Wednesday
July 30, 2014

Posts by DrBob222


Total # Posts: 43,219

Chemistry
Take 100 g sample for 58.5g C 4.1g H 11.4 g N 26.0 g O Convert to mols. I'll use approximations. 58.5/12 = 4.875 4.1/1 = 4.1 11.4/14 = 0.814 26/16 = 1.625 Now find the ratio in small whole numbers with the smallest number being 1.00. The easy way to do that is to divide al...

General Chem 2
2Al^3+ + 6I^- ==> 2Al(s) + 3I2(s) dGo = -nFEo n = 6

Chemistry - Science (Dr. Bob222)
x = 2 y = 1 How did I do that? V on the left has a oxidation state of +5 and on the right it is +4. S on the left is +4 and on the right is +6. V has changed by 1e S has changed by 2e So V couple must be multiplied by 2 and S couple by 1 to make each lose/gain 2 electrons.

Chemistry
mols = grams/molar mass

Chemistry - Science (Dr. Bob222)
Thanks. I just didn't think the 50% could be right. The concept behind disproportionation is that an element in an "intermediate" oxidation state (in this case Cu^+ is halfway between Cu below it and Cu^2+ above it) can "react with itself" if the potent...

chemistry - Science
I would do this. Calculate g Zn that goes into solution and g Cu that are deposited from solution. Coulombs = amperes x seconds = ?. 95,485 coulombs will use (65.4/2)g Zn and deposit (63.5/2)g Cu. Calculate g Zn used, convert to mols, and add to the 0.1 mol already there. Calc...

chemistry - Science
See your other post.

Chem Check Please!!!
2 is ok 3 is ok I don't agree with 4.

Chem Check Please!!!
1. Cris, I don't agree with C as an answer. Here is the way you keep these straight. Just remember the definition of oxidation and reduction. Oxidation is the loss of electrons. Reduction is the gain of electrons. The substance oxidized is the reducing agent. The substance...

chemistry
By the way, it's past my bed time but I'll be around tomorrow.

chemistry
87 is right. 37 and 50 are right Check your numbers for PEN. You can't possibly get 74 something. 50 x 1+ is about 50. 37 x 1+ = about 37 and add in a pinch for electron mass and you have AT LEAST 50+37+pinch = 87. And it can't be less than 86.909187 because it LOSES m...

chemistry
I can't follow what you've done. I have mass p + mass N + mass e = 87.723173 and that - 86.909187 = 0.813986 amu and that converted to kg = 1.3516563E-27 kg. Let me know if we are on the same page to this point and please show your work for as far as you are and we can...

chemistry
How would you answer these and why?

Chemistry
d2sp3 but obviously those atoms without d orbitals are not eligible for this.

chemistry
You can deposit 196.97/3 = approx 66 g Au with 96,485 coulombs of electricity. So how much will be required to deposit 19.7g 96,485 x (19.7/66) = approx 29,000 coulombs. coulombs = amperes x seconds. Substitute coulombs and seconds and solve for amperes. Note those numbers I u...

Chemistry
TiO2 + 2C ==> 2CO + Ti We don't need to make any corrections for molar mass and kg if we keep everything in kg. kg mols C = 14.0/12 = approx 1.17 kg mols TiO2 = 44.0/79.88 = approx 0.5 Using the coefficients in the balanced equation, convert kg mols of each to kg mols o...

Science
I'm not positive how to answer this. Certainly b and d are not driven by humans and can be eliminated. Global warming, c, is attributed to human impact so that's a definite yes. A is the one I'm unsure about. The greenhouse effect is the name we have given to gases...

CHEM 101
We can't draw pictures, structures, diagrams, etc on this forum.

chemistry
CaCO3 ==> CaO + CO2 mols CaCO3 = grams/molar mass. Using the coefficients in the balanced equation, convert mols CaCO3 to mols CO2. Now convert mols CO2 to grams. g = molls x molar mass.

chemistry chem science
time in seconds is 35 min x (60 seconds/min) = ? amperes = 160 mA = 0.160 A. Calculate Q = # coulombs = amperes x seconds. Then you know that 96,485 coulombs will deposit 112.4/2 grams Cd (that's molar mass Cd/valence). (112.4/2)g Cd x ?coulombs from above/96,485 = ?

chemistry
Instead of someone just giving you the answers, I would like to know what it is you don't understand.

Chemistry 1
The highest freezing point will be the one with the smallest delta T and that will occur for the material with the smallest number of particles; i.e., highest van't Hoff factor x molality or i*m A. 0.1M KCl im = 2*0.1 B. 0.05M NaCl im = 2*0.05 C. 1M AlPO4 im = 1*3 D. 0.1...

chemistry
(P1V1/T1) = (P2V2/T2) You don't need to use moles of gas if you use this formula. Notice that you have no initial volume and no actual final volume (just twice the initial). I would pick a convenient number (any number) for V1 and multiply that by 2 for V2.

Chemistry
2NaOH + H2SO4 ==> Na2SO4 + 2H2O mols H2SO4 = M x L = ? Using the coefficients in the balanced e4quatioin, convert mols H2SO4 to mols NaOH. Now M NaOH = mols NaOH/L NaOH. You know mols and M, solve for L NaOH and conert to mL if you wish.

Chemistry
mols C2H5OH = grams/molar mass m = mols/kg solvent

Chemistry
C2H8 + 5O2 ==> 2CO2 + 4H2O When working with gases we can use a shortcut in which we use L as if L = mols. Then we make the conversion form mols propane to mols O2 as usual. ?L O2 = 3.8 L C3H8 x (5 mols O2/1 mol C3H8) = 3.8 x 5 = ?

Chemistry
delta T = i*Kf*m 2 = 1*Kf*0.5 Solve for Kf.

chemistry
You know we can't draw pictures on this forum but the half reactions are MnO4^- + 3e + 2H2O ==>MnO2 + 4OH^- NO + 4OH^- ==> NO3^- + 3e + 2H2O I have written the MnO4^- as a reduction an the NO as an oxidation so as to keep the electrons on opposite sides. I think you ...

questions
When the car burns fuel (either gasoline or diesel) it combines with oxygen and under the best of conditions would produce CO2 and H2O. However, with the heat of the engine (due to the combustion that is necessary to power the car) some carbon monoxide, NOx which is NO, NO2, a...

Chemistry- is this correct?
To two significant figures, yes. If that 0.30 was really 0.300 (and you just omitted a zero) then you could have 3 s.f. and that would be 0.125M. As posted, however, 0.13 is right.

To JJ
Your problem is somehow intertwined with another and I can't post an answer there. Solve the problem by applying the dilution formula of mL1 x M1 = mL2 x M2

chemistry
Don't you have a graph or a table that gives you solubility at various temperatures?

Chemistry
You want 5L of O2. And if you could get 100% yield from the reaction you could calculate how much NaNO3 would be required to produce 5L O2. However, the problem says the reaction is only 78.4% yield so we must start with more NaNO2 so that at the end with just 78.4% yield we w...

Chemistry
2NaNO3 ==> 2NaNO2 + O2 5L O2 at 78.4% yield would need to be 0.784 = 5/x and x = about 6.4 6.4L at STP = ? mols mol = 6.4L/22.4L = approx 0.29 Convert mols O2 to mols NaNO3. That's 0.29mol O2 x 2 mol NaNO2/1 mol O2) = approx 0.57 mol NaNO3. Then g NaNO3 = mols x molar m...

chemistry
Use PV = nRT. T must be in kelvin. I don't know what 0.01m is. If you mean for that to be 0.01 mols, that will be n

Chemistry
M = mols/L. 0.142M NaI = 0.220 mols NaI/ L solution. Solve for L.

Chemistry
mL1 x M1 = mL2 x M2

Chemistry
Let's call this BNH2 to save some typing. ..........BNH2 + HOH --> BNH3^+ + OH^- I........0.223.............0.......0 C.........-x...............x.......x E.......0.223-x............x.......x But you know x = 9.7E-6. Evaluate 0.223-x and substitute into the Kb expressio...

chemistry
Please clarify the question. What is 5.75gmolecules?

chemistry
.........NH4HS(s) ==> NH3(g) + H2S(g) I........solid.........0........0 C........solid.........x........x E........solid.........x........x Kc = (NH3)(H2S) 1.8E-4 = x^2 x = 0.013M. Does this exhaust the 5.00 g NH4HS? 0.13 mols/L x 3L = 0.040 mols H2S and 0.040 mols NH3. How...

typo--Chemistry
Specific heat is 4.184 and not 4.194. I typed it right in the equation but wrong above that.

Chemistry
It would have helped if you had re-posted the question; however, I found it and here is the response I made. 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 gained...

Science
I think this is nonsense but the answer probably is B. That's the only one of the four that doesn't have the same thing on the right that's on the left.

Chemistry
I expect the difference in #1 is that I didn't read anything on the calculator but kept everything in until the final answer.

Chemistry
I agree with #2. For #1 I obtained 1.1E-11

Chemistry
If you have used the screen name Sha in the last day or so I worked this problem earlier. I may be able to find it if you didn't.

Chemistry
You made a typo in th equation. It should be CH3NH2 + HOH ==> CH3NH3^+ + OH^- I obtained 2.9E-2 for OH^- but we may not have used the same Kb. I used 5E-4.

Chemistry
NH4^+ is the only one hydrolyzed. You know NO3^-, Cl^- and K^+ are not hydrolyzed BECAUSE those hydrolysis products would be STRONG acid/bases. For example, Cl^- + HOH ==> HCl + OH- or K^+ + HOH ==> KOH + H^+ and that doesn't happen. Why NH4^+? BECAUSE it forms a WEA...

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

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