Tuesday
May 3, 2016

Posts by DrBob222

Total # Posts: 52,216

Chemistry
486 nm is in the visible part of the spectrum as are all of the lines in the Balmer series. In the Balmer series the end N = 2. w = wavelength; R is the Rydberg constant which is 1.09737E7 1/w = R(1/4 - 1/x^2) Solve for x.
October 21, 2015

Chemistry
Nope. The HH equation is for buffers. You have an acid listed but no base to use. This is just the ionization of an acid. CH3COONa = HAc .........HAc ==> H^+ + Ac^- I........0.2.....0......0 C.......-x.......x......x E.......0.2-x....x......x Substitute the E line into the ...
October 21, 2015

organic chemistry
When do these I ignore the water necessary to dissolve the impurity; often the minimum amount of H2O needed is just the amount to dissolve the major element and the impurity is dissolved in that same amount of water. 100 mL x (20g/6.67) = about 300 mL a 100 C. How much will ...
October 21, 2015

chemistry
Answered below.
October 20, 2015

Chemistry
4.32 pounds/gallon = 0.5176 kg/L The correct answer is 1.66 kg and A MIGHT look like the right answer but the exponent is not right. Correct answer is F.
October 20, 2015

Chemistry
100 mi = 160.932 km (96.15 cal/km) x 160.932 km x (1 bar/250.1 cal) = ? and round to whole number.
October 20, 2015

chemistry
The word equation tells you. C4H10(g) + O2(g) ==> H2O(g) + CO2(g)
October 19, 2015

chemistry
1. 0.62 is correct. 2. base/acid = 0.62 or base = 0.62*acid (equation 1) You want 0.1M x 1 L = 0.1 mol and base + acid = 0.1 mol (equation 2) Solve the two equation simultaneously (in which base and acid will be in mols), then convert mols to grams of each.
October 19, 2015

chemistry please help!
dHrxn = (n*dHf products) - (n*dHf reactants)
October 19, 2015

chemistry
3228 x (1.057 g/molar mass benzoic acid)= q in kJ q = Ccal*(Tfinal-Tinitial)
October 19, 2015

chemistry
Sure. Na2SO4 dissolved in water to prepare a solution will conduct electricity but the products are not the electrolysis of Na2SO4. This may not the question asked as Na2SO4 + H2O is not the same as pure Na2SO4.
October 19, 2015

whyyyyy
Perhaps it is because you haven't told anyone what your real problem is in solving these yourself and you haven't shown any work.
October 19, 2015

chemistry!!!!!!!!!
Do you know how to do stoichiometry. That comes first. Convert 1 L gasoline to grams with density; i.e., grams = volume x density. Convert grams to mols gasoline; i.e., mols = grams/molar mass gasoline. Use the coefficients in the balanced equation to convert mols gasoline to ...
October 19, 2015

chemistry
1 is no. Post your work and I'll find the error. Follow my steps. I suspect you didn't convert mg to grams. 2. ok
October 19, 2015

chemistry
1. What yu have gives you mg C. Convert that to grams, then to mols, then to atoms remembering there are 6.02E23 atoms in 1 mole. 2. You have mass Mg. Convert to mols, then to atoms.
October 19, 2015

chemistry
Ptotal = 1200 = pN2 + pH2 pN2 = 300 Solve for pH2, then find the ratio between pH2 and pN2.
October 19, 2015

Chemistry
All of them are ionized, at least partially. H2SO4 and HNO2 are not ionized completely. AgCl dissolves as a solid to form a solution in equilibrium between the solid and the undissociated aqueous solution and there is a Keq for that reaction. Then the solid solution ionizes to...
October 19, 2015

Chemistry
........A--> B + C I......1.0...0...0 C......-p....p...p E.....1.0-p..p...p Total P = 1-p+p+p = 1.5 Solve for p, evaluate 1-p, substitute into Kp expression and solve for Kp.
October 19, 2015

Chemistry
7.1 mg/L x (250/10) = ?
October 19, 2015

chemister
https://www.google.com/search?q=isomers+C7H16&ie=utf-8&oe=utf-8
October 19, 2015

Chem
As importantly, what is your question?
October 19, 2015

chemistry
mass acetone = volume x density = ? mols acetone = grams/molar mass = ? Then PV = nRT and solve for V.
October 19, 2015

Chemistry
I think you're right. Exothermic means heat is given off; therefore, T must rise.
October 18, 2015

Chemistry
pH = 11.17 so pOH = 14-11.17 Then pOH = -log(OH^-). Calculate OH^- ..........NH3 + H2O ==> NH4^+ + OH^- Plug in OH^- (also equal to NH4^+) into Kb expression and solve for NH3.
October 18, 2015

Chemistry
q = [mass H2O x specific heat H2O x (Tfinal-Tinitial)] + Ccal*(Tfinal-Tinitial) q = delta H/1.5 g and that times molar mass gives you delta H/mol
October 18, 2015

Chemistry
mg C = 269 x (12/44) = ? mg H = 111 x (2/18) = ? mg O = 95.6 - g C - g o = ? Then convert mg to g and to mols. Find the ratio of the mols to one another with the smallest being 1.00. The easy way to do that is to divide the smallest number by itself, then divide the other ...
October 18, 2015

chemistry-Dr BOB
I think I gave you a bum steer. I gave you the kJ/mol H2O and the question is for kJ/rxn. Your answer of -112 kJ was right from the beginning.
October 18, 2015

chemistry Dr. Bob
responded below.
October 18, 2015

chemistry-Dr Bob
Yes, of course. I dropped the - sign on the last step.
October 18, 2015

chemistry
C12H22O11(s) + 12O2(g) ==> 12CO2(g) + 11H2O(g) dH = -5.16E-3 kJ b is -5.16E+3 kJ/mol c is right
October 18, 2015

Chemistry- Dr. Bob
4 is not right. 5 I didn't look it up. 8b is right but too many sig figures. 11 is 7.93 x 10 to the what?
October 17, 2015

Chemistry
Use PV = nRT and use n = grams/molar mass
October 17, 2015

Chemistry
Ptotal = pN2 + pAr You know Ptotal and pAr. Solve for pN2. Then PV = nRT, substitute and solve for n N2 then use mols N2 = n = grams/molar mass and solve for grams.
October 17, 2015

Chemistry
n Ne = grams/molar mass = ? n Aar = grams/molar mass = ? Then PV = mRT and use n Ne to solve for pNe. Use n for Ar to solve for pAr.
October 17, 2015

chemistry
2 ferricyanide + ascorbic acid ==> 2 ferrocyanide + 2H^+ + dehydroascorbic acid
October 17, 2015

Chemistry
See your later post.
October 17, 2015

Chemistry
10 cm = 0.1 m 0.1 m = 1E-1 or 1 x 10^-1
October 17, 2015

AP Chem (Thank you for help)
http://www.webqc.org/balance.php?reaction=Cu+%2B+HNO3%28dilute%29+%3D+Cu%28NO3%292+%2B+H2O+%2B+NO
October 17, 2015

Chemistry
See your other post.
October 17, 2015

Chemistry
C + O2 ==> CO2 S + O2 ==> SO2 Let X = g C and Y = g S ----------- eqn 1 is X + Y = 9.0 g CO2 + g SO2 = 29.7 Convert this word equation into eqn 2 in terms of X and Y.(MM is molar mass and AM is atomic mass.) X(MM CO2/AM C) + Y(MM SO2/AM S) = 29.7 Solve eqn 1 and eqn 2 ...
October 17, 2015

chemistry
See my response to the corrected question above.
October 17, 2015

chemistry
As a quickie idea, look up the freezing points of each of the chemicals and see if they are sufficiently different to separate that way. If not that way, look up boiling points and compare.
October 17, 2015

chemistry
dHrxn = (n*dHf products) - (n*dHf reactants) Look up dHf for each and calculate.
October 17, 2015

chemistry/check my work I have to submit today
The heat is lost from system to surrounding, so ΔH is-ve For every 0.0136 mol of H2SO4 react, it releases 1516.74J of heat For 1 mole of H2SO4, ΔH= 1516.74/0.0136 = -111.525 kJ / mol = -112 kJ/ mol.......thank you, sIr This value is for 2 mols H2O so you need to to ...
October 16, 2015

chemistry
You really don't have 3 s.f. if you use 34 and not 34.0 for H2O2.
October 16, 2015

chemistry help DR. BOB
See my response above.
October 16, 2015

chemistry
2.9 x 3 = ?
October 16, 2015

chemistry Dr BOB
539 x 46= 24.79 24.79 x 1.43 x -221.50= -7852 J .539 x -40.5= -21,829 J 24.79 x 2.45 x -53.5 = 32930 J I would have rounded step 2 and step 3 differently but other than that I don't have any problems with steps 1, 2, or 3. For step 4 I think you made a typo here and put ...
October 16, 2015

Chemistry
.........NH4^+ + H2O ==> H3O^+ + NH3 I......0.049..............0.......0 C........-x...............x.......x E.....0.049-x.............x.......x Ka for NH4^+ = (Kw/Kb for NH3) = (x)(x)/(0.049-x) Solve for x = (H3O^+) and convert to pH.
October 16, 2015

chemistry
mols HCl = M x L = ? mols HNO3 = N x L = ? Total mols H^+ \ sum mols Ca(OH)2 = M x L = ? mols OH^- = 2xmols Ca(OH)2 mols RbOH = M x L = ? Total mols OH^- = ? You can take it from there.
October 15, 2015

Chemistry
molecules Mn2O3 = mols x 6.02E23 = ? molecules O in Mn2O3 = 3x that mols MnO2 = grams/molar mass = ? molecules MnO2 = mols x 6.023E23 =? molecules O atoms is 2x that. Total O atoms = sum of the two. 2 is worked the same way.
October 15, 2015

Chemistry
15.75g = mass Na + mass S -9.25g = mass Na ---------- 6.50 = mass S mols Na = mass/atomic mass = ? mols S = mass/atoic mass = ? Now find the ratio of the two elemenes to each other with the smaller number being no less than 1.00. The esy way to do this is to divide the ...
October 15, 2015

Chemistry
https://en.wikipedia.org/wiki/Solubility_table
October 15, 2015

C109
1.0 mL isn't very much. mols NaOH you want? mols = M x L = ? Then mols = grams/molar mass. YOu know molar mass and mols, solve for grams.
October 15, 2015

chemistry
correct? yes and no. I don't see anything wrong with the calculation but you aren't allowed that many significant figures. absorbs heat so q is + work done on it is +
October 14, 2015

chemistry
Atoms combine to form molecules.
October 14, 2015

chemistry
The gain or loss of electrons gives ions.
October 14, 2015

Chemistry
delta H = q = 827 J and since it absorbs heat the sign is +. delta E = q + work work = PdV = 0.66 kJ Since work is done ON IT, the sign of work is +. Substitute and solve.
October 14, 2015

CHEMISTRY!
M S2 = mols/L = ? .......C + S2 ==> CS2 I.....xs..?M.......0 C..........-x......x E.........?M-x.....x Substitute the E line into the Kc expression and solve for x (in mols/L) Then mols = M x L = ? Then g CS2 = mols CS2 x molar mass CS2
October 14, 2015

chem
initial concn Fe(NO3)3 = 2.00E-3 x (5/10) = ? initial concn KSCN = 2.00E-3 x (5/10) = ? .........SCN^- + Fe^3+ ==> Fe(SCN)^2+ I.......1E-3....1E-3..........0 C.........-x.....-x...........x E.......1E-3-x.,.1E-3-x.......x The problem tells you that x = 1.4E-4M Evaluate 1E-3...
October 14, 2015

chemistry
mols CaCO3 = g/molar mass = 25.0225/molar mass = ? Using the coefficients in the balanced equation, convert mols CaCO3 to mol HCl but the equations you wrote are not correct. I would use CaCO3 + 2HCl ==> CaCl2 + H2O + CO2 but that isn't the equation you were told to use...
October 14, 2015

chemistry
2Co + 3HgCl2 ==> 2CoCl3 + 3Hg mols Co = grams/atomic mass Using the coefficients in the balanced equation, convert mols Co to mols Hg. Now convert mols Hg to grams; i.e., g = mols x atomic mass = ?
October 14, 2015

Chemistry
mols Na^+ needed = M x L = 0.600 x 0.550 = ? mols Na3PO4 = ? mols Na^+ x (1 mol Na3PO4/3 mols Na^+) = ? Then g Na3PO4 = mols x molar mass = ? g
October 14, 2015

chemistry
Both look ok to me.
October 14, 2015

Chemistry
You have an equation in that lab procedure. Use that equation (balanced). mols NaOH = M x L = ? mols vitamin C. Using the coefficients in the balanced equation, convert mols NaOH to mols vitamin C. Then grams vitamin C = mols vitamin C x molar mass vitamin C = ? mass% = (grams...
October 14, 2015

Chemistry
Instead of us going through this long long calculation and you checking your work, why don't you show your work and let us check it for you.
October 14, 2015

Chemistry
I don't believe you have 51.98 g/mL but I might believe it is 51.98 g/L. 0.8655 mols/L x 60.05 g/mol = 51.97 by my calculations and that is g/L. Since you want %, that is 5.197 g/100 mL and since the density is 1 g/mL that is 5.197 g/100 g solution and that is 5.197% by ...
October 14, 2015

Chemistry: Equilibrium
I shall be happy to check your work if you show it and post as a new question at the top of the page. It's easier for us to check your work than to do all of the work ourself and have you go through and try to find your error.
October 14, 2015

chemitry
2H2S + 3O2 ==> 2H2O + 2SO2 mols O2 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols O2 to mols H2S. Now convert mols H2S to grams. g = mols x molar mass = ?
October 14, 2015

Chemistry
This is the long way around but I would do it this way but let me call your attention to the fact that CCl4 is NOT a gas at 25 C. Unless you clear up that part of the problem you are wasting your time on the rest of this. Use PV = nRT for H2 and solve for n = number of mols. ...
October 14, 2015

Chemistry
See your other post.
October 14, 2015

Chemistry
1.5 mg/L = 0.0015 g/L mols F = 0.0015 g/atomic mass F = ? and that is mols/L so = ? M = approx 8E-5 mols/L but that is an estimate. In 1E6 L there will be approx 8E-5 mols/L x 1E6 L = approx ? mols F. You will need 1/2 that mols CaF2 since CaF2 contains 2 mols F for every mols...
October 13, 2015

chemistry
I'm sticking with the original number but of course delta H should be -. I don't argue with the hint but I think we've done that. Both of us dropped the negative sign.
October 13, 2015

chemistry
That looks ok to me.
October 13, 2015

Chemistry
I know I'm being picky about this and I think you have answered the question correctly but I want to point out some of what I consider flaws in answer D. Building a model rocket is a physical process and mixing baking soda and vinegar is a physical process. It's only ...
October 13, 2015

chemistry
ok
October 13, 2015

Chemistry
You seem to be on the right track. Convert mols of products to pressure for each. To find the O2 pressure at the end of the reaction, you know moles O2 initially, convert mols CH4 used to mols O2 used, then mols O2 initially - mols O2 used = mols O2 left unreacted. Then change...
October 13, 2015

chemistry
I'll get you started. mols SCN^- initially = M x L = ? mols Fe^3+ initially = M x L = ? (SCN^-) initially = 0.002 x 4/10 = 8E-4M (Fe^3+) initially = 0.002 x 5/10 = 0.001M .........Fe^3+ + SCN^- ==> FeNCS^2+ I.......8E-4.....1E-3........0 C........-x.......-x.........x E...
October 13, 2015

Chemistry
I don't understand your last post. Using 3.5E-4 for Ka, that 7.58 you calculated is correct. I calculated it with and without the quadratic formula and got the same answer.
October 12, 2015

Chemistry
I can't check your answer because you don't give the Ka value you used for HF. Books differ with tables for Ka and Kb. I obtained 7.42 for pH If you will post your work I will check it.
October 12, 2015

Chemistry
mols HBr = M x L = ? mols KBr = mols HBr x (1 mol KBr/1 mol HBr) = ?
October 12, 2015

Chemistry
Yes and that's what Mr. Pursley told you. You must calculate the mols AgCl.
October 12, 2015

Chemistry
Use the CaCO3 equation you have and add this one for the titration. NaOH + HCl ==> NaCl + H2O mols HCl initially = M x L = 0.01 excess HCl = mols NaOH = 0.002 mols HCl used for the tablet = 0.008 0.008 mols HCl x (1 mol CaCO3/2 mols HCl) = 0.004 mols CaCO3 g CaCO3 = mols ...
October 12, 2015

Chemistry
I would take 49.5 as the freezing point or you could use 49.5, 49.6 and 49.5, take the average as 49.53 which rounds to 49.5. For #2, what is the solid? Is that Naphthalene (by the way, note the spelling) or is that the mixture of PDB and naphthalene.
October 12, 2015

Chemistry
See the other post.
October 12, 2015

Chemistry
2C2H2 + 5O2 ==> 4CO2 + 2H2O Use PV = nRT and solve for mols oxygen. Use the coefficients in the balanced equation to convert mols O2 from your first calculation above to mols C2H2. Then use PV = nRT to convert mols C2H2 to pressure. Post your work if you get stuck.
October 12, 2015

Chemistry
I don't know what quantum level 1, 2, 3 are. Are you talking about N = 1, 2, 3? or some other notation. Any what do you not understand that keeps you from counting them?
October 12, 2015

chemistry
Read the intro statement at the top of the page then click on some of the links below that for more information. https://www.google.com/search?q=are+pi+bonds+symmetrical&ie=utf-8&oe=utf-8
October 12, 2015

chemistry
I don't know what that means. The acetylene molecule is a linear molecule which makes it symmetrical in two dimensions but not in three. I suggest you Google sigma bonds and pi bonds and look at the pictures. If we knew what kind of symmetry the question was talking about ...
October 12, 2015

chemistry
You need to watch your typing. 2KClO3 ==> 2KCl + 3O2 mols KClO3 = grams/molar mass = ? Using the coefficients in the balanced equation convert mols KClO3 to mols O2 What do you mean by "How much"? If you want grams, that is grams = mols O2 x molar mass O2. If you ...
October 12, 2015

chem
The Na2S reacts with AgNO3 but not with NaNO3. Na2S + 2AgNO3 ==> Ag2S + 2NaNO3 mols Ag2S = 0.46/molar mass Ag2S = ? Using the coefficients in the balanced equation, convert mols Ag2S to mols AgNO3. Since the mixture has a mass of 1.27 g, 1.27- mass AgNO3 from above = mass ...
October 12, 2015

Chemistry
Let x = volume in mL of 0.149 M HCl to be added and mmols = millimols. mmols 0.285M + mmols 0.149M = mmols 0.205M (0.285*100) + (0.149x) = 0.205*(100+x) Solve for x. You should prove that by adding mmols 0.285M to mmols 0.149M and see if total mmols/total volume in mL = 0.205M
October 12, 2015

Chemistry
It would have been nice if you had just posted the problem. As it is I'm working in the dark. The Csys is the total and it's made up of the two components listed. Ccal is the heat capacity of the calorimeter. Csol is the heat capacity of the solution.
October 12, 2015

Chemistry
I believe you may have omitted the power of 10 for part A. For part b I get 1.68 but not the 10^-8
October 11, 2015

Chemistry
charge = 2*1.602E-19 C mass: convert amu to kg Calculate C/kg
October 11, 2015

chemistry
w = wavelength 1/w = 1.0973E7(1/1 - 1/x^2) Convert 93.73 nm to m and solve for x. That will tell you to which orbit the electron has been moved. Then, 1/w = 1.0973(1/y^2 - 1/x^2). Solve for y.
October 11, 2015

chemistry - HELP!
..........A + B ==> AB I.....0.1580..4.721E-5....0 C........-x....-x.........x E....0.1580-x..4.721E-5-x..x Substitute the E line into the Kc expression and solve for x, then evaluate A and B.
October 11, 2015

Chemistry
You don't need to memorize a new formula for this. Remember what you do for %yield. It is %yield = (actual amount/theoretical yield)*100 92.3 = actual amount/theoretical yield theoretical = actual/%yield
October 11, 2015

Chemistry
After you finish the calculation to find the g cyclohexanol needed with 86.2% yield, that is if the cyclohexanolis 100% pure. Since it is only 92.3% pure, the amount for 100%/0.923 = amount needed for 92.3% purity.
October 11, 2015

Chemistry
2MnO4^- + 5C2O4^2- ==> 10CO2 + 2Mn^2+ (Note: that doesn't balance all of the equation but the H2SO4, K^+, etc are just spectator ions.) mols C2O4^2- = M x L = 0.111 x 0.02115=? Using the coefficients in the balanced equation, convert mols C2O4^2- to mols MnO4^-. That ...
October 11, 2015

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