# Posts by DrBob222

Total # Posts: 55,193

Chemistry
1 mol has 5.02E23 molecules so 7.5E-3 mols will have 7.5E-3 mols x (6.022E23 molecules/mol) = ? number of molecules. Then grams = mols x molar mass = ?

Chemistry
10 m^3 = 10,000 L. 10% x 10,000 = 1000 L SO2 CaCO3 + SO2 ==> CaSO3 + CO2 Calculate n = mols SO2 in 1000 L. PV = nRT P = 1 atm V = 1000 L R = 0.08205 T = 298 K Solve for n = number of mols SO2. Convert that to mols CaCO3. mols CaCO3 - mols SO2 (look at the coefficients in ...

Chemistry
It should be obvious that one pair is HSO4^- and SO4^2- The other pair, not quite so obvious, is OH^- and H2O (HOH). But if you pick out the HSO4^/SO4^2-) you know what's left is the other pair. Most questions of this type don't stop here but want to know which is the ...

Chemistry
ICE is the way to go. Technically, one should use concentrations but in situations like this the volume (M = mols/L) cancels and we can use mols directly. The equation is and we use mols instead of molarity. Some profs will count off if you don't use M. If your prof does ...

Chemistry
ln(Ao/A) = akt Ao = 0.03 a = 1 k = 6.22E-4 t = 10 min x (60s/min) - 600 s Solve for (A) in mols/L Plug in L to solve for mols grams = mols x molar mass = ?

Chemistry
Size increases as you go down the periodic table and increases as you go from right to left on the table. https://en.wikipedia.org/wiki/Periodic_trends#/media/File:Periodic_trends.svg

Chemistry
I agree

chemistry
Co ==> Co^2+ + 2e Eo = ? Cu^2+ + 2e ==> Cu Eo = 0.34 ----------------------------- Co + Cu^2+ ==> Cu + Co^2+ E = 0.62 So Eo Co + Eo Cu^2+ = Ecell = 0.62 Therefore, Co ==> Co^2+ must be +0.28 v because 0.28 + 0.34 = 0.62 The half cell releasing electrons is the ...

chemistry
mols sucrose = grams/molar mass = ? Then m = mols/kg H2O

chemistry
For toluene (the solute): mass = volume x density. Substitute and solve for mass. Then mols = mass toluene/molar mass toluene. For benzene: mass = volume x density. Substitute and solve for mass benzene. Convert mass in g benzene to kg benzene (the solvent). Then m = mols ...

Chemistry
heat lost by water + heat gained by cool water = 0 [mass warm H2O x specific heat H2O x (Tfinal - Tinitial)] + [mass cool H2O x specific heat H2O x (Tfinal-Tinitial)] = 0. Tfinal is the only unknown. Substitute and solve for it.

Chemistry
A = ebc where A is absorbance, e is molar absorptivity constant, b is path length in cm and c is concentration in moles/L. Substitute for A, e, b, and solve for c in M. You have all of the numbers in the problem.

chemistry
The equation tells you heat must go IN so it is ENDOTERMIC. (See the connection to IN and EN)

Chemistry
Can't draw on this forum.

chemistry
heat lost by Al + heat gained by H2O = 0 [mass Al x specific heat Al x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0 The equation you found may be right. I didn't go through the algebra.

Chemistry
If l = 0, it's an s. If l = 1, it's a p. If l = 2 a d. If l = 3 an f.

Chemistry
I'm not quite sure what you're asking. There are 4f, 5f, 6f, etc. How I do you want to count? Or you might mean that there are 7 f orbitals. or something different?

Chemistry
I agree

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 = ?