Thursday
July 24, 2014

Posts by DrBob222


Total # Posts: 43,169

chemistry
Did you square 1.75 or multiply it by 2. I think you did the latter; you should have squared it.

Chemistry
Mn is +7 in MnO4^-. It is +2 in Mn^2+. To balance the change in electrons we have MnO4^- + 5e ==> Mn^2+. I do it that way and make this the first step of the process of balancing. Some say there is a shorter way and you do this the LAST step and not the first. To do it that...

Chemistry
MnO4^- + 8H^+ + 5e ==> Mn^2+ + 4H2O

chemistry 2
HAc + NaOH ==> NaAc + H2O First, determine the molarity of the HAc. mL x M = mL x M 22.5 x 0.21 = 50*x x = 0.0945M Now divide the titration curve into four sections. a. at the beginning. b. between initial and eq point c. eq pt d. after eq pt Which of these do you have trou...

chem090
I work these limiting reagent (LR) problems the long way. 2K3PO4 + 3BaCl2 ==> Ba3(PO4)2 + 6KCl mols K3PO4 = grams/molar mass = 100/212.26 = about 0.47 mols BaCl2 = 100/208.23 = about 0.48 Now convert mols K3PO4 to mols Ba3(PO4)2 using the coefficients in the balanced equati...

Chemistry
Here is the way I write these. The atomic number goes on the left, the mass number on the right. So the Po would be 84Po212 ==> 82Pb208 + AXZ where A is atomic number, Z is mass number, X is the element. The left side must add up and the right side add up; i.e., atomic numb...

Chemistry
Following my post above. atomic number on left, element in middle, mass number on right. Left numbers must add up on both side; right numbers must add up on both sides. So for Th we write 90Th234 ==> beta + ? beta is an electron which is -1e0. 90Th234 ==> -1e0 + AXZ So 9...

chem 101
q = mass x heat vaporization Change 42.8g to mols. mols = grams/molar mass

Chemistry
assume the question is to determine M I2. ascorbic acid + I2 ==> 2I^= + ..... mols ascorbic acid = grams/molar mass mols I2 = mols ascorbic acid (1:1 ratio from the equation) M I2 = mols I2/L I2.

chemistry
You don't ask a question. I assume the problem is to determine the heat of neutralization in kJ/mol. Also, I assume there is no calorimeter constant so we ignore that. Please check the post to make sure you have all of it correctly. The answer should be about 55 kJ/mol and...

Chemistry - Science (Dr. Bob222)
Cr on the left is +6 each so 6*14 = 84+ and on the right is 14*3 = 42+. 84-42 = 42 e xfrd. I on the left is zero. On the right each I is 7+ and 6*7 = 42+. 42-0 = 42e xfd.

Chemistry
CoCl2 is soluble; therefore, it has no Ksp. The easiest way to do these is to note that with a Kf so extremely high you know the solution at equilibrium will be far to the right; therefore, we set up an ICE chart and make the reaction go 100% to the right. That is an ok assump...

chemistry
Your equation is right. Your reasoning is wrong. Mg is more active because it replaces the Pb ions and forces the Pb out of solution. Here is how you tell which is more active. Here is the "activity series" of metals. https://www.google.com/search?q=activity+series+m...

chemistry
See your post above. Pb is above Ag in the table; therefore, Pb is the more active metal and it will displace Ag^+ from solution.

chemistry
You have written it correctly.

Radioactivity
When an element loses an electron (from the nucleus) it is because one of the neutrons becomes a proton and the electron is ejected as a beta particle. The mass number doesn't change because the number of protons + number of neutrons is the same but the number of protons h...

Science radioactivity
Alpha and beta particles really are particles in that sense of the word. The alpha particle is a helium nucleus and a beta particle is an electron. A gamma is a ray; i.e., an electromagnetic wave much like a radio or TV wave (but a much shorter wavelength and much higher energ...

chemistry
The general gas formula can be modified from PV = nRT to P*molar mass = density*RT Substitute and solve for density.

Chemistry
See your other post.

Science
How far can you get on this problem? What don't you understand about the next step>

Chemistry
Changing screen names won't help. Read over your post carefully and make sure you have included everything. With no data to calculate it and no calorimeter constant given, 4,5,6, et al are dead in the water..

chemistry
4. You don't have enough information to calculate the amount of heat absorbed/lost by the calorimeter. You need the calorimeter constant or data to calculate and you have neither. 5,6,7 depend upon 4.

chemistry
1. HCl + NaOH ==> NaCl + H2O 2. H^+ + OH^= ==> H2O 3. q = mass H2O x specific heat H2O x (Tfinal-Tinitial) assuming the calorimeter can be ignored. ' 4. I'm surprised there is no 4th question to calculate kJ/mol for the heat of neutralization.

Chemistry
mols Zn = grams/atomic mass = ? mols HCl = twice that (from the coefficients in the balanced equation). M HCl = mols HCl/L HCl. You know M and mols, solve for L HCl and convert to mL.

Chemistry
I looked on Google and under potassium hydroxide it lists as being soluble in alcohol. You can do the same for the others. Wikipedia is the best link and scroll down until the right hand boxes get to solubility.

Biology help please
Sorry, I can't help.

Chemistry - Science (Dr. Bob222)
Interesting because at 25C H3PO4 is not solid. It freezes about 17 C. mols H3PO4 = 0.4g/molar mass H3PO4 = estimated 0.004 mols NaOH added = M x L = estimated 0.02 You need to clean up the numbers before continuing. ......H3PO4 + 3NaOH ==> Na3PO4 + 3H2O Starting with 0.02 m...

Chemistry
Yes, unless you were told that the HCl you had was 1.000 M. Usually you are given instructions for preparing 1M HCl but those instructions only get a solution that is close to being 1.00M. You must standardize to find out EXACTLY what it is such as 0.1011M or 0.09876M

Chemistry
mols NaCl = grams/molar mass Then M = mols/L solution.

science
Frankly I don't think this is a very good question. Too many ifs in the answers. 1. I don't agree with a flying bird as an answer; however, it the bird were flying at the same speed (reference the ground) as the train and in the same direction, that could be the right ...

Chemistry
Do you have the heat of combustion? If not you can calculate it this way. 2C8H18 + 25O2 ==> 16CO2 + 18H2O dHrxn = dH combustion = (n*dHo formation products) - n*dHo reactants). So you will obtain that many kJ for 228 g octane. Convert that to grams needed for 5410 kJ. Post ...

science
Jaco, I worked this for you rour posts down under "chemistry".

Chemistry
Use PV = nRT and solve for n = number of mols. Then n = grams/molar mass. You know n and grams, solve for molar mass. You can do it another way knowing that an ideal gas at STP will occupy 22.4L. Therefore, n = 1.15L/22.4L = number of mols, then n = grams/molar mass.

Chemistry Equilibrium
......NO2 + NO ==> N2O + O2 I......x.....x.....0......0 C.....-y.....-y....y......y E.....x-y...x-y....y......y So you want (N2O) = (O2) = 0.0446M mols = 0.0446*5L = 0.223 = y Kc = (N2O)(O2)/(NO2)(NO) Kc = (x-0.223)(x-0.223)/(0.223)(0.223) Solve for x = mols NO2 = mols NO T...

Chemistry Equilibrium
You need to find the arrow keys on your computer and use them. (N2O) = 0.174mol/4.00L = estimated 0.04 (NO2) = 0.337 mol/4.00L = estd 0.08 ...........N2O(g) + NO2(g)==> 3NO(g) I.........0.04.....0.08........0 C.........-x........-x.........3x E.........0.04-x...0.08-x.........

chemistry
A. I assume M^+ and A^- but it could be M^2+ and A^2- etc. (MA) = 0.0031 x (1000 mL/200 mL) = 0.0031*5 = ? Ksp = (M^+)(A^-) = (0.0031*5)^2 B. dG = -RT*lnK

Chemistry
I don't get anywhere near that figures but I may have made some wrong assumptions. If you wish to show your work I'll be happy to check it.

Energy question
q = mass ring x specific heat ring x (Tfinal-Tintial) You know q, mass ring, Tf and Ti. Solve for specific heat.

Chemistry
By definition, M Ca(OH)2 = mols/L solution. mols HClO4 = M x L = ? mols NaOH = 1/2 that (from the coefficients in the balanced equation). Then M Ca(OH)2 = mols Ca(OH)2/L Ca(OH)2.

Chemistry
You've worked more difficult problems than this. What's the trouble here?

word problem
q = mass metal x specific heat metal x (Tfinal-Tinitial) An easy way to do this is to assign some convenient number for q, give it some convenient starting T and solve for Tfinal. Or you can reason it out. If sp.h. Ag is 0.235 and that of Cu is 0.385 then it takes more heat to...

Chemistry
Your problem isn't chemistry. You just need a little help with algebra. 5.00-4.74 = 0.26 = log 15/x 15/x = antilog 0.26 = 1.82 So 1.82 = 15/x. Solve for x and convert to g/500 mL.

Chemistry
I worked this below. I can find it if you wish.

chemistry
avg rate = (12.5-10)/50 min = ? mM/min. rate = k(NPP). You know NPP initially and the rate, solve for k. Plug all of this into the Arrhenius equation an solve for activation energy.

CHEMISTRY
Convert g to mols. mols = g/atomic mass mols C = 97.30/12 = ? mols H = 16.22/1 = ? mols O = (200-16.22-97.3) = 86.48/16 = ? Now find the ratio of each element to the others(in small whole numbers) with the smallest number being 1.00. The easy way to do that is to divide the sm...

Energy question
Another thought. Incandescent bulbs don't pollute the environment with mercury. Most fluorescent bulbs(I don't know if all do or not) have mercury in them.

Energy question
This is my personal opinion but I don't think they are. My experience is that the new fluorescent bulbs don't live up to the hype on the box. Supposedly those incandescent bulbs burn out faster and it takes several to last as long as the newer fluorescent bulbs. In add...

Science help!!!!
These fill in the blanks are hard to do because more than one work/phrase often fits. A____solar panel__________________ is a tool used to capture the energy in sunlight. Recycling aluminum cans and taking shorter showers are two ways to practice the ___conservation___________...

Chemistry
q = -192 kJ since that is evolving heat. w = pdV = 125*(2) an that is - since it is expanding; i.e., it is doing work against the atmosphere while expanding. Note that w is in L*atm and need to be changed to J. Do that by x 101.325 then convert to kJ. Note: work is given in te...

chemistry
delta H at constant pressure is q. Or perhaps I should say it another way,k q at constant pressure is delta H. So delta H in this case is +252 kJ.

chemistry
q = 252 kJ and it's + so is endothermic w = 105 kJ and it's - since it is doing the work. delta E = q+w delta E = +252 kJ + (-105 kJ)

chemistry
a. pH = 4.74 + log(base)/(acid) = approx 5.00 b. millimoles NaAc = mL x M = 500 mL x 0.030M = = 15 mmoles. 5.00 = 4.74 + lot (15/x) Solve for x = millimoles acetic acid and convert that to grams in 500 mL solution.

Chemistry
John, did you read the post I left for you? If you will show your work we can spot the problem. Otherwise we're working in the dark.

Chemistry
See your other post above.

Chemistry
I gave you the formula for doing this yesterday. If you still have problems show your work so I can spot the error.

chemistry
.......Mg(OH)2 ==> Mg^2+ + 2OH^- I......solid........0........0 C......solid........x........2x E......solid........x........2x So Ksp = 1.2E-10 You want solubility Mg(OH)2 to be 2.51E-8M = (Mg^2+) = x in the above equation. Plug those values into Ksp expression and solve f...

water chemistry
millimoles HAc = mL x M = 35.0 x 0.150 = approx 5.25 mmols NaOH = 17.5 x 0.150 = 2.625 ..........HAc + NaOH ==> NaAc + H2O I........5.25....0........0......0 add.............2.625............... C.......-2.625..-2.625...+2.625..+2.625 E.......2.625.....0.....2.625.....2.625...

Chemistry
q = [mass ice x specific heat solid ice x [0-(-12)] + [mass ice x heat fusion] + [mass melted ice x specific heat liquid H2O x (29.6-0)]

chemistry
..........A --> 2B I.......1.60.....0 C........-x......2x E......1.60-x....2x Assuming Kc listed is at 500K, substitute the E line into Kc expression and solve for x and 1.60-x.

chemistry
H2SO4 + 2NaOH ==> 2H2O + Na2SO4 mols NaOH = M x L = 0.1896 x 0.01109 = ? mols H2SO4 = mols NaOH/2 M H2SO4 = mols H2SO4/L H2SO4. You have mols H2SO4, L H2SO4 = 10 mL(0.010L), solve for M H2SO4. That's the (H2SO4) in the 10 mL. That solution came from 1:10 dilution so the...

Chemistry
dGo = -RTlnK dGo = -nFE

chemistry
John, what's the problem here. It's just a matter of looking up the half reaction and adding one to the other after reversing one of them.

Chem
Why don't you help by looking up delta Ho formation for the products and reactants. That way we'll be using the same set of numbers.

chemistry help~Please!!!
I found this table of Ka values. Zn = 2.5E-10 Cl^- is not hydrolyzed. http://bilbo.chm.uri.edu/CHM112/tables/KaTable.htm

orgo chem
fn = [(1+Kd*(Vo/Va)]-n where fn = fraction solute REMAINING in aq layer after n extractions. Vo = volume organic layer Va = volume aqueous layer Kd = distribution constant for organic/aqueous

chemistry
mols NH4NO3 = grams/molar mass Use the coefficients in the baalanaced equation to convert mols NH4NO3 to mols H2O. Now convert mols H2O to grams H2O. g = mols x molar mass

chemistry
See your other post.

chemistry
Use the coefficients in the balanced equation to convert mols NH3 to mols H2O. Now convert mols H2O to grams. g = mols x molar mass

Ap Chem
Ecell = Eocell - (0.05916/n)log[(Fe^2+/Cu2+)]

Chemistry
Use Ecell = EoCell - (0.05916/n)log(M^x+) Eocell is the reduction potential you look up in the table in your text/notes. M^x+ is the concentration of the ion in the problem. (You will note that if you substitute 1 for the ion the log M is 0 and Ecell = Eocell from the tables)....

Chemistry
And you don't understand exactly what?

Chemistry
I worked this below.

Chemistry
Coulombs = amperes x seconds Convert 48 hr to seconds and that x 7500. That number is close to 173,000 but you should get a better number and that x 7500 = about 1.3E9 C. 96,485 coulombs will plate out 40/2 = 20 g Ca. So you should be able to plate 20 x 1.3E9/96,485 = g Ca at ...

chemistry
Ksp Ag2SO4 = 1.2E-5 = (Ag^+)^2(SO4^2-) Ksp CaSO4 = 4.93E-5 = (Ca^2+)(SO4^2-) So CaSO4 ppts first. How do you know that. Calculate the (SO4^2-) when each bgins to ppt. Ag2SO4. (SO4^2-) = Ksp/(Ag^+)^2 (SO4^2-) = you do it. I get approx 2.7E-2M CaSO4. (SO4^2-) = Ksp/(Ca^2+) = you...

CHEMISTRY
Do you mean at equilibrium (NH3) = 1.23E-4M? and (H2) at equilibrium = 2.75E-3M? that is, is that M? ........N2 + 3H2 ==> 2NH3 E.......x....2.75E-3....1.23E-4M Keq = (NH3)^2/(x)(H2)^3 Substitute and solve for x

Chemistry
I'm glad you corrected that. I was scratching my head trying to figure out your last post. Good luck in your studies.

Chemistry
You didn't waste my valuable time as much as you wasted your valuable time. But I would round my answer to 1.0E-7M.

a note--Chemistry
Note that 1.01E-7 is too many significant figures.

Chemistry
How about 1.01E-7? You should have 3.9E-26/1.4E-6 and that = 3(X)^3 I suspect your error is in the next step. You should divide by 27 and take the cube root of the what is left. But note that if you had shown what you did at the beginning I would have already seen the found th...

Chemistry
And I can't read the brain waves to know what you obtained as an answer.

Chemistry
....Ag3Co(CN)6 ==> 3Ag^3+ + [Co(CN)6]^-3 I..solid............0.........0 C.....solid.........3x........x E.....solid.........3x........x Ksp = 3.9E-26 x (3x)^3(x) Solve for x. (Ag^+) = 3x

Chemistry
I obtained this reaction from Wikipedia. Compare with the reaction in your text/notes. If not the same you will need to adjust my post. Zn(s) + 2MnO2(s) is in equilibrium with ZnO(s) + Mn2O3(s) [e° = 1.43 V] molsZn = grams Zn/atomic mass Zn Using the coefficients in the ba...

CHEMISTRY
I answered this for you below.

CHEMISTRY
You didn't show an equilibrium but the reverse Kreverse is 1/Kforward.

Chemistry
........Fe(OH)3 ==> Fe^3+ + 3OH^- I.......solid........0........0 C.......solid........x........3x E.......solid........x........3x Ksp = (F^3+)(OH^-)^3 Substitute the E line into Ksp expression and solve for x, = [Fe(OH)3] in mols/L. That x molar mass = grams.

chemistry
I assume you mean 73.9% complete. N2 + O2 ==> 2NO This is a limiting reagent (LR) problem. First we determine the LR. atm NO formed if we used all of the N2 and an unlimited supply of O2. 0.352 atm N2 x (2 mols NO/1 mol N2) = 0.352 x 2/1 = 0.704 atm NO produced. atm NO form...

Chemistry
What nitrates did you have? I assume you have list from which to choose. You could have Ni, Co, Mn, Fe, Al, Cr, Zn

Chemistry
OK. Step by step #2 and I'll assume you know how to get from grams to mols. 6.59g CO2 = 0.150 mols CO2 = 0.150 mols C. 2.7 g H2O = 0.150 mols H2O = 0.300 mols H(atoms) So now we have 0.150 g C 0.300 g H We want to find the ratio, in small whole numbers, with no number bein...

Chemistry, Science
Just follow the written statements. 2NaOH(aq) + Pb(NO3)2(aq) --> Pb(OH)2(s) + 2NaNO3(aq) Pb(OH)2(s) + 2NaOH(aq) --> [Pb(OH)4]^2-(aq) + 2Na^+(aq). However, this leaves it in ionic form and I think the problem wants it in molecular form so I would make the product Na2Pb(OH...

Chemistry
C7H12 + 10O2 ==> 7CO2 + 6H2O moles C7H12 = 7.6g/96 = estimated 0.08 mols CO2 = 0.08mols C7H12 x (7 mols CO2/1 molC7H12) = estimated 0.55 Then mass = mols CO2 x molar mass CO2 = ? Do the same for mols C7H12 to mols H2O, convert mols H2O to grams. then add the g CO2 + g H2O =...

chemistry
A confusing problem. Use PV = nRT and solve for n of the 4.70 g gas at STP, the convert n to molar mass. That is n = grams/molar msss. You know n and grams, solve for molar mass. Then use PV = nRT again at the new conditions and solve for n in the new container at the new cond...

chemistry
velocity is a vector quantity; i.e, both speed and a direction. Speed is a scalar quantity. You can read more about it here. http://en.wikipedia.org/wiki/Velocity

chemistry help~~~~ Please!!!
If you intend to do well in chemistry you had better find the caps key. For example, m stands for molality; M stands for molarity. They are different. If you are trying to ask about the difference between the K and the Na salts, there will be none as far as pH is concerned for...

CHEMISTRY HELP !!!! Check
Looks good to me.

chemistry
millimols = mL x M = ? millimols K from K2CO3 = 2*234*1.2 = ? mmols K from K3PO4 = 3*312.5*0.32 = ? (K^+ final) = total K mmols/total mL = ?

CHEMISTRY HELP !!!!
Here is how you do these. ........NH4^+ + H2O ==>H3O^+ + NH3 Ka = (H3O^+)(NH3)/(NH4^+) Ka for NH4^+ = (Kw/Kb for NH3)= ?

PLEASE HELP D:
Personally, I think that will result in nothing getting done. I suspect there must be a central coordinating agency. At first glance the federal gov might be the obvious choice but I shudder at the thought of another federal czar, more gov red tape, more cost overruns, and all...

Chemistry
The assumption for my response was years.

Chemistry
k = 0.693/t1/2 = approx 4.95E-11 Rate at time zero = k*N and for 1 mol Th, N will be 6.02E23 atoms. Solve for R, which will be in disintegrations/year . Convert tht to d/hour.

Chemistry
With regard to H^+. You added 0.9375 mols H^+ to the buffer. ALL of it will react with the 15.0 mmols NH3 (H^+ is the limiting reagent so there won't be any of it left). With regard to the NH4+ you should add and my ICE chart shows that; however, I said subtract in my inst...

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