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May 1, 2016

Posts by DrBob222

Total # Posts: 52,204

chemistry
We can't draw diagrams on this forum.
November 14, 2015

Chemistry
.......2HBr + 2K ==> 2KBr + H2 mols K = grams/molar mass Using the coefficients in the balanced equation, convert mols K to mols HBr. Now convert mols HBr to volume using M HBr = mols HBr/L HBr. You know M and mols, solve for L.
November 14, 2015

chemistry
I can't tell the difference between the question and what I assume is your answer.The skeleton equation is simply 5Fe^2+ + MnO4^- ==> 5Fe^3+ + Mn^2+ and you can add the states. Most of the rest of what you wrote is not right but the final equation you came up with is ...
November 14, 2015

chemistry
Use PV = nRT with n = g N2/molar mass N2. Remember T must be in kelvin.
November 14, 2015

Chemistry
a cd b However, I prefer to say the water molecules are attracted to the Na ions (of the crystal) and Cl ions (of the crystal).
November 14, 2015

Chemistry
The correct answer is b.
November 14, 2015

chemistry
........NH3 + H2O ==>NH4^+ + OH^- I........5............0.......0 C.......-x............x.......x E.......5-x...........x.......x Substitute the E line into Kb expression and solve for x = OH^-, then convert to pH.
November 14, 2015

Chemistry
q = [mass H2O x specific heat H2O x (Ttinal-Tinitial)] + Ccal x (Tfinal-Tinitial) and that gives you q for 2.1. Change to q for 1 g.
November 13, 2015

Chemistry
See your other post. Apparently you ignore the Ccal.
November 13, 2015

Chemistry
1000 kg coal = 1,000,000 g coal and if that contains 0.050% FeS2, then 1,000,000 x 0.0005 = ? g FeS2 to start. Go through the stoichiometry to find how much SO2 is produced, then do the stoichiometry to find NaOH required.
November 13, 2015

Chemistry (Check)
You did it right; I used 11/760 and left it in the calculator.
November 13, 2015

Chemistry (Check)
You have too many s.f. in that answer for A. Also, I don't get that exactly; the problem, I suspect, is that you rounded with intermediate numbers and I didn't. B is ok.
November 13, 2015

Chemistry
right
November 13, 2015

NOTE: Chemistry
I want to point out that you aren't allowed 4 significant figures.
November 13, 2015

Chemistry
Nope. Right digits but wrong decimal. By the way, the problem below with an answer of 0.530 is ok but the site wouldn't let me post an ok.
November 13, 2015

Chemistry (Check)
good. Come back anytime.
November 13, 2015

Chemistry (Check)
The difference: If I use 900/760 and round that number to 1.18 (which is correct), I get 12.22 which rounds to 12.2. However, if I set my calculator to read 6 places (which I do routinely for all of my work) then go through without taking anything out of the calculator; ie., ...
November 13, 2015

Chemistry (Check)
My calculator reads 12.267 so I would round that to 12.3 g.
November 13, 2015

Chemistry (Check)
500 mL x (742/795) = 467 mL
November 13, 2015

Chemistry
OK
November 13, 2015

Chemistry (Check)
ok
November 13, 2015

Chemistry (Check)
OK. You should always include units.
November 13, 2015

Chemistry (Check)
I obtained 0.129 cc. If your answer is in L that is ok.
November 13, 2015

Chemistry (Check)
no. Right digits, wrong decimal.
November 13, 2015

Chemistry (Check)
good
November 13, 2015

oops--Chemistry (Check)
Also 1.00/760 is not 1.32 but 1.32E-3. Thus 1E-6/760 = 1.32E-9 I think.
November 13, 2015

Chemistry (Check)
985mLN / 1000 = .985 L 0.0 degrees C + 273 = 273 K 1.00x10^-6 mmHg / 760 mmHg = 1.32 atm YOU forgot the 10^-6 1.32 atm x .985 L = n ( .08206 Latm / molK)x273K n = .0580 moles x 6.022x10^23 = 3.50 x 10^23 molecules. For digits I obtained 3.48; the difference is that you rounded...
November 13, 2015

Chemistry (Check)
I don't like that answer either. Post your work and let me find the error. By the way, the 12 atm to 25 atm problem below is OK but the site will not let me post an OK.
November 13, 2015

Chemistry (Check)
The digits are close but the 10^? is missing.
November 13, 2015

Chemistry
mass # = #protons + #neutrons
November 13, 2015

Chemistry-Dr.Bob
This is a limiting reagent (LR) problem. You know that because an amount is given for both reactants. 3KOH + Fe(NO3)3 ==> Fe(OH)3 + 3KNO3 mols KOH = M x L = ? mols Fe(NO3)3 = M x L = ? Using the coefficients in the balanced equation, convert mols KOH to mols Fe(OH)3. Do the...
November 13, 2015

Chemistry
EDTA forms 1:1 complexes with metals; therefore, 6.25E-5 mols from the previous problem will be that amount with EDTA. M = mols/L 0.00420 = 6.25E-5/L. Solve for L and convert to mL if desired.
November 13, 2015

chemistry
Write the hydrolysis equation. Call aniline BNH2, then ........BNH2 + H2O ==> BNH3^+ + OH^- I........1M.............0.......0 C........-x.............x.......x E........1-x............x.......x Kb = (x)(x)/(1-x) Solve for x = OH and convert to pH.
November 13, 2015

Chemistry
See Damon's response below.;
November 13, 2015

Chemistry
Calculate the oxidation state of each atom in the equation and note that each has the same oxidation state on the left that it has on the right.
November 13, 2015

Chemistry
See your other post.
November 13, 2015

Chemistry
dHrxn = (n*dHf products) - (n*dHf reactants)
November 13, 2015

chemistry
OK, so I'll start over. Below I have erased all I wrote but kept what you wrote. My response is in bold. A chunk of iron weighs 4.32 g. a) How many iron atoms are there in this sample? 55.85 g Fe = 1.00 mol Fe = 6.022 x 1023 atoms Fe What you have written is exactly right...
November 12, 2015

chemistry
A chunk of iron weighs 4.32 g. a) How many iron atoms are there in this sample? 55.85 g Fe = 1.00 mol Fe = 6.022 x 1023 atoms Fe mols Fe = grams Fe/55.85 Then mols Fe x 6.022E23 = ? no. atoms. b) How many moles of iron are there in this sample? See above. 2. . You have a ...
November 12, 2015

Chemistry
You have a typo in #1, that should be 3C(s). Reverse #1, add to 3x #2, and to 4x #3.
November 12, 2015

Chemistry
Basically it's the size of the atom. Here is a table. http://www.science.uwaterloo.ca/~cchieh/cact/c120/bondel.html
November 12, 2015

chemistry
Great!
November 12, 2015

chemistry
No, No, No. The 2 in front of the Ca is a coefficient, not the charge. It is a zero oxidation state because it is a free element. All free elements (those not in a compound) are zero. O2 is zero for the same reason. So Ca goes from zero on the left to 2+ on the right; ...
November 12, 2015

chemistry
Oxidation is the loss of electrons. Ca is zero on the left and +2 on the right. O is zero on the left and 2 on the right. Which element (Ca or O) lost electrons?
November 12, 2015

chemistry
You misunderstood on 1. mols = M x L = 0.600 x 0.450 = 0.270. Then you omitted the second step which I wrote in my first response which is grams = mols x molar mass = ? That will be grams = 0.270 x molar mass CaCl2 = ?
November 12, 2015

chemistry
1. You forgot to change 600 mL to L. The answer is 0.270 mols. 2. is yes 3. I don't get your answer. M x L = 1.75 x 3.65 = ? ? x molar mass = ? x 111 = approx 710 grams.
November 12, 2015

chemistry
1. mols CaCl2 = M x L = ? Then grams = mols x molar mass 2. The base is what's left after the H is gone. 3. How many mols do you need? That's mols = M x L How many grams is that many mols? That's grams = mols x molar mass = ?
November 12, 2015

Chemistry
Look up delta H formation and plug into dHrxn = (n*dHf products) - (n*dHf reactants). If the sign is - it is exothermic; endothermis is + sign.
November 12, 2015

Chemistry
xxx
November 12, 2015

Chemistry
mols Ag2O = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols Ag2O to mols Ag.
November 12, 2015

Chemistry
Calculate dH for each reaction of interest (or all of them) as dHrxn = (n*dHf products) - (n*dHf reactants) then compare to answer the question. Yes it is a state function because the sum is equal to the individual parts and to be a state function it doesn't matter how we ...
November 12, 2015

Chemistry (Check)
Off hand I wouldn't think so. q = mass H2O x specific heat H2O x delta T = ?,I think the question is stated improperly. This is the dH for the reaction as shown. What the problem wants, I think, is dH for the reaction/mol. That is Then q/mol CH4 = dH for the reaction. I ...
November 12, 2015

Chemistry
46.9 psi = 3.19 atmospheres. Then use PV = nRT and solve for n
November 12, 2015

Chemistry
-2511.14 kJ/2 mols x 2 mols = ? -2511.14 kJ/2 mols x 1 mol = ?
November 12, 2015

Chemistry Lab Work Help!
I don't get what you did? Burets usually are used to measure the volume taken FROM the buret and the final reading is greater than the initial volume. You seem to be adding to the buret. Explain what you did. If you want the volume that was ADDED you subtract 49.97-30.49. ...
November 12, 2015

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

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