Sunday
May 29, 2016

Posts by DrBob222

Total # Posts: 52,447

Chemistry
"equal volumes of these low" WHAT? If the acids are strong acids we can take 100 mL of each. For pH = 10 we have 100 x 1E-10 = 1E-8 millimols. Add 100 mL pH = 12 and we have 100 x 1E-10 millimols. Add 1E-8 mmols and 1E-10 mmols = 1.01E-8 millimols and that is in 200 ...
December 27, 2015

problem's on gay lussac's equation
This looks like a pure de ol' stoichiometry problem to me. 2C2H2 + 5O2 ==> 4CO2 + 2H2O By using volumes directly as if they were mols, a short cut can be used which cuts out a couple of steps. I suppose we assume that C2H2 and O2 are there is proportional amounts and ...
December 26, 2015

Chemistry
a. Take a 100 g sample which gives you 61.7g Cl and 38.3 F. Convert to mols. 61.7/19 = about 3.25 38.3/25.5 = about 1.1 Determine the empirical formula. The easy way to do this is to divide the smaller number by itself and divide the other number by the same small number. 3.25...
December 26, 2015

chemistry
You mean sulfuric acid (US) or sulphuric acid (UK). And you need to know what the beginning concentration of H2SO4 is. Also you need to know how much stock solution you need. Let's assume you want 1000 mL of the 0.04M solution. The stuff in the pure bottle comes out to be ...
December 24, 2015

Chemistry
I do these the long way. 1. Balance the equation. 2. Convert g NH3 to mols. mols = grams/molar mass = ? 3. Convert g O2 to mols. 4. Using the coefficients in the balanced equation, convert mols NH3 5o mols NO. 5. Do the same and convert mols O2 to mols NO. 6. It is quite ...
December 21, 2015

Chemistry
What's an ff solution? 25% w/v NaCl. How much do you want? Let's say you want 100 mL. Dissolve 15 g NaCl in some water and make to a final volume of 100 mL.
December 21, 2015

chemistry
...........PbSO4 ==> Pb^2+ + SO4^2- I.........solid.......0........0 C.........solid.......x........x E.........solid.......x........x Ksp = 1.6E-6 = (Pb^2+)(SO4^2-) Substitute the E line into the Ksp expression and solve for x = (PbSO4) in mols/L. Convert to grams Pb/L ...
December 21, 2015

Chemistry
https://en.wikipedia.org/wiki/Ionic_strength
December 21, 2015

Chemistry
http://dwb.unl.edu/Teacher/NSF/C06/C06Links/www.uis.edu/7Etrammell/organic/introduction/polarity.htm
December 20, 2015

Chemistry
Take a 100 g sample which gives you 39.9 g C 6.9 g H 53.2 g O Convert to mols. mols C = 39.9/12 = approx 3.3 mols H = 6.9/1 = approx 6.9 mols O = 53.2/16 = 3.3 Now find the ratio of the three to each other with the lowest number being 1. The easy way to do this is to divide ...
December 19, 2015

Chemistry
See your other post. Show your work if you have further questions.
December 19, 2015

Chemistry
(NO2) at equilibrium = 0.250 mols/5 L = 0.05 Kc = (NO2)^2/(N2O4) = 0.133 (NO2)2 = x^2 (N2O4 = 0.05 Solve for x
December 17, 2015

CHEMISTRY
If you're looking for dHrxn it is dHrxn = (n*dHfo products) - (n*dHfo reactants) = ?
December 17, 2015

Chemistry
How many mols do you need? That's mols = M x L = ? Then mols = g/molar mass. you know molar mass and mols, solve for grams.
December 13, 2015

CHEMISTRY
% w/w = (grams solute/g solution)*100 = ?. M = 8.4 mols/L. mols = grams/molar mass so g = mols x molar mass = 8.4 x 62 = approx 521 g in the solution so g solute = approx 521. The solution has a mass of 1.3g x 1000 = approx 1300 grams. Now % = approx 521/1300)*100 = ?
December 13, 2015

Chemistry
HI + KOH ==>KI + H2O mols HI = M x L = ? mols KOH = M x L = ? One of them will be the limiting reagent; i.e., the one with the smaller mols. That will give you the mols of H2O produced. You know q is 1.52 kJ and that is dHrxn. USUALLY you want kJ/mol. Then dHrxn/mols H2O ...
December 11, 2015

Chemistry
What's wrong with using the Arrhenius equation?
December 11, 2015

Chemistry
Wouldn't you think CH3CH2CH3 would be the highest since it has only London forces. CH3OCH3 would have the next (that's acetone) and you know that is volatile. Then ethyl alcohol has H bonding so should be the next one up. I believe I have ranked them in reverse order (...
December 11, 2015

Chemistry
Apparently you don't know where the caps key is. You should find it because 2.61 m and 2.61M don't meant the same thing. I will assume that is 2.61 M and 0.855 M. 2KOH + H2SO4 ==> K2SO4 + 2H2O mols KOH = M x L = ? mols H2SO4 = 1/2 mols KOH. Look at the coefficients ...
December 11, 2015

Chemistry
See your other post.
December 11, 2015

Chemistry
Do you have an equation for the reaction? I assume the reaction is 3CCl4 + 2SbF3 ==> 3CCl2F2 + 2SbCl3 mols CCl4 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols CCl4 to mols CCl2F2. Then g CCl2F2 = mols CCl2F2 x molar mass CCl2F2 = ?
December 11, 2015

Chemistery
N2O5 + H2O ==> 2HNO3 If you want XHNO3 = 0.5 and mols H2O to be 1.0, then mols HNO3 must be 1.0. XHNO2 = 1.0 mol HNO3/2 mol total = 0.5 To obtain 1 mol HNO3 will require only 1/2 mol N2O5.
December 11, 2015

Chemistry 12
You're right. You started out wrong. q = mols H2O x heat condensation mols H2O = grams/molar mass = 3/18 = ? q = (3/18) x 42,000 J = ? J released.
December 10, 2015

Chemistry
4Fe + 3O2> 2Fe2O3 + heat and light
December 10, 2015

Chemistry
yes. There is more motion at a higher T; therefore, delta S is + from going to a higher T.
December 10, 2015

Chemistry
Yes, Fe in Fe2O3 is going from +6 total to +4 total in 2FeSO4. Fe on the left is going to +2 on the right. The easiest way to do this is to write it in half equations; i.e., Fe2O3 ==> 2Fe^2+ and Fe ==> Fe^2+ and add the spectator ions later. S
December 8, 2015

applied chemistry
We can't draw on this forum; however, you can google lewis dot structure CO2 etc and find them on the web.
December 8, 2015

Chemistry
Scroll down in the link below starting with "ionic compounds have high melting points...." http://chemistry.about.com/od/moleculescompounds/a/Ionic-Compound-Properties.htm
December 8, 2015

chem
Yes, adding HCl will do it because the H^+ combines with F to make HF and that is a weak acid. Adding a salt that will ppt with F will work also. BaF2, MgF2, PbF2 are insoluble so adding MgCl2 should work.
December 8, 2015

Chemistry
I would consider Cu3(PO4)2 to be polar. It is an ionic compound (the phosphate part is covalent)
December 7, 2015

Chemistry
mols of the gas = 16.3/22.4 = ? Then mols = g/molar mass. You know mols and grams, solve for molar mass.
December 7, 2015

chemistry
Convert names to chemical formulas. KF(aq) + CuSO4(aq) ==> copper(II) fluoride + potassium sulfate. KF(aq) + CuSO4(aq) ==> CuF2 + K2SO4 Then by trial and error balance.(remember to balance you may change ONLY the coefficients--you may NOT change the subscripts) The easy ...
December 7, 2015

Chemistry
Two stoichiometry problems but they can be done at the same time. mols Zn = grams/atomic mass = ? mols HCl = M x L = ? Using the coefficients in the balanced equation, a. convert mols Zn to mols H2. b. convert mols HCl to mols H2. Compare a and b.
December 7, 2015

Chemistry-Dr.Bob
I would not rank them that way.
December 7, 2015

chemistry
dHrxn is -114.14 kJ/mol for what reaction?
December 7, 2015

Chemistry
Yes for both
December 6, 2015

Chemistry
E = R(1/16 - 1/25) and that is a positive number. You probably got a negative number by making it 1/25 - 1/16.
December 6, 2015

chemistry
Interesting but I don't see a question.
December 5, 2015

Chemistry
Is that low density polyethylene, high density polyethylene, or something between the two? I think there is one between now. You really need to know the molar mass of the molecule to which the problem refers.
December 5, 2015

chemistry
Law of Conservation of mass. reactants = 168+72 = 240 g products = 232 + 8 = 240 g
December 5, 2015

chemistry
What procedure are you using? What blank for what? You don't provide enough information to even know what you're doing.
December 4, 2015

Chemisty
0.15 x 520 = 0.25 x mL
December 4, 2015

Chemistry
CaCO3 + 2 HCl ==> CaCl2 + CO2 + H2O Ain't no way.
December 4, 2015

Chemistry
Use (P1V1/T1) = (P2V2/T2) Use the same units for P1 and P2. Use celsius for T1 and T2. Use the same units for volume Then calculate T2 and convert to F.
December 4, 2015

chemistry 101
Kp = Kc(RT)^delta n. delta n = nproducts-nreactants
December 4, 2015

chemistry
........Fe(OH)3 ==> Fe^3+ + 3OH^- I........solid.......0.......0 C........solid.......x.......3x E........solid.......x.......3x Ksp = (Fe^3+)(OH^-)^3 You know Ksp, OH can be calculated from pH, solve for x which is the solubility.
December 4, 2015

Chemistry
Here is a site that shows how to do all of this. If you still have trouble, be specific and we can help you through the next step. http://www.chemteam.info/Redox/Redox.html
December 4, 2015

Chemistry
X(OH)2 + 2HCl =-> XCl2 + 2H2O mols HCl = M x L = ? Using the coefficients in the balanced equation, convert mols HCl to mols X(OH)2 Then mols X(OH)2 = grams/molar mass. You know mols and grams, solve for molar mass.
December 2, 2015

Chemistry
Because mols is not equal to d*v. mass (grams) HBr soluton = density x volume = approx 67 g as the mass of that 38.5 mL sample. How much HBr is in that 38.5 mL sample? That's mols KOH = M x L = ? Using the coefficients in the balanced equation, convert mols KOH to mols HBr...
December 2, 2015

Chemistry
delta T = Kf*molality mols benzene = grams/molar mass = ? molality = mols benzene/kg cyclohexane You know m and delta T, solve for Kf.
December 2, 2015

Chemistry
The equation isn't balanced. Did you use bond energies or dHo values.
December 1, 2015

chemistry
q = mass x specific heat x (Tfinal-Tinitial)
December 1, 2015

Chemistry
I don't see a question here. Even if I did I have no idea what UCM or mT-365.25 means.
December 1, 2015

Chemsitry
NiCl2 + 2NaOH ==> Ni(OH)2 + 2NaCl mols NiCl2 = M x L = ? Using the coefficients in the balanced equation, convert mols NiCl2 to mols NaOH. Then M NaOH = mols NaOH/L NaOH. You know M and molsk solve for L NaOH and convert to mL.
December 1, 2015

Chemistry
You must be missing something. I obtained 1E-3 for H^+. millimols NaOH = 30 x 0.02 = 0.6 mmols HCl = 70 x 0.01 = 0.7 mmols HCl in excess = 0.7-0.6 = 0.1 M HCl = mmols/mL = 0.1/100 = 1E-3 So OH must be 1E-14/1E-3 = 1E-11.
December 1, 2015

chemistry
q = mass H2O x specific heat H2O x (Tfinal-Tinitial). 4 q = 4.0g x 4.184 J/g*C x (8-Tinitial). Can't do it without Tinitial. That 8.0 C may be to raise the T BT 8.0 C. in which case Tfinal-Tinitial = 8.0
December 1, 2015

Chemistry
K, Rb, Fr all readily form cations that will form ionic bonds with group 7A elements (Cl, F, Br, I). So S must be the answer.
December 1, 2015

Chemistry
You need to read up on these bonds. Look up the definition of an ionic bond.
December 1, 2015

Chemistry
I believe there is an error in the problem. It appears to me that the mass of the total is less than the mass of the solute.
December 1, 2015

chemistry
How can you dilute 0.1 M solution and make it more concentrated? Great trick if you can do it.
December 1, 2015

HELP!! PLEASE CHEM LAB
It really doesn't matter as long as you use reasonable amounts. The trick is that amount stuff in the flask must be know EXACTLY (you can't measure it with a graduated cylinder). For the stuff in the buret, I make a habit of filling the buret to the top every time. At ...
December 1, 2015

Chemistry
#1. mols HCl = M x L = ? mols NaOH = M x L = ? Subtract to find excess of which is present. If excess HCl, that is the mols HCl. If excess NaOH, that is the mols NaOH. Then M (of the excess) = mols/total L. That gives either H3O^+ or OH-. The other one is found from (H3O^+)(OH...
December 1, 2015

Chemistry Dr BOB
Congratulations on your graduations and good luck with your future.
November 29, 2015

Chemistry
Pb(NO3)2 + SrI2 => PbI2 + Sr(NO3)2 mols Pb(NO3)2 = M x L = ? mols SrI2 = M x L = ? Using the coefficients in the balanced equation, find the mols PbI2 formed from each starting regent; the smaller amount formed will be the correct amount. Then grams SrI2 = mols SrI2 x molar...
November 29, 2015

chemistry Dr. BOB
The only thing I might suggest is to go back and leave all of those numbers from above(start with 142798 J) in the calculator. If I do that I come up with 1.86E-25 but I wouldn't think a data base would count that wrong.
November 29, 2015

Chemistry
............BaCO3 ==> Ba^2+ + CO3^2-I I............solid.....0.......0 C............solid.....x.......x E............solid.....x.......x Ksp =(Na^2+)(CO3^2-) .......Na2CO3 --> 2Na^+ + CO3^2- I.......0.05M......0.......0 C......-0.05......0.1.....0.05 E.........0.......0....
November 29, 2015

Chemistry
I agree
November 29, 2015

Chemistry Dr Bob
I see.
November 29, 2015

Chemistry Dr Bob
Could it be that you have reported 4 significant figures and you are allowed only 3.
November 29, 2015

Chemistry
Yes but you must account for HCl separately. Of the acids listed with a pKa value, HClO2 is the strongest. Then HCl has pH of 4 so A is correct.
November 29, 2015

Chemistry
You want how many mols? That's mols = M x L = ? Then mols NH4Cl = grams NH4Cl/molar mass NH4Cl. You know molar mass and mols, solve for grams.
November 29, 2015

Chemistry Dr BOB
See my response above.
November 29, 2015

chemistry
mlstock x Mstock = mLwaned x Mwanted
November 28, 2015

Chemistry
Ba(OH)2 + 2HCl ==> BaCl2 + 2H2O You don't have enough info to answer. To know the M of the HCl you need the M of the Ba(OH)2.
November 28, 2015

Chemistry
H2SO4 + 2NaOH ==> Na2SO4 + 2H2O mols NaOH = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols NaOH to mols H2SO4. Now convert mols H2SO4 to volume. M H2SO4 = mols H2SO4/L H2SO4. You know mols and M, solve for L.
November 28, 2015

chemistry
q = mass Cu x specific heat Cu x (Tfinal-Tinitial) Substitute and solve for Tfinal. b. Same for H2O but specific heat is not the same.
November 27, 2015

Chemistry
Why are you having trouble with this. You can look up the answers is many places, including your text/notes. Sc is #21. 1s2 2s2 2p6 3s2 3p6 3d1 4s2
November 27, 2015

Chemistry
mL1 x M1 = mL2 x M2 mL1 x 10.5 = 255 x 0.650
November 27, 2015

Chemistry
0.759 mols ben x (17 C atoms/1 mol ben) = ?
November 27, 2015

Chemistry
2BaO2 ==> 2BaO + O2 mols BaO2 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols BaO2 to mols O2. Then use PV = nRT and the conditions listed and solve for L O2.
November 27, 2015

Chemistry
How many mols NaOH do you need? That's M x L = ? mols NaOH. Then mols NaOH = grams NaOH/molar mass NaOH. You know mols and molar mass, solvle for grams NaOH.
November 27, 2015

Chemistry
mols P4 = grams/molar mass = ? mols Cl2 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols P4 to mols PCl3. Do the same and convert mols Cl2 to mols PCl3. It is likely that the two values for mols PCl3 sill not agree which means one of them is...
November 26, 2015

Chemistry
It would be helpful if you didn't change screen names.
November 26, 2015

Chemistry
(V1/T1) = (V2/T2)
November 26, 2015

Chemistry
Try doing this to get you started. HAc + NaOH ==> NaAc + H2O mols HAc initially = 0.05 x 0.4 = 0.02 mols NaOH added = 0.055 x 1.10 = 0.065 Appears to me that the NaOH will neutralize all of the acetic acid and you no longer have a buffer solution.
November 26, 2015

Chemistry
You answer this the same as the previous question; however, I don't get the options. It takes TWO of them to make a buffer, not one of them (although HCO3^- alone gives a pH of about 8.3
November 26, 2015

Chemistry
You write out the ionization expression and see what you have. H2CO3 ==> H^+ + HCO3^- k1 = (H^+)(HCO3^-)/(H2CO3) = ? Since you want pH of 6, use the closest pKa value which is 6.35. That dictates you use HCO3 and H2CO3.
November 26, 2015

Chemistry
I don't understand why you have a problem? The question tells you the buffer ratio is (A^-)/(HA). It tells you (A^-) is 0.30 mol (0.3mol/0.1L = ? M) and it tells you (HA) is 0.6 mol (0.6mol/0.1L = ?). So 3/6 = ?
November 26, 2015

Chemistry
mols NaOH = grams/molar mass = ? Then M = mols/L (OH^-) = M NaOH pOH = -log(OH^-) Then pH + pOH = pKw = 14
November 26, 2015

Chemistry
eqn 1 Br2 + Br <-> Br3 eqn 2 Br3 <-> Br2 + Br Equation 2 is the reverse of equation 1. If k1 is 18, then k2 is 1/18.
November 26, 2015

Chemistry - Energy Phase Changes
The heat of vaporization is 40.66 kJ/mol for water. I believe your 6.01 must be heat fusion for H2O.
November 25, 2015

chemistry
2Bi + 3Cl2 ==> 2BiCl3 mols Cl2 = 575/22,400 = ? Using the coefficients in the balanced equation, convert mols Cl2 to mols Bi. Now convert mols Bi to grams. g Bi = mols Bi x atomic mass Bi.
November 25, 2015

Chem
mols CH4 = grams CH4/molar mass CH4 = ? Using the coefficients in the balanced equation, covert mols CH4 to mols CO2. Now convert mols CO2 to grams (I suppose you want it in grams) by grams = mols CO2 x molar mass CO2 = ? This is the theoretical yield in grams.
November 25, 2015

Chemistry
2NaN3 -> 2Na + 3N2. mols NaN3 = grams/molar mass Using the coefficients in the balanced equation, convert mols NaN3 to mols N2 Finally, convert mols N2 to grams. g N2 = mols N2 x molar mass N2.
November 25, 2015

chemistry
Is this a liquid? What's the density?
November 25, 2015

Chemistry
NH4CN NH4ClO3 (NH4)2SO4 etc.
November 25, 2015

Chemistry
You have it. Congrats!
November 25, 2015

Chemistry
Yes, that's what you do.
November 25, 2015

chemistry
Add water, Na2CO3 dissolves, filter, PbCO3 stays in the paper and dissolved Na2CO3 goes through as the solution. Dry the PbCO3 and you have the dry solid.
November 25, 2015

Chemistry
1. Use the Henderson-Hasselbalch equation. KaKb = Kw and you get Ka from that and pKa follows. 2. Ditto for 2. 3. Ditto for 3.
November 25, 2015

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