Tuesday
July 28, 2015

Posts by DrBob222


Total # Posts: 49,559

chemistry
Reverse equation 1 and add to the reverse of equation 2 and add equation 3 as is. Remember to change the sign of dH when reversing an equation. Post your work if you have questions.
March 26, 2015

chemistry
I've shown you how to do these above. Try your hand at this. There is little I can do except do it for you and I don't want to do that. If you still have trouble explain in detail what your problem is and I'll try to help you through it.
March 26, 2015

chemistry
Haven't you seen this before? dHrxn = (n*dHf products) - (n*dHf reactants) Post your work if you get stuck.
March 26, 2015

chemistry
q = [mass H2O x specific heat H2O x (Tfinal-Tinitial)] + [Ccal*(Tfinal-Tintiial)] Substitute and solve for q, then convert to kJ.
March 26, 2015

chemistry
q = mass x specific heat x (Tfinal-Tinitial)
March 26, 2015

Science
Do you have choices. I think several words might go there.
March 26, 2015

chemistry
8.3 mol H2S used. Use the coefficients in the balanced equation to convert mols H2S to mols H2O. That's 8.3 mol H2S x (2 mols H2O/2 mols H2S) = 8.3 x 2/2 = 8.3 mols H2O formed. Convert that to grams. grams H2O = mols H2O x molar mass H2O = estimated 149 g (but you need to ...
March 26, 2015

To Ty---chemistry
Did you read Bob Pursley's message? He is telling you that you didn't write the "above reaction". We can't read your mind and you wrote the problem part but not all of the question. Write the equation and we may be able to help.
March 26, 2015

chemistry
PV = nRT n = total mols if you want total pressure. n = mols of each if you want partial pressure of each gas by itself.
March 26, 2015

to tt---chemestry
If you want to post a question, please go to the top of the page and click on "Post a new Question".
March 26, 2015

chemestry
Explain what you don't understand about this and I can help you through it. Or if you have it worked out I'll be glad to check your answers.
March 26, 2015

Chemistry
What mass does that 7.0 mL vinegar have? You need the mass or the density of the vinegar to calculate that. NaOH + CH3COOH --> CH3COONa + H2O mols NaOH = M x L = ? mols CH3OOH = mols NaOH since the equation tells you 1 mol NaOH = 1 mol CH3COOH. Then grams CH3COOH = mols ...
March 26, 2015

chem
You posted a long string of questions a few days ago and I responded that I would be glad to help if you would tell me what you didn't understand. You didn't respond. On this long list I will do the same but I'm not interested in doing a lot of typing so you can ...
March 26, 2015

chemistry
Ptotal = pH2 + pN2 + pO2 + pCH4. Substitute and solve for pCH4 in atm and convert to kPa.
March 26, 2015

Chemistry
Use PV = nRT and solve for n = number of mols. Convert that to grams if needed; i.e., mols = grams/atomic mass.
March 26, 2015

chemistry
You need to look on the boxes or on the internet and find % caffeine in each bag and/or each serving of tea. I think you may come up largely empty handed because the FDA does not require that to be listed. I went through the same kind of thing for decaffeinated coffee and ...
March 26, 2015

Chemistry
2Zn + O2 ==> 2ZnO mols O2 = grams/molar mass = ? Using the coefficients in the balanced equation convert mols O2 to mols ZnO. That will be just mols ZnO = mols O2 x 2. Then convert mols ZnO to grams ZnO with grams = mols x molar mass.
March 26, 2015

Science
If you will show your work on this and the questions you've posted below and explain exactly what you don't understand I will be glad to critique what you have written and give you some helpful hints.
March 26, 2015

practical chemistry
Please tell me what you don't understand about this. Do you realize you're asking someone to write a book on qualitative analysis? That's what book stores are for.
March 26, 2015

AP Chemistry
This question can't be answered without know the pH of the solution. If you know the pH of the solution, substitute it into the Henderson-Hasselbalch equation and solve for the ratio of base to conjugate acid.
March 26, 2015

oops--Chemistry
Note that 12.67 is mL and must be converted to L before multilying by M to get mols.
March 25, 2015

Chemistry
I don't follow much of what you've done. That doesn't mean it isn't right. Apparently your database thinks you haven't corrected for the blank and I don't see that in your work either. Do you know how to do that? From your post I surmise that the data ...
March 25, 2015

Chemistry
I'm leaving this one for you. After the last two you should be able to do large chunks of this on your own. If you have trouble post the balanced equations and explain in detail what you don't understand about the problem/next step. I can help you through it but one ...
March 25, 2015

Chemistry
I've gone over this many times and found nothing UNTIL I checked the formula. I found two errors. The first is mols Cr2O7^2- x 3 (not divided by 3) = mols ethanol (and you should have caught that too). When I first responded I balanced the equation with dichromate + C2H5OH...
March 25, 2015

Chemistry
No. But large chunks are ok. Here is your work. moles for dichromate initially. That's 0.024M x 0.05L = 0.0012 mol Fe^2+ used in the back titration 0.1255M x 0.019L = 0.0023845. Convert that to mols Cr2O7^2- (that's 1/6 the iron(II) So 3.974 x 10^-4 and subtract from ...
March 25, 2015

Chemistry
3C2H5OH + Cr2O7^2- ==> 2Cr^3 + 3CH3COOH Again, I've not worried about the rest of the stuff here. In the back titration part. 6Fe^2+ + Cr2O7^2- ==> 6Fe^3+ + 2Cr^3+ How many moles did you have for dichromate initially. That's M x L = ? How many mol Fe^2+ used in ...
March 25, 2015

Chem
mols KMnO4 is M x L = 0.02805 x 0.1 =? You dissolved the sample in 50 mL, the titration with KMnO4 was 28.05 mL. Correct that step and follow through with the rest of the problem The set up looks ok for the rest of it. I ran through it and obtained approx 0.35 g Fe/g sample.
March 25, 2015

Chem
I don't like the Fe2 business. Probably you mean Fe^2+ and even though that is a perfect way of writing it the Fe2 bit makes one think iron is diatomic and it isn't. 5Fe^2+ + KMnO4 ==> 6Fe^3+ + Mn^2+ (I know the equation is balanced but the redox part is and we aren...
March 25, 2015

CHE 107
SA ==> ASA You want 90/0.95 = 94.7g ASA in order to produce 90 g at 95% yield. mols ASA = 94.7/molar mass ASA mols SA = mols ASA since the rxn is 1:1. g SA = mols SA x molar mass SA.
March 25, 2015

chemistry
The nice thing about balanced equations is that they allow you to convert mols of anything to mols of any other material in the equation. Use the coefficients. Here is how you do a. I'll let you do b. mols N2 = 1.75 x (2 mols N2/2 mols NH4NO3) = 1.75 x 2/2 = 1.75 mols N2. ...
March 25, 2015

Chemistry
In essence you will place the same number of mols that occupy 1.81 m^3 into a volume of 0.0155 m^3 so the pressure will increase by the inverse of the volumes; i.e., 1 atm (the initial P) x (1.81/0.0155) = ? atm
March 25, 2015

chemistry
This is a limiting reagent (LR) problem and you know that because amounts are given for BOTH reactants. 4Cr + 3O2 ==> 2Cr2O3 mols Cr = grams/molar mass = ? mols O2 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols Cr to mols Cr2O3. Do the ...
March 25, 2015

college chemistry
It most certainly does. I worked it and it produced exactly that number. If you will post your work I will find the error but I expect I can tell you without looking at your work. You probably wrote (0.1)(2x). It should be (0.1)(2x)^2 and x = 4.44E-5M big as life.
March 25, 2015

chemistry
NaOH + HCl ==> NaCl + H2O mols NaOH = M x L = ? mols HCl = mols NaOH since the ratio in the equation is 1:1. Then M HCl = mols HCl/L HCl. YOu knowL and mols, solve for M
March 25, 2015

chemistry
Set up K expression, substitute the equilibrium mixture of N2 and H2 and solve for NH3.
March 25, 2015

chemistry
Follow up on your later post but the answer really is 4.44E-5M. You just didn't set it up right. Probably didn't square F^- OR didn't include the 2 which squared is 4.
March 25, 2015

chemistry
This is a Ksp problem with a common ion add on. Two equilibria. Sr(NO3)2 is a strong electrolyte and ionizes 100% in solution. ..........Sr(NO3)2 ==> Sr^2+ + 2NO3^- I..........0.100........0........0 C.........-0.100.......0.100...0.200 E...........0..........0.100...0.200 ...
March 25, 2015

Physical Science
This is a limiting reagent (LR) problem and I know that because amounts are given for BOTH reactants. I solve these the long way--there is a shorter way but I think it's harder to explain, especially by typing. 2Bi + 3F2 ==> 2BiF3 mols Bi = grams/molar mass = ? mols F2...
March 25, 2015

Chemistry CP
Because of intermolecular forces, H2O is not a simple H2O molecule but a cluster much like (H2O)n where n represents a small whole number. The last time I read something on this n was something like 6 at room temperature but was 1 as steam at 100 C. So the molar mass of H2O is...
March 25, 2015

chemistry cp
If you mean increasing boiling points from top to bottom, yes.
March 25, 2015

chemistry cp
What's your main problem with this. You do it with intermolecular forces, H bonding, molar mass, etc.
March 25, 2015

chemistry
Technically, H bonding occurs between H and O, N, F atoms. Look at H bonding of HF.
March 25, 2015

Chemistry
You need to supply all of the question.
March 25, 2015

chemistry
Is that m/10 or M/10. I assume you know there is a difference. Also you must assume the volumes are additive. Technically they are not. 0.1M x (400/600) = ?
March 25, 2015

Chemistry
Convert pH 2.3 to (H^+) with pH = -log(H^+) Then convert 9 cups H2O to mL and I'll call that ?mL Then (H^+) x (volume original lemon juice/? mL in 9 cups) = ? = (new H^+ in mols/L. Convert that back to pH.
March 25, 2015

chemistry
3 mols x 24 mol/dm^3 = ?
March 25, 2015

Physical science
I didn't look up the values but my best guess is, from slowest to highest: water, methylated spirits, ethanol, nail polish remover.
March 25, 2015

Physical science
Look up the vapor pressure of each at whatever temperature is of intrest and compare. The highest vp evaporates fastest.
March 25, 2015

chemistry
Tartaric acid has two ionizable H^+ but k1 is very close to k2; I assume the 0.50 mols reduced both and that's the equivalence point to which you refer. H2T + 2NaOH ==> Na2T + 2H2O 0.5 mol NaOH x (1 mol H2T/2 mols NaOH) = 0.5 x 1/2 = 0.25 mols H2T
March 25, 2015

Chemistry
You can get pH from HH equation. From that calculate pOH. I assume you can get K easily. Then for H3PO4 calculate the fraction in that from from H3PO4 = (H^+)^3/D where D is (H^+)^3 + k1(H^+)^2 + k1k2(H^+) + k1k2k3
March 25, 2015

chemistry
ln(No/N) = kt
March 25, 2015

chemistry
http://www.chemguide.co.uk/physical/basicrates/orders.html
March 25, 2015

chemistry
mols H3PO4 = 2.00 # molecules H3PO4 = mols x 6.02E23 # atoms O is 4x that.
March 25, 2015

math
That's right.
March 24, 2015

math
If it is 31 F now and it drops by 15 F, then the new T will be 31-15 = ?
March 24, 2015

chemistry
Use the HH equation. I would start with any convenient number for the initial concentration of HA. Any number will work but I would choose 1 to make it easy. So if we start with 1M HA it will be 0.25 at 75% titrated and the salt (the base) will be what? Plug those values into ...
March 24, 2015

Chemistry
I would write the reaction as Zn|Zn^2+(0.4M)||Zn^2+(1.45M)|Zn Zn ==> Zn^2+(0.40) + 2e at the anode Zn^2+(1.45) + 2e ==> Zn at the cathode ----------------------------- Zn + Zn^2+(1.45M) ==> Zn + Zn^2+(0.4) Then Ecell = Eocell - [0.05916/2]*log Q where Q is 0.40/1.45. ...
March 24, 2015

math
b is correct for #1.
March 24, 2015

chemistry
You remember that 1 mol of a gas at STP occupies 22.4 L.
March 24, 2015

chemistry
You can convert any mol in this equation to any other mol in this equation by using the coefficients in the balanced equation. For example: How many mols NaN3 are necessary to obtain 10 mols Na? 10 mols Na x (2 mols NaN3/2 mols Na) = 10 x 2/2 = 10. The number on the top of the...
March 24, 2015

Chemistry
2C4H10 + 13O2 ==> 8CO2 + 10H2O This is a limiting reagent (LR) problem. mols C4H10 = grams/molar mass = ? mols O2 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols C4H10 to mols CO2.' Do the same for mols O2 to mols CO2. It is likely ...
March 24, 2015

Chemistry
right
March 24, 2015

Science
If that is 0.3 ohm apiece, then total R is 0.1. Then E = IR = 8*0.1 = ? Is that right?
March 24, 2015

Chemistry
Why don't you post this under a physics banner? This is more a physics question than a chemistry question. I would answer that F = m*a. Since m is the same and a is the same (it isn't moving) then F must be the same. But I would feel better if you got your answer from ...
March 24, 2015

Science
Look up life cycle of mosquito on Google. Each stage will be there. Or see if it's in your text (and don't tell me you don't have a text).
March 24, 2015

Analytical Chemistry
I found it. http://www.jiskha.com/display.cgi?id=1425612744
March 24, 2015

Analytical Chemistry
Didn't I do one of those "list all species of H3PO4" for you recently? I don't want to write all of that stuff again. Look at your notes (you do take notes here I would think). What can you do on your own?
March 24, 2015

chemistry
Look up Ksp for PbCl2 and solve for solubility PbCl2 @ 25 C. (You will get solubility at 25C because that temperature is used for determining Ksp). Then convert M to mols/L, then to grams/L. If the solubility is >1.0 g no ppt; if < 1.0 g, yes a crystallization will occur.
March 24, 2015

Chemistry
I don't think so. dHrxn = (n*dHf products) - (n*dHf reactants) 4*-973.49 = (8*dHfCO2 + 10*dHf H2O) - (4*dHf glycine) Solve for dHf glycine
March 24, 2015

chemistry
I've been burned on question like this in the past and vowed to leave them unanswered. However, it appears to me that c is the way to go. I'm assuming when they say "less work" that is compared to the work available if the piston were to fully compress the ...
March 24, 2015

Chemistry
No, I don't get that answer. I only went through it once so I could have made an error. Here is what I did. The reverse of twice equation 3 + the reverse of equation 2 + 3x equation 1 and that gave me 6FeO + 6CO ==> 6Fe + 6CO2 and -101 kJ/mol. That divided by 6 = about...
March 24, 2015

Chemistry
Note that Fe2O2 isn't correct. Didn't you intend to type Fe2O3
March 24, 2015

chemistry
I would choose NH3.
March 24, 2015

chemistry
If you have a fat (heavy--really big) dog and thin (skinny) dog, which one can move faster? It works the same way with molecules. The heavier ones move slower than the lighter ones.
March 24, 2015

chemistry
I agree
March 24, 2015

Chemistry
You have the balanced equation. That's always the first step. Convert 24.4 g Al to mols. mols = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols Al to mols H2SO4. Now convert mols H2SO4 to grams. g = mols x molar mass = ?
March 24, 2015

Delete Question
A question and a comment. 1. Do those questions really disappear? I can look at posts back to 2010 (actually earlier than that). 2. Can they be deleted? Yes if the question has not been posted too long.
March 24, 2015

Chemistry
My calculator gives me 10.85 which I would round to 10.8 to three significan figures. Your set up is correct.
March 24, 2015

Chem
Many thanks for showing your work. It makes it easy to spot the problem. mass 2.0 L H2O is 2,000 g and not 2 g
March 24, 2015

Chem
heat lost by granite + heat gained by water = 0 [mass granite x specific heat granite x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0 Substitute the numbers and solve for Tf.
March 24, 2015

chemistry
This can't be answered until you know the concentration of the concentrated solution. By the way, you used FAR too much space for a two line question.
March 24, 2015

college chemistry
You don't have any concentrations listed so I can't write Qc. The equation is 2As2O3(s) + 10F2(g) ==> 4AsF5(l) + 3O2(g) Qc or Kc expresion is (O2)^3/(F2)^10
March 24, 2015

chemistry
How does one combust CO2? Burn it with oxygen? fat chance.
March 24, 2015

Chemistry
I don't think you can do that. pH 2.67 is acidic. pH 9.25 is basic. You can't make the solution more basic by adding HCl.
March 24, 2015

Chemistry
That's exactly right and I agree with both of the values you have. The profs purpose in assigning a problem like this is to illustrate just how much the solubility increases when one takes into account the activity coefficients. You see when you use molarity by itself you ...
March 24, 2015

Chemistry
Note: the first post noted Tl, not Ti. Ksp = (Tl^+)(SCN^-) and the activity is supposed to be substituted directly; i.e. Ksp = aTl^+ x aSCN^-. Since you know activity of each(if those numbers are really activities), substitute those and solve for solubility just as you did for...
March 24, 2015

Chemistry
what you must do is calculate the solubility of TiSCN as if concn in M is the same as activity. In the other case you want to use ionic strength to calculate activity of Ti and activity of SCN and use that to calculate solubility. Compare the solubility by the two methods.
March 24, 2015

chemistry
I'll get you started. C5H11N is the base which I will call B. You have approx 0.18 mols in 15 g but you need a more accurate answer than that. ...........B + H^+ ==> BH^+ I.......0.18...0........0 add............x........... C.........-x..-x.........x E......0.18-x..0...
March 24, 2015

chemistry
My take on this is as follows. B. Does changing shape, hardness, or transparency change odor? I don't think so. So I rule out B. C. Does change P change mass? no. Does changing mass change density? no. So I rule out C. D is already ruled out because we know changing ...
March 24, 2015

chemistry
I repeat, it can't be D. Molar mass doesn't change when pressure or temperature changes.
March 24, 2015

chemistry
Well, you know it can't be D. Molar mass doesn't depend on T, P, or number of mols does it?
March 24, 2015

chemistry
grams = mols x molar mass = ?
March 24, 2015

Chemistry
Probably I should have said I didn't read the question "carefully enough". But thoroughly fits in there somewhere.
March 23, 2015

Chemistry
You're right. I didn't read the question thoroughly enough. The secret word in the problem is increase. And when T increases the density decreases because the volume increases. density = mass/volume so when volume goes up density goes down. As for B, I looked up the ...
March 23, 2015

Chemistry
I told you above it was a. a is the only one that gives you a straight line on the graph. All you had to do was look at the graph and see which gives a straight line. A straight line is the only way you can get a linear relationship (if you plot directly and not log or ...
March 23, 2015

Chemistry
I think you have defined "directly proportional" which is the opposite of "inversely proportional". Here is the definition of linear from the web. https://www.google.com/search?q=define%3Alinear&ie=utf-8&oe=utf-8 Notice it talks of a straight line. You had ...
March 23, 2015

Chemistry
What does linear mean?
March 23, 2015

Chemistry
No. Look at the P vs V plot at that same site. It certainly is not linear. Do you know what linear means?
March 23, 2015

Chemistry
See the V vs T graph. https://www.google.com/search?q=graph+volume+gas+vs+T&ie=utf-8&oe=utf-8
March 23, 2015

Chemistry
yes
March 23, 2015

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