Monday
June 27, 2016

Posts by DrBob222

Total # Posts: 52,586

Organic Chemistry
% aspirin = (0.082/5.00)*100 = ? %caffeine = )0.21/5.00)*100 = ?d etc for acetanilide. For #2, convert grams given in the problem to mols. mol = grams/molar mass = ? Then mol% aspirin = (mols aspirin/0.600)*100 = ? etc. for the others.
June 27, 2016

chemistry
We can't write Lewis dot structures on this forum. Google Lewis dot structure of each of these and you can see how they look.
June 27, 2016

Chemistry
If what you have is a pure compound and not a mixture, yes.
June 27, 2016

Chemistry
20 gm of what?
June 27, 2016

Chemistry
That's why you've been stuck on this question for hours. There isn't enough information. You MUST know how much Na2SO4 there is. This is just like asking "You're driving your car to the supermarket that's down the road 5 miles. How long will it take ...
June 26, 2016

Chemistry
Na2SO4 + BaCl2 ==> BaSO4 + 2NaCl So how much Na2SO4 do you have?
June 26, 2016

chemistry
The s orbital is not degenerate. The p orbital is with pz, px, py orbitals. The d orbital is with 5 orbitals. You can google and get the shapes of the five.
June 26, 2016

Chemistry
If you knew the answer why did you post the question?
June 26, 2016

chemistry
You are correct that both ii and iii are incorrect and for the reason you cite. i is correct. If n = 4, l can be 0,1,2,or 3; ml can be -3.-2,-1,0,1,2,3; ms can be +/- 1/2. Note: for iii, I think you meant to write "l can be 0,1,2,3 or 4." t-4 doesn't make sense ...
June 26, 2016

chemistry
It's a statement about the Heisenberg Uncertainty Principle. That says that if you can know exactly where the electron is sitting, you can not know its velocity. The reverse is true, also. If you know how fast it is traveling, you can not at any instant exactly where it is...
June 26, 2016

chemestry
A quadratic is not required and you can let 0.0667-x = 0.0667.
June 26, 2016

chemestry
First, please spell chemistry right. I'm annoyed. Second, this is a buffer problem for the first addition. They throw you a curve with the second addition because it is NOT a second buffer problem. Here is the scoop. Call acetic acid, CH3COOH, as HAc. millimols HAc = mL x ...
June 26, 2016

Chemistry
Look up the delta Hof values for each, then dHrxn = (n*dHf products) - (n*dHf reactants). This dHrxn will be for 34 g NH3. For 2.5 g it will be dHrxn x (2/34) = ?
June 26, 2016

chemestry
I ASSUME this is a beginning class and they expect you to view H2SO4 as a dibasic acid; i.e., 0.05M x 2 = 0.1M in (H^+). Actually, that isn't right as (H^+) really is closer to o.059M and not 0.1. But we will go with the assumption. Let's call formic acid as HFm to ...
June 25, 2016

CHEMISTRY
If you understand the post below you will know how to do this. I'll check your answers.
June 24, 2016

CHEMISTRY
But you know those answers are wrong. You should follow my rules above to get the correct answers.
June 24, 2016

CHEMISTRY
Here is how you do a couple of them. Then you try the others. Sr and NO3^-1 Sr is a +2 charge. There is no Sr with a +3 charge. Sr(NO3)2. You can see Sr is +2 and 2 NO3^- is -2 so the +2 neutralizes the -2. All compounds will be zero charge and that's how you know what ...
June 24, 2016

Chemistry
Those don't react but if they did it would be this. 2FePO4 + 3Na2SO4 ==> 2Na3PO4 + Fe2(SO4)3 mols FePO4 = grams/molar mass = ? Then using the coefficients in the balanced equation, convert mols FePO4 to mols Fe2(SO4)3. That's mols FePO4 x (1 mol Fe2(SO4)3/2 mols ...
June 24, 2016

CHEMISTRY
I'm sure you mean [NO3]^-, [SO4]^2- etc. Then In(NO3)3, In2(SO4)3, etc. If we could write subscripts very well on this forum the nitrate would be [NO3]-
June 24, 2016

CHEMISTRY
See your other post.
June 24, 2016

Science-chemistry
If %A = 22.22%, then %B = 77.78. Take 100 g sample to give you 22.22 g A 77.78 g B. Convert to mols. 22.22/40 = 0.5555 mols A. 77.78/atomic mass B = ? mols B. You know the ratio is A2B5; re-write this way letting X stand for atomic mass of B. 22.22/40 = 0.5555 x some # = 2 77....
June 24, 2016

chemistry
How many mols do you need? That's M x L = ? mols NaOH. Then grams = mols NaOH x molar mass NaOH
June 23, 2016

chemistry
........BaCrO4 ==> Ba^2+ + CrO4^2- I.......solid.......0.......0 C.......solid.......x.......x E.......solid.......x.......x Substitute the E line into Ksp expression and solve for x = solubility
June 23, 2016

another approach---Chemistry
Calculate % each element. %X = (0.36/0.56)*100 = 64.3% %O = (0.2/0.56)*100 = 35.7% Take 100 g sample to give 64.3 g X 35.7 g O Convert to mols. 64.3/at mass X = ?mols X. 35.7/16 = 2.23 mols O. We know this is in the ratio of 2:3 so, letting X = atomic mass X 64.3/X = ?......*...
June 23, 2016

Chemistry
Use PV = nRT and solve for n. Look up the vapor pressure of H2O at 20 C. It is approximately 20 torr BUT that's just a guess (although a very close guess). Ptotal = pH2O + pAr You know ptotal and pH2O, solve for pAr and use that for P in PV = nRT. Substitute the other ...
June 22, 2016

Chemistry
1 carat = 0.2 g; therefore, 15 carats = 3 g. Then mol = grams/molar mass = ? That gives you mols in the mineral. Since there are 3 mols of Si in 1 mole of the mineral, mols Si will be 3x mols in the mineral.
June 22, 2016

Chemistry
No and yes. You don't need to use dHrxn = (n*dHf products) - (n*dHf reactants) because the problems has already done that for you. For the reaction given dH is -2511.0 kJ and that is for 2 mols of C2H2 or 2*26 = 52 g. So the revised question is if 52 g releases 2511.0 kJ ...
June 22, 2016

Chemistry
mols KCl = M x L = ? mols PbCl2 formed = ?mols KCl x (1 mol PbCl2/2 mols KCl) = ?mols KCl x 1/2 = ? mols PbCl2. Then grams PbCl2 = mols PbCl2 x molar mass PbCl2.
June 22, 2016

chemistry
The ethyl group on both 3 and 4 make the chain one C longer. I can't draw it on this forum but try google the names you have and see how they look then count the longest C chain.
June 22, 2016

chemistry
Take a look at 3 and 4. 3 appears to be a pentanol to me. 4 appears to be a hexanol to me. Check it out.
June 22, 2016

Chemistry
22.4 L NH3 at STP has a mass of 1 mol or 17 grams. So 800 cc (0.800 L) will contain 17 x (0.800/22.4) = ?
June 22, 2016

chemestry
I've done all but the water. You can fill that in. 2Cr2S3 + 30PbO2 + 24H2SO4 --> 30PbSO4 + 2H2Cr2O7 + ?H20 Check it out. Make sure I made no typos.
June 22, 2016

chemestry
I REALLY wish you would spell chemistry right. You've posted the last several days with the wrong spelling.
June 22, 2016

chemistry
right
June 21, 2016

Chemistry
The answer is here. https://en.wikipedia.org/wiki/Free_expansion
June 21, 2016

Chemistry
It is symmetrical in three dimensions so it is non-polar.
June 21, 2016

chemistry
See your other post.
June 21, 2016

Chemistry
What does P = 40% mean? You don't need the density. mols needed = M x L = ? Then grams = mols x molar mass. You know mols and molar mass, solve for grams HF.
June 21, 2016

Chemistry
First, a correction. The Henderson-Hasselbalch equation is pH = pKa + log (base)/(acid). That negative sign is either a typo in the book or by you in the post. What you are asking isn't exactly clear. I think you want to know why a. is the solution a buffer b. why it is ...
June 21, 2016

Chemistry
I don't think the molar mass of the 58.3 mg sample is 122.44 nor do I think you can calculate what it is. The NaClO4 contains Cl35, Cl36, Cl37in this sample. You know the percent Cl36 but you don't know the percentages of the other two (except of course in naturally ...
June 21, 2016

Chemistry
It's all here. The last links defines what an isotonic solution is for NaCl. https://en.wikipedia.org/wiki/Tonicity http://differentmedicalcareers.com/hypertonic-hypotonic-isotonic-solutions/ https://www.google.com/search?q=what+concentration+NaCl+is+isotoinic&ie=utf-8&oe=...
June 21, 2016

chemistry
For the same reason that no reaction every completes. For reversible reactions there is always at least one molecule that is "ready" to reverse direction.
June 21, 2016

chemistry
If you are in beginning chemistry, the easy answer is that it is 0.2M in (H^+) so pH = -log(0.2). Then pH + pOH = pKw = 14 and you get pOH from that. However, that isn't quite right since the second H^+ is not a strong acid and more advanced classes will do it slightly ...
June 20, 2016

chemistry
Ba(OH)2(aq) + 2HCl(aq) BaCl2(aq) + 2H2O (g) molBa(OH)2 = M x L = ? Now using the coefficients in the balanced equation, convert mols Ba(OH)2 to mols HCl. Finally, M HCl = mols HCl/L HCl.
June 20, 2016

Chemistry
K2SO4 = potassium sulfate NH4)F = ammonium fluoride
June 20, 2016

Chemistry
KaKb = Kw. You know Ka and Kw, solve for Kb .
June 20, 2016

chemestry
Please explain what the recipient is. Are all gases 2.4 moles or is that CO and H2 = 2.4 mols.
June 19, 2016

chemestry
.......SO2Cl2(g) ⇄ SO2(g) + Cl2(g) I......1.2..........0........0.8' C.......-x..........x.........x E.....1.2-x.........x......0.8+x Kp = 2.4 = (x)(0.8+x)/(1.2-x) Solve for x and evaluate each of the components.
June 19, 2016

chemestry
P.S. Note the correct spelling of chemistry.
June 19, 2016

chemestry
Essentially one ignores the contribution of H^+ from the HCN but you can calculate how much that is. .......HCN ==> H^+ + CN^- I......1........0.....0 C......-x.......x.....x E......1-x......x.....x For HCl, remember it is a strong electrolyte and ionizes completely...
June 19, 2016

chemestry
Note the correct spelling of chemistry. NH3 + HCl ==> NH4Cl mols NH3 = M x L = 0.1 x 0.05 = 0.005. mols HCl 0.2 x 0.025 = 0.005. You see this is an exact neutralizing solution; you have no HCl or NH3 left and have formed 0.005 mols NH3 in 75 mL solution so (NH4Cl) = 0.005/0...
June 19, 2016

@ kandace---chemistry
I should point out here that your problem makes no sense to me. True that the CO2 bubbled into Ca(OH)2 produces CaCO3 BUT you say the mass of the hydrocarbon is 10 g. So did you start with 10 g hydrocarbon or did the CaCO3 weigh 10 g. I don't call CaCO3 a hydrocarbon but ...
June 19, 2016

chemestry
Use the Henderson-Hasselbalch equation. Note the correct selling of chemistry. ALSO, and this is important, do you man m or M. m stands for molality. M stands for molarity. Also, I don't believe Ka for acetic acid is 1.76 x 10^-6. You either looked it up wrong or y you ...
June 19, 2016

Chemistry
I don't know many who have the solubility tables of thousands of chemicals memorized. I know I don't. Surely you have a table that lists the solubility of KClO3 at 80 C and 10 C. Or perhaps it's a graph that gives those numbers. If you will post those perhaps we ...
June 18, 2016

Organic chemistry
vanillan from vanilla
June 16, 2016

chemistry
What you have looks ok to me. Cr will go to Cr^3+.
June 16, 2016

CHEMISTRY
2F^- --> F2 + 2e -2.87 2I^- ==> I2 + 2e -0.535 But somehow I don't think this is the answer your are looking for. As to WHY the potentials are that way-- I suppose that's the nature of the beast. F^- being such a small ion isn't likely to give up electrons. ...
June 16, 2016

Chemistry
Why didn't you show us how you came up with 1.69. If we don't know how you got there how can we tell where you're going wrong? I cam up with approx 1
June 16, 2016

Chemistry
%bu ,ass = (grams solute/total grams)*100 = ? grams solute = 200 g total grams = 200+500 g = ?
June 15, 2016

Chemistry
1.25 g C/12 = mols C Convert to mols soap. grams soap = mols soap x molar mass soap.
June 14, 2016

chemistry lab
I suppose you meant "weigh". I can't answer because I don't know what you're doing.
June 14, 2016

Chemistry
mass % = g solute/100 g sample. M = mols/L solution. So you have 4.6 g C2H5OH/100 g solution. molar mass C2H5OH = 46 mols C2H5OH in 4.6 g is 4.6/46 = 0.1 mol. What is the volume? That's mass = volume x density or volume = mass/density = 100 g/0.93 = 108 mL or 0.108 L. Then...
June 14, 2016

Chem
There is none in what you have written. If you have water of crystallization it would show something like this: Fe(NO3)2.xH2O where x is 1, 2, 3, or some other whole number.
June 14, 2016

Chemistry
The right line of thought but you missed a turn somewhere. That's rate = k[x]^2[y]^1, then rate = k(2)^2(3)^1 = 12*k
June 14, 2016

CHEMISTRY
You don't have enough information to answer this. I assume you are talking about the electron in a H atom. It will different for other elements. How much energy do you get from a photon falling from n = 6 to n = 1? That's delta E = 2.180E-18J(1/1^2 - 1/6^2) = ?J/photon...
June 13, 2016

chemistry
CuO + H2SO4 ==> CuSO4 + H2O The reaction proceeds because the driving force is the formation of a weakly ionized material; i.e,in this case it is water. The reaction is a double replacement.
June 13, 2016

chemistry
The driving force is that PbI2 is a solid that is insoluble in the aqueous solution present with Pb(NO3)2 and KI
June 13, 2016

Chemistry
wavelength = h/mv wavelength = 5E-26. Convert to m. Convert 60 mph to m/s Substitute and solve for mass in grams and convert to pounds.Post your work if you get stuck.
June 13, 2016

Chemistry
Not quite. mols in each = M x L = ? Then after you know (H^+) in mols/L (i.e., molarity) then use the pH formula Bob Pursley gave you in the last line to get pH.
June 13, 2016

Chemistry
The idea here is that you add an excess of HCl to the sea shells and that completely reacts with ALL of the calcium carbonate. The excess HCl is titrated with NaOH. CaCO3 + 2HCl -> CaCl2 + 2H2O mols HCl added initially = M x L = 0.025 x 5 = 0.125. How much HCl was in excess...
June 13, 2016

Chemistry
Instead of posting to get my opinion why don't you OBSERVE this in the lab yourself. Then you will know.
June 12, 2016

chemistry
-COOH is a carboxylic acid.
June 12, 2016

chemistry
Convert g CO2 to grams C. Convert g H2O to grams H. Then grams O = mass sample - grams C - g H. Convert grams C to mols C. Convert grams H to mols H. Convert grams O to mols O. Now find the ratio of C,H,O to each other with the smallest number being one. The easy way to do ...
June 11, 2016

Science
2Mg + O2 ==> 2MgO mols Mg = grams/atomic mass = ? Using the coefficients in the balanced equation, convert mols Mg to mols MgO. In this case that is mols Mg x 1 = mols MgO Then convert mols MgO to grams. g MgO = mols MgO x molar mass MgO = ?
June 11, 2016

Chemistry
You're welcome.
June 11, 2016

Chemistry
C3H8 + 5O2 == 3CO2 + 4H2O Look up the delta H for this reaction or calculate it from dHrxn = (n*dHo products) - (dHo reactants) = ? Then that is the dH for the reaction for 44 g C3H8. Call that Y. Then Y x (355/44) = ? energy available.
June 11, 2016

chemistry
I don't believe there is enough information to answer that. pH2 = XH2*Ptotal. XH2 = 0.5 but you don't have a total pressure and I don't see a way to calculate it.
June 10, 2016

chemistry
I think the question is worded wrong because 500 mL of Pb(NO3)2 and 500 mL Na2CrO4 will ppt PbCrO4 big time. I think the problem is asking for volume of 0.1M Pb(NO3)2 needed to start pptn of PbCrO4 in 500 mL of 0.2M Na2CrO4.l If you start with 0.2M Na2CrO4, then (CrO4^2-) = 0....
June 9, 2016

chemistry
2Fe2O3 + 3C → 4Fe + 3CO2? C:Fe = 3/2. Look at the coefficients.
June 9, 2016

Chemistry
A is correct at 15.77 rounded to 15.8%
June 9, 2016

chemi
Your post isn't quite clear. What DID YOU OBSERVE? I don't know what you saw. ZnCO3 ==> ZnO + CO2 What do you mean by APPARENT loss in mass. It either lost mass or didn't lose mass. There is nothing apparent about it.
June 9, 2016

Chemistry
Your error is in thinking the Ac is the same as HAc. They are equal in a solution of acetic acid but the problem tells you that NaAc has been added. Now the solution has H^+ one number and the Ac is whatever you've added. So make that Ka = (0.0025)(Ac^-)/(0.9975) and solve...
June 9, 2016

chemistry
This is not a buffer problem; therefore, the HH equation is not applicable. ......HCOOH ==> H^+ + HCOO^- I......Y........0......0 C......-x.......x......x E.....Y-x.......x......x You know pKa, convert that to Ka. Ka = (H^+)(HCOO^-)/(HCOOH) The problem gives you pH so you ...
June 8, 2016

Chemistry
4Fe + 3O2→ 2Fe2O3
June 8, 2016

Chemistry
right
June 8, 2016

Chemistry
/both. Taught for 50 years. Now retired.
June 8, 2016

Chemistry
yes
June 8, 2016

Chemistry
You have the best when you have Bob Pursley.
June 8, 2016

Chemistry
In your first attempt I saw two errors. There may be more but I quit looking. One error is that x = (OH^-) but you used it as (H^+). The second is I don't know where the 3E-12 came from. In the second trial you made a math error right off the bat and I quit looking. 5E-4 ...
June 8, 2016

chemistry
Ahhh---but we do that sometimes. It is a GREAT learning experience. We aren't likely to do it twice.:-)
June 8, 2016

chemistry
The easy way. pKa + pKb = pKw = 14 You have pKa of 9.26 which is right but you took the -log of 4.26 which isn't right. pKa = 9.26 = -log Ka Ka = ?
June 8, 2016

Analytical Chemistry
Your question (are these two questions) is too general. What do you want? pH, OH or something else. What are you titrating it with; i.e., you need to know the final volume. Example. 0.1mol NaOH titrated with 0.1M HCl. 0.1 x 0.99 = 0.099 titrated. That leaves 0.1-0.099 = 0.001 ...
June 8, 2016

chemistry
I think of molecular compounds as being made up of molecules with covalent bonds. CO2 for example. NaCl is an ionic compound and consists of discrete Na^+ and Cl^- so it is not molecular while CO2 exists as discrete CO2 molecules. SO2 and SO3 are other molecular compounds.
June 8, 2016

chemistry
So far you are good. So Q = 1E-40 < K = 1.4E-37 which lets you know c and d can't be right. The answer must be a or b. Now write the Keq expression. Keq (which is really Ksp) = Cu3(PO4)2 = (Cu^2+)^3(PO4^3-)^2 = 1.4E-37 Q must be larger. How can it get larger? No way ...
June 7, 2016

chemistry
Reverse eqn 1(change sign of dH), add to eqn 2 and 2 x eqn 3.
June 7, 2016

chemistry
By the way, the Ka value has no units and don't let anyone tell you they do. When they are used, most of the time they are called just units, but often they are called "tentative units". "temporary units", "trial units", or
June 7, 2016

chemistry
You can get the definition of an acid from you text/notes/google. For the HA problem. For pH = 3.50 convert to (H^+). I obtained approx 3E-4 but you need to confirm since that's an estimate. .......HA ==> H^+ + A^- E......x....3E-4...3E-4 Substitute the E line into the ...
June 7, 2016

chemistry
Your text or notes contain all of these definitions. YOu don't need us to do your homework for that. As the for Lewis structure, we can't draw structures on this forum.
June 7, 2016

Chemistry
If the 35 is a superscript and the 15 is a subscript, then C is correct.
June 7, 2016

Chemistry
I think you can heat K2CO3 up to 110 C without decomposition. Spread crystals out on a watch glass and heat at 110 for 2 Hrs. Cool in a desiccator.
June 6, 2016

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