# Posts by DrBob222

Total # Posts: 54,974

Chemistry
The first two lines. E = hc/wavelength E = 6.626E-34 x 3E8/420E-9 = ? J/photon.

Chemistry
E/photon = hc/wavelength E/photon = approx 5E-19 J but you should confirm that for a more accurate answer. 32W = 32 J/s * 2s = 64 J Then 5E-19 J/photon x # photons = 64 J. Solve ofr # photons.

Organic Chemistry
You must have a table or a graph showing the solubility of aspirin at 37 C and 25 C. Without that I'm in the dark.

Chemistry
Energy needed to excite an electron from the n = 1 to the n = 2 level is E = 2.18E-18 J(1/1^2 - 1/2^2) Compare that energy needed with what you have in a 480 nm beam of light. E = hc/wavelength Post your work if you get stuck.

chemistry
I don't see a question here.

ORGANIC CHEM QUESTION
You didn't look at all of the sites. One gives the beta. It's a ring.

ORGANIC CHEM QUESTION

chemistry
1.79E-20 WHAT?

chemistry
q = mcdT q = 445/76 J m = 50.0 g c = ? dT = (Tfinal - Tinitial) Substitute and solve for c in J/g*C

More Chem
2221 kJ is dH. You lose 40%. So 60% of what number is 2221. That must be about 3700 kJ which is what you need (that's just a close guess) C3H8 + 5O2 ==>3O2 + 4H2O molar mass C3H8 is 44 grams You know 44 g C3H8 must be burned to produce about 2221 kJ. So common sense ...

Chem
heat lost by warm water + heat gained by cool water = 0 [mass warm water x specific heat H2O x (Tfinal-Tinitial)] + [mass cool water x specific heat H2O x (Tfinal-Tinitial)] = 0 Substitute and solve for Tf.

Chemistry Heat
Use stoichiometry to determine the limiting reagent then use the common sense I showed you earlier to determine the heat generated.

Chemistry
Yes, it is a dHo (formation) which is the reverse of what you want.

Chemistry
Ag^+ + Cl^- ==> AgCl dH= -65.5 so AgCl ==> Ag^+ + Cl^-, the reverse of what is -65.5 gives you +65.5 kJ/mol.

Chemistry
What's the molar mass FeBr2. That's about 55.85 + 79.9 + 79.9 = approx 216 but you need a more accurate answer. Now you know this. 216 g FeBr2 are formed when 249.8 kJ of energy are released. You only have 10.0 g. Use common sense to tell you how much 10.0 g will ...

CHEMISTRY
You have posted in the last day or so several problems that are similar. They are stoichiometry problems and all of those are worked the same way i a 4-step process. Here are the steps with this problem. I suggest you print and save this. 1. Write and balance the equation. ...

Chemistry
First you must assume that the volumes are additive; i.e., the total volume will be 850 (HCl) = 0.5M x (50/850) = ? Then pH = -log(HCl) = ?

Chemistry
Pressure H2. Use P1V1=P2V2 Pressure N2. Use P1V1 = P2V2 Convert pN2 to torr. Add pH2 to pN2 to find Ptotal.

chemistry
4800 m^3 = 4.8E6 L but you should confirm that. PV = nRT. T is 273 K. Substitute from the problem and solve for n = number of mols. Then add 20% (0.20) to that to make up for the 20% loss. Convert mols H2 to mols Fe. 1 mol H2 requires 1 mol Fe according to the equation. Then g...

science
C'mon. It takes us a little time to type this stuff in. I've posted a response to your earlier post.

Physical Science
Was the fence built Jan 1, 2005 or December 31, 2005? I'll assume Jan 1, 2005 distance = rate x time d = 3.5 cm/yr x #years. Plug in the # years between the time the fence was built and 2030 and solve for distance in cm. Approximately 90 cm if I plug in 26 years.

Physical Science
See your other post. d - r*t or t = d/r

chemistry
Kc is what they want you to calculate. Initial (N2O) = 10 mols/2L = 5.0 M Eq (NO2) = 2.1/2 = 1.1 M. Your equation isn't balanced. .......2N2O ==> 2N2 + O2 I......5.0M......0.....0 C......-2x......+2x....x E......1.10M.....2x....x So 2x = 5.0-1.1 = 3.9 Solve for x, fill ...

Science
It starts in the mouth but most of the absorption takes place elsewhere. https://en.wikipedia.org/wiki/Human_digestive_system

Chemistry
Use PV = nRT Remember T must be in kelvin. P = 758/760 = ? n = mols = grams/molar mass = ?

@Scott--Chemistry Homework
But you don't have 55.55 mols H2O because you don't have 1000 g H2O. You have a total of 1000 mL solution which has a mass of 1000 g since the density is 1.0 g/mL. So the total mass is mass H2O + mass CO2 and that weighs 1000 g. The amount of H2O is <1000g and <...

my proof: 10.2 M means 10.2 mols/L solution. 10.2 mols x 44g/mol = 448.8 g CO2 density solution is 1.0 g/mL so mass = volume x density or 1000 mL x 1.0 = 1000 g. Then mass H2O = mass solution-mass CO2 = 1000-448.8 = 551.2 g H2O. mols CO2 = 10.2 mol H2O = 551.2/18 = 30.62 Total...

Chemistry Homework
XCO2 = 0.25 Therefore, XH2O = 1.0 - 0.25 = 0.75 Take enough sample to have 1.0 mol total. You will have 0.25 mol CO2 and 0.75 mol H2O. g CO2 = 0.25 x 44g/mol = 11 g CO2 gH2O = 0.75 x (18 g/mol = 13.5 g. Total mass is 24.5 g. Density is 1.0 g/mL; therefore, volume = g/density...

chemistry
% m/m = grams solute/g solution. You have 0.84 g solute and 500 solution.(density soln is 1.0 g/ml. You have 500 mL and 500 mL x 1.0 g/mL = 500 grams).

Chemistry
You have how many mols? That's M x L = 0.25 x 0.05 - 0.0125 The reaction releases 57,200 J/mol so in this reaction it releases 57,200 x 0.0125 = 715 J. Now, as Victor has said, substitute that into Q = mcdT 715 = 100 x 4.18 x (Tfinal - 19.5) and solve for Tfinal. I ...

Chemistry
You didn't tell us 0.250 WHAT.

Chemistry
# coulombs = amps x seconds = 1E5 x (24 hr/day) x (60 min/hr) x (60 sec/min) = ? 96,485 coulombs will electrolyze approx 27/3 g Al (atomic mass Al/3) and I'll call that 9 g Al but you should look up the atomic mass Al and go from there. So g Al = 9 g Al x (# coulombs/96,...

I've observed that when I started teaching full time in the late 50s most of my college students did not try to cheat. As the years passed I saw more and more tries and in my last years in the mid 90s just before retirement I saw blatant tries. I still remember my last ...

chemistry

Chemistry
You're welcome. Besides helping someone who needs help we get to exercise our brain and that keeps us running. Also, I like to think that it will delay the onset of diseases such as Alzheimer's etc.

Chemistry
yes

Chemistry
I assume that is CH3COOCH3. That is an ester. RCOOH acid RCOOCH3 ester RCH2NH2 amine RCH3CONH2 amide (a primary amide in this case)

Just Curious
I want to get into this free for all. If you want help and you are willing to put in a little work on your own, Jiskha is a good site. As for the answers, those given by students may be good and they may not be so good. As Steve points out, most of the regular guys/gals here ...

Chemistry
Since you quote concentrations I assume the K of 5.00 is Kc. Then Kc = 5.00 = (SO3)^2/(SO2)^2(O2) Qc = (9.00)^2/(6.00)^2(0.45) = 5.00 Since Qc = Kc, the system is in equilibrium.

chemistry
L x M x molar mass = grams. Substitute and solve for L, then convert to mL.

Chemistry
All of the products are gases but I can't show that without using more than one line. ....(NH4)2CO3(s) = 2NH3 + CO2 + H2O ....solid...........2p......p.....p So the total pressure of the system is due to the gases. Total P = 2p + p + p = 0.8944 atm. Solve for p and 2p and ...

Chemistry
1. | phase boundary 2. || salt bridge 3. Ag(s) | Ag+(aq) cathode 4. Cu2+(aq) | Cu(s) anode A. Cathode Half Reaction B. Phase boundary C. Salt Bridge D. Anode Half Reaction

Chemistry
Note Al goes from zero oxidation state to 3+ so each Al loses 3e. For 2Al that will be 6 electrons. To check that, Ni^2+ gains 2 electrons for each Ni or 6e for 3 Ni. 6 electrons again. So n is 6.

chemistry
a. Add 1:1 NH3 slowly. Keep at boiling point for several minutes. b. Compare the molar masses of Al(OH)3 vs Al2O3. If you leave Al(OH)3 + Al2O3 instead of all Al2O, which is heavier. c. Methyl red indicators assures you know the right pH range. NH4Cl added to NH3 is a buffer. ...

Chemistry
NOCl at equilibrium is 115/760 = approximately 0.15 atm but you can use a more accurate number. ......2NO + Cl2 --> 2NOCl I......P.....P........0 C....... E....................0.15 Here is how you figure the rest. Do the C line next. We know equilibium NOCl is 0.15. Since ...

Chemsitry
dGo is -418600 R is 8.314 T is not given but since they say dGo, I assume it is 298 K.

Chemsitry
dGo = -RTln*K Solve for Keq. Then set up Keq expression (remember solids don't enter the expression). You have Keq from above and pO2 is given in the problem, solve for pSO2. Post your work if you get stuck.

chemistry
IDON'T GET IT EITHER. There is no reaction between CaCl2 and NaCl.

Chemistry
From your answer above, you have k = [Pb2+]*[cl-]^2 k you have. (Pb^2+) is x as you have it. (Cl^-) is 0.023 from the problem BUT you didn't square it. Do that and solve for x. Note: I don't think it will make much difference BUT since the Ksp for PbCl2 is so large, a ...

Chemistry
Yes, you are solving for the pH of the solution BEFORE the 0.01 mol HCl is added. The problem is asking for the pH AFTER the addition of 0.01 mol HCl. .......RCOO^- + H^+ ==> RCOOH I.....0.035.....0........0.013 add...........0.01............. C....-0.01...-0.01........+0....

Chemistry
I must confess I don't know what the question wants. I'm guessing here but I would try 1 0 0 0 3 2 for question 1.

Chemistry
Call benzoic acid HA, then .....HA --> H^+ + A^- E.....x..... pH = -log(2.04) Ka = (H^+)(A^-)/HA) You know H^+. A^- is the same. You know Ka. Solve for x = HA. I get approximately 1.6 mols/L. For 250 mL you would need 1/4 that amount.

Chemistry
Write the Ksp expression. Substitute 0.0050 for (Fe^3+) and solve for (OH^-).

Chemistry
Ksp = (Fe^2+)(OH^-)^2. If pOH is 2 then OH^- is 10^-2 or 0.01. Plug that in, solve for (Fe^2+) and that will be the solubility in mols/L. You have 1 L of solution so that is the # mols.

Chemistry
First you need to calculate the wavelength correctly.I can't make the symbols you did but it is c = freq x wavelength 3E8 = 5.2E14 x wavelength wavelength = 3E8/5.2E14 = 5.77E-7 m and that converted to 577E-9 m (or 577 nm). Here is a chart that will show you the color. It...

Chemistry
E = 2.18E-18 J(1/2^2 - 1/4^2)

chemistry
The flask contains 0.60 g OF WHAT???? n = grams/molar mass of the material. Then PV = nRT

Chemistry
mols HCl = M x L = ? mols HNO3 = M x L = ? Total mols H^+ (from the two) = just add them. The part about the dilution has no effect. It affects the CONCENTRATION OF H^+ but not the number that are there.

Chemistry
millimols KSCN = mL x M = 0.2 mmols Fecl3 = 0.2 M KSCN = mmols/mL = 0.2/130 = ? M FeCl3 = 0.2/130 mL = ? mmols didn't change. M didn't change. Why would the equilibrium shift?

Chemistry
Zn + 2Ag^+ ==> 2Ag(s) + Zn The problem tells you AgNO3 is the limiting reagent. You have how many mols Ag? That's mols = M x L = 0.250 x 0.1 = 0.0250. Convert mols Ag^+ to mols Zn. That's 1/2 x 0.0250 (from the coefficients in the balanced equation) = 0.0125. So ...

Chemistry
Forget the n and just go with + and we won't try to balance the electrons. (1) means statement 1; (2) means statement 2 etc. And note that Z ==> Z^+ means Z has lost electrons which means it is oxidized which means it is an reducing agent. (1) So X is stronger than E. X...

Chemistry (science)
HCl is a polar covalent compound while K2SO4 is an ionic compound. Most ionic compounds have high melting/boiling points.

Chem Help!!!
Nonsense. How do you know solution A had any sodium salicylate in it?

Chemistry
Ag+(aq) + e– ? Ag(s) E° = 0.80 V AgBr(s) + e– ? Ag(s) + Br–(aq) E° = 0.07 V You want this. AgBr(s) ==> Ag^+ + Br^- so that Ksp = (Ag^+)(Br^-). So reverse eqn 1 and add it to eqn 2 to get this. Ag(s) + e– ? Ag^+ Eo=-0.80 AgBr(s) + e– ? Ag(s...

chemistry
I think you made a typo. You may have meant A + B ==> C + D Increasing A shifts the rxn to the right which decreases B and increases C and D.

Chemistry
Cd ==> Cd^2+ + 2e Eo = ? Ni^2+ + 2e ==> Ni E =-0.25 ------------------------ Cd + Ni^2+ ==> Cd^2+ + Ni Ecell=0.2 Look up the Eo value for Cd^2+ and reverse it. Look up the Eo value for Ni since the Eo value is the definition for 1 M solution. You want the total for ...

Chemistry
You're making this harder than it is. What's the definition? 20% NaOH w/v means 20g NaOH/100 mL solution. You want 300 mL solution so you will need ? grams NaOH. Would you believe 3*20 = 60? or if you want it as an equation it is 20 x (300/100) = 60. If 20/100 is the ...

eqilibrium /physics
So the rod is 200 cm long and pivot is at 80 so length 1 is 80 and length 2 is 120 cm. So 3*80 = x*5 where x is the distance from the pivot. How far will that be from the 120 cm end?

Chemistry
(P1/T1) = (P2/T2)

chemistry
You have it. Take a 100 g sample which gives you 40 g C, 6.71 g H and (100-40-6.71) g O. You go from there. Post your work if you get stuck.

Chemistry
Isn't it 6. 2Al ==> Al^+ + 6e

Chemistry
I know I'm being picky BUT that answer, while true in most instances in reality, technically it is true ONLY when the volumes are additive. In some cases they are not.

Chemistry
What is the molarity (M) of the HCl? That's 1000 mL x 1.18 g/mL x 0.36 x (1/36.5) = ? Then use mL1 x M1 = mL2 x M2. Substitute and solve for the unknown. Post your work if you get stuck.

chemistry
I believe that's 3,3- dimethylheptane

Chemistry
I believe you have a typo Both are H2SO4. Did you mean one to be HNO3?

Chemistry
Use the Henderson-Hasselbalch equation, use pKa for acetic acid of 4.76 (I think but you should confirm that), then solve for (base)/(acid)

Chemistry
Follow the size of the anion.

chemistry
The short way is this. 3.238 x (molar mass what of you want/molar mass of what you have) = ?

Chemistry
I agree

AP Chem
No. K is K. It changes ONLY with temperature. Ksp is given Kf is given. If you wonder how I know Keq is Kf*Ksp, here is what you do. Write the Ksp expression and multiply that by the Kf

AP Chem
Fe(OH)2 ==> Fe^2+ + 2OH^- Ksp = ? Fe^2+ + 6CN^- ==> [Fe(CN6]^4 Kf = ? -------------------------- Fe(OH)2+ 6CN^- => Fe^2+ +2OH^- +[Fe(CN)6]^4- CN^- is the ligand Keq for the rxn as shown is Kf*Ksp = ?

Chemistry
Right b will increase it for the reason you cite. Adding HCl certainly will increase the solubility. CuCO3 ==> Cu^2+ + CO3^2- You will not that adding HCl reacts with the CO3^2- to form H2CO3 which then decomposes to H2O and CO2. So decreasing the (CO3^2-) forces the ...

Chemistry
This is Le Chatelier's Principle. What do you not understand about. D it? Do you have any ideas what to do?

Chemistry
No and no. First, the volume will be 200 mL ONLY IF the volumes are additive and they are not(but they will be so close you will call that being picky). If you assume they are additive then the final concn will be 2.00 M x (100 mL/200 mL) = ? Just a note: If you add 50 mL ...

Chemistry
You want twice the reverse reaction given in the problem. So that's -(-286)*2 = ?

Chemistry
No but I'm having a little trouble understanding the problem. Look up the dHo formation for NH3. I'll call that x. IF THE problem is asking for dH rxn it is N2(g) + 3H2(g) ==> 2NH3(g) + 2x kJ BUT IF THE problem wants dHo formation for NH3/mol it is 1/2 N2(g) + 3/2 ...

Chemistry
The problem says so much heat is EVOLVED. That means that much heat is released so the sign is negative. However, I would redo the numbers. My calculator reads slightly over 560 ane 570. Also, note that you made a typo on the last line but you plugged in the right number.

Chemistry
Looks ok to me.

Chemistry
The problem is poorly worded. If you answered correctly you would answer, carbonate, sulfite, nitrate, bromate, chlorate, iodate, and phosphite. By merging those into answers both B and D are correct. Check to make sure there isn't a typo. That might be bromite or ...

Chemistry
That's right. Nitrite(NO2-) and hypochlorite(ClO-) and sulfate [SO4]^2- don't have 3. B is OK. Isn't D OK too?

Chem
Add equation 1 to the reverse of equation 2. I did this in my head so write it down and confirm it before proceeding.

Chemistry
Looks ok but I didn't check the calculation.

Chemistry
The equation is correct. Br2 in the elemental state is a liquid. It vaporizes easily and boils about 60C.

Chemistry
Add 0.02 mol HCl to 1L means (H^+) = 0.02M .......CN^- + H^+ ==> HCN I....0.150....0.......0.2 add.........0.02......... C...-0.02..-0.02......+0.02 E....0.130...0.......+0.22 (HCN) = 0.22M assuming the HCl was added as a gas

AP chem
Here are tutorials on each phase of the redox process you may need. If you had shown your work I could hav found your problem easily. As it is I have no idea what you're doing wrong. The equation you posted isn't balanced, though, so you know it can't be right. ...

Chemistry
(P1V1/T1) = (P2V2/T2) Remember T must be in kelvin.

Chemistry
mols benzoic acid = grams/molar mass = ? Then q = mols benz acid x Ccal(delta T) q is +3238 kJ. Substitute and solve for Ccal.

chem
That won't get it. We HELP you do your homework; we don't do it for you. I told you how to work the problem. If you don't understand, show what you've done or explain what it is you don't understand. I'll be glad to help you through it but I won't ...

Chemistry
Yes and no. Yes, the correct number is 572 kJ/reaction (not /mol since it's for two mols) AND I don't think you should call it dHo. dHo is -285 kJ/mol is for the H2 + 1/2 O2 ==> H2O. When you turn it around it becomes for the reaction and multiplying by 2 makes is ...

Chemistry
Right except for the typo. It's Al and not A in one of the equations.

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