Tuesday
August 30, 2016

Posts by DrBob222

Total # Posts: 52,879

Chemistry
How many mols do you want? That's M x L = mols. Then mols = g/molar mass. You know mols and molar mass, solve for grams.
March 21, 2016

chemistry
You don't have the entire problem copies. What you need is the volume of NaOH added in your titration but here is what you do. mols NaOH = M x L. That's 0.75M x L you used in the titrant. mols HCl = mols NaOH from above. Then M HCl = mols HCl/L HCl. The problem says L ...
March 21, 2016

Chemistry
I don't know what experiment you did.
March 21, 2016

chemistry
We try not to do your work for you. Use PV = nRT and solve for n = number of mols. Then n = grams/molar mass. You know grams and n, solve for molar mass.
March 21, 2016

Chemisrty
2KI(aq) + 2HOH(l) ==> H2(g) + 2KOH(aq) + I2
March 20, 2016

chemistry 1020
mL1 x M1 = mL2 x M2 67.0 x 0.4M = mL2 x 0.1M Solve for mL2 which will be the TOTAL volume. Since you had 67.0 mL initially, subtract from the total to find how much must be added.
March 20, 2016

Chemistry
Something is missing here; namely, how much Pb ion is present?
March 20, 2016

Chem
You need the density of the acetic anhydride.
March 20, 2016

Chemistry
Br^-, ClO4^-
March 20, 2016

Chemistry
Your equation is not balanced. I'll bet if you balanced it the stoichiometry would work. If it still doesn't work post you work and I'll find the error.
March 20, 2016

chemistry
a. 196 kJ x 2.65/2.00 = ? kJ produced. b. 2 mols H2O2 = 2*34 = 68 g. 196 x (234/68) = ? kJ produced.
March 20, 2016

Chemistry
I should point out here that since CaS is soluble in water that extenuation circumstances will be necessary (temperature, saturation points, etc) in order to produce a solid. % yield = 100*(actual/theoretical) 85% = 100*(3.0/theoretical) Theoretical = 3.0/0.85 = about 3.6 ...
March 20, 2016

Chemistry Honors
(0.580-0.238)/8 = ?
March 20, 2016

chemistry
(H^+)(OH^-) = Kw = 1E-14 You know OH, solve for H^+. If H = OH neutral If H > OH acid If H < OH basic
March 20, 2016

chemistry
That's right. 8.5 x 4 x 142 = ?
March 20, 2016

chemistry
No. How many mols do you want? That's niks = M x L = ? Then grams = mols x molar mass = ?
March 20, 2016

Chemistry
34 x (500/100) = ?
March 19, 2016

chemistry/statistics
And what is your problem with this. Can't you just substitute these numbers into the formula; i.e., plug and chug.
March 19, 2016

chemistry
N2 + 3H2 ==> 2NH3 If you want the volume of NH3 at the same conditions, it is just 23.7 L x (2 mols NH3/3 mols H2) = ? If you want it at STP, use PV = nRT and convert.
March 19, 2016

Chemistry
g NaOH = mols NaOH x atomic mass Na = ?
March 19, 2016

chemistry
C5H10 is correct for the alkene. The alkane will be C5H12 or pentane, isopentane, or neopentane. Wouldn't the alkanes be there in equimolar proportions; i.e., the mole fraction would be 0.5.
March 19, 2016

chemistry
You need to find the caps key and use it. 5E3 means 5 x 10^3 = 5000 = 5 times 10 to the third power. 1 mol contains 6.02E23 ions. 3E22/6.02E23 = approx 0.05 mol Cl^- ions. mols CaCl2 = 1/2 that since 1 mol CaCl2 contains 2 mols CaCl2. Then M = mols/L = approx 0.05 mols/0.200 L...
March 18, 2016

Chemistry
Bob Pursley is correct. I want to add some additional information here. A strong acid such as HCl or a strong base such as NaOH act as buffers by themselves. Not very good buffers but that solution IS buffered with just HCl. Look at the titration curve of a strong acid at this...
March 18, 2016

Chemistry
Look at the oxidation state of each element on both sides. If they are the same redox does not occur. If they are different it is a redox reaction.
March 18, 2016

chemistry
You have the answer. What else is to explain? The AgSCN ppts, the SCN concn is decreased, the reaction shifts to the left to compensate and less FeSCN^2+ complex is formed.
March 18, 2016

Chemestry
Will, you need to learn how to spell chemistry. Volume of a solid makes no sense to me unless there is more to the problem.
March 18, 2016

chemistry
I don't know what experiment you did but if the pressure of the atomosphere was the same then smaller temperature means smaller volume.
March 18, 2016

chemestry
See the above and spell chemistry correctly.
March 18, 2016

chemestry
Oxidation is the loss of electrons. Which is losing electrons. A. Pb is +4 on the left and +2 on the right. That's a gain of electrons so A can't be right. B. O doesn't change oxidations state. B can't right. C. H doesn't change oxidation state so C can'...
March 17, 2016

chemestry
Louren, are you paying attention to the answers? Please use the correct spelling of chemistry. A. H2 has an oxidation state of zero on the left and +1 on the right so it is losing electrons. That makes it oxidized so A can't be right. B. If H2 is being oxidized then Cl2 ...
March 17, 2016

Chem101
Hydrocarbons + oxygen give CO2 and H2O. C7H16(l) + 11O2(g)→ 7CO2(g) + 8H2O(g)
March 17, 2016

Chemistry
dGrxn = dGo + RTlnQ dGo = -RTlnKa dGo = about +18.5 kJ RTlnQ = about -31.5 kJ dGrxn = about -13 kJ/mol
March 17, 2016

Chemistry
dGrxn = dGproducts - dGreactants Then dGrxn = -nFEo Solve for Eo.
March 16, 2016

chemistry
The hint tells you how to work the problem. mols NaOH = M x L = ? mols acid = mols NaOH since it is 1:1 ratio. Then M acid = mols acid/L acid = ?
March 16, 2016

Chemistry
This done the same way as you other acid/NaOH problem. The only difference is in this problem the acid is given a name and they want grams and not M. KHP + NaOH ==> NaKP mols NaOH = M x L = ? mols KHP = mols NaOH Then mols KHP = grams KHP/molar mass KHP. You know molar mass...
March 16, 2016

chemistry
I assume you want to prepare 500 cc of the CuSO4. How many mols do you want? That's M x L = 0.1 x 0.500 = ? Then convert to grams. g = mols x molar mass = ?
March 16, 2016

Chemistry DR BOB
I assume you mean the reaction in which electrons flow from the anode to the cathode spontaneously. Anode is on the left, it is oxidized; therefore, Eo oxidation = -0.37 Cathode is on the right so it receives the electrons and it is reduced so Eo redn = 0.67. EoCell = Eox + ...
March 16, 2016

Analytical Chem
Use PV = nRT and solve for pSO3 at the beginning and at equilibrium. I obtained about 1 for pSO3 initially but you need to get a more accurate answer. Then ..........2SO3 ==> 2SO2 + O2 I.........1.0.......0......0 C.........-2x.......2x.....x E........1.0-2x.....2x.....s ...
March 16, 2016

chemestry
Just as an add on, you really need to learn to spell chemistry correctly.
March 16, 2016

chemestry
Let's think about this. If a neutral solution is 1E-7 M for (H^+) and 1E-7 M for (OH^-), that means for the solution to be basic the (OH^-) must be larger than 1E-7 M. Is 4.2E-8 M larger than 1E-7 M?
March 16, 2016

chemestry
The correct answer is "none of these" which is not a choice. The answer your prof wants is B but that isn't correct. Many texts, if you can find the problem addressed, explains this very well but many texts don't even address this segment of chemistry. I have...
March 16, 2016

chemestry
Yes, A is the correct answer. In the acid, HA, it ionizes as HA ==> H^+ + A^- Ka = (H^+)(A^-)/(HA) The acidity of a solution depends upon the (H^+) so the higher that is the stronger the acid. Look at Ka values. If Ka is large then the numerator (the H^+) is larger. For the...
March 16, 2016

Chem
XH2SO4 = 0.2 so XH2O = 0.8 Take 1 mol of the solution. That will contain 0.8 mols H2O. How many grams is that? 0.8 mol x 18 gH2O/mol = 14.4 g or 0.0144 kg. molality = mols H2SO4/kg solvent 0.2/0.0144 = ?m
March 16, 2016

Chemistry
Yes, that final post looks good. Good work.
March 15, 2016

Chemistry
You need to learn to do these by yourself and me doing them will not help you. Here is a site that will help or if you have trouble show what you can do and explain fully what you don't understand about the next step. Cr goes from +6 on the left(for each) to 3+ on the ...
March 15, 2016

Chemistry
The numbers may be slightly different but the process is the same. http://www.jiskha.com/display.cgi?id=1458010856
March 15, 2016

Chemestry
I would convert 100 mM to M and mL to L. Then, how many mols do you need? That's mol = M x L = ? Next step is grams = mols NaCl x molar mass NaCl = ?
March 15, 2016

Chemestry
See your other post. Same process.
March 15, 2016

Chemistry
pH = 9 means pOH = 5 so (OH^-) = 1E-5 Substitute and solve for Qsp. Qsp = (Cd^2+)(OH^-)^2 and compare that with Ksp. If Ksp is smaller there is a ppt. If Ksp is larger there is no ppt.
March 15, 2016

Chemistry
I assume the 0.145m is a typo and you meant 0.145 M. Also I assume you meant NaOH and not naoh which means nothing to me. 2NaOH + H2SO4 ==> Na2SO4 + 2H2O mols H2SO4 = M x L = ? Using the coefficients in the balanced equation, convert mols H2SO4 to mols NaOH. That's mols...
March 15, 2016

chemestry
no. A has the least.
March 15, 2016

chemestry
Absolutely no.
March 15, 2016

Chemistry
Ba(OH)2 + 2HNO3 -> Ba(NO3)2 + 2H2O mols Ba(OH)2 = M x L = ? mols HNO3 = 2x that (look at the coefficients). Then M HNO3 = mols HNO3/L HNO3.
March 14, 2016

Chemistry
(mass solute/mass soln) = 0.06
March 14, 2016

Chemistry
How many mols do you need? That's mols = M x L = ? Then mols = grams/molar mass. You know molar mass and mols, solve for grams.
March 14, 2016

Unscramble
You might want to check your spelling/typing.
March 14, 2016

Chemistry
Volumes are not additive.
March 14, 2016

chemistry
Write the molecular equation and balance it. CrBr3(aq) + K3PO4(aq) ==> CrPO4(s) + 3KBr(aq) Separate into the complete ionic equation. It should be obvious that the aq solutions ionize and the solid is shows as the molecule since it doesn't dissolve. Cr^3+(aq) + 3Br^-(aq...
March 13, 2016

Chemistry
How many moles do you need? That's mols = M x L = ? Now mols = grams/molar mass. You know molar mass and mols, solve for grams.
March 13, 2016

chemistry
The problem isn't worded very well. Calculate the concn IN WHAT UNITS. BELOW IS THE COnCN IN M = mols/L For part b M NaOH in 1 L is: 1000 mL x 1.19 g/mL x 0.70 x 1/molar mass NaOH = ? approx 33 M Then use the dilution formula for part C. mL1 x M1 = mL2 x M2 250 x 0.1 = mL2...
March 12, 2016

chem 121
2HClO4 + Ba(OH)2 ==> Ba(ClO4)2 + 2H2O mols HClO4 = M x L = ? mols Ba(OH)2 = 1/2 mols HClO4 (from the coefficients in the balanced equation) Then mols Ba(OH)2 = M x L. You know mols and M, solve for L.
March 12, 2016

Chemistry- DrBob222
........HA <----> H+ + A- I.....0.05........0.....0 C....-5E-5........5E-5..5E-5 E......?..........5E-5..5E-5 Substitute the E line (after evaluation 0.05-5E-5) and solve for Ka.
March 12, 2016

Chemistry
I suggest you check the numbers.
March 12, 2016

Chemistry-DrBob222
Close but not there. Since that other problem was close, too, perhaps you are not rounding right. Post your work here and I will check it. MY answer is 63.2 mL.
March 12, 2016

Chemistry -DrBob222
Looks ok to me.
March 12, 2016

Chemistry-DrBob222
I get 167 but that difference may be due to rounding errors.
March 12, 2016

Chemistry
A and B look ok to me but I don't agree with C.
March 12, 2016

chem 12
right
March 12, 2016

General Chemistry
I think the secret is "assuming that all dissolved CO2 is present as H2CO3". .......H2CO3 ==> H^+ + HCO3^- I.......0.12......0.....0 C.......-x........x.....x E......0.12-x.....x.....x Set up the E line into k1 and solve for H^+ and convert to pH.
March 11, 2016

Chemistry
No, of course not. It depends upon how much of each reactant is present.
March 11, 2016

Chemistry-DrBob222
I'm not sure I understand the question. The assumptions don't change the way you work the problem; i.e., no heat is lost is obvious and it means density of the solution is 1.00 g/mL which means mass of the solution is 30.0 grams.
March 11, 2016

Chemistry
I worked c the same way you did and another way and got the same answer each way. Then I used both ways to to do A and came up with your answer. I assume the others are ok. Here is the OTHER way to do density. Density at STP is 32/22.4 = about 1.43 g/L. Not convert from STP to...
March 11, 2016

Chemistry
No. The temperature increased from 15 to 26.5 and that makes it an exothermic reaction so dH is -.
March 11, 2016

Chemistry- DrBob222
See above
March 11, 2016

Inorganic Chemistry
q = mass H2O x 4.184 x 4.63 x 1/1000 = ? kJ heat produced. That is for 0.680 x 0.07 mols H2O = ? So dHrxn is q/mols = ?. I think the answer is about 56 kJ/mol or so.
March 11, 2016

chemistry
os h what What does 6m mean?
March 10, 2016

chemistry
Use the Henderson-Hasselbalch equation.
March 9, 2016

Chemistry
What's the density?
March 9, 2016

Chemistry
You need more information than that. density? molarity? molality? something. The stuff sold in grocery stores is approximately 3-5%.
March 9, 2016

chemistry
pH = pK3 + (K3PO4^3-)/(K2HPO4^2-) Plug in the numbers and solve for (K2HPO4^2-) in M = mols/L. Then mols = M x L = ? and mols = grams/molar mass. You know molar mass and mols, solvle for grams.
March 9, 2016

chemistry
Saturated.
March 9, 2016

chemistry
mols Sb2S3 = 3.87E23/6.02E23 = ? Then mols Sb2S3 x (3 mols FeS/1 mol Sb2S3) = ? Finally, grams = mols x molar mass
March 9, 2016

chemistry
Use the coefficients to tell you. 13.7 mols N2 x (4 mols NH3/5 mols N2) = ? mols NH3 13.7 mols N2 x (6 mols NO/5 mols N2) = ? mols NO
March 9, 2016

chemistry
EMF = ? Add the oxidation half to the reduction half. Use pH = -log (H^+) for the other two.
March 9, 2016

chemistry
I don't see a question here.
March 9, 2016

chemistry
q1 = heat needed to raise T ice froom -20 to zero C. q1 = mass ice x specific heat ice x (Tfinal-Tinitial) q2 = heat needed to melt ice @ zero C to liquid water @ zero C. q2 = mass ice x heat fusion ice. q3 = heat needed to raise T water at zero to 100 C. q3 = mass water x ...
March 9, 2016

Chemistry-DrBob222
mols Mg = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols Mg to mols H2. That is a 1:1 so mols Mg = mols H2. Then use PV = nRT to solve for volume in L and convert to mL. For n use mols from above. R and T are the usual. For P use Ptotal = ...
March 8, 2016

Chemistry
A is ok but you didn't calculate the total pressure. Of course, it's 2.2 atm. B. You want XO2 to be 0.5 (pO2/Ptotal) = 0.5 What must total pressure be. (1.6/y) = 0.5 Solve for y and you get 3.2 for the total pressure; i.e., that way, 1.6/3.2 = 0.5 So what pAr is needed...
March 8, 2016

Chemistry
q = mass H2O x heat vaporization = ?
March 8, 2016

Chemistry
See your post above.
March 8, 2016

Chemistry
Do you know the definition. M = mols/L. You know mols and you know L. Substitute and solvle for M.
March 8, 2016

chemistry
mass pure CaCO3 initially. 200 x 0.95 = 190 g. Then 190 g CaCO3 x (molar mass CaO/molar mass CaCO3) = ?
March 8, 2016

Chemistry
mL1 x M1 = mL2 x M2 10 x 12 = 250 x M2. Solve for M2.
March 8, 2016

Chemistry
This is not a chemistry problem to me. Frankly, I call this a stoichiometry problem but I don't know that it makes any difference what one calls it. Many students call it a "I don't know how to work this problem" problem.
March 7, 2016

Chemistry
sulfur trioxide ==> sulfur + oxygen The second equation will not react to produce anything. The names are potaqssium iodide + magnesium chloride --> Magnesium iodide + potassium chloride.
March 7, 2016

Chemistry
http://academics.wellesley.edu/Chemistry/chem211lab/Orgo_Lab_Manual/Appendix/ClassificationTests/phenol_amine_nitro.html#IronChloride
March 7, 2016

Chemsistry
H3O^+(aq) + CaCO3(s) => Ca^2+(aq) + (HCO3^-)(aq) + H2O(l)
March 7, 2016

Chemistry
I don't get all of the mumbo jumbo at the end of the question. I assume you want this. ..........NH4Cl --> NH3 + HCl If pNH3 is 1.51 atm then pHCl is 1.51 atm. Plug These numbers into the Kp expression and solve. Kp = pNH3*pHCl Kp = (1.51)(1.51) = ? Note that NH4Cl ...
March 7, 2016

Chemistry
delta T = i*Kb*m delta T = 4.4 i for CaCl2 = 3 Kb for water you know solve for m.
March 7, 2016

Chemistry
20 x (2*atomic mass Na/molar mass Na2CO3) = ?
March 7, 2016

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