Tuesday
July 22, 2014

Posts by DrBob222


Total # Posts: 43,159

AP chemistry
I don't like to do it this way because students ALWAYS get confusted so I'll put it together for you. heat lost by Al is mass Al x specific heat Al x (Tfinal-Tintial) heat gained by H2O is mass H2O x specific heat H2O x (Tfinal-Tinitial) So set heat lost + heat gained ...

AP chemistry
heat lost by aluminum + heat gained by water = 0 heat lost by Al = mass Al x specific heat Al x (Tfinal-Tinitial) heat gained by water = mass H2O x specific heat H2O x (Tfinal-Tinitial) Substitute into the heat lost + heat gained = 0 and solve for Ti.

Chemistry
I don't know where you obtained the 85 C? m = 312, right c = unknown, right The problem tells you delta T is 15, where did the 85 come from?

Chemistry
I hesitate to answer all of these for you for that way you aren't learning how to do them yourself. I will get you started. For the others show what work you've done, how you think the problem should be solved. and/or exactly what you don't understand about the pr...

Chemistry
Do you have suggestions for these?

Chemistry
.........Ag + ....xN2 --> AgxNy I......344.588.....0........0 add.............15.906......... C.....-344.588.....-x......359.503 So you end up with 359.503 You started with...344.588 How much N2 was added? Then N2 remaining = start-end = ?

Chemistry
If we look at this the reverse direction. H2(g) + 1/2O2(g) --> H2O(l) that's the heat formation liquid H2O in kJ/mol and my text shows that as -285.8 kJ/mol Then H2O(l) ==> H2O(s) is another 6.0 kJ/mol to form ice and freezing water to ice is exothermic so that shoul...

chemistry
PV = nRT

Chemistry
That's the best choice.

Chemistry
delta T = i*Kf*m So you want the highest delta T. i is the van't hoff factor, Kf is constant, molality is constant in this case so it appears to depend upon i. i = 1 for A i = 1 for B i = 2 for C i = 2 for what you have but I suspect you made a typo and that should be MgCl...

Chemistry
I don't know. I looked up the numbers in my text. Although they are slightly different I obtained essentially the same values you did; i.e., 128.2, 6.05, and -58.2 all in kJ/mol. I also looked up dGo in the same text and it was 130.4 at T = 298 and using dG = dH - TdS I ob...

Chemistry
heat gained by cold water + heat lost by warm water = 0 [mass cold H2O x specific heat H2O x (Tfinal-Tinitial)] + [mass warm H2O x specific heat H2O x (Tfinal-Tinitial)] \ 0 Substitute and solve for the only unknown, which is Tf.

chemistry
Look up the reduction potentials and add the oxidation half cell to the reductin half cell to obtain the Eocell. If it is + the rxn is spontaneous; if Eocell is - it is not spontaneous.

chemistry
What are you starting with?

Chem
mols Pb(NO3)2 = M x L = approx 0.28 mols PbCl2 formed = mols Pb(NO3)2 (see the 1:1 ratio for Pb(NO3)2/PbCl2 Then g PbCl2 = mols PbCl2 x molar mass PbCl2.

Chemistry
http://www.jiskha.com/display.cgi?id=1400465598

Chemistry
If you post your work so we know what you did perhaps we can find the error. Especially important is what are you using for Eo values.

chemistry
You should make a habit of looking to see if an earlier post has been answered. I answered this about 5-6 hours ago.

science help
For 1 read about tectonic plates. For 2 you didn't list them.

Chemistry
Mg^2+ + 2e --> Mg 2Cl^- ==> Cl2 + 2e

chemistry
If you are talking about HNO3, nitric acid, a suitable procedure is to bubble gaseous N2O5 into distilled water until saturation is achieved.

Chemistry
If you will show what you did perhaps we can find the problem. Other than guessing, however, we don't know what you've done.

Chem
You don't give enough information to know if you want the Eocell for a spontaneous or non-spontaneous cell. I assume you want the spontaneous reaction. Al(s) ==> Al^3+ + 3e Eo = +1.66 Fe^2+ + 2e ==> Fe(s) Eo = -0.440 -------------------- 2Al + 3Fe^2+ ==> 2Al^3+ + ...

Chemistry
dGorxn = (n*dGo formation products) = (n*dGo formation reactants)

Chemistry
mols AgNO3 = grams/molar mass = approx 0.06 but that's only an estimate as are all of the other calculations I do here. mols NaCl = M x L = approx 5E-4 .......NaCl + AgNO3 ==> AgCl + NaNO3 I......5E-4......0........0......0 add...........0.06.................. C.....-5E...

Chemistry
You want 15 g CaCl2. You will need 15 g CaCl2 x [(molar mass CaCl2.2H2O/molar mass CaCl2)] = ? g CaCl2.

chemistry
It may be possible depending upon how many other metals have specific heats close to the unknown metal. In any case, however, you probably can narrow the choice to one of a few and more importantly you can eliminate many metals.

Chemistry
I see a problem below that has been answered by Mathmate that isn't the same problem as this one. This one doesn't allow water to be added and both of the solutions available are more concentrated than the final desired one. I don't think this one is possible.

Chemistry
This can be done?? If you use 2L of the weaker solution of 150g/L and zero L of the more concentrated solution, then you have 300g/2L and that is too concentrated.

Chemistry
I don't believe this can be done with the data listed. I think at least one equation is missing.

chemistry
A catalyst lowers the activation energy

Chemistry
2.07L, yes.

Chemistry
(V1/T1) = (V2/T2) Remember T must be in kelvin.

Chemistry
To find pH for each equivalence point. For HNO3 + NaOH ==> NaNO3 + H2O That is a strong acid vs a strong base. Neither Na^+ nor NO3^- is hydrolyzed; therefore, the pH at the equivalence point is just that of pure H2O which is 7.0. For NaOH + HCN ==> NaCN + H2O The CN^- i...

add on--Chemistry
Don't forget to make that 107 g.

Chemistry
Print these steps. 1. Write and balance the equation. NH3 + HCl ==> NH4Cl (The problem doesn't say it reacts with HCl and you only need to know that 1 mol NH3 is in 1 mol NH4Cl but I think an equation makes it more obvious.) 2. Convert what you have, in this case NH3, i...

AB Chemistry4
Yes, that's the only way to find the number of mols in 36.0 g H2O then to convert mols MnCl2 to g MnCl2.

chemistry
This 4-step procedure will work all simple stoichiometry problems. Limiting reagent problems take an addition one or two steps. 1. Write and balance the equation. You have that. 2. Convert what you have (in this case H2O) to mols. mol = g/molar mass = 133.6/18 = approx 7.5 but...

chemistry
This is a buffer problem. Use the buffer equation. Use the Henderson-Hasselbalch equation.

Simple question about music
Here is an article you may want t read. I don't know how accurate the figures are. I googled "number copies Thriller sold" and came up with many web sites to read. This is just one of them. http://www.newyorker.com/online/blogs/culture/2013/01/did-michael-jackson...

Chemistry
For a. eqn 1. mols NaOH = M NaOH x L NaOH eqn 2. mols acid = mols NaOH eqn 3. M acid = mols acid/L acid You're right, the NaOH is diluted which means you will add MORE NaOH when you titrate the acid. Look at eqn 1, If you add more volume you THINK you have more mols NaOH, ...

Science help PWEASEEEE
I would pick c.

Choosing Courses
I would think it would be ok, especially if you did well in algebra I.

chemistry
Look up the reduction potentials and calculate Ecell. If Ecell is positive the reaction is spontaneous. The element oxidized is the element that lost electrons. Reduction is the gain of electrons.

chemistry
There are 33+18+2 atoms in 1 mol of C33H18O2. How many moles do you have? That's 33g/molar mass C33H18O2

chemistry
http://wiki.answers.com/Q/What_is_the_difference_between_biochemical_pharmaceutical_and_diagnostic_chemical_reactions_in_health_care?#slide=1

chemistry
You are absolutely correct and I goofed. I didn't do what I preach so much about making sure the units come out right. I should have written it as 4.7 L/s x ? sec = L to be pumped. Solve or ? sec.

chemistry
This is a math problem, not a chemistry problem. I would convert everything to cm. 50 m = 5000 cm 25 m = 2500 cm 2 m = 200 cm Volume of pool is width x length x depth = ? cc. Convert to L. 1000 cc = 1L = initial volume of pool in L. You want to lower by 5 cm so now the dimensi...

analytical
Google them. You can get their formula and their properties.

chemistry
Nope. You didn't substitute. And you know the answer can't be right. You start with 0.343 mol, it decomposes and you have more than you started with after 43 mn. I don't think so.

chemistry
The units of min^-1 tell you that the reaction is first order. So ln(No/N) = kt. No is starting. N is end k from problem t = 42 min

chem
looks ok to me.

chem
7.42E-5 kg x (1000g/1 kg) x (1000 mg/g) = ?

chemistry
yes. You reversed the sign because the reaction is reversed. So that makes it positive. Then double that for e.

chemistry
You have the reaction as shown. You want the reverse reaction and double that. So take dH that you have, change the sign (because of the reversal) and double it.

Math 2
I would ask 1/4 what of fabric?

chemistry
Read and correct your post. Clarify. It makes no sense as is. delta T in kJ?

chemistry
You can see from your previous ost how this is done. I'll be glad to check your numbers.

chemistry
Calculate mg morphine in each of the choices. a. 20% w/v means 20 g morphine/100 mL. I wouldn't recommend this choice (if you want the patient to live). b. 2M solution. How many mols is that. mols = M x L = 2M x 0.050 L = 0.1. g = mols x molar mass = 0.1 x 283 = 28.3 g or ...

Chemistry
The two half reactions are 2Al ==> 2Al^3+ + 6e Eo = 1.66 3Fe^2+ + 6e ==> 3Fe Eo = -0.44 -------------------- Add half cells to obtain rxn. Add Eo to obtain Eocell.

Chem
dGorxn = (n*dGo products) - (n*dGo reactants)

Chemistry
n stands for number of mols. It is 1 for CaO, 1 for CaCO3, and 1 for CO2. Look up dHo formation CO2, CaO, and CaCO3. Calculate dHo reaction. Look up dSo for CO2, CaO, and CaCO3. Calculate dSo reaction. Then dGorxn = dHorxn - TdSorxn

Chemistry
dHorxn = (n*dHoformation producs) - (n*dHoreactants) dSo rxn = (n*dSo formation products( - (n*dSo formation reactants) dGrxn = dHrxn - TdSrxn dG<0 spontaneous dG=0 equilibrium dG>0 not spontaneous.

NO SCHOOL
I presume this is a tax, probably Goods and Services Tax in Canada. Your post isn't clear. If you have 100 to spend on an item it will cost you 100 + 10% of 100. Or you may mean that the total cost of an item, including GST, is 100.00. And you want to know the cost without...

chemistry
Surely it's in your text. You're right. Bases are proton acceptors according to the Bronsted-Lowry theory of acids/bases.

chemistry
This isn't in your text/notes. The first half is According to this theory, acids are proton donors. So bases must be proton ........?

chemistry
Metals with a small heat capacity heat faster and cool quicker than metals with a higher heat capacity.

chemistry
That's right. % = (mass solute/total mass)*100 = ?

chemistry
You have half of it right. The other half you have ignored. q1 = heat needed to raise T of water from 15C to 100 C is what you have calculated. q2 = heat needed to change T of water at 100 C to steam at 100 C. That is q2 = mass H2O x heat vaporization.

math
Change meters to cm. 1 meter x (100 cm/1m) = 100 cm 100 cm + 5 cm = ?

Chemistry
I would say an oxidizing agent, a reducing agent, and a salt bridge/porous barrier. If you want to get technical I suppose you might add a cell (something to hold the oxidizing agent/reducing agent and the salt bridge).

chemistry
H3PO4 + 3NaOH ==> Na3PO4 + 3H2O

Chemistry
What does the equation tell you? That 89.3 kJ are absorbed when 1 mol (76.1g CS2) are formed. You have 6.33 g; therefore, 89.3 kJ x (6.33/76.1) = ? kJ

science
60 meters in 34 seconds. That is avg velocity of 60m/34s = ? m/s.

chemistry
20L propane = 20L x (1 mol/22.4L) = about 0.892 mols propane. You get 2220 kJ for 1 mol; therefore, you will get 2220 x (0.892 mol/1 mol) = ? kJ released.

Chemistry
1. Write the equation. 2. Balance it. 3. dHrxn = (n*dHo formation products) - (dHo formation reactants)

Chemistry
You're cluttering the board now. Spend your time solving problems instead of typing.

Chemistry
Same 'ol same 'ol. See your other posts.

Chemistry
I don't see anything new here. See your other posts.

Chemistry
See your other posts.

Chemistry
Zn^2+ + 2e ==> Zn from the table is -0.76v. Your half cell reaction is Zn ==> Zn^2+ + 2e E = +0.76v Ag^+ + e ==> Ag E = 0.80 v. --------------------------- Add rxnx; add half cell oxidation half to reduction half. Cell rxn is Zn + 2Ag^+ ==> Zn^2+ + 2Ag Ecell = 0.76...

Chemistry
n = 2 and you know that from the equation I wrote earlier of Zn + 2Ag^+ ==> Zn^2+ + 2Ag The term you are talking about is (RT/nF)ln[(Zn^2+)/(Ag^+)] and if you want to substitute R, T, n, and F in there you may. However, if you do all of that AND multiply by 2.303 to convert...

Chemistry
It really helps us help you if you use the same screen name. Tom, Tyler, help ASAP etc is not helpful at all. You know from your previous post how to calculate the standard Zn/Ag^+ cell potential. That is Eocell and that is for standard concentrations of 1M Zn^2+ and Ag^+. Whe...

Chemistry ASAP
yes

Chemistry ASAP
Look up the reduction potential for Zn^2+ + 2e ==> Zn(s) in your text. Reverse the sign. Add that to the reduction potential for Ag^+ + e ==> Ag(s) That potential will be for the reaction of Zn(s) + 2Ag^+(aq) ==> 2Ag(s) + Zn^2+(aq)

Chem 130
E= 2.180E-19 J x (1/n^2)

Chem 130
[Kr]4d25s2 http://www.webelements.com/zirconium/atoms.html

Math 6th Grade
Do you honestly think -15 = -21? How can that be. 2 = 2 and 6 = 6 and -2 = -2 but -15 = -21?

chemistry
You have two typos in your equation. The correct equation, balanced, is CaCO3 + 2HCl ==> CaCl2 + H2O + CO2 mols CaCO3 = grams/molar mass mols CO2 = mols CaCO3 from the coefficients in the balanced equation. Now g CO2 = mols CO2 x molar mass CO2.

Chemistry
I would first convert 40% HCl into molarity. 40% (I guess that's w/w) HCl means 40g HCl/100 g solution. 40g/36.5 = approx 1.10 mols HCl mass = volume x density so volume = mass/density. That 100 g soln = 100/1.2 = approx 80 mL or 0.08 L; therefore, the molarity is 1.1/0.08...

science
You can add the phases. You have it partly balanced but I am removing the 2 and 3 and start over. First you write the products (and that isn't considered part of the balancing). H3PO4(aq) + CaCl2(aq) ==> Ca3(PO4)2 + HCl You do these by trial and error; basically that me...

SIG FIGS
1.75E2

college chemistry
To melt ice requires q1 = mass ice x heat fusion. To raise T of melted ice at zero C to Tfinal requires q2 = mass melted ice x specific heat liquid H2O x (Tfinal-Tinitial) To cool the water from 75C to Tfinal requires q3 = mass liquid water x specific heat x (Tfinal-Tinitial)....

chemisty
q1 = heat needed to raise temperature of liquid water from 15 C to 100 C. q1 = mass x specific heat H2O x (Tfinal-Tinitial) q2 = heat need to convert H2O at 100 C to steam at 100 C. q2 = mass H2O x heat vaporization.

college chem
Devron answered this for you below.

Physical Science
Just because this may be a little foreign don't let it intimidate you. It's a matter of plugging in the numbers. The formula is q = mass x specific heat x (Tfinal-Tinitial). The numbers are mass = 0.75g from the problem. specific heat = 0.385 J/g*C from the problem. Tf...

Science
Just remember that a force always has an equal and opposite force opposing it. If I sit on a chair the chair (and floor) must push back with the same force I exert during sitting. When I was a student in physics class I asked "but how can that be?" and the prof answe...

End of Year question
Mine would be "awesome". "Great" as a second choice. "Beautiful" as a third choice.

chemistry
I don't think so. If the 1000 has no period after it it has only 1 s.f. and the answer 1E3. If it has a period, the answer is 1056.

chemistry
I suspect that is because molecular and ionic formulas have flaws in them (or they could be typos--in fact some appear to be typos). NaHCO3 + H2SO4 ==> NaHSO4 + H2O + CO2

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