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May 29, 2016

Posts by DrBob222

Total # Posts: 52,449

Chemistry
Combustion reactions produce heat. This is a combustion reaction. It can be measured with a calorimeter.
November 12, 2015

Chemistry
A is probably right but I don't there there is enough information there to know that. You must go to a periodic table to check it out. I don't think B is right. The average of all of the isotopes is 40.078 but Ca-40 is not that mass. C is ok. D is not right. D would be...
November 12, 2015

chemistry
empirical mass is 25.846 103.38/25.846 = 3.999 which rounds to 4 So molecular formula is (BCH3)4 or B4C4H12
November 12, 2015

Chemistry
1 mol contains 6.02E23 so 4.53E-15 must contain ......?
November 12, 2015

Chemistry - Energy: Phase Changes
Why didn't you tell us where you THINK you should start? Let y = mass ice cube To melt ice cube at zero C it is y*heat fusion. Add that to in as this, Then (y*heat fusion) + [y*specific heat H2O x (Tfinal-Tinitial)] + [(mass H2O in cup x specific heat H2O x (Tfina-Tinitial...
November 12, 2015

Chemistry - Energy: Phase Changes
Yes, 2.23 mols ice are melted? How many grms is that? grams = mols x molar mass = approx 40 g. How much ice did you have? That's 1,000 g. How much ice is left. Approx 1000-40 = ?
November 12, 2015

Chemistry
Yes on both answers.
November 12, 2015

Chemistry
q = mass benzene x heat vaporization = ? heat vaporization must be available in tables.
November 12, 2015

Chemistry
So the neutral atom will be [Kr]4d^10 5s^2 5p^2 and that adds to 36 + 10 + 2 + 2 = ? as the atomic number and look that up on the periodic chart.
November 12, 2015

Chemistry-Dr.Bob
I think you are confused with the definition. Here is a site that gives you the effective nuclear charge for Na^+ and F^-. Zeff = #protons -#inner electrons = ? For Na^+ that is 11-2 = 9+. For F^- that is 9- 2 = 7+. https://www.google.com/search?q=effective+nuclear+charge&ie=...
November 12, 2015

chem
mols = grams/molar mass = ?. Then M = mols/L solution.
November 12, 2015

chemistry
mols KClO3 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols KClO3 to mols O2. Using PV = nRT convert mols O2 to volume O2 at the conditions listed. For pressure you will need to take into account that the O2 was collected over water, thus ...
November 12, 2015

chemistry
Ac is acetate and HAc is acetic acid .......Ac + H^+ ==> HAc I....0.58...0........0.68 add........0.02........... C...-0.02..-0.02......+0.02 E.....0.56...0.........0.70 Plug the E line into the HH equation and solve for pH.
November 11, 2015

chemistry
Frankly, I think this is crazy but this must be what you're expected to do. Na3PO4 has no Ksp in my opinion. ........Na3PO4 ==> 3Na^+ + PO4^3- I........0.025....3*0.025..0.025 C.......-0.025 E.........0........0.075...0.025 Plug that E line into Ksp expression and solve.
November 11, 2015

chem
q = mass H2O x specific heat H2O x (Tfinal-Tinitial) Since this is an exothermic reaction, the prof MAY want a negative sign on it; one never knows. I wouldn't use one since if heat is being transferred into the surroundings it MUST have been exothermic.
November 11, 2015

chemistry
So plug in the numbers and solve for velocity. The mass of an electron is 9.11E-31 kg.
November 11, 2015

chemistry
6.26E14 x 413E-9 = ? and compare with c = 3E8.
November 11, 2015

Chemistry
I assume that's a typo on the second HCOOH. mols HCOOH = M x L = ? mols NaOH = the same M NaOH = mols NaOH/L NaOH. YOu know mols and M, solve for L
November 11, 2015

chem
Use PV = nRT and solve for n = number of mols, the n = grams/molar mass. You know grams and n, solve for molar mass.
November 11, 2015

chemistry
What can I help you with so you can do these in the future by yourself?
November 11, 2015

chemistry
See your other post.
November 11, 2015

Chemistry- Dr. Bob
http://chemistry.stackexchange.com/questions/19179/why-doesnt-rubidium-react-with-nitrogen-gas
November 11, 2015

chemistry
Grams of what that will react with 90 g acetic acid?
November 11, 2015

Chemistry
mL1 x N1 = mL2 x N2 mL1 x 18 = 125 x 6.0 Solve for mL1.
November 11, 2015

chemistry
ln(No/N) = kt No = 100 N = 98 k is to be found time is 1 min or 60 seconds depending upon how the answer is to be displayed. For #2, N is 50 For #3 N = 25.
November 11, 2015

Chemistry
Convert 16782.7 J to Calories and that will be calories per 0.8 gram. (Note: you may want to look at the number of significant figures if your prof is picky about that.) So this will give you calories/gram of nut and that's what the problem asks for.
November 10, 2015

Chemistry
How many coulombs were needed to deposit the 5.4 g Ag. That's 96,485 coulombs x (5.4/108) = approx 4824. How many grams Cu will be deposited with 96,485? That is 64/2 = 32 g. You didn't have 96,485; you had 4824. So 32 x (4,824/96,495) = ? Redox reactions are Ag^+ + e...
November 10, 2015

Chemistry
Look at your earlier post below. I think you just dropped the negative sign and didn't use enough significant figures.
November 10, 2015

Chemistry
What's your problem with using dG = -RT*ln K as I suggested earlier.
November 10, 2015

Chemistry
Two formulas for mols. If solution, then mols = M x L = ? If mass(grams) then mols = grams/molar mass (or atomic mass)
November 10, 2015

CHEMISTRY!!!!!!!!!!
I get 0.0988. I think you dropped the - sign AND you are allowed more than two significant figures in the answer.
November 10, 2015

chemistry
[2*atomic mass N/molar mass (NH4)2SO4]*100 = ?
November 10, 2015

Chemistry
I was gone for awhile. I think you just misplaced the decimal. fraction = atomic mass Fe/molar mass Fe(NH4)2(SO4)2 = (55.85/392.14) = 0.142 Then mass Fe = mass Fe(NH4)2*(SO4)2 x fraction = 0.0218 x 0.142 = 0.00318 g Fe which is not larger than 0.0218. Convert that to mg which ...
November 10, 2015

Chemistry
OK, but first I made a typo. That is supposed to be 0.0218 g. You are weighing Fe(NH4)2(SO4)2.6H2O but you don't want to calculate mg/L of that stuff, you want to calculate mg/L of Fe. Not all of that stuff is Fe. What fraction is Fe? That is [atomic mass Fe/molar mass Fe(...
November 10, 2015

Chemistry
Convert 0.218 g of the compound to g Fe. That is done by 0.218 x (atomic [mass Fe/molar mass Fe(NH4)2(SO4)2.6H2O]*100 = ? Convert g Fe to mg = ? Convert 250 mL to L. Then mg Fe/L = your answer.
November 10, 2015

Chemistry
mols Fe = 4.86 g Fe/atomic mass Fe = ? Using the coefficients in the balcned equation, convert mols Fe to mols Fe2O3. Now convert mols Fe2O3 to grams Fe2O3. g = mols x molar mass = ? and this is the theoretical yield (TY) The actual yield (AY) is 6.76. %yield = (AY/TY)*100...
November 10, 2015

chemistry
As I see it you haven't listed a volume; i.e., only mols/L. Without a volume you can't calculate q.
November 10, 2015

chen
I think the idea here is that CaSO4 is so much more soluble than PbSO4 that the CaCl2/CaSO4 equilibrium will determine the sulfate concentration and that in turn will determine the solubility of PbSO4. .........CaSO4 ==> Ca^2+ + SO4^2- I........solid.....0........0 C...
November 10, 2015

Chemistry
Yes.
November 10, 2015

Chemistry
If it has 8 electrons you have the right configuration. You may not know the elements name but that is how it must be for 8 electrons. If you knew the element had a zero charge (not an ion), then you would know O was the element since that has 8 electrons. 8 0 = 1s2 2s2 2p4 ...
November 10, 2015

Chem
mols Zn = grams/atomic mass = ? Using the coefficients in the balanced equation, convert mols Zn to mols H2. Then convert mols H2 to L using mols H2 x 22.4 L/mol = ?L.
November 9, 2015

chemistry
If you have delta G, then dG = -RTlnK Substitute and solve for K
November 9, 2015

Chemistry
They want you to show the heat in terms of kJ or perhaps kJ/mol. MgCO3(s) + ?kJ ==> MgO(s) + CO2(g) delta Hrxn = (n*dH products) - (n*dH reactants). dH rxn will be in terms of kJ/mol. I don't see any numbers in your post that would indicate the amount of MgCO3 you are ...
November 9, 2015

Chemistry
q1 = heat needed to raise solid ice from -50 to zero C. q1 = mass H2O x specific heat ice x (Tfinal-Tinitial) q2 = heat needed to melt solid ice at zero C to liquid water at zero C. q2 = mass H2O x heat fusion q3 = heat needed to raise T of liquid water from zero C to 100 C. ...
November 9, 2015

Chemistry
See your other post.
November 9, 2015

Chemistry
mols Na2CO3 = M x L = ? Using the coefficients in the balanced equation, convert mols Na2CO3 to mols HNO3. Now M HNO3 = mols HNO3/L HNO3 solution. You know M and mols, solve for L and convert to mL.
November 9, 2015

Chemistry
Ptotal = pN2 + pH2O Ptotal is 745. pH2O = vapor pressure H2O. You can get this in tables in your text. Look for vapor pressure H2O at 21 C. I don't have these tables memorized but at 21 C it will be approximatly 18 or 19 torr.
November 9, 2015

chemistry
This is a limiting reagent (LR) problem. You know that because amounts are given for BOTH reactants. 1. Write and balance the equation. You have that. 2a. Convert grams NaNO2 to mols. mols = g/molar mass = ? 2b. Do the same for sulfamic acid = ? 3a. Using the coefficients in ...
November 9, 2015

CHEMISTRY - BATTERIES
Look up reduction potential for Sn^2+. Look up oxidation potential for Al. Add the two potential for Ecell. Using the reduction potential for Sn, plug in the values for concentration and recalculate E Sn. For the Al, change the sign of the oxidation potential you had, plug in ...
November 9, 2015

Chemistry
2Al(OH)3 + 3H2SO4 ==> Al2(SO4)3 + 6H2O mols Al(OH)3 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols Al(OH)3 to mols H2SO4. Then M H2SO4 = mols H2SO4/L H2SO4. You know M and mols, solve for L and convert to mL.
November 9, 2015

Chemistry
I would calculate the percentage of N in each of the compounds. The with the highest percentage will supply the most N per grams, per pound, per anything. You can do it another way. Convert 1 g of the compound to ? grams of N. For example, #1 would be 1 g Fe(N3)2 x (6*atomic ...
November 9, 2015

Chemistry
The long way is to do each one. Assume 100 g sample and convert to grams CO2 which is the weight loss. For example, MgCO3, molar mass about 84.3 MgCO3 => MgO + CO2 and what you want is for CO2 to come out to be 36.1% (or 36.1 g from a 100 g sample). mols MgCO3 = grams/molar...
November 9, 2015

chemistry
CH3CH2COOH(l) + H2O(l) ==> H3O^+(aq) + CH3CH2COO^-(aq)
November 9, 2015

Chemistry
Probably I would have marked it right; it may be that you omitted the heat sign over the arrow OR the word "heat" on the left side.
November 9, 2015

chemistryyy
Let's say your molarity is 2.0 M. M = mols/L solution % w/v = grams solute/100 mL. So you have 2.0 M = 2.0 mols/L. Convert 2.0 mols of whatever you have to grams solute. That will be grams = mols x molar mass. That gives you grams/L solution so you divide both numerator ...
November 8, 2015

chem
The easy way to do this is to recognize that you use PV = nRT and that P, R, and T are constant; therefore we can re-write the equation as k1V = n*k2*k3 or V = n*k2k3/k1 and since k2k3/k1 is just another constant we can re-write that as V = nk. Solve for k = V/n - 8.1/2.51...
November 8, 2015

chemistry
mL1 x M1 = mL2 x M2 258 x 5.00 = 574 x M2.
November 8, 2015

Chemistry
Details? What are you doing? How?
November 8, 2015

chemistry
Zn + CuSO4 ==> ZnSO4 + Cu mols Zn = grams/atomic mass = ? using the coefficients in the balanced equation, convert mols Zn to mols Cu. Now convert mols Cu to grams. g = mols x atomic mass. By the way, wouldn't copper(II) sulfate be a better name for CuSO4?
November 8, 2015

Chemistry
0.05 g PEG/molar mass = mols. Easy enough to do. mass solution = density x volume. You know mass (1 gram), use density and solve for volume of 1 gram of the solution. The problem is that you don't know the volume of the solution. Convert volume to liters, then M = mols/L ...
November 8, 2015

Grade 12 Chemistry
mass % (or % w/w) = [grams solute/grams solution] x 100 = ? grams solute = 5.85 g. grams solution = 5.85 + 250 = ?
November 8, 2015

Chemistry
1. I suggest you think of the various compounds of copper and ask yourself how you distinguish between them. The question is ambiguous to begin with because it doesn't specify by physical means or chemical means. 2. Again, if you synthesized these compounds you must have ...
November 8, 2015

chemistry
https://www.google.com/search?q=characteristics+of+nonmetals&ie=utf-8&oe=utf-8
November 7, 2015

Chemistry
I would do this. 1/wavelength = R(1/1 - 1/9) R you can find in tables in your book or on the web. Calculate wavelength and from the wavelength look in your book or on the web for the spectrum and see where that wavelength falls.
November 7, 2015

chem
Make sure the equation is balanced. Convert 15.0 g CaO to mols. mol = grams/molar mass = ? Now use the coefficients in the balanced equation to convert mols of what you have to mols of what you want.
November 7, 2015

chemistry
molecules
November 7, 2015

Chemistry- Dr. Bob
#1, 2, 4 are right.
November 7, 2015

Chemistry- Dr. Bob
#5. "ell" may vary from zero to n-1 in whole numbers.
November 7, 2015

Chemistry- Dr. Bob
1/wavelength = R(1/x^2 - 1/n^2) R is the Rydberg constant. I assume you have that in your tables. Remember wavelength must be in meters. n is 7
November 7, 2015

Chemistry
mols glucose = grams/molar mass = ? M = mols/0.250 L = ? I get an answer of 0.16 = M
November 6, 2015

chem
Use the Henderson-Hasselbalch equation. You can use mols and the answer will be the same as if you had used M. mols = M x L = ?
November 6, 2015

Chemistry
Boyle's Law is correct.
November 6, 2015

Chemistry
2Fe2O3 + 3C ==> 3CO2 + 4Fe mols Fe2O3 = grams/molar mass Using the coefficients in the balanced equation, convert mols Fe2O3 to mols C. If you want C in grams, then g C = mols C x atomic mass C.
November 6, 2015

Chemistry
This is a limiting reagent problem (LR) and you know that because amounts for both reactants are given. Use PV = nRT to calculate n for N2 Do smae for mols O2. Using the coefficients in the balanced equation convert mols N2 to mols NO. Do the same for mols O2 to mols NO. It is...
November 6, 2015

chemistry
(Ba^2+)(SO4^2-) = 1E-10 (Pb^2+)(SO4^2-) = 1.7E-8 How many mmols Ba(NO3)2 do you have. That's 1 mmol. How much Pb(NO3)2 = 1 mmol. (Ba^2+) initially = 1 mmol/301 mL = 3.22E-3M (Pb^2+) = 3.22E-3M If you start dripping H2SO4 drop wise into the solution the BaSO4 will start ...
November 4, 2015

Chemistry
No, I thought the question was not a good question. My problem with it is I don't understand why each possible answer has anything about randomness(delta S). Perhaps I don't understand what the question means by more or less energy. I equated this with delta G (Gibbs ...
November 4, 2015

Chemistry
I agree with you but I don't think much of the question.
November 4, 2015

chemistry
https://www.google.com/search?q=reactivity+in+periodic+table&tbm=isch&imgil=6b9R1xKTxlVtrM%253A%253BnhrIrtf6yb5J8M%253Bhttp%25253A%25252F%25252Femployees.csbsju.edu%25252Fcschaller%25252FPrinciples%2525252520Chem%25252Fatoms%25252Fatomperiodic.htm&source=iu&pf=m&fir=...
November 4, 2015

chemistry
metals: reactivity increases going down the table. For example, group I top to bottom increases. non-metals: reactivity increases going up the table. For example, group 17 bottom to top.
November 4, 2015

chemistry
Note Br is 79.9 and I is 126.9 molar mass Br2 is 79.9 x 2 = 159.8 molar mass I2 is 126.9 x 2 = 253.8 In 50 g I2 there are 50/253.9 = 0.197 mols I2 or 2*0.197 = 0.394 mols I atoms (which is what you have above but I've gone about it a different way). Now you have 0.197 mols...
November 4, 2015

Therochem
Who knows? Do you have an equation? Do you have a reaction rate constant? Do have the order?
November 4, 2015

Chemistry
delta E = hc/wavelength
November 4, 2015

chemistry
You should have set up an ICE chart. .........2SO3 ==> 2SO2 + O2 I.........0.5.....0.......0 C.........-2x.....2x......x E......0.5-2x.....2x.......x The problem tells you that 0.5-2x = 0.2 Solve for x and evaluate SO2 and O2, substitute into Keq and solve for K. I get 0....
November 4, 2015

Chemistry
Use the Henderson-Hasselbalch equation.
November 4, 2015

Chemistry VERY URGENT PLEASE
Reverse equation 1 and add to equation 2 and that gives equation 3.
November 3, 2015

Chemistry (Check)
I answered this for you below much earlier in the day.
November 3, 2015

Chemistry
Practically this is right; technically it is not. Technically, the volumes are not additive; therefore, what you do is pipet 4 and 1/6 mL of the 12 M into a 500 mL volumetric flask and add enough water to make exactly 500 (fill to the mark of the flask). That way you KNOW you ...
November 3, 2015

Chemistry (Help)
a is right. b and c. There is more than one way to do these. The easiest, I think, is to see what the factor is; i.e., you are diluting 10 mL to 500 so the new concn is 0.0324 x (10/500) = ? Then c is answer from a x (10/250) = ? Another way is to use the definition of ...
November 3, 2015

Chemistry.
0.00082 mols Mg x (1 mol H2/1 mol Mg) = 0.00082 x 1/1 = mols H2. grams H2 = mols H2 x molar mass H2.
November 3, 2015

Chemistry (Check and Help)
You got sucked in. The question did NOT ask for grams NaCl; it asked for the concentration of NaCl and the problem TOLD you #1 was 0.2M and #2 was 0.25M. 0.25M is a larger number than 0.2. All of the work you did is for naught. :-)
November 3, 2015

Chemistry (Check)
right
November 3, 2015

chemistry
OK. The long way. Almost all stoichiometry problems are worked this way. 1. Write and balance the equation, You have done that. 2. There are 22.4 L in a mole of gas (at STP and this probably is not at STP which is why I used the shortcut). mols NH3 = 250/22,400 = 0.0112 3. ...
November 3, 2015

chemistry
If all of these are gases you may use a shortcut and use volumes as mols directly. 260 cc NH3 x (4 mols NO/4 mols NH3) = 260 x 1 = ? cc NO. Do the same with O2 using the coefficients for NH3 and O2.
November 3, 2015

Chemistry
3KOH + H3PO4 ==> 3H2O + K3PO4 mols H3PO4 = M x L = ? Using the coefficients in the balanced equation, convert mols H3PO4 to mols KOH. M KOH = mols KOH/L KOH. You know M and mols KOH, solve for L KOH.
November 3, 2015

1CHEM
See your other post.
November 3, 2015

Chemistry
See you other post.
November 3, 2015

chemistry
grams acetone = volume x density = approx 115 grams but you need a more accurate number than that. So you get 1790 kJ for 58 g C3H6O; how much will you get from 115 g. 1790 x (115/58) = ? kJ released.
November 3, 2015

AP Chemistry
(rate 1/rate 2) = (mm 2/mm 2) where mm is molar mass. (0.05/0.025) = (mm 2/17) solve for mm and compare with the answers. The answer is approximate; pick the closest gas.
November 3, 2015

chem
2CH2 + 3O2 ==> 2CO2 + 2H2O mols CO2 = 44/44 = 1 mols O2 = 1 mol CO2 x (3 mols O2/2 mols CO2) = 1*3/2 = ? You can check this to see you get the same number using water.' mols H2O = 18/18 = 1 mols O2 = 1 mol H2O x (3 mols O2/2 mols H2O) = 1*3/2 = ? Convert mols O2 to ...
November 3, 2015

chem
I don't think so. How do you add 8 and -8 and get -11.
November 3, 2015

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