Friday
July 25, 2014

Posts by DrBob222


Total # Posts: 43,171

chemistry
Let's just eliminate some answers. You know A can't be right because there are a number of "essential" inorganic compounds. You know B can't be right--why do we need H2 and O2? What about C? D is ludicrous. I know people who live to be 100 and never at fi...

Chemistry
My tables aren't quite the same as your (but I have an old old text). But dSrxn = (n*dSproducts) - (n*dSreactants) dSrxn = (2*NaOH + H2) - (2*Na + 2H2O) What stands out is the -S(H2) you have. Shouldn't that be a +. If this doesn't fix the problem please repost thi...

Chemistry
You have two sets of P, T, V. (P1V1/T1) = (P2V2/T2)

college chemistry
When you can do the one before this you can do this one.

College chemistry
Where in the world are you getting your numbers. I don't see 2.02 or 12.01 in the problem. Wait, I suspect you are using molar mass H2 and molar mass C and molar mass. That isn't what the problem is all about. dGrxn = (n*dGproducts) - (n*dGreactants) They give you dGrx...

College chemistry
Instead of me flying in the dark why don't you post your work on the products-reactants you've tried and let me find the error in your work.

Chemistry
For #2. The half rxn are Zn ==> Zn^2+ + 2e and Cu^2+ + 2e == Cu To find Ehalf cell for Zn use E = Eocell - (0.05916/n)*log[1/(Zn^2+)]. Plug in the (Zn^2+), calculate Ehalf cell (using the reduction potential you find in your standard potential table), then reverse the sign ...

Chemistry
You haven't asked a question here but more like a book of questions. Do you just want to "compare" answers or do you have a real problem with understanding a particular part? Clarify what you don't know and explain in detail and we can help you through it. I ...

science
You apparently have no concept of how the freezing point of a pure material such as water is affected by the solute. Out of four choices you guessed wrong on three so th answer obviously must be A. Also it is obvious you didn't look up anything about colligative properties...

science
B is not true. C is not true. Look up colligative properties.

Buying A Car
I agree with Ms. Sue.

8th grade science
Check out horizon.

chemistry
You can reason through it this way PV = nRT. Since P, R and T are constant, then V = n*constant which I'll call k and V = nk. Evaluate k by 31.4 = 1.5k and k = 31.4/1.4 = 20.93. Then V = nk 41.4 = n*20.93 and n = 41.4/20.93 - 2.03 mols. OR you can reason that a higher volu...

Chemistry
heat lost by pebble + heat gained by water = 0 heat lost by pebble = 532.1 J heat gained by water = mass H2O x specific heat H2O x (Tfinal-Tinitial) Set q = heat gaine by water and solve for mass H2O.

Chemistry
heat gained by cold water + heat lost by hot water = 0 [mass cold H2O x specfic heat H2O x (Tfinal-Tinitial)] + [mass hot H2O x specific heat H2O x (Tfinal-Tinitial)] = 0 Substitute the numbers and solve for Tf.

Chemistry - check answers
These look good to me. Good work.

Chemistry
My guess is that you didn't take into account the total volume. millimols HCl=mL x M = 25 x 0.250 = 6.25 mmols NaOH = 15 x 0.35 = 5.25 NaOH + HCl ==> H2O + NaCl mmols HCl = 6.25 mmols NaoH = 5.25 difference is excess HCl by 1.00 mmol. So you have 1.00 mmols HCl in a tot...

chemistry
You need to write the entire problem. There isn't enough information here to answer anything.

Chemistry
millimoles NH3 = mL x M = 100 x 0.1 = 10 mmols NH4^+ = 100 x 0.1 = 10 mmols HCl added = 5 x 0.1 = 0.5 .......NH3 + H^+ ==> NH4^+ I.....10.....0........10 added.......0.5............... C....-0.5..-0.5......+0.5 E.....9.5.....0......+10.5 pH = pKa + log(base)/(acid) pH = pKa...

CHEMISTRY HELP !!!!
Your post said "E measured" so I assume you have that given to you. If it isn't given, add the oxidation half cell to the reduction half cell to obtain Ecell.

CHEMISTRY HELP !!!!
n = number of electrons transferred. In this case that is 2. Sn ==> Sn^2+ + 2e and Cu^2+ + 2e ==> Cu F is the Faraday constant of 95,485 coulombs E is the cell voltage. T is kelvin temperature. substitute and go. Don't foget the - sign.

CHEMISTRY HELP !!!!
See your post above for dG. For K, that is dG = -RTlnK. You know dG now, the - sign, R is 8.314. Substitute and solve for K.

Chemistry
Sn ==> Sn^2+ + 2e 2H^+ + 2e ==> H2 --------------------add 1 to 2. Sn + 2H^+ + 2e ==> Sn^2+ + 2e + H2 Then cancel the two e on each side and you're left with the balanced equation.

Chemistry
We need to know if the reaction is endothermic or exothermic. We can calculate dH for the reaction through the heats of formation as follows: dHorxn = (n*dHo products) - (n*dHo reactants) Look in your text/notes and find the dHo vaues for CO, COCl2 and Cl2. I've done that ...

Chemistry
1/2N2 + 1/2O2 --> NO dGfo = +86.58 kJ/mol. dG = -RTlnKp 86,580 = -8.314*298*lnK K = approx 10^-16 With a + sign for dG and the VERY small Kp, it is obvious that not much N2 will react with O2 to produce NO.

Chemistry
What's the problem here. You know increased T ALWAYS gets higher S. solid to gas ALWAYS increases S. Etc, so what's to ask questions about?

Chemistry
OK except NH4NO5 is not ammonium nitrate. That's NH4NO3. 2NH4NO2 + O2 ==> 2NH4NO3 Fe2O3 + 3H2SO4 ==> Fe2(SO4)3 + 3H2O

Chemistry
q = mass x specific heat x delta T. q = 2000 J mass = 4g sp.h. solve for this delta T = 5 degrees C.

Chemistry
Cl^- + Ag^+ ==> AgCl Cl^- comes from the last Cl (the Cl outside the sphere of coordination) and the Ag^+ comes from the AgNO3.

chemistry
Use the dilution formula of mL1 x M1 = mL2 x M2

Chem
Easy. There is no reaction. Are you sure you don't have this confused with Cu + HNO3?

Chemistry
For what? You haven't asked a question. And you haven't supplied any information.

Chemistry
How would you like for us to help you with this assignment?

chemistry
m stands for molality; I'm assuming that's what you mean. mols Ca(NO3)2 = 76g/molar mass = ? Then m = mols solute/kg solvent m = 0.509 = ?mol/x kg ?mols from above. Solve for x kg.

Chemistry
I think 1 is right and 2 is wrong. The conjugate acid of S= is HS^-. The conjugate acid of HS^- is H2S.

chem
The general gas equation can be modified to include density as follows: P* molar mass = density x RT

Chemistry
Figure it out. Assume M NaOH is 0.1M. NaOH + HCl ==> NaCl + H2O millimols NaOH = mL x M = 30 x 0.1 = 3 mmols HCl needed =3. M = mmols/mL or mL = mmols/M = 3/0.1 = 30 mL HCl For H2SO4. 2NaOH + H2SO4 --> Na2SO4 + 2H2O mmols NaOH = 3 mmols H2SO4 needed = 3 x (1 mol H2SO4/2 ...

college chemistry
When working with gases like this you can take a short cut and use L as if they were mols. Then just use the coefficients to change anything you have to anything you want. a. 205L NH3 x (5 mols O2/4 mols NH3) = ? L NH3 You try the others.

chemistry
Use PV = nRT and solve for n.

chemistry
PV = nRT

chem
1 mol NH3 (17 grams) is present in a volume of 22.4 L at STP. You have 0.725L

college chem
Dalton's Law of partial pressure says that the total pressure in a system of gases is the sum of the individual pressures. So add 'em up.

college chem
(P1V1/T1) = (P2V2/T2)

college chem
P1V1 = P2V2

chemistry
It takes 96,485 coulombs to plate out 1 equivalent weight of Mg which is 24.3/2 = 12.15g Mg. You want 29 g so it will take 96,485 x 29/12.15 = ? coulombs amperes x seconds = coulombs. You know amperes and coulombs, solve for seconds and convert to minutes.

chemistry
H2SO4 + 2NaOH --> Na2SO4 + 2H2O mols H2SO4 = M x L mols NaOH = 2 x mols H2SO4 (look at the coefficients) M NaOH = mols NaOH/L NaOH Convert L to mL.

science
I think the answer is D.

Chemistry
This is too much like doing all of you homework for you. I'm glad to help but help is the operative word. What do you not understand about this.

Chemistry
Look in your text/notes. If the acid or base is listed in the table of ionization constants it is weak. It it isn't listed it is strong. If it has an ionizable H it is and acid. Look for bases to have OH groups. It it isn't an acid or base it is a salt.

Chemistry URGENT
1 is ok. 2 and 3 are not. 2. M = mols/L not mols/mL. M = 0.5mol/0.5L = 1 M 3. % w/w = (mass solute/100 g solution)*100. Should be [10 g KCl/(90+10)]*100 = [10g KCl/100 g solution]*100 = 10%

Chem
How many mols do you want? That's M x L = mols Then mols = grams/molar mass. You know mols and molar mass, solve for grams.

Chem.
Yes, but it should be 2NaNO3

Chemistry
(H3O^+)(OH^-) = Kw = 1E-14 Substitute and solve.

Cheměstry
millimols Fe(NO3)3 = mL x M = 150 x 3.5 = 525 mmols NO3^- from Fe(NO3)3 = 3*525 = approx 1500 but you need it more accurately. mmols Mg(NO3)2 = 760 x 1.6 = 1216 mmols NO3^- from Mg(NO3)2 = 2*1216 = approx 2400 Total NO3^- = approx 2400 + 1500 = approx 3900 mmols. Total volume ...

Chemistry
See your other post.

Chemistry
yes

Chemistry
6CO2 + 6H2O ==> C6H12O6 + 6O2 mols CO2 = grams/molar mass mols H2O = grams/molar mass You need to redo the math because these are only approx but I obtained approx. About 2 mols CO2; about 3.5 Convert 2 mols CO2 to mols glucose; that's 2 x (1 mol glucose/6 mol CO2) = ab...

Chemistry
Surely you have more information than this. A table you can use? A graph? Something.

Chemistry
dE = q+w. If q = 0, then dE = w If work is done on it by the surroundings then w is + and that makes dE +. Wouldn't that be d?

Chemistry
a. oxidizing agent H2O2 + 2e + 2H^+ ==> 2H2O b. reducing agent H2O2 ==> O2 + 2e + 2H^+ c. disproportionation. One O goes from -1 to zero; the other O goes from -1 to -2. -1 to zero is loss of electrons; -1 to -2 is gain of electrons. Therefore, one O atom is oxidized and...

Homework helpline?
I can't give specific information and know that's what you want; however, I know that most colleges/universities have study sites/special lectures/study sessions/and that kind of thing. Talk to a counselor at the school and ask. Most of the chemistry profs where I taug...

chemistry
I assume that 18.0 is 18mm Hg. 2KClO3 ==> 2KCl + 3O2 Calculate mols O2 from PV = nRT Since the pressure is listed in kPa and the vapor pressure in mm Hg you must convert one of them. I would convert 18.0 mm to kPa. 18.0 mm Hg x (1 atm/760 mm Hg) x (101.325 kPa/1 atm) = 2.39...

Chemistry: Please check my work!I am stumped
I didn't check the oxidation numbers and electron change but the coefficients appear to be ok. To continue, convert 239 g nitro into mols. mol = grams/molar mass Use the coefficients in the balanced equation to convert mols nitro to mols N2, mols H2O, mols CO2, mols NO. Th...

Science chemistry
A word to the wise. mgs I read as milligrams. The cap key is there for a reason. Use it. This is a limiting reagent (LR) problem. You know that because amounts are given for BOTH reactants. Mg + S ==> MgS Convert 20 g Mg to mols. mol g= grams/molar mass. Do the same for 20 ...

Chemistry: please help, I am stumped
See your post above.

chemistry
dGrxn = dG products - dG reactants Then dG = -RTlnK

chemistry
1.00 what? grams? molar? L?

chemistry
delta T = Kb*m Solve for delta T and add to 100 C to find the new boiling point.

chemistry
total mols = mols toluene + mols cholesterol mol fraction toluene = X = mols toluene/total mols. The ptoluene = Xtoluene * Potoluene

chemistry
Balance the equation. N2 + 3H2 ==> 2NH3 Using the coefficients in the balanced equation, convert mols N2 to mols H2. Then convert mols H2 to g. g = mols x molar mass.

Chemistry
I wonder if that is [UO2]^2+? U^4+ ==> UO2^+ Here is how I do it which is not the short way. Oxidation state of U on left is +4. On right is +5. Balance the change in oxidation state by adding electrons to the appropriate side. U^4+ ==> UO2^+ + e Count the charge on the ...

Chemistry
The half reactions are Cu(s) ==> Cu^2+ + 2e (you had 1+ for Cu) O2(g) + 4e ==> 2O^2- (you can see how this differs from what you had). The Cu is the oxidation half; O2 is the reduction half.

Chemistry
I don't think it will but it might be wise to try it on a small scale in the lab before taking a chance on a large scale.

Chemistry
2C2H6 + 7O2 --> 4CO2 + 6H2O dGrxn = (n*dGo products) - (n*dGo reactants)

Simple Chemistry
a. How many mols do you want? That's M x L = 0.150 x 0.250 = ? Then mols = grams/molar mass. You know molar mass and mols, solve for grams CoCl2. Add that many g CoCl2 to a 250 mL volumetric flask, add a little water, swirl until dissolved, make to the mark with distilled ...

Chem
See your other post.

Chemistry
I don't get 5.04 for K but you're on the right track. -4010 = 8.413*298*lnK K = ? I obtained approx 0.2 Then ...........A + B ==> C I.......0.30.0.40...0.0 C.........-x...-x....x E.....0.30-x..0.40-x..x Substitute the E line into Kc expression and solve for x, then ...

Chemistry URGENT/DR BOB
See your other post.

Chemistry URGENT
mass soln = mass solvent + mass solute unless it is a density problem and that is mass = volume x density

Chemistry URGENT
I will make some assumptions for #2. That the 85.5 g solubility you quote later is 85.5g BaCl2/100 g water @ 60 C. If that's so then you will be able to dissolve 85.5g x (150gH2O/100 gH2O) = approx 128 g BaCl2 that can be dissolved at 60 C. The only piece of information ne...

Chemistry URGENT
#1. Take the solubility at 30 and subtract solubility at 20 and divide by 10. That gives you an average solubility per degree C. You have it at 20, then add 3*solubility/degree and you will have it at 23 c. #2. Surely you have a solubility curve or a graph that will tell you t...

Chemistry
You mean name three? There are literally hundreds. Solutions of NaOH, HCl, NaCl, Na2CO3, Na2SO4 etc etc and all of these are STRONG electrolytes (not weak electrolytes).

problem solving
If the picture is square then it must be sqr6 3600 = 60 cm each edge. If the picture frame is 5cm wide, and assuming no overlap between the picture and the frame, the total length of frame + picture is 60 + left side frame + right side frame = 70 cm. The perimeter is the dista...

Chemistry
Andrea, Luke, you want a secnod opinion?

Chemistry
Both are effective as far as neutralization of acids but NaHCO3 is mild enough that humans can tolerate it; NaOH will cause serious issues with the body especially in stronger doses.

chemistry
Aren't these the same problem? You didn't look to see your old post? http://www.jiskha.com/display.cgi?id=1398649923

chemistry
HCl + NaOH ==> NaCl + H2O mols NaOH = M x L =? Using the coefficients in the balanced equation, convert mols NaOH to mols HCl. Then M HCl = mols HCl/L HCl. Solve for M HCl.

Chemistry
Use PV = nRT P in kPa V in L n = grams/molar mass R = 8.314 T = kelvin = 273+C

Chemistry
I would assume a convenient number for the rate of Xe, say something like 5 L/min. Then rate unknown gas, x, is 1.86*5. (rate x/rate Xe) = (MM Xe/MM X) Solve for MM = molar mass X.

Chemistry
Use PV = nRT and solve for n = number of mols. Then n = grams/molar mass. You know n and grams, solve for molar mass. Don't forget P is in atm, V in L and T in kelvin

science/ ms. sue
The oil reduces the friction between the two metal pieces.

Chemistry
q = mass x specific heat x (Tfinal-Tinitial)

Chemistry
Use PV = nRT and solve for n = number of mols in the cylinder. Do the same and solve for n in the smaller balloons. Then determine how many can be filled.

chemistry
A. It isn't a stupid website. B. They aren't stupid questions. C. You see by looking. Use your eyes, not your keyboard.

Chemistry
If it's still in that 48.0 L container the volume will be, guess what, 48.0L. I assume you are asking what volume if the gas were allowed to expand freely but the question isn't clear on that. (V1/T1) = (V2/T2) Remember T must be in kelvin.

chem
1 mol C5H11OH contains 12 mol H atoms. Each mol contains 6.02E23 individual atoms so 12 mols will contain ....... atoms.

chemistry
Hi back. If you have a question post it at the top of the page.

chemistry
a. joules H2O absorbed = mass H2O x spcific heat H2O x (Tfinal-Tinitial) b. joules absorbed by H2O = heat gained by metal d. q metal = mass metal x specific heat metal x (Tfinal-Tinitial) c. q = mass metal x delta T

Chemistry
I worked this for you a few days ago. Did you not see it? not understand it? Show your work that you've done and we can go from there. The empirical formula is C8H20Pb

Chemistry
K = (NH3)^2/(N2)(H2)^3 You know N2 and H2, substitute with Kc and find NH3 in M = mols/L. Then to find mols in 10L, that is mols = M x L Then mol = grams/molar mass. You know molar mass and mols, solve for grams.

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