Saturday
March 28, 2015

Posts by DrBob222


Total # Posts: 47,990

Chemistry (Electrochemistry)
96,485 C will stip 107.9 g Ag. 107.9 x 0.600/96.485 = g Ag stipped g = v x d. You know g and d, solve for volume. Area of the unmasked section is A = pi*r^2 = pi*(0.5/2)^2 = ? volume = A * thickness. You know volume and you know A, solve for thickness in cm and convert to um. ...
January 10, 2015

Chemistry
First off I think it is important for you to realize that you are not using (or thinking about) an ordinary balance. This mass measurement must be used in conjunction with an externally applied magnetic field. If the element has unpaired electrons it is paramagnetic and will ...
January 9, 2015

Chemistry
For every one Fe(NO3)3 molecule you have you get three NO3^- ions when the molecule dissociates. So the (NO3^-) is 23.1 ppm x 3 = ?
January 9, 2015

science
q1 = heat removed in changing T from steam at 122 to steam at 100. q1 = mass steam x specific heat steam x (Tfinal-Tinitial) q2 = heat removed on condensation at 100 C to water at 100 C. q2 = mass steam x delat H(heat condensation) q3 = heat removed in changing T of liquid ...
January 9, 2015

Chemistry
The procedure I wrote and the one Devron wrote is essentially the same. Assuming the reaction proceeds, the correct balanced equation is 2Al(NO3)3 + 3K2SO4 ==> Al2(SO4)3 + 6KNO3
January 9, 2015

Chemistry
I don't think any Al2(SO4)3 will be produced because there is nothing to drive the reaction. The reasons for a reaction are 1. gas is formed. none here 2. ppt formed. everything soluble here. 3. Slightly ionized material. not true here. But in the spirit of the question ...
January 9, 2015

Chemistry
w of Na2CO3 = 105.94, Thus moles Na2CO3 = 1.234/105.94 = 0.011. My calculator gives 0.011648. Why did you throw those other numbers away? You have 4 significant figures in 1.234 so you should be able to have AT LEAST 4 places and I like to carry one extra place--then round a ...
January 9, 2015

ap chemistry
Which was the solute and which the solvent? I'm assuming from the question I answered last night about lauric acid that the lauric acid is the solute and benzoic acid is the solvent. (1)delta T = Kf*m (2) m = mols/kg solvent (3) mols = grams/molar mass Follow from the ...
January 8, 2015

Chemistry 1010
mols AgNO3 = L x M = 0.0700 x 0.692 = ? Use the coefficients in the balanced equation to convert mols AgNO3 to mols Ag2CO3. That's ? mols AgNO3 x (1 mols Ag2CO3/2 mols AgNO3) = ? mols AgNO3 x 1/2 = ? Then g Ag2CO3 = mols Ag2CO3 x molar mass Ag2CO3.
January 8, 2015

chemistry PLEASE HELP URGENT
I'll do the middle one. 0.2 mols/L (NH4)2SO3 The cation is NH4^+ For every 1 mol (NH4)2SO3 you have 2 mols NH4^+; therefore, (NH4+) = twice the (NH4)2SO3 and that give 0.2 mols/L x 2 = 0.4 mols/L = 0.4 M. a is Na2CO3 formula. c is Fe2(SO4)3 formula.
January 8, 2015

Science
I don't see two equations. I think I may see your problem. H3PO4 is not one equation and H4P2O7 a second. H3PO4 is part of an equation and H4P2O7 is another part of an equation. To answer your question, however, you're right about H3PO4. H4P2O7 has 4 H atoms, 2 P atoms...
January 8, 2015

chemistry
I believe the answer provided by this solution is three times too large. The problem asks for grams Na3PO4 to provide 0.25 M SODIUM ION. Since there are 3 Na ions per Na3PO4 molecule you need to divide 0.25/3 to begin with, then proceed s in the above.
January 8, 2015

chemistry
Co is 1s2 2s2 2p6 3s2 3p6 3d7 4s2 Co^2+ is 1s2 2s2 2p6 3s2 3p6 3d7 For the d orbitals draw 5 boxes. I can't do this on this forum but 5 boxes in a line (row). The boxes look like this for Fe and Fe^3+. https://www.google.com/search?q=Co+orbital+boxes&tbm=isch&tbo=u&source=...
January 8, 2015

chemistry
In what? mols/L, M, g/L, etc. I'll assume M or moles/L. moles (NH4)2CO3 = grams/molar mass = ? Then mols NH4^+ = 2 x mols (NH4)2CO3. M = mols NH4^+/L = ?
January 8, 2015

Chemistry
This is not a dilution problem. mols KHP = grams/molar mass = ? mols NaOH = mols KHP M NaOH = mols NaOH/L NaOH Solve for L NaOH and convert to mL.
January 8, 2015

chemistry
I see from another post that you are asking about the weight. I also note you seem to be using the weight of a lemon and the pure lemon juice almost interchangeably. You know, of course, they are not the same. Did you weigh the whole lemon? That's not pure lemon juice. Did...
January 8, 2015

chemistry
And think you are right. I think the density of pure lemon juice is fairly close to that of water. Perhaps the lemon juice you used has seeds? or pulp? I think 1.36 g/mL sounds high to me. In answer to your last question no, it means the answer should be closer to 1.0 g/mL. Or...
January 8, 2015

SCIENCE
I don't see a question here.
January 8, 2015

sdvfsd
Probably the longest sentence I've ever seen but I don't see a question.
January 8, 2015

lauric acid
http://www.jiskha.com/display.cgi?id=1420733562
January 8, 2015

science
You can't calculate it without numbers, other than looking it up. Post your question instead of trying to summarize it. You've posted the question with no details.
January 8, 2015

Chemistry
4.5 mols C will produce 4.5 mols CO2 at STP. One mole CO2 occupies 22.4 L at STP so 4.5 mols CO2 will occupy .....?
January 8, 2015

Chemistry
2Fe2O3 + 3C ==> 3CO2 + 4Fe 5.6 mols Fe2O3 x (3 mols C/2 mol Fe2O3) = 5.6 x 2/3 = ?
January 8, 2015

Chemistry
Oxidation is the loss of electrons. Cu goes from zero on the left to 2+ on the right. Cu ==> Cu^2+ + 2e Reduction is the gain of electrons. Ag goes from +1 on the left to zero on the right. Ag^+ + e ==> Ag
January 8, 2015

ap chemistry
(1)delta T = Kf*m Substitute delta T and Kf; solve for m (2)m = mols/kg solvent Substitute m and kg solvent; solve for mols (3)mols = grams/molar mass. Rearrange to molar mass = grams/mols. Now follow through with equation 1, 2, and 3. If some of the lauric acid (but you have ...
January 8, 2015

oops-typo---Chem-Stoich
Ignore the last line. I don't know how it got posted; it shouldn't be there. The rest of the problem is ok.
January 7, 2015

Chem-Stoich
mmol = millimole mmol HCl initially = mL x M = 35.00 x 1.00 = 35.00. mmols NaOH used to titrate excess is 31.51 x 0.0950 = 3 approx but you need to do a more accurate calculation. All of the other numbers that follow are approximations, too, so you need to redo all of this ...
January 7, 2015

chemistry
See your post below.
January 7, 2015

chemistry
I don't think you have enough information. dG = dH - TdS At boiling, dG = 0 Then TdS = dH and dS = dH/T = 540/373 but that gives you cal/g and you want cal/mol. Without knowing the molar mass (I assume this is water but the problem doesn't say that), I can't ...
January 7, 2015

Science
Probably not. I think it wants the number of DIFFERENT atoms (H,S,O or 3) and the total number of atoms.7. The question isn't worded very well.
January 7, 2015

chemistry
Don't you think that is proprietary information?
January 7, 2015

colligative
I don't understand the question I don' think. You use a thermometer to measure T.
January 7, 2015

ap chemistry
I get 2.00 atm also. If you have a density in the problem we can correct for and use M and not m but with no density in what you posted we have no choice but to use m for M.
January 7, 2015

ap chemistry
moles in 4.9g = grams/molar mass = ? m = molality = mols/kg solvent delta T = Kf*m. Solve for delta T and subtract from the normal freezing point of H2O (0C) to find the new freezing point. pi = MRT M is molarity but in dilute solutions M and m are almost the same. R is 0....
January 7, 2015

colligative properties
What exactly do you not understand. XH2O = 19.6/23.8 = 0.824 Then 0.824 + XCH4N2O = 1 XCH4N2O = 1-0.823 = ? You may be confused by where did I get the one. The sum of the mole fractions in EVERY solution must add up to 1. Remember 100% is all of something and that is 1 when ...
January 7, 2015

colligative properties
I answered this below.
January 7, 2015

chemistry
http://www.jiskha.com/display.cgi?id=1420508318
January 6, 2015

chemistry
After you have XH2O, then use the next equation, XH2O + XCH4N2O = 1 0.824 + X = 1 Solve for X.
January 6, 2015

chemistry
The first line is the equation you use. You know psoln = 19.6 torr and you know Po H2O is 23.8 torr. Solve for XH2O. It's as simple as 19.6/23.8 = ? Then convert to XCH4N2O.
January 6, 2015

chemistry
psoln = XH2OPoH2O Then XH2O + XCH4N2O = 1. Solve for XCH4N2O
January 6, 2015

chemistry
Answered above.
January 6, 2015

college chemistry
Answered above.
January 6, 2015

ap chemistry
Answered above.
January 6, 2015

Chemistry
I found your answer to my response last night and I expect you are ok. I used 2257 J for heat vaporization and 334 for heat fusion and 4.184 for specific heat H2O and came up with 5460 g, Your 40.6 kJ/mol is about 2253 J/g and I used 2257. I used 4.184 and you used 4.18. Your ...
January 6, 2015

Chemistry
You type in the work like the rest of us. Give me a second and I'll work the problem and see if 5.36 is about right.
January 6, 2015

Chemistry
Then why not post your work and let us check it?
January 6, 2015

Chemistry
2P4 + 7O2 ==> 2P4O7
January 6, 2015

Chemistry
Mols Cu dissolved in A is amount Cu in solution from the dissolution. That is the 0.048 figure. Step B simply removes the SOLID copper (excess Cu) that did not dissolve. You're left with the same solution from step A. So whether you take the solution from step A or the ...
January 6, 2015

Chemistry
A is right, as far as you went, but probably will be counted wrong on an exam BECAUSE you have 4 significant figures in that 3.067 and only 2 in the answer. You need to read and transcribe ALL of those numbers in your calculator (up to 4 of course). I usually carry everything ...
January 6, 2015

AP Chemistry
I would try to do each step separately. 1*25 = -25 L*atm 0.1*50 = -5 L*atm Total is -30 L*atm and convert L*atm to calories. I don't know the conversion factor BUT L*atm to joules is x 101.325 and joules to calories is divide by 4.184.
January 6, 2015

Science
I agree with 2 and 4 but not 1 and 30 Read this for 1 and 3. http://www2.lbl.gov/abc/wallchart/chapters/03/4.html
January 6, 2015

chemistry
Yes, when I write M that is molarity in moles/L. M = molarity. I ALWAYS write the words molar mass out since there is no official abbreviation. The atomic mass in grams is 1 mol of any element. The molar mass in grams of any compound is 1 mole of that compound.
January 6, 2015

chemistry
1 mol CH3COOH in 1L = 1M 2C = 2*12 = 24 4 H = 4*1 = 4 2 O = 2*16 = 32 Total = 60 That's if you use acetic acid and not vinegar.
January 6, 2015

chemistry
Your question in print now makes a lot more sense. All you need to do is to list the concentrations of each reagent. I would do that in molarity. For acetic acid, you put in 60 g and that will be 1 M if the total volume is 1L. (Remember vinegar will be about 5% stuff AND it ...
January 6, 2015

chemistry
No, and that was the point of my response. They don't necessarily react together. The acetic acid MAY just provide an acidic medium, the lemon juice may just react with grease, the water may just clean those materials soluble in water, etc. Since you don't really ever ...
January 6, 2015

chemistry
Must you write an equation? What about just writing the formulas for vinegar, salt, water, and citric acid. Most of these clean particular agents so you only need to write the equation between that specific chemical and the particular dirty spot it works on. That's if you ...
January 6, 2015

Science
I disagree with C6H7O2(OH)3. There are 21 atoms. C = 6 H = 7 O = 2 (OH)3 = O = 3 and H = 3 Total 21
January 6, 2015

ap chemistry
Don't swith screen names. Your other post says answer is 0.976E-6M You need to find out what your teacher used for K; in fact, s/he should have given it to you. A K of 3.1E-2 mol/L*atm will give you 9.3E-6M
January 6, 2015

chemistry
answered below.
January 6, 2015

ap chemistry
same song, second verse.
January 6, 2015

ap chemistry
answered below on one of the piggy back post.
January 6, 2015

ap chemistry
answered below at the LONG long thread.
January 6, 2015

college
Answered below.
January 5, 2015

chemistry
responded below. mass % should be 2.5%. M and m are right.
January 5, 2015

college chemistry
I responded below. mass percent is not right (should be 2.5%) but M and m are right.
January 5, 2015

college chemistry
Don't be coy. How much do you know how to do and exactly what do you not understand? I'm not working these so you can check your answer but I will be glad to help you through what you don't understand.
January 5, 2015

ap chemistry
For the (CO2) I used 3.4E-2 for K in mol/L*atm and 29.41 for K in L*atm/mol (just the reciprocal). Your teacher may have used a different K value. Mine came from Wikipedia. A K of 3.25 mol/L*atm will give you 9.75E-6M
January 5, 2015

ap chemistry
Yes, and I missed that. The solution has a mass of 1000 g if the density is 1.0 g/mL but 25g of that is NaCl so the mass solvent is not 1 kg (as I led you to believe) but 1000g-25g = 975g or 0.975 kg. Then m = mols/kg solvent = 0.428/0.975 = ? I have answered above that both M...
January 5, 2015

ap chemistry
25g/58.44g NaCl=.428 mol 1000 grams of solvent H20 25g/58,44 g x100= 42.8 % mass percent No, you have 25 g NaCl in 1000g which is 2.5 g/100 so it is 2.5%. molarity .428 mol/1.0 L= .428 M molality= .428 mol/1 Kg= .428 molal is that right? The M and m are right.
January 5, 2015

ap chemistry
k for CO2 is 3.4E-2 mols/L*atm c=KP Substitute p of 3.4E-2 for K and 3E-4 for P, solve for C (in M or mols/L)
January 5, 2015

ap chemistry
The problem doesn't ask for % benzene. The mole fraction toluene is right (but I obtained 0.252 when rounded). mole fraction benzene is not but problem doesn't ask for that. However, it is 1-mols fraction toluene = 1-0.252 = ? M toluene = mols toluene/L soln and soln ...
January 5, 2015

ap chemistry
28.4% tolune is right.
January 5, 2015

oops--typo--ap chemistry
I have bold faced the typo sentence below. I will get you started with mass percent. mass percent = (grams solute/mass solution)*100 = % What mass benzene do you have? Use density to calculate that. What mass toluene do you have? Use density to calculate that. mass solution = ...
January 5, 2015

ap chemistry
I will get you started with mass percent. mass percent = (grams solute/mass solution)*100 = % What mass benzene do you have? Use density to calculate that. What mass toluene do you have? Use density to calculate that. mass solution - mass toluene + mass benzene. Now Substitute...
January 5, 2015

ap chemistry
http://www.jiskha.com/display.cgi?id=1420516971#1420516971.1420518334
January 5, 2015

chemistry
A long drawn out problem. How much do you know how to do and exactly what do you not understand about the problem.
January 5, 2015

chemistry
You have 10 g sugar/100 mL ; therefore, you have 60g sugar/600 mL. Or you can do it another way; i.e., 10g sugar x (600 mL/100 mL) = 60 g sugar. 4g sugar/tsp x #tsp = 60 g sugar. Solve for #tsp.
January 5, 2015

Chemistry
First, convert 100 lbs ice to grams. 100 lbs x (454 g/lb) = ?grams. You may want to use 453.6 g/lb or 453.59 g/lb.. Second, determine q needed to heat the ice & water. q1 = heat needed to melt ice. q1 = mass ice x heat fusion. q2 = heat needed to raise liquid water from zero C...
January 5, 2015

chemistry
Would you please read you post and translate it for me. "Given a teaspon.....? makes no sense to me. By the way, how many mL in a teaspoon?
January 5, 2015

Math
x^2 * x^3 = x^5 and not 2x^5
January 5, 2015

chemistry
You have a limiting reagent (LR) problem here. I know that because amounts are given for BOTH reactants. Zn + 2HCl ==> H2 + ZnCl2 mols Zn = grams/molar mass = about 0.34 but you need to do all of these calculations more accurately. mols HCl = M x L = about 0.048 Using the ...
January 5, 2015

chemistry
Your post doesn't specify ppm by mass or ppm by volume. I will assume ppm by mass is what you want. 5 ppm is 5g O2/1,000,000 g H2O Divide both numerator and denominator by 1000 for 5E-3g O2/1,000 g H2O = 5E-3g O2/1 L H2O mols O2 = 5E-3/32 = about 1.6E-4 but you need to do ...
January 5, 2015

chemistry
2H2 + O2 ==> 2H2O 10 mol H2 x (2 mols H2O/2 mols H2) = 10 mol x 2/2 = ? mols H2O grams H2O = ? mols H2O x molar mass H2O = ? Assuming the density of water is 1.0 g/mL, then mL H2O = grams H2O.
January 5, 2015

chemistry
3 m = 300 cm 2 m = 200 cm volume = 300x300x200 = ? cc.
January 5, 2015

expressions and equations
Is this an equation? What are you to do? If you are to evaluate it, first clear the parentheses. 0.5(12z-7)-3.5z+3.5 6z-3.5-3.5z+3.5 The two z terms add to 2.5z The two numbers evaluate to zero. If you had shown your work we could tell you where you went wrong.
January 5, 2015

chemistry
This is a limiting reagent problem (LR) and you know that because amounts are given for both reactants. Convert g Al2O3 to mols. mols = g/molar mass. Convert g HCl to mols. same procedure. Using the coefficients in the balanced equation, convert mols Al2O3 to mols AlCl3. Do ...
January 5, 2015

AP Chemistry
If you have posted the problem exactly as is then the 4.2 has two s.f. and the 20.6 has three s.f. and you will be allowed 2 in the answer. You would need 4.2000 and 20.600 to be able to use 5 s.f.
January 5, 2015

oops--typo--AP Chemistry
......so the 12.36 rounds to 12.4 mols.
January 5, 2015

AP Chemistry
My best educated guess is that you are reporting the number with more significant figures than you are allowed. I obtained 12.36 also, however, you're allowed only 2 s.f. (from the 4.2) so the 12.35 rounds to 12.4 mols. Try that. If that doesn't fix the problem let me ...
January 5, 2015

math
Looks ok to me.
January 5, 2015

chemistry
molar mass NaCl = 23 for Na, 35.5 for Cl; total = 58.5 # mols = grams/molar mass = ? I've used the atomic mass Na and Cl from memory, you should confirm them by looking on the periodic table or a chart.
January 5, 2015

Chemistry
Are you talking about experimentally or knowing in advance without any resources except what you know? Experimentally you add an indicator to an aqueous solution. For knowing the state you need to know something about the reaction. Most solid compounds don't react but many...
January 4, 2015

Chwmistry
You don't give enough information to answer the question. From 21.4 C to what higher temperature? But here is what you do. q in cal = mass CHCl3 x specific heat CHCl3 x (Tfinal - Tinitial). Then q in cal x 4.184 J/1 cal = ? J
January 4, 2015

chemistry
Volume used NaOH: 35.8 mL (I subtracted 50 mL from 14.20 mL.. Am I doing this right??) You did it right but said it wrong. Volume is 50-14.20 = 35.8 mL NaOH BUT you subtracted 14.20 from 50 not the other way around. Moles of NaOH: 3.58 mol Because n= C xV n= (0.100 mol/L)(35....
January 4, 2015

chemistry
Both c and d give you pH 9.26 since base/acid = 1 and log 1 = 0. But d is the better answer because the more concentrated solutions make the buffer capacity larger; i.e., the more concentrated solutions can handle MORE of an added base and/or acid before changing more than...
January 4, 2015

chemistry
What pressure? What temperature? If you have P and T you can use PV = nRT and solve for volume in L. If you don't have those, you make the assumption that you have STP conditions (standard temperature and pressure) and under those conditions 1 mol of any ideal gas (and you...
January 4, 2015

Chemistry
Add them up. Fe = about 55.85 atomic mass P = about 31 O = about 16 and 16x4 = 64 Sum = mass of 1 mol FePO4. You should confirm all of these numbers from a periodic chart or another appropriate table.
January 4, 2015

Chemistry
1 mole of anything (atoms in this case) contains 6.022E23 anythings (atoms in this case). So atoms in 2.58 mol = 2.58 mol x 6.022E23 atom/mol = ?
January 4, 2015

AP Chemistry
This is a humongous problem and requires several steps. I would start with PV = nRT and solve for mols CO2 present after equilibrium the reaction is complete. You will need this eventually so mols CO2 initial - mols used = mols CO2 after equilibrium. Then write the equation ...
January 3, 2015

chemistry
acetic acid is HAc KOH + HAc ==> KAc + H2O millimols KOH = 10 x 0.4 = 4 mmols HAc = 15 x 0.3 = 4.5 mmols KAc formed = 4 mmols HAc left unreacted = 0.5 Substitue into the Henderson-Hasselbalch equation and solve for pH. You will need to look up the pKa for acetic acid. I ...
January 1, 2015

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