Saturday
April 25, 2015

Posts by DrBob222


Total # Posts: 48,506

Physics
14 posts inside of a minute by the same person.
February 10, 2015

chemistry
a. Ag^+(aq) + e ==> Ag(s) 4OH^- ==> 4e + 2H2O + O2 b. 25.8639 ..-25.0782 mass Ag metal deposited = ? 96,485 coulombs will deposit 107.868 g Ag so C used = 96,485 x (?g Ag/107.868) = ?coulombs. C = amperes x seconds. Substitute and solve for amperes. c. ?C from above = 96...
February 10, 2015

Science
The number of protons is the same. The number of neutrons is different. It can be rephrased to say the same thing as The atomic number is the same, the mass number is different.
February 10, 2015

chemistry
rate = -d(Cl)/dT = -d(O3)/dT = d(ClO)/dT = d(O2)/dT d stands for delta and T for time; i.e., delta(x)/delta time
February 10, 2015

chemistry
What's Ppan? If this is a first order reaction, you do this. k = 0.693/t1/2. Solve for k. If this is a second order reaction the above is not the way to go.
February 10, 2015

Chemistry
You get better help if you don't change screen names. 2C6H6 + 15O2 ==> 12CO2 + 6H2O Use the coefficients in the balanced equation to convert mols benzene to mols CO2. That's 32 mol C6H6 x (12 mols CO2/2 mols C6H6) = 32 x (12/2) = ?
February 10, 2015

Chemistry
What base? If you're using NaOH or KOH, then mLa x Ma = MLb x Mb Substitute and solve for the only unknown.
February 10, 2015

chemistry
Is the reaction 2H2 + O2 ==> 2H2O 2 mols H2O/s x (1 mol O2/2 H2O) = 2 x 1/2 = ? mols O2/s.
February 10, 2015

chemistry
The question posted under Joe says calcium bicarbonate and that's what I answered. For CaCO3 is is a different equation but the process is exactly the same. Step 1. Write and balance the equation. CaCO3 + H2SO4 ==> CaSO4 + H2O + CO2 Step 2. How many mols do you need to ...
February 10, 2015

science
https://www.google.com/search?q=solar+elipse&ie=utf-8&oe=utf-8
February 10, 2015

chemistry
I explained a slightly different problem below when you posted under the screen name of Joe. Just reposting doesn't help; if you will tell us exactly what you don't understand (and you should have done that the first time) we would know more how to help. http://www....
February 10, 2015

Chemistry
I don't think you posted the question you want; i.e., I think you mis-read the question. It makes no sense as is.
February 10, 2015

chemistry
Ca(HCO3)2 + H2SO4 ==> 2H2O + 2CO2 + CaSO4 I presume your pH 7 part assumes that is the pH at the equivalence point. mols H2SO4 = M x L = ? mols Ca(HCO3)2 = mols H2SO4 and you tell that by looking at the coefficients in the balanced equation. Then grams = mols x molar mass ...
February 10, 2015

chem
3.50 mols HNO3 x (1 mol H2S/2 mols HNO3 = 3.50 x 1/2 = ?
February 10, 2015

chemistry
Right. You have fewer mols in the 10 mL but the molarity is the same.
February 10, 2015

chemistry
I don't know what energy change = (tive) means.
February 10, 2015

chemistry
Make up masses--any convenient number will work. mols SO2 = grams/molar mass = ? mols O2 = grams/molar mass = ? Total mols = ? XSO2 = mols SO2/total mols. Then pSO2 = XSO2*Ptotal
February 10, 2015

chemistry
..........N2O4 ==> 2NO2 I........0.800.......0 C.........-x........2x E........0.800-x....2x Substitute the E line into Kc and calculate x and evaluate 0.800 -x. This give you M, the volume is 1 L, solve for mols. b) Calculate new (N2O4)= 0.800/0.5 = 1.600 Redo part a as ...
February 10, 2015

Chemistry
heat needed to raise T from 25C to 100 C. q = mass H2O x specific heat H2O x (75) q = approx 32,000 J (BUT THAT'S APPROXIMATE--YOU NEED TO GET A BETTER ANSWER) That leaves 50,000-32,000 to be used to convert to steam. q to convert to steam = mass x heat vap APPROX 18,000...
February 10, 2015

chemistry
I don't understand the question.
February 10, 2015

chemistry
24.8% HCl w/w means 24.8 g HCl/(100 g solution) 100 g solution = 24.8g HCl + 75.2g H2O. mols HCl = grams/molar mass = ? mols H2O = grams/molar mass = ? total mols = ? XHCl = mols HCl/total mols.
February 10, 2015

chemistry
NH3 + H3PO4 ==> NH4H2PO4 mols NH3 = grams/molar mass mols NH3 = mols NH4H2PO4 (from the 1:1 ratio in the balanced equation) g NH4H2PO4 = mols NH4H2PO4 x molar mass NH4H2PO4
February 10, 2015

chemistry
CH4 + O2 --> CO2 + 2H2O Calculate volume of CH4 at the conditions. Calculate volume of CO2 at the conditions listed (although I wonder how CH4 will burn with a T of zero C). Then w = -pdV = -p(vfinal-Vinitial) I assume you want work in J; using bar won't get that. I ...
February 9, 2015

Chemistry AP
I'll try to remember that but it isn't the usual. So all I can do is see if the set up is ok. Your set up on the earlier problem was ok. That isn't your x in this hydrolysis equation. Calling NH2NH2 just BNH2, I would convert pH to pOH and use OH as x in the ...
February 9, 2015

chemistry
See your earlier post.
February 9, 2015

Chemistry
rate = k(NO2)^2 rate is 1/2delta(NO2)/time
February 9, 2015

Chemistry
dG = dGo + RTlnQ. Q if you have forgotten is (HCl)^2/(Cl2)(H2) for this reaction and plug in those concentrations in the problem. Remember R is 8.314, convert -10.5 to kelvin and remember to use dGo and dG in joules (not kJ)
February 9, 2015

Chemistry
The bubble is gone which means the volume measured is the volume of the titration + the volume of bubble; i.e., it is too large. If you are doing a titration with acid so that mL acid x M acid = ml base x M base, then Mbase = mLacid x Macid/mL base So mL base is too large how ...
February 9, 2015

Chemistry
How do you suggest I help you? You can't look up the pKa?
February 9, 2015

Chemistry
mols strong acid = M x L mols weak acid = M x L mols NaOH = M x L. So when mols NaOH = mols of EITHER the indicator turns. The indicator doesn't know what kind of acid is present. When mols = mols the indicator turns (if you're using the right indicator for the pH).
February 9, 2015

Chemistry AP
Your set up is ok. My answer is 4.026E-4M. However, you're allowed only two significant figures (set by the 4.3E-7 Ka value) so I would round that to 4.0E-4M. I suspect the s.f. thing is catching you.
February 9, 2015

Chemistry AP
When you have problems like this post your work. That way we can see at a glance what is wrong.
February 9, 2015

chemistry
(SO2) = 4 mol/2L = 2M (O2) = 5 mol/2L = 2.5M .......2SO2 + O2 = 2SO3 I.......2M...2.5M....0 C......-2x...-x......2x E......2-2x..2.5-x...2x I presume you mean (O2) AT EQUILIBRIUM is 2M. That means 2.5-x = 2; therefore, x = 0.5. Evaluate SO2 and SO3 at 4equilibrium, substitute ...
February 9, 2015

science
If it is inside a closed (sealed) container it is a closed system. If it is reacting in an open vessel on the counter or table top it is an open system. I think each system is self explanatory.
February 9, 2015

Chemistry
http://en.wikipedia.org/wiki/Calcium_carbonate see uses as fertilizer, antacid, dietary calcium supplement, etc. Isn't calcium carbonate a perfectly good name?
February 9, 2015

chemistry
I would convert that to Angstroms and compare with this site. http://csep10.phys.utk.edu/astr162/lect/light/spectrum.html
February 9, 2015

chemistry
What is it reacting with?
February 9, 2015

chemistry (Bohr model)
The Bohr model is a function of RZ^2(1/n^2 - 1/n^2) where the first n is n1 and the second is n2 Z is the atomic number. He is 2 and 2^2 = 4 Li is 3 and 3^2 = 9
February 9, 2015

organic chemistry
I don't know if you are talking about the anti-markonikov's rule or not but here is. http://en.wikipedia.org/wiki/Markovnikov%27s_rule#Anti-Markovnikov_reactions
February 9, 2015

Chemistry
What is your problem in doing this?
February 9, 2015

chemistry
KHP + NaOH ==> NaKP + H2O mols NaOH = M x L = ? mols KHP = mols NaOH since the reaction is 1:1 grams KHP = mols KHP x molar mass KHP. %KHP = (mass KHP/mass sample)*100 = ?
February 9, 2015

Chemistry
How many moles do you want? That's M x L = ? Then mols = grams/molar mass. You know molar mass and mols, solve for grams. Add that many g benzylamine to a 50 mL volumetric flask, add some acetonitrile, swirl until solute is dissolved, make the to 50 mL mark with solvent, ...
February 9, 2015

chemistry
Look up the freezing point constant for bernzene (Kf). Delta T is given in the problem as 4.19C. Then delta T = Kf*m Substitute delta T and Kf and solve for m m = mols solute/kg solvent. You know m and kg solvent, solve for mols solute. mols solute = grams/molar mass. You know...
February 9, 2015

chemistry
I can get you started. rate for 100 s is 237/100 = 2.37 rate for 200 s is 224/100 = 2.24 Then rate1 = 2.37 = k(A)^x=k(237) and rate2 = 2.24 = k(A)^x = k(224)^x solve for x. Then plug rate and (A) into any one of the trials and solve for k.
February 9, 2015

chemistry
If you will show your work I will find the error.
February 8, 2015

chemistry
Alex, James, ..... You must be punching in the wrong numbers again.
February 8, 2015

oops--typo--chemistry
psoln = Xhexane*Pohexane
February 8, 2015

chemistry
11.39% w/w is 11.39g naph/100 g solution. 100 g soln = 11.30g naph + 88.61g hexane. n = mols naph = nnaph = grams/molar mass nhexane = grams/molar mass. Take sum of mols = ntotal = nnaph + nhexane. Xhex = nhexane/total mols psolution = Xhexane*Pohexane</sub
February 8, 2015

Chemistry
Water COOLS when it goes from 18 to 70 C? Strange.
February 8, 2015

chem II
Use the freezing point depression formula. dT = Kf*m Substitute and solve for m = molality. m = mols/kg solvent. Substitute and solve for mols. mols = grams/molar mass You know mols and grams, solve for mola rmass.
February 8, 2015

Chemistry, HELP!!
Cu^2+ + 2HOH ==> Cu(OH)^+ + H3O^+ Cu(OH)^+ + 2HOH ==> Cu(OH)2 + H3O^+ Why do I need the log K for the equatiions?
February 8, 2015

science
2Na + 2H2O ==> 2NaOH + H2
February 8, 2015

Chemistry
You didn't write the equation but it appears you used Fe2S3 as the product. I think perhaps it is FeS that forms Sb2S3 + 3Fe ==> 2Sb + 3FeS Try that and see if it is any better. Your process looks ok if you started with the right equation.
February 8, 2015

chemistry
Convert 1.36g PbCl2 to Pb. 1.36 x (atomic mass Pb/molar mass PbCl2) = ? g Pb in 25 mL. Convert that to what ever concentration units you want. The problem doesn't specify. Note: I don't think it makes any difference what form the Pb is as long as it's soluble.
February 8, 2015

Chemistry
pi = MRT Substitute and solve for M. Now you must convert M to mols sucrose needed. M = mols sucrose/L solution. mols = g/molar mass = g/342 so M = g sucrose/342 Now calculate the volume in L. You will have 447g solvent + g sucrose as a mass. The density is 1.00 g/mL so the ...
February 8, 2015

Chemistry
I don't think so. 40 -(-20) = 60 and for an exothermic reaction you add Ea forward to |dH| so that is 40+20= 60 kJ/mol.
February 8, 2015

chemistry
1 mol of a gas at STP occupies 22.4L; therefore, 7.08 mols must occupy .....L.
February 7, 2015

chemistry
How much heat do you need? q = mass H2O x specific heat H2O x dT q = 150g x 4.18 J/g x 75 = approx 47000 J but you need to go through all of these calculations and redo them for better accuracy. You will lose 75% (or keep 25%) so we must increase that to approx 47,000/0.25 = ...
February 7, 2015

Chemistry
I answered this under the science post.
February 7, 2015

science
What's the M of the NaOH after mixing and before reaction? 0.200 M NaOH x (14.0/(14.0+42.4) = approx 0.00025. Since there is 1 Na^+ in 1 molecule of NaOH, 0.00025 is the M of the Na^+. The nitrate is done the same way. You need not worry about the reaction since Na^+ and ...
February 7, 2015

chemistry
Isn't this the same as your previous two or three dG problems?
February 7, 2015

chemistry
volume = mass/density
February 7, 2015

chemistry
Works the same way as dG but this is dH. Write ad balance the equation. dHrxn = (n*dHo products) - (n*dHo reactants). Of course you will need ton convert 25 lbs to grams.
February 7, 2015

chemistry
dGorxn = (n*dGo formation products) - (n*dGo formation reactants) gives you the dG for the reaction. Call that Y. Then dG for 4.70 g Ca will be Y kJ/mol x (# mols Ca in 4.70g) = ? You may want to write and balance the equation.
February 7, 2015

chemistry
I wonder if that is Cu(NO3)2. mols = grams/molar mass. Then M = mols/l. mols is ? from above. Solve for L. You know m = 0.180
February 7, 2015

To the impersonator
You are welcome to answer questions on this board but not under my name. Please use another screen name. You're use of Bob is acceptable but not DrBob222. I CAN ban you from the site if it becomes necessary.
February 7, 2015

Chemistry
You use the molar mass of the material for which you have a mass; i.e., if your material weighed is KH2PO4 then mols KH2PO4 = grams KH2PO4/molar mass kH2PO4.
February 7, 2015

Chemistry
The base is K2HPO4. The acid is KH2PO4. Convert g base to mols. mols = grams/molar mass. Do the same for the acid. Convert each to M. M = mols/L. Then substitute into the HH equation and solve for pH.
February 7, 2015

Chemistry
What's the question?
February 7, 2015

Physical Science
WHICH ONE HAS A HALF-LIFE OF 60.6?
February 7, 2015

Physical Science
So the Bi has gone through 1 half life since it has decreased from 200 g to 100 g. And it did that in 60.6 minutes so the half life of the isotope must be 60.6 minutes. and that is .......?
February 7, 2015

chemistry
Which do you think has more randomness? and why?
February 7, 2015

chemistry
Balance the equations. dGorxn = (n*dGoformation products) - (n*dGo formation reactants) The rxn is not spontaneous if dGo rxn at std conditions is +.
February 7, 2015

chemistry
Same question here. Which do you think move from more random to less random and why? For example, #4 is more random because there are more moles gas on the right than left. #5 is less random because the molecules in liquid water are more free to move around than in ice where ...
February 7, 2015

chemistry
dG = dH - TdS Set dG = 0 and solve for T in kelvin. Remember to make the units the same (they aren't now).
February 7, 2015

math
Ms. Sue gave you the numbers. All you had to do was to divide them. 576,650,390,625/38,443,359,375 = 15. Punch it in your calculator and see. The way I did it is a short cut. No matter how you slice it, however, the answer is 15.
February 7, 2015

math
A few typos but the answer is right at 15. 1510/159 = 1510-9 = 151 = 15
February 7, 2015

math
1510/159</ = 1510-9 = 151 = 15
February 7, 2015

Chemistry
A = ebc where e = molar absorptivity 0.600 = e*1.0*9.8E-6 e = ?
February 7, 2015

chemistry
NH3 + HNO3 ==> NH4NO3 + H2O millimols NH3 = 100 x 0.2 = 20 mmols HNO3 = 50 x 0.5 = 25 So you've added enough HNO3 to neutralize all of the NH3 and have an excess of 5 mmols HNO3 left. That's in 100 + 50 = 150 mL M HNO3 = mmols/ml = ?M
February 7, 2015

chemistry
The highest pKa value means the weakest acid. Why not look up the Ka or pKa values and see. http://clas.sa.ucsb.edu/staff/Resource%20Folder/Chem109ABC/Acid,%20Base%20Strength/Table%20of%20Acids%20w%20Kas%20and%20pKas.pdf
February 7, 2015

chemistry
pKb = 3.8. Kb = -log 3.8 Kb = approx 1.6E-4 but you should get a better answer than that. .......BNH2 + HOH --> BNH3^+ + OH^- I......0.01............0.......0 C......-x..............x.......x E......0.01-x..........x.......x Kb = 1.6E-4 = (x)(x)/(0.01-x) Solve for x = (OH...
February 7, 2015

chemistry
pk of 1 is stronger than pk of 2 is stronger than pk 9, etc. That should make it easy to arrange.
February 7, 2015

chemistry
The way you have displayed the answers I can't tell what is what. Here is the Ka equation for the NH4^+. NH4^+ + H2O ==> NH3 + H3O^+ Except for the missing charge on H3O^+, #4 appears the closest.
February 7, 2015

chemistry
#5 is a quite strong "weak" acid. The pKa value is about 0.7. All of the other acids listed are weaker.
February 7, 2015

Chemistry (Gen Chem 1)
140 pm/atom x #atoms = 6.70E10 pm
February 7, 2015

Chem/Hydrocarbons
I don't think there are any mathematical formulas that will tell you how many isomers a particular compound has, even for the simple straight chain compounds. There may be some hints on this page. http://www.ehow.com/how_6931563_calculate-number-isomers.html 1 or 2 or 3 ...
February 7, 2015

chemistry
You're guessing. Volume = l x w x h density = mass/volume. volume = 6.88 x 2.03 x 1.85 = ? cubic centimeters density = g mass/volume cc = ?
February 6, 2015

Chemistry
Did you look at my answer below? Don't post an exact duplicate without acknowledging that answer.
February 6, 2015

Chemistry
Thanks for letting me know.
February 6, 2015

Chemistry
I don't know what you did. My crystal ball is not working very well today.
February 6, 2015

chemistry
How many sides does this block have. Only two?
February 6, 2015

Chemistry
I made a typo so I erased the page and reposted this. I can't visualize it and my attempted drawings doin't help. I found this site on the web and appears to be what you are describing if you look at the pink one (I think three from the left) and the"clear" ...
February 6, 2015

Chemistry
Does 8 + 38 = 17 + 19 ?
February 6, 2015

Chemistry
Use the Henderson-Hasselbalch equation. pH = pKa + log (base)/(acid) Your two big problems. 1. What pKa do you use? 2. which is the acid and which the base. 3. (Actually, it doesn't matter which is the acid and which the base because the concentrations are equal which ...
February 6, 2015

Chemistry
2KClO3 ==> 2KCl + 3O2 Loss in mass = mass O2 lost = 1.042-0.943 = 0.099 mols O2 = grams/molar mass Using the coefficients in the balanced equation, convert mols O2 to mols KClO3. Then convert mols KClO3 to grams KClO3 with g = mols x molar mass.
February 6, 2015

chemistry
Yes there are. mols = grams/molar mass and 1 mol of anything(NaCl for example) contains 6.02E23 molecules of anythings (molecules NaCl for example) The two facts will work all of the question marks although some of the equations must be rearranged.
February 6, 2015

Chemistry AP
Thanks for the update. Someone should tell that Quest system that it is not doing the students a favor by implying that those additional digits are good ones. I guess those extra digits are being used to know if the answer is correct or not; the thinking must be that this way ...
February 5, 2015

Chemistry AP
I can assure you that the pH is 4.80 ad not that long string of numbers you have. You're allowed only 3 significant figures--all of the numbers after that don't count.
February 5, 2015

Chemistry AP
I forgot to mention that there is another way to do it if yu want to go to the trouble. You can not ignore the x and make a quadratic equation out of it, then solve the quadratic. However, you will get the same answer. 5.55E-10 = x^2/(0.44-x) 5.55E-10*(0.44-x) = x^2 5.55E-10*0...
February 5, 2015

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