas. n = grams/molar mass Then Ptotal = pO2 + pHe
March 5, 2015

Energy&Society
This may help. http://www.comfortsystems.ws/WhatsNew/Fuel%20cost%20comparision%20information.pdf
March 5, 2015

chemistry
A. mols acetone = M x L = ? B. 5.00 M x (10 mL/total volume)= ? C. final (I2) = 0.005M x (10 mL/total volume) = ?. Then rate rxn = final (I2)/400 D. repeat of C. You should be able to use these numbers to do part B yourself.
March 5, 2015

Chemistry
I think the question is "last of all how can I calculate the molar mass?). HA + KOH ==> KA + H2O mols KOH = M x L = ? mols HA = mols KOH since the ratio of the coefficients is 1:1. Then mols HA = grams HA/molar mass HA. You have grams and mols, solve for molar mass.
March 5, 2015

chemistry
(V1/T1) = (V2/T2) Since they don't give a volume, just make up a convenient number for V1(say 100 L) then V2 will be 113 L.
March 5, 2015

chemistry
You need to know if this is psia or psig. If psia you can use P1V1 = P2V2 diectly. In the absence of anything in the problem that tells you, I would assume psia.
March 5, 2015

CHEMISTRY!!!!
What is it that you don't understand about the problem? The pH at the equivalence point of formic acid and NaOH is determined by the hydrolysis of the salt, i.e., sodium formate.
March 5, 2015

chimestry
What do you not understand about this? The pH is that of a salt of a strong base/strong acid.
March 5, 2015

Inorganic Chemistry
SF6 for sure. http://en.wikipedia.org/wiki/Point_reflection#Inversion_with_respect_to_the_origin
March 5, 2015

chemistry
(V1/T1) = (V2/T2) Don't forget T must be in kelvin.
March 5, 2015

using skills
I agree with choice c, also, but frankly I don't think much of the answers. In my opinion all of the answer are true (well, maybe B is not that true). I liken these answers to walking in a mine field and you're having to choose between quite similar answers to come up ...
March 5, 2015

using skills
What does your book say. "According to the text," tells me the answer is in your text.
March 5, 2015

Chemistry
Write and balance the equation. mols HBr = M x L = ? mols NaOH = M x L = ? Which reactant is in excess. If HBr, the pH = -log(HBr) If NaOH, the pOH = -log(NaOH) and pH + pOH = pKw = 14.
March 5, 2015

chem
Use the dilution formula mL1 x M1 = mL2 x M2
March 5, 2015

chemistry
See your other post.
March 5, 2015

chemistry
Generally, there are three reasons why a reaction will occur. 1. A gas is formed. You need to know those gases. H2, N2, O2, Cl2, plus usual compounds like CO2, CH4, acetylene (C2H2), NO2, and a few others. 2. A precipitate (an insoluble compound) is formed. You need to know ...
March 5, 2015

chemistry 12u
I don't see a question here. Also I think you have a typo in the equation.
March 5, 2015

Ap chemistry
I'll be happy to help. Tell me exactly what you don't understand about the question. Do you know what Q is? Do you know what equilibrium is?
March 5, 2015

CHEMISTRY
Write and balance the equation. Using the coefficients in the balanced equation, convert mols I2 to mols AgI Now convert mols AgI to grams AgI. grams AgI = mols AgI x molar mass AgI.
March 5, 2015

Science
Those look ok to me IF you made a typo on #3 and it should read and electric motor instead of electric meter.
March 4, 2015

Science
Evaporation of water cools the wet bulb.
March 4, 2015

chemistry
Convert g each to mols and convert to XCS2 Then psolution = XCS2*Po CS2 Post your work if you get stuck and I can help you through it.
March 4, 2015

Chemistry
http://www.ausetute.com.au/metallic.html
March 4, 2015

CHEMISTRY
THANK YOU for showing your work. I can tell at a glance that your work is right and the process is right. My only comment is that if your prof is picky about the number of significant figures s/he may not concur with an answer with that many places.
March 4, 2015

Chemistry
Also you can use the Henderson-Hasselbalch equation which is a little easier to handle.
March 4, 2015

Chemistry
ln(No/N) = kt No = 100 N = 89 t = 62 min solve for k. Then k = 0693/t1/2
March 4, 2015

Chemistry
What do you know about this? Show your work of what you have done. Explain fully what you don't understand.
March 4, 2015

CHEMISTRY
What do you not understand about this?
March 4, 2015

Chemistry
It's all done with mL1 x M1 = mL2 x M2 Substitute the numbers and you have it.
March 4, 2015

Chemistry Dr. Bob222
I don't know why the delay in discussing/asking questions about limiting reagents but then I'm not teaching the course. To recap, I think you had 2.02g NaHCO3 and 0.77 g citric acid (or was that 0.76 g). To determine the LR reagent and the theoretical yield, I do these...
March 4, 2015

Chemistry
q = mass H2O x heat vaporization
March 4, 2015

Chemistry
Just use the dilution formula. Substitute and turn the crank. mL1 x concn1 = mL2 x concn2
March 4, 2015

Chemistry
OH is 2x Ba(OH)2. pOH = -log(OH^-)
March 4, 2015

Chemistry
I don't necessarily agree with your description. NaN3 dissociates to Na^+ ad N3^-. The N3^- hydrolyzes in solution to HN3. Can you write and balance the equation for the hydrolysis of the azide ion. Where do you get stuck from there?
March 4, 2015

chemistry
How much of the solution? mols needed = M x L = ? Then grams = mols x molar mass
March 4, 2015

Chem - solubility
Can you write the ICE chart and Ksp equation? Show what you can do and explain where you have problems.
March 4, 2015

Chem
What do you not understand about the problem? This is Le Chatelier's Principle in action.
March 4, 2015

Chemistry Dr. Bob222
I think I must have answered this elsewhere.
March 4, 2015

Chemistry
Six problems in one post. What do you not understand about this. I can help you through it if I know where to start. Show what you know to do.
March 4, 2015

chemistry
I can't read this post.
March 3, 2015

chemistry
q = -15.3 kJ/mol x (18.8/molar mass KC2H3O2) = approx - 3.03 kJ or 3030 J. Then -3030 = mass H2O x specific heat H2O x Tfinal-Tinitial) Substitute the numbers and solve for Tfinal
March 3, 2015

Chemistry Dr. Bob222
You know I know how to calculate the TY and AY and %Y now, but I'm confused on the finding limiting reactant? umm Let me see if I can figure it out and you let me know if I'm on the right track... 2.02g NaHCO3 mols = 2.02/84 = 0.0240 mols the ratio is 3/1 for ...
March 3, 2015

Chemistry Dr. Bob
. Show that the equivalence amount of citric acid for 2.00 g of sodium bicarbonate is 1.52 g. *** 1 mol citric acid reacts with 3 mols sodium bicarbonate, molar mass NaHCO3=84g/mol 2 moles in 2 g? = 2/84? = 0.0238 mols 2g NaHCO3? then to find the citric acid? is it.. 0.0238/3...
March 3, 2015

chemistry
Like charges repel; unlike charges attract.
March 3, 2015

chemistry
Wouldn't you expect it to get stronger (as long as the electron is in the same shell).
March 3, 2015

Chemistry Ap
We can't draw diagrams on this forum but it is easy to see if I could draw a graph. Basically this is what you do. XH2O = Pomethanol-Ptotal/(Pomethanol-PoH2O) That gives you (89.0-35.5)/(89.0 - 17.5) = 0.748 for H2O I can never remember the formula; I draw it out with a ...
March 3, 2015

chemistry
I agree Good work.
March 3, 2015

chemistry
I see. I do all of the typing so you can check your values. How about us turning that around. You do the typing (show me what you have or tell me what you don't understand) and let me check your results. You have the right equation, the right products, and it's ...
March 3, 2015

chemistry
This looks simple enough. What do you not understand? Acid + base = salt + H2O
March 3, 2015

Chemistry
12. Negative charge must equal positive charge since all elements are neutral.
March 3, 2015

AP CHEM LAB
mols HCl = M x L = ? mols NaOH = mols HCl (since there is 1 mol HCl reacting with 1 mol NaOH) Then M NaOH = mols NaOH/L NaOH. You know mols and M, solve for L NaOH.
March 3, 2015

Chemistry
Atomic masses are average masses of the different isotopes of that element that occur naturally. For example, the mass of Cl-35 and the mass of Cl-37 are averaged (about 76% for 35 and 24% for 37) and the weighted average is about 35.5 for naturally occurring Cl2.
March 3, 2015

Chemistry Dr. Bob
You did the 1 g NaHCO3 vs 0.76 g citric acid (as you posted earlier) correctly. For #2 you use YOUR numbers. mols in 1g NaHCO3 = 1.02/84 = about 0.012 Convert to mols CO2. That's approx 0.012 x 1 mol CO2/1 mol NaHCO3 = about 0.012 mols CO2. Convert to grams CO2. 0.012 mol ...
March 3, 2015

chemistry
1 for Cu in the ground state. 5 are in the valence shell of As.
March 3, 2015

Chemistry
The first ionization energy (first IP) generally increases as one moves from the left to the right on the periodic table (in the same period). That's because the nuclear charge in increasing but the added electrons are going into the same shell so the attractive force is ...
March 3, 2015

chemistry
Those intermolecular forces add up to extra holding power; therefore, it is harder to break the bonds from a liquid to a vapor state. That means more energy must be transferred to the liquid and that means a higher boiling point.
March 3, 2015

chemistry
NH4I(s) + H2O(l) ==> NH4^+(aq) + I^-(aq)
March 3, 2015

Chemistry
You would expect the boiling point to be higher for H2O than for H2S because of hydrogen bonding in H2O. The problem didn't ask about boiling point, you say? Yes it did. It asks for volatility, that is vapor pressure, and that leads to boiling point.
March 3, 2015

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