Wednesday
September 2, 2015

Posts by DrBob222


Total # Posts: 49,866

Chemistry
Calculate concentrations. Set up an ICE chart. Solve. I like to do the concentrations first but it may be easier to do it in mols first, THEN make the conversion. The only problem is that we ofte forget to mak the conversion. .........2SO3 ==> 2SO2 + O2 I......0.755...........
April 28, 2015

Physics Help Please! Decay Questions
I know it's cool to use no caps and no periods but it sure makes it hard to read when you don't help with proper sentence structure. (Well, you did use some.) ln(No/N) = kt No = 600 N = 180 k = 8270 t = ?
April 28, 2015

Chemistry
P1V1 = P2V2
April 28, 2015

Freezing point
I believe you are over thinking the problem. delta T for ethylene glycol is dT = Kf*m. You can calculate m, then dT. Substitute that dT and Kf and solve for m of CH3OH. Then m = mols/kg; you know kg and m, solve for mols. I think that is 5 mols CH3OH. The reason for the ...
April 28, 2015

Chemistry
See your other post.
April 28, 2015

Chemistry
dHrxn = (n*BE reactants) - (n*BE products)
April 28, 2015

chemistry
Yes, it involves the activity series. The reaction is Zn + CuSO4 ==> ZnSO4 + Cu Here is a site you can find delta H formation values. https://www.delsearegional.us/academic/classes/highschool/science/chemistry/firstyear/reference/referencesheets/heats.pdf dHrxn = (n*dH ...
April 28, 2015

Chemistry
I assume you have solved for the pKa. Here is what you do for the NaOH addition. The addition of HCl is handled the same way. I like to work in millimoles instead of M but you may use your choice. mmols HPO4^- = (mg/molar mass) = approx 10 but you need a more accurate answer. ...
April 28, 2015

Chemistry
If the solution is basic, the OH is more than the H3O^+. (H3O^+)(OH^-) = Kw = 1E-14 Knowing either allows you to calculate the other.
April 28, 2015

Chemistry
By using most of one of the components. Generally, it's considered out of it's range if the pH changes by more than +/- 1 pH unit.
April 28, 2015

chemistry
You need to find the arrow key on your keyboard and use it. I will use acetic acid (ethanoic acid) as HAc. .........HAc + H2O ==> H3O^+ + Ac^- I........0.1...........0........0 C.........-x...........x........x E.......0.1-x..........x........x Substitute the E line into Ka...
April 28, 2015

Chemistry
Sorry I was late getting back. I was typing in the answer, I received a call to go to lunch, I had to RIGHT THEN, just now returned. So here goes. I can write that epsilon so I'll use e. A @ 725 nm = eCo*Ccobalt + eNi*CNickel A @ 700 nm = eCo*Ccobalt Calculate C Cobalt at ...
April 28, 2015

analytical chemistry
mL x M x millimolar mass = grams mL NaOH M NaOH millimolar mass KHC8H4O4 = grams KHC8H4O4
April 28, 2015

Chemistry
mols AlCl3 = grams/molar mass = ? Then M = mols/kg solvent.
April 27, 2015

Chemistry
9.6% w/v = 9.6 g sugar/100 mL solution. g sugar in the can is 9.6 x (355/100) = approx 34 g (but you should do it more accurately). What does that 1 tsp = 4g mean? 4g of what? 4g of the fluid? 4 g of sugar? the mass of the teaspoon? I will assume the mass sugar in 1 teaspoon ...
April 27, 2015

Chemistry
I don't see a Ksp given for PbCrO4; therefore, I will assume this is just another limiting reagent problem. I work these the long way. mols Pb(NO3)2 = grams/molar mass mols K3CrO4 = M x L = ? Using the coefficients in the balanced equation, convert mols Pb(NO3)2 to mols ...
April 27, 2015

chemistry
What do you not understand about this. Do you know what an isotope is?
April 27, 2015

chemistry
http://en.wikipedia.org/wiki/Effective_nuclear_charge
April 27, 2015

chemistry
As you down the table in a group, the last electron (in this case the single electron in the outside shell) is farther and farther away from the nucleus. So it gets easier to pull that electron away.
April 27, 2015

Chemistry
There aren't very many people in this world, including me, that has all of the solubility tables memorized for the thousands of known compounds. Surely you have a graph, a table, or some data from which to read/calculate the solubility. As it is I can't do anything ...
April 27, 2015

chemistry
P1V1 = P2V2
April 27, 2015

Freezing solution
mols ethylene glycol = grams/molar mass = ? 81.4 mL at density of 1.00 g/mL = 81.4g Convert 81.4 g to kg. molality = mols eth gly/kg solvent, then delta T = Kf*m You know Kf is 1.86 and you know m from above. Solve for delta T and subtract from 0 to find new freezing point. ...
April 27, 2015

Analytical Chemistry
I would proceed this way. A = abc and since these measurements were made with the same length cell (I assume) we an ignore that. We need to 1. graph the data for a working curve (A vs C) or 2. determine a from the data and that is easily done. A = a*c 0.120 = a*0.1 and 0.360...
April 27, 2015

Chemistry
....Ca(OH)2(s) ==> Ca^2+(aq) + 2OH^-(aq) I...solid...........0...........0 C...-x..............x..........2x E..solid-x..........x..........2x Substitute the E line (ignore the solid-x since we don't include solids in Ksp) into Ksp expression and solve for x = ...
April 27, 2015

Chemistry
k for the decay = 0.693/1.83 = approx 0.4 but you need a better answer than that. Then, ln(No/N) = kt You can pick any number you like for No, then N is that number x (100-68.5) but I suggest you make it easy and do this. No = 100 N = 31.5 k is from above t = ? solve for this...
April 27, 2015

Chemistry
millimols HCl = mL x M = 3.60 mmols NaOH = approx 5 but you need a better answer than that. .......HCl + NaOH ==> NaCl + H2O I......3.6....5........0......0 C....-3.6...-3.6................ E......0...aprx 1.4........ So you have an excess of approx 1.4 millimols NaOH; the ...
April 27, 2015

chemistry
In the activity series, a METAL above will replace an ION below it but not the other way around. Since Al is below K, no reaction will occur.
April 27, 2015

chemistry
Correct on a,b,c. I don't know on D. When pressure is increased the reaction shifts to the side with fewer GAS moles. You didn't write the phases. If Br2 is a liquid, increasing P will have no effect since there are 2 moles on each side; if Br2 is a gas, the rxn will ...
April 27, 2015

Chemistry
It has to do with the order in which the subshells fill; i.e., after 18 electrons are in the 4th shell, (that's the 1s2(K shell 2) 2s2 2p6(Lshell 8) 3s2 3p6 3d10(M shell 18) 4s2 4p6 4d10(N shell 18) 5s2 5p5), the 5s and 5p subshells are lower energy and fill next. Here is ...
April 27, 2015

Chemistry
Since this gas was collected over H2O, I think we should correct for the vapor pressure of H2O at 25C which is 23.8 mm Hg. That makes the pressure of the gas 1.0086 atm which is too many s.f. but I just leave that in my calculator. That makes a difference of 3 or 4 in the ...
April 27, 2015

Chemistry
......4NH3 + 5O2 -----> 4NO + 6H2O I......x......y..........0.....0 C....-4z.....-5z........+4z...+6z E.....x-4z..y-5z.........4z....6z pH2O = 6z = 0.784 from the problem z = ? Then NO is 4z = ?
April 27, 2015

chemistry
It is odd for the question to ask about equivalent weight but use M instead of N. The following equation uses N but how it affects the problem will still come out right. mL x N x mew = grams. mew = grams/(mL x N) So if gram is ok and mL is OK, how will putting too large a ...
April 26, 2015

chemistry
I thought of a mull first but since mulls are liquids (nujol mull for example) my guess is it will be soluble in that also although we don't normally think of nujol as a solvent. As for thin films, I don't know how you get a thin film of a solid (powder) although if it...
April 26, 2015

chemistry
Mix the organic compound with KBr and make a KBr pellet. Run the IR spectrum.
April 26, 2015

Chemistry
You have assigned the values wrong. v is nu (which I don't know how to make) and that is frequency. You already have frequency so that v = C/lambda is not only not needed but is incorrect. So you substitute directly into E = hv = 6.626E-34*5E14 = 3.3E-19 J.
April 26, 2015

chemistry
See your other post.
April 26, 2015

chemistry
Let's call pyridinium chloride just BNHCl so it's the BNH^+ that is hydrolyzed. ...........BNH^+ + H2O ==> BN + H3O^+ I..........0.2..............0.....0 C...........-x..............x.....x E.........0.2-x.............x.....x Ka for BNH^+ = (Kw/Kb for pyridine) = (x...
April 26, 2015

chemistry
pKa goes from weak acid to strong acid as the number goes down; i.e., pKa 2 is a stronger acid than pKa 5 which in turn is stronger than a pKa of 9. You can arrange them with that information.
April 26, 2015

chemistry
See your other post. Which is the strongest acid in the group.
April 26, 2015

Chemistry
AgCl + 2 NH3 --> Ag[(NH3)2]^+ + Cl^- K for the rxn shown is Kf*Ksp Kf*Ksp for AgCl is about 2.9E-3 Kf*Ksp for AgBr is about 8E-6 Kr*Ksp for AgI is about 2.4E-9 As we proceed from AgCl to AgI the Ksp and Krxn shifts smaller and smaller to the solubility of the AgBr is about ...
April 26, 2015

Chem
The problem asks for kJ; convert your answer in Joules to kJ.
April 26, 2015

Chem
q = mass x heat fusion = ?
April 26, 2015

chemistry
mols K2SO4 in the 40 mL sample = g/molar mass = 5.00/molar mass K2SO4 = ? Then M of the 40 mL sample is mols K2SO4/0.04 = ?
April 26, 2015

pre ap chemistry
OK, so you can't read and follow directions. You want me to do all of the work and you just copy it. Here goes BUT you must wade through the explanation as I go. How many grams do you want? That's L x M x molar mass = grams. 100 mL is 0.1 L from the problem. M is 0.500...
April 26, 2015

pre ap chemistry
Also, I'm trying to figures out just what pre-AP chemistry is.
April 26, 2015

pre ap chemistry
How many grams do you want? That's M x L x molar mass = grams. You know L, M, and molar mass. Solve for grams. What do you not understand about making this up? You always add grams to a volumetric flask, add some water, swirl until all solid is dissolved, make to the mark...
April 26, 2015

chemistry
If this is just a dilution problem, then 0.12 mM/dm-3 x (5.0 mL/25.0 mL) = ?
April 26, 2015

chemistry
What is MB?
April 26, 2015

Chemistry
I don't understand the problem either.
April 26, 2015

Chemistry
I understand the question, vaguely, but can you clue me in on the concentrations at the end of the post. You have two mM for both. Which is right for each?
April 26, 2015

Chemistry 2
dSo system = (n*dSo formation products) - (n*dSo formation reactants) dHo system = (n*dHo formation products) - (n*dHo reactants) dSo surroundings = -dHosystem/T Plug dSo surroundings and dSo system into the following and solve for dSo universe. dSouniverse = dSosystem + ...
April 26, 2015

gravimertic prob
The problem tells you %Cl = 8.43%. Is this gravimetric analysis to check that number? Convert 0.0831g AgCl to Cl. That is easiest done by 0.0831 x (atomic mass Cl/molar mass AgCl) = g Cl Then %Cl = [(mass Cl/mass sample)]*100 =
April 26, 2015

chemistry
You prepare standard solutions of anthracene and quinine in the range you expect unknowns to be, go through your procedure, measure the fluorescence of each standard and plot that [I guess you don't call it A if it is emitting :-)] against the concn to get a standard curve...
April 26, 2015

chemistry
Without any data all I can do is get you started generally. Use the excitation spectra of each to determine the wavelength to use for excitation (either at the same time or in separate runs), then use the fluorescent data (emission data) to determine the wavelength to use to ...
April 26, 2015

CHemistry
Refer to your other problem that Jai worked for you.
April 26, 2015

chemistry
jae means ==> i followed by upper case _ is ' That Ything is delta H = ?
April 26, 2015

Chemistry 2
After reading Devron's reply I realize I read your initial question wrong. His response and mine agree; the only problem with mine is I thought you were quoting dG as -220 kJ/mol where you were quoting dH. Therefore, that part I wrote about "not agreeing with" ...
April 25, 2015

Chemistry 2
First, this is at 426K and not 298 K; therefore, any number you obtain by dGo = dHo - TdSo will not agree with 220 kJ/mol. So you substitute the values you have for dHo and dSo along with 426K for T and calculate dGo. Remember dH is given in kJ/mol and dS in J/mol.
April 25, 2015

Masinde university
https://www.google.com/search?q=lattice+energies+table&tbm=isch&imgil=WmpfcEfIGpFZQM%253A%253BahYcvs4Erq8XAM%253Bhttps%25253A%25252F%25252Fusflearn.instructure.com%25252Fcourses%25252F986898%25252Ffiles%25252F31116966&source=iu&pf=m&fir=WmpfcEfIGpFZQM%253A%252CahYcvs4Erq8XAM%...
April 25, 2015

chemistry
You don't give a reaction; I assume you just didn't type it into the post. I'll write one. CaI2 + 2AgNO3 ==> 2AgI + Ca(NO3)2 4 mols CaI2. Using the coefficients in the balanced equation, convert mols CaI2 to mols AgI.
April 24, 2015

chemistry
Have you tried to read what you post with no periods? Where the hell does the sentence end and the next one start. Fortunately I know enough chemistry that I may be able to guess. You can hope that I guess right. ........2NH3 ==> N2 + 3H2 I........0......1.3....1.65 C...
April 24, 2015

Chemistry
How much solution do you have? What is the molarity of the HCl you have?
April 24, 2015

Chemistry
First, the name depends upon where the groups are located. If that is a straight chain hexane, then the ethyl group is named first followed by the number and dimethyl as in 3-ethyl-2,2-dimethyl hexane. Here is a well illustrated site. http://www.kentchemistry.com/links/organic...
April 24, 2015

Chemistry
You can't have that without having a 5-valent carbon and that isn't allowed.
April 24, 2015

chemitry
I would do this. pH = pKa + log (base)/(acid) 4.40 = 4.76 + log (base)/(acid) base = 0.3/2 = ? acid = x/2 Solve for x = mols acetic acid.
April 24, 2015

chemistry
mols NaOH = M x L = 0.01 mols HCl = M x L = 0.01 NaOH + HCl ==> NaCl + H2O 0.01...0.01 So you will form 0.01 mols NaCl and have just NaCl and H2O in the solution at the end; therefore, the pH will be that of pure H2O.
April 24, 2015

chemistry
Is this the equation? You should have given it. .........H2S ==> H2 + S I......0.102......0...0 C........-p.......p...p E......0.102-p....p...p Substitut the E line into the Kp expression and solve for p, then evaluate 0.102-p. Finally, add the partial pressures and the sum...
April 24, 2015

chemistry
Ka = ? KaKb = Kw. Substitute Ka and solve for Kb. Compare Ka with Kb.
April 24, 2015

chem
Correct products but not balanced. You should know it isn't balanced. Let's check it. I see 2 H atoms on left and right. ok I see 2 o on left aide and 3 on the right. not ok. 2H2O2 ==> 2H2O + O2
April 23, 2015

chem 2
millimols HAc = mL x M = ? = acid mmols NaAc = mL x M = ? = base. Plug these into the Henderson-Hasselbalch equation and solve for pH. part 2. mmols HCl added = 20 I will make up some numbers for mmols HAc and NaAc to make this easier to do but these aren't real numbers. ...
April 23, 2015

chemistry
The ppt is Cu(OH)2. So Cu(OH)2 ==> black? + H2O Since the problem tells you there is no oxidation/reduction, just take out the water and see what's left. And you should know CuO is black. Cu(OH)2 ==> CuO)(black) + H2O
April 23, 2015

Chem
If that is rate = k[NO]^2[Br] It us second order with respect to NO and first order with respect to Br and 3rd overall.
April 23, 2015

chemistry
k = 0.693/t1/2 Then ln(No/N) = kt No is 9.00 N = ? k from above t = 1 y or 10 y (two separate problems.)
April 23, 2015

science
This may help. http://www.livescience.com/49594-electric-fuel-cell-vehicles-explainer.html
April 23, 2015

Chemistry
You need to identify DCPIP and write the equation. It would help if you wrote the procedure you followed.
April 23, 2015

Chemistry
First I object to saying you titrated Ca(IO3)2 with S2O3^-. You didn't do that; you added I^- to IO3^- and titrated the liberated I2 with S2O3^- Here are the equations. Ca(IO3)2 ==> Ca^2+ + 2IO3^- IO3^- + 5I^- ==> 3I2 (which isn't complete but the redox part is ...
April 23, 2015

Chem
Devron is right. You need to know the order of the reaction. I copied the following from Wikipedia. For order zero, the rate coefficient has units of mol·L−1·s−1 (or M·s−1) For order one, the rate coefficient has units of s−1 For ...
April 23, 2015

Chemistry
The word I was trying to think of when I wrote "temporary" was conditional. Many authors write conditional units; I suppose that's because they don't like to see numbers with no units. Technically, however, activities don't have units so neither do Kc, Kp...
April 23, 2015

Chemistry
It depends upon the k. Ksp, Ka, Kb, Keq, Kc, Kp and the like have no units because activities are supposed to be used for the species and activities have no units. Some authors use units and some argue these Ks have units but they do not. The units used (and they vary) are ...
April 23, 2015

Chemistry
If it's a strong acid it will ionize 100% so the pH will be -log(acid). If it's a weak acid the acidity will be less than that and you can gauge that with the pH.
April 23, 2015

Chemistry
Same process as your Hvap problem.
April 23, 2015

Chemistry
How many mols in 8.51E10 molecules? That's 8.51E10 moleceles x (1 mol molecules/6.02E23 molecules) = ? Then q in kJ = mols H2O x Hvap(kJ/mol)
April 23, 2015

Science
refrigerators, freezers, microwaves/ranges to boil water, etc.
April 23, 2015

chemistry
I2 + 2S2O3^2- ==> S4O6^2- + 2I^- mols S2O3^2- = M x L = ? Convert mols S2O3^- to mols I2 using the coefficients in the balanced equation. Then M S2O3^2- = mols S2O3^2-/L S2O3^2-
April 23, 2015

chemistry
C6H8O6 + I2 + H2O → C6H6O6 + 2I^- + 2H^+ mols I2 = M x L = ? mols vit C = mols I2 since the ratio is 1:1 in the balanced equation. g vit C in the titrated portion = mols x molar mass. Convert to mg vit C the multiply by 500/25 to give mg vitamin C in the tablet.
April 23, 2015

Science
I do these limiting reagent problems the long way. HCl + NaOH ==> NaCl + H2O mols HCl = M x L = about 0.056 but you need a better answer than that estimate. That will produce 0.056 mols NaCl mols NaOH = M x L = approx 0.0625. That would produce approx 0.0625 mols NaCl. In ...
April 23, 2015

chemestry
Convert 1.453 g benzoic acid to mols. mols = grams/molar mass = ? q = Ccal x (Tfinal-Tinitial) +3227000 x mol = Ccal x (delta T) You know everything but Ccal. I wonder if that is 2.265 T increase.
April 23, 2015

chemestry
Note that you need to spell chemistry correctly. The heat of solution which is the heat lost when KCl dissolves, is given by the decrease in temperature of the water as q = mass H2O x specific heat H2O x (Tfinal-Tinitial) That q is for 0.75g which is 0.75g/molar mass KCl = ...
April 23, 2015

Physical Science
In multiplication and division, which is all you have in this problem, the rule is that you may have as many significant figures in the answer as you have in any of the numbers. So where did the 4.49 come from? 5.00 x (750/760) x (273./300.) = 4.49. You're allowed 3 s.f., ...
April 23, 2015

DrBob222-re: chem question
[H^+](OH^-] = Kw = 1E-14 You have OH^- and Kw, solve for H^+
April 23, 2015

Chemistry
This is the equilibrium equation. Are you looking for the Keq expression? Keq = (Fe^2+)(H2S)(H2O)^2/H3O^+)^2 Some may not include the H2O in the constant; the general rule is it isn't included EXCEPT where it is involved in the reaction. Since it is produced in the ...
April 23, 2015

Chem - Acid & Bases
I see two statements but no question. And is tht [H-] a typo?
April 23, 2015

chemistry
What's the powder? Is there a reaction? What's the product?
April 23, 2015

chemistry
mL x (1 L/1000 mL) x M x molar mass = grams or you can do it in pieces. mols Mg(NO3)2 = grams/molar mass Then M = mols/L. You know M and mols, solve for L and convert to mL.
April 23, 2015

chemistry
Read it from the graph.
April 22, 2015

chemistry
http://www.jiskha.com/display.cgi?id=1429763582
April 22, 2015

chem
% w/v = (g solute/mL)*100 = ?
April 22, 2015

Chemistry
See your post below on NO/NO2
April 22, 2015

Chemistry
dGorxn = (n*dGo formation products) = (n*dGo formation reactants) dGorxn - is spontaneous. dGorxn + is not spontaneous. dGorxn = 0 reaction is at equilibrium.
April 22, 2015

Thank you
You're welcome.
April 22, 2015

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