Friday
May 22, 2015

Posts by DrBob222


Total # Posts: 49,010

chemistry
How many mols do you need? That's M x L = mols. Then mols = grams/molar mass. You have mols and molar mass, solve for grams.
April 30, 2015

chemistry
1 mol A ==> 1 mol B grams A = determined from density. mass = volume x density = 10 mL x 0.75 g/mL = 7.5 g. mols A = grams/molar mass = ? Since the reaction is 1 mol A to 1 mol B, then mols B = mols A Grams B = mols B x molar mass B = ?g theoretical yield (TY). The actual ...
April 30, 2015

Chemistry-is this right?
Thanks for letting me know.
April 30, 2015

chemistry
OK. My guess is that "theoretical pH) means to calculate what you think it should be based on the dilution of the original 0.1 M solutions. In that case you go with the 0.1 M HCl x (1/10) = 0.01 M HCl for HCl and theoretical pH of 2 and 0.1 M NaOH x (1/10) = 0.01 M NaOH ...
April 30, 2015

chemistry
You didn't have any of that information in the first post and I'm not sure I understand what you want now. However, if you took 1 drop of 0.1 M HCl and diluted it with 9 drops of DI water the concn of HCl in the diluted solution is 0.1 M HCl x (1 drop/10 drops total...
April 30, 2015

chemistry
I've responded to this also. If you can't find it I'll look and send you a link.
April 30, 2015

Chemistry
mols NaOH = M x L = ? mols acetic acid = mols NaOH since the reaction is 1 mol acetic acid = 1 mol NaOH. Then M acetic acid = mols acetic acid/L acetic acid.
April 30, 2015

Chemistry
I work these limiting reagent (LR) problems the long way. mols CH3COOH = M x L = ? mols NaHCO3 = M x L = ? Using the coefficients in the balanced equation, convert mols CH3COOH to mols CO2. Do the same and convert mols NaHCO3 to mols CO2. It is likely these two numbers will ...
April 30, 2015

chemistry
This looks ok to me; I assume you've seen my earlier response.
April 30, 2015

Science/Conversion
You don't have conversions here. You may ask how to convert 10 ug/mL to ng/uL but you already have the ng/uL filled in. Are we to check to see if this is correct?
April 30, 2015

chemistry
You know you get 802.3 kJ for burning 16 g CH4 and you know that from the question. All you need to do is to convert that to (it's just a proportion) to 237 and not 16 g CH4. heat produced is 802.3 kJ x (237/16) = ?
April 29, 2015

chemistry
And it's still wrong. Look at my earlier response. I told you EXACTLY how to do it. You only need to that equation I wrote and change the 0.139 to 0.129 and punch in the numbers.
April 29, 2015

chemistryH
Your net ionic equation is correct. Good work. However, I think the problem is a little misleading since the net ionic equation doesn't have a conjugate base for the acid. If you write H^+ + CO3^2- ==> HCO3^- as the net ionic equation, which I believe is correct, then ...
April 29, 2015

chemistry
And I think it is wrong. q = mass Pb x specific heat Pb x (Tfinal-Tinitial) = 225 x 0.139 x 20 = ?
April 29, 2015

chemistry
I have some serious problems with this equation. Is this the equation you were given; i.e., were you given the products?
April 29, 2015

Chemistry
Frankly, I don't think it is a very good buffer; however, small amounts of OH will be neutralized by the H3O^+ but I wouldn't bank on it.
April 29, 2015

Chemistry
#1. How many mols NaCl do you want? That's mols = M x L = ? Then mols = grams/molar mass. You know mols and molar mass, solve for grams. To prepare the solution you place that many grams (the ? calculated above) in a 250 mL volumetric flask, add some water, swirl until all...
April 29, 2015

Chemistry-is this right?
No. You must be pushing a wrong button. Hit the 10^x button, then -4.9 and read 1.256E-5M for H3O^+ For the second part, then pOH = 14- pH = 9.1 (NOT OH = 14-pH) then OH = 10^-pOH OH = 7.94E-10
April 29, 2015

Chemistry
I beg your pardon. PV = nRT DOES work. That provides at least some information to answer the second part. I didn't answer the second part. Frankly I think the second part is a guess since we don't know how strong the can is; however, I would hazard a guess that at ...
April 29, 2015

Chemistry
Use PV = nRT n = grams/molar mass. Calculate P. For the others, read this. http://en.wikipedia.org/wiki/Intermolecular_force
April 29, 2015

Chemistry
1. The original chemical has been changed to something different. 2C6H8O6 + O2 ==> 2C6H6O6 + 2H2O mols vit C = grams/molar mass = 1g/molar mass = ? Using the coefficients in the balanced equation, convert mols vit C to mols to mols O2. Convert 1.00 g O2 to mols. mols = 1.00...
April 29, 2015

Chemistryh
1. pH = -log(HCl) = -log 0.1 = 1 2. pOH = -log(NaOH) = -log(0.1) = 1 The pOH + pH = 14; pH = 14-pOH = 14-1 = 13
April 29, 2015

Chemistry
Is this just to keep me busy? What do you not understand about this? Remember -dH is exothermic. Large Keq means the reaction is favorable; small K means not very favorable. Le Chatelier's Principle says when a system at equilibrium is disturbed, it will shift so as to ...
April 29, 2015

Chemistry
Use the Henderson-Hasselbalch equation which I think is the same answer I wrote about 12 hours ago.
April 29, 2015

chem
I never heard of this. Obviously there be a beginning. A phase where the forward and reverse directions are adjusting themselves with respect to one another. When equilibrium is established you have the final stage. I have no idea if this is what you want or not but these what...
April 29, 2015

Chemistry
Very good. Go to the top of the class.
April 29, 2015

Chemistry
a is not right. 6 mols NH3 x (2 mols O2/2 mol NH3) = 6 mols O2. b. just half that since a is 2x too high. c and d are ok.
April 29, 2015

science
I would think a dead tree was already decomposed (at least parts of it are decomposed) so this organism must be a scavenger.
April 29, 2015

chemistry
All of that looks ok to me.
April 29, 2015

chemistry
I would not round from 1.82 for pH of 0.015 M HCl. In logarithms the 1 of 1.82 just tells you the location of the decimal point in the 0.015 number so that counts as only two significant figures in 1.82 you can get OH either of two ways. pH + pOH = 14 and after you know pH you...
April 29, 2015

Chemistry-is this correct?
For 1 the pH for (H^+) of 1.10E-11 is 10.95. I would not round that to 11. 2 is ok. 3 is not right. pOH is 8.39 which makes pH = 14-8.39 = ? and since pH < 7 it is acidic.
April 29, 2015

chem
My guess it had a high vapor pressure as a solid (like moth balls) and sublimed under suction.
April 29, 2015

chemistry
What's the concentration of the acid?
April 29, 2015

Chemistry
pH = -log(H^+). Calculate H^+. Then (H^+)(OH^-) = Kw = 1E-14
April 29, 2015

Chemistry- is this right?
Surely you meant for one of those lines to read pOH. I don't follow your work but the bottom line is right. If yu have 0.1M NaOH, then OH = 0.1, pOH is 1, which makes pH = 13. In that first line it should be (H^+) = 10^-pH
April 29, 2015

Chemistry
0.1 M is pH = 1 Yes, it is (H^+) = 10^-pH If you have (H^+) = 10^-2, that is 0.01
April 29, 2015

Chemistry
Assuming volumes are additive: 0.100 x (4.5/10)
April 29, 2015

Chemistry
mL x M x millimolar mass = grams OR mols = M x L = ? Then mol = grams/molar mass. You know grams and mols, solve for molar mass.
April 29, 2015

Chemistry
H2SO4 + 2NaOH ==> Na2SO4 + 2H2O mols H2SO4 = grams/molar mass Using the coefficients in the balanced equation, convert mols H2SO4 to mols NaOH. Then M NaOH = mols NaOH/L NaOH. You know mols and M, solve for L.
April 29, 2015

CHEMISTRY
How much heat is released? That's 3.27E6 J x (5.35/molar mass C6H6) = ? Then q = mass H2O x specific heat H2O x (Tfinal-Tinitial). Convert kg H2O to grams. Use specific heat in J/g*C
April 29, 2015

chemistry
Convert M to m, then delta T = Kf*m
April 29, 2015

Chemistry
Use the Henderson-Hasselbalch eqauation.
April 29, 2015

science
|..........|..........| Each side is 2.5 m.The 40 kg boy is 1.5m from the end or 1m from the center. 40*1 = 25*x x is the distance from the center to the girl.
April 28, 2015

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

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

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