Sunday
November 23, 2014

Posts by drbob222


Total # Posts: 45,550

Chemistry
1. 2H2O2 ==> 2H2O + O2 mols H2O2 = grams/molar mass = 10/34 = 0.294/ Using the coefficients in the balanced equation, convert mols H2O2 to mols O2. That's 0.294 mols H2O2 x (1 mol O2/2 mols H2O2) = 0.294 mols H2O2 x 1/2 = 0.147 mols O2. Now convert mols O2 to grams. g ...
November 13, 2014

Chemistry
You must scroll down and find the original post. Here is a link. http://www.jiskha.com/display.cgi?id=1415924736
November 13, 2014

Chemistry
Bob Pursley answered your first post. It's below.
November 13, 2014

Chemistry
I've tried to help at your other post.
November 13, 2014

chemistry
3CaSO4 + 2K3PO4 ==> Ca3(PO4)2 + 3K2SO4
November 13, 2014

chemistry
Convert g H2 to volume using 1 mol H2 occupies 22.4 L at STP (alternatively you can use the PV = nRT and solve for volume). Convert g He to volume He the same way. Then plug into your v/v formula and solve for percent each.
November 13, 2014

Chemistry 11
I'm not sure I understand what you did. Here is what I would do. % anything = (g/total mass)*100 = ? Atomic mass Zn = 65.4 from your post. molar mass Zn(ClO3)2 from your post = 232.3 molar mass H2O = 18 The 21.5% Zn is (note you used 21%) percent Zn in the hydrate so %Zn...
November 13, 2014

chemistry
work in joules = kg x 9.81 x height in m = ?
November 13, 2014

chemistry
Yes but if your prof is picky about the number of significant figures you will get marked down. You're allowed 2 places (because of the 8.1 so you should round that number fo 0.26 AND place a unit on it of L.
November 13, 2014

chemistry
The usual formula for %v/v is (volume gas/total volume)*100 = %. (x L CO2/3.16L)*100 = 8.1% Solve for x L CO2.
November 13, 2014

Average problem word solving epicness
He needs a total of 5*65 = 325 points. He has(55+60+65+65) = 245 He needs 325-245 = 80 If you want to set this up in equation form it will be (55+60+65+65+x)/5 = = 65 and solve for x
November 13, 2014

chemistry
Use PV = nRT and solve for n = number of mols. Then n = grams/molar mass. You know molar mass and n, solve for grams.
November 13, 2014

science
Perhaps I may interject a little insight into this rudeness thing. 1. This is a homework help site, not a homework do site; i.e., our objective on this site is to help students understand a concept so they may work through a problem. That is to say that we USUALLY do NOT ...
November 13, 2014

Urgent- Science
Do you not get the disconnection between "indivisible" by Dalton and "pieces" by the neutron and electrons. Read about the plum pudding by Thomson. Do you understand what Rutherford showed with his alpha particle bombardment experiment?
November 13, 2014

Urgent- Science
Dalton thought atoms to be indivisible. JJ Thomson discovered electrons as a part of atoms and used the plum pudding model for the pieces of an atom. Rutherford was responsible for showing that the mass of an atom was concentrated in a very small center and the rest of the ...
November 13, 2014

Chemistry
Yes, 2-2x is right but you didn't finish. 2x is 2*0.947 = 1.89 Then 2-1.89 = 0.11 = (HI)
November 13, 2014

Chemistry
Yes, that's exactly what you do. 19x = 18 19x/19 = 18/19 x = 18/19 = 0.947 But I wouldn't round to 0.95. You're allowed 3 s.f. You have 4.00 mols, 2.00 L, 81.0 for K and all of those have 3 s.f. You're multiplying and/or dividing so that allows 3 s.f. I would ...
November 13, 2014

Chemistry
You're ok so far. You've done the hard part. What's left? move the x to one side and numbers to the other and solve for x 18 = 19x x = ?
November 13, 2014

newsome
1. How many mols do you need? That's mols = M x L = ? Then mols = grams/molar mass. You know molar mass and mols from above, solve for grams. 2. You have mols/L and you know grams/L from 1. % w/v = grams/100 mL. Just change grams/L to grams/100 mL.
November 13, 2014

Chemistry (Equilibrium)
Close but no cigar. You didn't square the (0.5-0.171) which makes the 0.329 squared also. I have 0.0675
November 13, 2014

Chemistry (Equilibrium)
You went wrong on the C step and E step. (HBr) = mols/L = 0.5/1 L = 0.5M which you hvave correctly. ..............2HBr <==> H2 + Br2 I..............0.5.......0....0 C..............-2x.......x....x E............0.5-2x......x....x The problem states that (Br2) is 0.0855 (...
November 13, 2014

chemistry
I don't get it. rastor? I assume molar mass is 46. You don't list grams water. Is that density of 1.86? 1.86 WHAT units? That isn't the density of ethanol. What about just reposting the question.
November 13, 2014

Equilibrium
Yes and no. 3.9 is the correct answer and I would not round up to 4 since you are allowed two s.f. in the answer. But you choose 4.0 as the answer since that's the closest of the choices.
November 13, 2014

Equilibrium
Looks like the second set up is correct but you punched in the wrong numbers on your calculator. I get about 4 or close to that.
November 13, 2014

Chemistry
It makes it easier if you don't change screen names. Use the HH equation as in in the formic acid/sodium formate buffer There is one difference. In the formic/formate buffer you have the components separated. In this one you must combine the acid and base, calculate how ...
November 13, 2014

Chemistry
Use the Henderson-Hasselbalch equation. Convert Ka to pKa. 10.0 mL x 1.0 M sodium format is 10 millimols base. 20.0 mL x 1.00 M formic acid is 20 mmols of the acid. Plug and chug.
November 13, 2014

sixth grade math
12/15 is a fraction already. Both 12 and 15 are divisible by 3 to make it 4/5. As a decimal divide 4 by 5 to obtain 0.80 and multiply that by 100 to obtain 80%.
November 12, 2014

Chemistry (Equilibrium)
I have removed the (g) designation in order to get all of this on one line. ..........H20 + CO <==> H2 + CO2 I.........5.0...4.0.....0.....0 C.........-x.....-x.....x.....x. E.......................2......... If 2.0 mols H2 are present at equilbrium then x must be 2.0 ...
November 12, 2014

chemistry
mols solute = M x L = ? Calculate each and the highest wins.
November 12, 2014

chemistry
It was 0.1 in the V1 (whatever volume that is) and you diluted it to 250 sothe new concn is It's 0.1 x (V1/250) = ? I don't know why you wrote it was placed in a V2.0 volumetric flask. If it were brought to 250.0 mL I would assume it was placed in a 250 mL flask.
November 12, 2014

chemistry
You just do the reverse of the previous problem. How many mols do you need? That's M x L = ? Then mols = grams/molar mass. You have mols and molar mass, calculate grams.
November 12, 2014

chemistry
mols CaCl2 = grams/molar mass M CaCl2 solution = mols CaCl2/L solution.
November 12, 2014

Chemistry 11
I'm glad you asked that question. All of the work you have done is exactly right BUT you haven't worked the problem. You worked a similar problem but not the one stated. % Na FROM THE DATA IN THE PROBLEM is (g Na/total g)*100 = (13.45/24.34)*100 = 55.26% Then % Cl = ...
November 12, 2014

Chemistry
That's right. You start with 2.0 (intial), take away -2x (the change) and end up with 2-2x (equilibrium).
November 12, 2014

Chemistry
To do the equilibrium sign you simply use the < the > and == like this <==>. Most of use just use a straight arrow, either --> or ==> and let it go. (HI) = mols/L = 4.0/2.00 = 2.00M Set up an ICE chart as below: ........2HI ==> H2 + I2 I.......2.0M.....0...
November 12, 2014

Chemistry
Cl2(g) + 2NaBr(aq) ==> Br2(l) + 2NaCl The second part of the question. You "bubble in" (I guess it means mark in) E which is Br2 and D which is NaCl.
November 12, 2014

chemistry
Three equations work almost all of these. In general here they are. Fit them to your problem. WITHIN a phase (all liquid, all steam, all ice) use q = mass of the phase x specific heat of the phase x (Tfinal-Tinital) At a phase change (example melting point) use q = mass of the...
November 12, 2014

chemistry
mass = volume x density. You will need to look up the density. You can look it up on Google. I'm not sure I remember it right but I think it is 0.789 g/mL.
November 12, 2014

Chemistry
Volume = mass/density volume Fe = 52.3/7.87 = ? New volume water is the sum of initial volume + volume Fe. Note that two objects can't occupy the same volume at the same time; therefore, the Fe must displace the water by the iron's volume.
November 12, 2014

chemistry
You can do a ratio/proportion like this: (g/atoms) = (g/atoms) (28.09g/6.02E23atoms) = (x g/1.06E25 atom) and solve for x. OR you can remember that 1 mol of atoms contains 6.02E23 atoms so how many mols do you have? That's 1.06E25/6.02E23 = ? 1 mol has a mass of 28.09 g so...
November 12, 2014

Chemistry
See your post above.
November 12, 2014

chemistry
2NaOH + H2SO4 ==>Na2SO4 + 2H2O 1. The NaOH is the titrant; H2SO4 is the analyte. 2. mols NaOH = M x L mols H2SO4 = 1/2 mols NaOH (Look at the coefficients in the balanced equation.) 3. M H2SO4 = mols H2SO4/L H2SO4 4. g H2SO4 = mols H2SO4 x molar mass H2SO4 5. mass S = mass ...
November 12, 2014

chemistry
2K + 2H2O ==> 2KOH + H2
November 12, 2014

chemistry
See your post above.
November 12, 2014

Chemistry
Zn(OH)42-
November 11, 2014

Chemistry
Ag is 2 Cd is 4 (en) is 2 + 2Br = 4.
November 11, 2014

AP Chem
OK. We'll take your number of 0.116M for the solubility of KBr in a saturated solution. I don't know what value you used for Ksp but I used one from the web and ended up with 0.0118M so the answers are pretty close. You probably used a value for Ksp close to what I ...
November 11, 2014

Chemistry
Use PV = nRT T will have units of kelvin
November 11, 2014

chemistry
ln(k2/k1) = A*Ea*(1/T1 - /T2)/RT Substitute and solve for k2. Remember to convert kJ to J.
November 11, 2014

chemistry
This is a limiting reagent (LR) problem and you know that because amounts are given for BOTH reactants. Pb(NO3)2 + 2KIO3 ==> Pb(IO3)2 + 2KNO3 mols Pb(NO3)2 = M x L = ? mols KIO3 = M x L = ? Using the coefficients in the balanced equation, convert mols Pb(NO3)2 to mols Pb(...
November 11, 2014

Chem
Yes. n, l, and mL are the same BECAUSE one of the electrons is ms = +1/2 and the other one is ms = -1/2.
November 11, 2014

Ochem
How would you like for us to help you with this assignment?
November 11, 2014

Chemistry
See your original post.
November 11, 2014

Chemistry
Since can't draw diagrams on this forum here is the best I can do. Below are the electrons changes; you can draw the lines/arrows and whatever else you need to do but this is the heart of the problem. C2H5OH. Both carbons are -4 total. CH3COOH. Both carbons are zero each(...
November 11, 2014

chemistry
The pressure inside the container will be 100 mm Hg when equilibrium is reached. Use PV = nRT and solve for n, then n = grams/molar mass to solve for grams. Compare grams in the vapor with grams of the liquid to know if all will have evaporated.
November 11, 2014

chemistry
You didn't give the specific heat of the metal but see this post and response. http://www.jiskha.com/display.cgi?id=1415735118
November 11, 2014

chem
This is a limiting reagent (LR) problem and you know that because amounts are given for BOTH reactants. mols Ba(NO3)2 = M x L = ? mols Na2SO4 = M x L = ? Using the coefficients in the balanced equation, convert mols Ba(NO3)2 to mols BaSO4. Do the same for mols Na2SO4 to mols ...
November 11, 2014

Chem 130
Look at the limiting reagent problem you posted just above. This is worked the same way. Your equation looks ok.
November 11, 2014

Chemistry
Frankly I don't know how to answer this question. I don't know if it is a trick question or not. Here is my problem. The equivalence point is the theoretical point at which the acid just neutralizes the base. The end point (different from the equivalence point) is the ...
November 11, 2014

Chemistry
Tell me your problem here. Do you know how to write the Keq expression? It tells you in the problem what Keq is.
November 11, 2014

Chemistry
Are those the equilibrium concentrations? I assume they are. Writ the Keq expression, substitute those numbers and solve for Keq. Post your work if you get stuck.
November 11, 2014

Chemistry
Note the correct spelling of celsius. You have half of it but not the other half. The metal is heated to 95 C then placed in the water. Then heat lost by the metal + heat gained by the water = 0 heat lost by metal is q = mass metal x specific heat metal x (Tfinal-Tinitial) ...
November 11, 2014

Science-Chemistry
I suggest you look in your text or notes and if that is not an option look for the tables on Google.
November 11, 2014

Chem 2 help
http://en.wikipedia.org/wiki/Half-life See the above for q 1 and 2. For q 3, depending upon the age, the method may be used. Here is another link that describes the other "dating" methods starting with paragraph 3 then see the table just below that with a list of the...
November 11, 2014

science
Do you know the proportions (average I guess) of each in the human body.
November 10, 2014

science
q = 1673 J = mass H2O x specific heat H2O x delta T. You will need to look up the specific heat of liquid water. Delta T is 2.0 C and mass will come out i grams if specific heat is substituted in joules/g*C.
November 10, 2014

incomplete--chemistry
You didn't post a question AND you didn't post the total amount of solution for each nor the amount of each solution.
November 10, 2014

science
q = mass graphite x specific heat graphite x (Tfinal-Tinitial) q = 350 J mass graphite is 33.0 g You will need to look up the specific heat graphite. delta T is Tfinal-Tinitial and you are to solve for delta T.
November 10, 2014

science
q = mass H2O x specific heat H2O x (Tfinal-Tinitial)
November 10, 2014

History (1 word)
Jane, I apologize but the devil made me do it. I think the word you're looking for is "nullify". Here are a couple of links to read. http://en.wikipedia.org/wiki/Nullification_%28U.S._Constitution%29 http://www.cato.org/publications/commentary/yes-states-can-...
November 10, 2014

History (1 word)
stupid?
November 10, 2014

Chemistry
35.0 what of NaCl? What is the total volume. If you don't know that then what is the density of the solution. Why? Because NaCl + 125 mL H2O is MORE than 125 mL volume.
November 10, 2014

Chemistry
M = mols/L. 12.0 M = mols/10.5L Solve for mols.
November 10, 2014

Intro to Chemistry
mols CaCO3 = grams/molar mass = ? mols HCl = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols CaCO3 to mols CaCl2. Do the same to convert mols HCl to mols CaCl2. It is likely that the two values will not agree which means one of them is not ...
November 10, 2014

Intro to Chemistry
This is a limiting reagent (LR) problem; you know that because amounts are given for BOTH reactants. mols H2O2 = grams/molar mass = ? mols N2H4 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols H2O2 to mols N2. Do the same to convert mols ...
November 10, 2014

chemistry
The molecular weight of the compound would be some kind of a weighted average between the compound and the air that was left.
November 10, 2014

Science
https://www.google.com/search?q=define+ecosystem&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=sb
November 10, 2014

Quotes
http://www.brainyquote.com/quotes/keywords/find.html
November 10, 2014

Chemistry
(P1V1/T1) = (P2V2/T2) Remember T must be in kelvin.
November 10, 2014

no statements--science

November 10, 2014

statistics help needed--Dine

November 10, 2014

Science
high, low, diffusion
November 10, 2014

Science
http://www.sciencelearn.org.nz/Science-Stories/Earthworms/Characteristics-of-living-things
November 10, 2014

Science
Generally enzymes are the catalysts for specific reactions in a living organism. More specifically they lower the activation energy for a chemical reaction.
November 10, 2014

chemistry
Here is one form of the dilution equation. mL1 x M1 = mL2 x M2 ?mL1 x 5.50M = 350.0 x 0.500M ?mL1 = ?
November 10, 2014

chemistry
That doesn't help. What you posted is your answer. What I need is your WORK. I need to see your work to find your error; however, I think I see what you did (with a little help from my crystal ball). You followed half of my instructions and quit. You need to look at the ...
November 10, 2014

chemistry
I can't guess what you've done. Post your work and I'll find the error. My first guess is that you didn't convert 750 mL to 0.750 L.
November 10, 2014

chemistry
How many mols do you want? That's mols = M x L = ? Then mols = grams/molar mass. You know molar mass and mols, solve for grams.
November 10, 2014

chemistry
A good conversion factor to remember when dealing with ppm and ppb is 1 ppm = 1 mg/L so if you have 355 ug/L that is 0.355 mg/L = 0.355 ppm.
November 10, 2014

chemistry
q = mass H2O x specific heat H2O x (Tfinal-Tinitial)
November 10, 2014

Science
https://answers.yahoo.com/question/index?qid=20090422184611AAnbEvc http://www.youtube.com/watch?v=cIfpKL0brwQ
November 10, 2014

Science
what kind of impacts?
November 10, 2014

Science
Without you writing everything in section 8.1 we don't have any idea what the central theme is.
November 10, 2014

Science
The only statement you've posted is false.
November 10, 2014

no statements---Science

November 10, 2014

chemistry
mL1 x M1 = mL2 x M2 ? mL1 x 4.50 = 400 mL x 0.500 ? mL1 = ?
November 10, 2014

chemistry
How many mols do you want? That's M x L = ? Then mols = grams/molar mass. You know mols and molar mass, solve for grams.
November 10, 2014

chemistry
mols = M x L = ?
November 10, 2014

Science
2HgO ==> 2Hg + O2 mols HgO = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols HgO to mols O2. Now convert mols O2 to whatever unit you want. The post doesn't say. If grams, then grams O2 = mols O2 x molar mass O2. If volume at STP, then...
November 10, 2014

Chemistry
Increased pressure, decreased volume; more moles of the gas, decreased T
November 10, 2014

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