Saturday
June 25, 2016

Posts by DrBob222

Total # Posts: 52,572

Chemistry
Bob P set up the chemistry part. What you are having trouble with is the math. No, you don't put zero for q. You don't need to solve for q. The heat lost by one material + the heat gained by the other material must = to zero and that's the way Bob P set up the ...
January 8, 2016

Chemistry
Jennifer, Bob P set it up for you. All you need to do is to solve for Tf (and look up specific heats).
January 8, 2016

chemistry
Pick a number. Any number you choose will be correct because you didn't specify how much (NH3)3PO4 you have. I assume you means for 1 molecule. There are 3N, 9H, 1P and 4O for a total of 17 per molecule.
January 8, 2016

Chemistry
A limiting reagent problem. 2AgNO3 + Cu ==> Cu(NO3)2 + 2Ag mols Cu = grams/atomic mass = ? mols AgNO3 = grams/molar mass = ? Using the coefficients in the balanced equation: Convert mols Cu to mols Ag Convert mols AgNO3 to mols Ag The smaller number wins; i.e., if AgNO3 is ...
January 8, 2016

Chemistry-Dr.Bob, I need you!!!!
I don't agree with either answer. q from H2O = 200*4.184(5.98) = ? q from calorimeter = 100*5.98 Total q for 0.1 mols is the sum of the two above. Then q/mol = sum/0.1 = ? I get about 55 kJ/mol
January 8, 2016

chemistry
Pb(NO3)2 + 2HCl ==> PbCl2 + 2HNO3 Assuming you meant 0.1M and not 0.1m, millimols Pb(NO3)2 = mL x M = ? millimols HCl = mL x M = ? Determine the limiting reagent and you should see that to be HCl so that means you heave 10 millimols Pb(NO3)2 excess. Convert to mols, then ...
January 8, 2016

Chemistry
What do you mean by "results are attached"? Are those the answers in the key or your answers. Check you typo. H2SO3- should be HSO3^-. ..........NaHSO3 ==> Na^+ + HSO3^- I..........0.05.......0......0 C........-0.05.......0.05....0.05 E..........0.........0.05.......
January 7, 2016

CHM 105
mols CH3COOH = mols NaOH = M x L = ? grams CH3COOH = mols CH3COOH x molar mass CH3COOH % w/w = (mass CH3COOH/mass sample)*100 = ?
January 6, 2016

Chemistry
BeCl2 is a polar compound and is soluble in water. There is no such compound as H-C=C-H. If you mean ethylene (H2-C=C-H2) it is hardly soluble. If you mean acetylene (HCtripleCH) it is slightly soluble but neither are polar.
January 6, 2016

Chemistry
If you have trouble with a problem like this with "reasoning it out", I suggest you assign numbers. Perhaps something like this. Say A = 100 g and is twice B which makes B 50 g. Check that. Specific heat A = 1. B is 2x A so B is 2. Check that. Initial T A = 100; ...
January 6, 2016

Chemistry
You would have done better to post the problem. It's harder to explain in words and not numbers. mols MgCl2 = grams MgCl2/molar mass MgCl2. Then there is 1 mol Mg atoms in 1 mol MgCl2. That is, the number of mols Mg atoms will be the same as the mols MgCl2.
January 6, 2016

Chemistry
CCl4 is the highEST boiling point which means CCl4 should be at the top. CH4 has the lowest b.p. so it should be at the bottom. CH4.....(CHCl3/CH3Cl).....CCl4. So place CHCl3 and CH3Cl in the proper order to make it increasing b.p. from CH4 to CCl4.
January 6, 2016

Chemistry
Try this. The higher boiling point often is the compound with the higher molar mass.
January 6, 2016

Chemistry
There are 6.02E23 atoms in 1 mol. mols Cl2 = 1.2E24/6.02E23 = ? grams = mols x molar mass = ?
January 6, 2016

Chemistry:normal notation plz help
Is that the last electron, the single electron, the outside electron. I assume it's the single electron. Go through each one this way. 19K = 1s2 2s2 2p6 3s2 3p6 4s1 For the 4s1 electron, n = 4 so it can't be K. Also note that s electrons have l = 0; another reason it ...
January 6, 2016

Chemistry
Cu(OH)2 ==> Cu^2+ + 2OH^- i. Adding HCl. The H^+ reacts with the OH^- to produce H2O (H^+ + OH^- => H2O), the OH^- is reduced and that shifts the equilibrium to the right (to increase the OH) which means the solubility is increased. ii. Cu(NO3)2 ==> Cu^2+ + 2NO3^2- ...
January 3, 2016

Chemistry
1. First, balance the Fe/MnO4 equation but correct it first. The part that matters is 5Fe^2+ + MnO4^- ==> 5Fe^3+ + Mn^2+. a. Millimols MnO4 used = M x mL = 12.08 x 0.200 = approx 2.4. Using the coefficients in the balanced equation, convert mmols MnO4 to mmols Fe. That'...
January 3, 2016

chemistry
You need to explain what the direct and indirect methods are.
January 3, 2016

chemistry
Adding a common ion to an insoluble salt decreases the solubility of the salt. Cl from the HCl is the common ion (to Cl in AgCl).
January 3, 2016

chemistry
lead nitrate is soluble. The white ppt formed with NH3 is Pb(OH)2. NH3 + H2O ==> NH4^+ + OH^- Pb^2+ + 2OH^- ==> Pb(OH)2
January 3, 2016

Chemistry
Of course there are but doesn't it all depend upon what you want it to do? For example, it is very good at measuring the masses of groups of atoms but not very good at measuring the boiling point or freezing point of a material.
December 29, 2015

chemistry
How much of the stock solution do you need to prepare? Then mols you need = M x L = ? Then mol = grams/molar mass. You know molar mass of the material and mols, solve for grams.
December 29, 2015

Chemistry
I assume methyl benzene will dissolve sulfur. Dissolve, filter and the iron filings stay in the filter paper. Let the filtrate sit and the solvent evaporates leaving the S behind.
December 29, 2015

chemistry
Your question isn't clear to me. The amount of water necessary to dissolve 10g of the compound is 100 x (10/6.8) = ? but that isn't what is needed to crystallize.
December 29, 2015

chemistry
How much do you need to prepare? mols needed = M x L = ? Then mols = grams/molar mass. You know mols and molar mass, solve for grams.
December 29, 2015

chemistry
mols NaOH = M x L = ? Using the coefficients in the balanced equation convert mols NaOH to mols H2SO4. Then M H2SO4 = mols H2SO4/L H2SO4 = ?
December 27, 2015

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

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