Tuesday
July 28, 2015

Posts by DrBob222


Total # Posts: 49,558

Chemistry
E = hc/wavelength You know h,c, wavelength, calculate E. Also f come either of two ways; 1. c = freq x wavelength or 2. E = h*freq.
April 17, 2015

Chemistry
See your post above. E = hc/wavelength
April 17, 2015

chemistry
part 2. I looked up the %H2SO4 in density of 1.425 g/mL and it is 52.63%. M H2SO4, then, is 1.425 g/mL x 1000 mL x 0.5263 x (1/98) = mols in 1 L and that is M.
April 17, 2015

oops--chemistry
Well, I screwed up big time. The problem says in big print H2SO4 and I used HCl.
April 17, 2015

chemistry
Equal volumes will average the % HCl so (30+70)/2 = 50% HCl. mols in 1000 mL will be 1.425 g/mL x 1000 mL x 0.50 x (1/36.5) = ? And that's the M since mols/L = M. Answer this Question
April 17, 2015

chemistry
By the way, I posted a response to your NaCl/CaCl2 ratio problem. If you haven't found it let me know and I can give youa link.
April 17, 2015

chemistry
2Al + 3H2SO4 ==> Al2(SO4)3 + 3H2 mols Al = grams/atomic mass = 0.1 mols H2SO4 used = 0.1 mol Al x (3 mols H2SO4/2 mols Al) = 0.15 mol H2SO4 used. mols H2SO4 initially = 1.18 g/mL x 75 mL x 0.247 x (1/molar mass H2SO4) = approx 0.2 but you need a better answer than that. ...
April 17, 2015

chemistry
I don't understand the problem. Na2CO3 + H2SO4 ==> Na2SO4 + H2O + CO2 There is the equation. I have no idea what "nature of the mixture" means but let's see what happens. How many grams Na2CO3 will the H2SO4 use? That's ml x N x milliequivalent weight ...
April 17, 2015

Science
Here is #2 first before we tackle #1. 2. How many types of molecules are represented? Is there a difference or what? How do I recognize an exact type? For example if there are two CO2, would that be considered 1 type? SO2 is one type, H2O is a second type, H2SO4 is a third and...
April 16, 2015

Science
An element is an element is an element. An element has ONLY one kind of atom and there are a few more than 110 elements known to man at this time. Here is a periodic table. Each symbol on the periodic table represents an element. That means that all of the atoms in that ...
April 16, 2015

Chemistry
PV = nRT and solve for n = number of mols. Then n = grams/molar mass. You know molar mass and n, solve for grams.
April 16, 2015

Science
This is all about Le Chatelier's Principle and it's easy if you just remember a couple of things. 1. The principle tells us that when a system at equilibrium is disturbed, it will react to undo what we did to it. a. An increase in pressure shifts it to the side with ...
April 16, 2015

science
Since dH is +, I include that in the equation this way. 2SO3 + heat ==> 2SO2 + O2 So an increase in heat causes the reaction to get rid of the heat and it fcan do that by shifting to the right. That's the way to use up the added heat. You're right. But if you cool ...
April 16, 2015

oops--Chemistry
I'll get in on the fray here. Irving has it wrong. Devron made a typo. I've copied Devron's work and replaced the typo part with a bold 5.0 M=[(0.0200L)*(3.0 M)+(0.0300L)*(5.0M)]/(0.0200L+0.0300L) The answer comes out to be about 4.2 which is the weighted average ...
April 16, 2015

To Jaimi--chemistry
I responded to your post(the one on ratio of +/- charges) that's way down the list (I think on page 2 or 3 by now). Here is a link. http://www.jiskha.com/display.cgi?id=1429203638
April 16, 2015

science
1. Since the values are given to more places that you have shown, I would recalculate and don't throw digits away. For example, pN2 you have only two places in your answer but more than that in the Ptotal and X. Same for H2 and NH3. Redo that. 2. Where do you go from here...
April 16, 2015

science
I should point out that the total doesn't add up to 100% (almost but not quite) so you may want to check your problem vs your post. %by volume = mole fraction or X. Therefore, XN2 = 0.96143; XH2 = 0.003506; XNH3 = 0.03506 pN2 = XN2*Ptotal pH2 = XH2*Ptotal pNH3 = XNH3*...
April 16, 2015

AP Chemistry
Did you use -p(Vfinal-Vinitial) 0.0100(5.1-3) = ? L*atm. The problem wants joules, convert by L*atm x 101.325 = ?J. Work should be a negative value; make sure to include the - sign when you enter into the database. Keep me posted.
April 16, 2015

AP Chemistry
Do you really care how many moles are there? 1 mol expanding or 100 mols expanding, the only thing that counts is volume difference and p.
April 16, 2015

chemistry
q = mass x Ccal x (Tf-Ti) q = 2.85 x Ccal x (29.19-24.05) Solve for Ccal. You will need to look up the value of q which is the heat of combustion for benzoic acid and substitute that for q. Note that heat of combustion is - but this heat is being added to the calorimeter so ...
April 16, 2015

Chmistry
Note that you have the equation going from right to left. If that's the way you want it, ok. This is Le Chatelier's Principle which, in basic words, tells us that when we stress a system at equilibrium it will try to undo what we did to it. I'm going to rewrite the...
April 16, 2015

chemistry
Is this an introductory course; how complicated can it get? I wuld think you could add enough NaOH solution (weak) to neutralize the acid and that makes it soluble. Then you can filter the sand and dump it. Back to the aqueous solution, add HCl to bring the benzoic acid back ...
April 16, 2015

chemistry
2C2H6 + 7O2 --> 4CO2 + 6H2O + 2834 kJ How many kJ does it take to do the water thing. q1 = heat needed to heat H2O from 54 C to 100. q1 = mass H2O x specific heat H2O x (Tfinal-Tinitial) q2 = heat needed to boil away the water. q2 = mass H2O x heat vaporiation. Total heat ...
April 16, 2015

Science
You would do better to place asterisks next to your answers. Scrolling down to see your answer, back up to see the choices, back down to see answers is too time consuming.
April 16, 2015

Chemistry
It would be more than nice if you didn't switch screen names.
April 16, 2015

Chemistry
Reverse the Cd half cell and add to the Cu half cell as written. Calculate Eo cell. Then dG = -nFEcell. n is 2 and F is 96,485.
April 16, 2015

Chemistry
Ag.............0.8.........? Cu ...........+0.34.........0 H..............0..........-0.34 Ni...........-0.23..........? You just move everything down the page from Cu to h so you reduce everything by 0.34.
April 16, 2015

Chemistry
q1 = heat needed to raise T of solid ice from -10 to solid ice at 0 C. q1 = mass ice x specific heat ice x (Tfinal-Tinitial) q2 = heat needed to melt ice (change solid ice to liquid water). q2 = mass ice x heat fusion. Total = q1 + q2
April 16, 2015

Chemistry
If you have a Ag electrode dipping into the mixed solution and a Cu electrode dipping into the mixed solution, you get the battery reaction up front; i.e., Cu + 2Ag^+ ==> Cu^2+ + Ag(s)
April 16, 2015

chemistry
Obviously reduction is the gain of electrons.
April 16, 2015

chemistry
Oxidation is the loss of electrons.
April 16, 2015

chemistry
.........HX + NaOH ==> NaX + H2O mols NaOH taken = M x L = ? mols HX = mols NaOH since 1 mol HX = 1 mol NaOH in the balanced equation. Then mols HX = grams HX/molar mass HX. You know grams and mols, solve for molar mass.
April 16, 2015

Chemistry
mols CaCO3 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols CaCO3 to mols CaO. Now convert mols CaO to grams CaO with g = mols x molar mass = ?
April 16, 2015

chemistry
I don't see a question here. M = mols/L = 0.947/0.1 = ?M
April 16, 2015

chemistry
3.78 g NaCl/100 mL = 37.8 g/L solution and that's how many mols. 37.8/molar mass = approx 0.6 mols/L but you need answer than this estimate. This makes (Cl^-) = approx 0.6M You want to make 250 mL of BaCl2 and since BaCl2 has 2 Cl atoms/1 Bacl2 molecule, you only need 0.3 ...
April 16, 2015

chemistry
Let's assume for the moment the water is not there. How many mols do we want. That is M x L = mols = 0.5 x 60 = ? (I've used molarity since mols and equivalents for NaOH are the same). How many grams is that? grams = mols x molar mass IF IT WERE PURE STUFF BUT IT'S...
April 16, 2015

Inorganic chem
muriatic acid is HCl. HCl + NaHCO3 ==> NaCl + H2O + CO2 mols HCl = M x L = ? mols NaHCO3 = mols HCl since 1 mol HCl reacts with 1 mol NaHCO3. Then g NaHCO3 = mols NaHCO3 x molar mass NaHCO3.
April 16, 2015

chemistry
This is a limiting reagent (LR) problem and you know that because amounts are given for BOTH reactants. I do these the long way---easier to exlpain for me. AgNO3 + HCl ==> AgCl + HNO3 mols AgNO3 = grams/molar mass = ? mols HCl = M x L = ? Using the coefficients in the ...
April 16, 2015

Chemistry
Ba(NO3)2 + Na2SO4 ==> BaSO4 + 2NaNO3 mols Ba(NO3)2 = M x L = ? Using the coefficients in the balanced equation, convert mols Ba(NO3)2 to mols Na2SO4. Then M Na2SO4 = mols Na2SO4/L Na2SO4. You know mols and M, solve for L and convert to mL.
April 16, 2015

chemistry
I think what you want to do is this. Let's take a volume (choose anything but I'll pick 100 mL of the 0.2M NaCl) and calculate the amount of CaCl2 needed to meet the problem. 100 mL of 0.2M NaCl + xmL of 0.1M CaCl2, we have millimols + charge = 100*0.2 = 20 for Na in ...
April 16, 2015

Chemistry
Do you mean to boil all of the water away? That's q = mass H2O x heat vaporization Or do you mean to boil the first molecule of water? If so that takes much less heat.
April 16, 2015

Chemistry
All of these are worked with that magical formula of q = mc*delta T q = 90 x specific heat H2O x (Tfinal-Tinitial) specific heat H2O is 4.184 J/g*C Tf = 100 Ti = 0
April 16, 2015

Chemistry
It's the old q = m*heat vaporization m = 3.15g/18 = ? mols H2O heat vap = 44.0 kJ/mol q = ? kJ.
April 16, 2015

Science
It can't possibly be A. Why? There are 8 atoms Fe on the left and 5 on the right. There are 8 atoms S on the left and none on the right. Don't guess. Count the atoms on the left and see if that number is on the right. If not that one can't be the answer.
April 16, 2015

Science
I think you are right.
April 16, 2015

chemistry
That's my answer too but I think you should say the answer is 1.25%. By the way, it would be much better for everyone if you didn't change screen names. We can follow the thread better with the same name. It also helps on follow up questions to have the same screen name.
April 16, 2015

chemistry
I disagree with 0.15%. It's 0.15 as a fraction or 15% as a percent but not both at the same time. 15% x 25/300 = ?% Or you can do 0.15 x 25/300 and convert that fraction to a % by x 100 = ?
April 16, 2015

chemistry
Use PV = nRT and solve for mols NH3. I get about 0.016 but you need to do it more accurately. 2NH3 + H2SO4 => (NH4)2SO4 N H2SO4 = # equivalents/L #equivalents NH3 = 0.016 2 mols NH3 = 1 mol H2SO4 or 1 equivalent NH3 = 1/2 mol H2SO4 N H2SO4 = approx 0.016/2/0.134 = ?
April 16, 2015

chemistry
I don't know that I buy the argument that SnSb is the empirical formula but I agree you don't need it.
April 15, 2015

Chemistry 11 grade -
(P1V1/T1) = (P2V2/T2) Ptota = pH2 + pH2O. You are given Ptotal and pH2O. 98.125 = pH2 + 2.99 Solve for pH2(dry) and use that in the equation above. You know all but V2.
April 15, 2015

SCIENTIFIC NOTATION
16E5.Convert.
April 15, 2015

To Michelle
I posted a response to that potentiometric analysis problem but it's pretty far down the list. Let me know if you can't find it and I can help.
April 15, 2015

chemistry
I don't agree. Why did you convert from % to M? I don't think you can convert to M without knowing the density. I would keep it in % and use 15 x 25.0 = % * 300 % = ? Or another way, you are diluting it by a factor of 300/25 or 12 times. So 15%/12 = ?%
April 15, 2015

chm 112
I don't think it has any effect; at least I don't know about it if it does. The test is to add strong base to an ammonium salt and it releases NH3 gas. Both KOH and NaOH are strong bases.
April 15, 2015

Chemistry
Use the Henderson-Hasselbalch equation. You need pKa. If you have Kb, convert that to pKb (-log Kb) and then to pKa (pKa + pKb = pKw = 14). Plug this into the HH equation with EITHER M or mols and calculate pH. But note you didn't calculate mols. mols = M x L = 0.20 x 0....
April 15, 2015

oops--chemistry
What Mathmate gave you is correct for grams acetic acid in the solution. The problems ask for mols and that is obtained by mols = M x L = ? (in this case just omit the 60).
April 15, 2015

Chemistry
I don't think you are to find the number of electrons ejected; I think you are to compare. That is, I think that one beam ejects more or less electrons than the other and you tell that from the threshold frequency. http://en.wikipedia.org/wiki/Photoelectric_effect
April 15, 2015

chemistry
KHP + NaOH ==> NaKP + H2O mols NaOH = M x L = ? mols KHP = mols NaOH since the equation tells you 1 mol KHP = 1 mol NaOH Then mols = grams/molar mass. You know molar mass and mols, solve for grams.
April 15, 2015

chemistry
See your post below.
April 15, 2015

chemistry
mL1 x M1 = mL2 x M2 1000 x 0.1 = mL2 x 6 Place mL2 in a 1 L volumetric flask, and add water to the mark of the flask, mix thoroughly, stopper.
April 15, 2015

chemistry
43 won't do it.
April 15, 2015

chemistry
How many doesn Au element have? That's the same as the number of protons and that's the atomic number in the periodic table. To make it +1 ion you must lose 1 electron.
April 15, 2015

Chemistry
Why can't you do this? It's just like the last problem. After you see a problem worked you should be able to use that as a template and work similar problems.
April 15, 2015

chemistry
Why are you having trouble with equations?
April 14, 2015

Chemistry
If you had posted your work I wouldn't have to guess what you did. M HCl = 2.7E-4 pH = -log(HCl) since HCl is a strong acid and ionizes 100%. Then (H^+)(OH^-) = Kw = 1E-14
April 14, 2015

Chemistry
PV = nRT. Remember the units. Also T must be in kelvin.
April 14, 2015

Chemistry
2HNO3 + Ca(OH)2 ==> Ca(NO3)2 + 2H2O mols Ca(OH)2 = M x L = ? Using the coefficients in the balanced equation, convert mols Ca(OH)2 to mols HNO3. Then M HNO3 = mols HNO3/LHNO3. You have mols and M, solve for L.
April 14, 2015

Chemistry
Is this 2% w/v. I'll assume so. [(g solute/mL solution)]*100 = % Substitute and solve for g solute.
April 14, 2015

Chemistry
XN2 = 0.745 pN2 = XN2*Ptotal pN2 = 0.745*1 atm = 0.746 atm or 0.745*760 = ? mm = pN2
April 14, 2015

chemistry
2HClO4 + Li2CO3 --> 2LiClO4 + H2O + CO2
April 14, 2015

Chemistry: Potentiometric Anyalysis
Sorry to get back so late but here is what I think based on what you wrote. IF (and only IF) you used the titration CURVE to determine the equivalence point on the computer (that is you determined the eq pt graphically on the computer), then mols acid comes from mols NaOH and ...
April 14, 2015

Chemistry: Potentiometric Anyalysis
I don't know what lab you did. Did you place a weak acid or base in solution, measure the pH, calculate what? what else do you know?
April 14, 2015

chemistry
First, calculate the M of the initial solution. mols CuSO4.5H2O = grams/molar mass = ? Then mols/L = M So the diluted solution is M of first x (13.6/500) = ? For the last part. How many mols do you have in the second solution? That's mols = M x L = ? Then mols = grams/...
April 14, 2015

Chemistry
See your other post under Tim.
April 14, 2015

Chemistry
1. mols = M x L = ? Then mols = grams/molar mass. Substitute mols and molar mass and solve for grams. 2. Just like 1 but in reverse. mols Na2SO4 = grams/molar mass = ? Then M x L = mols. You know mols and M, solve for L. 3. I think this is just #1 again. I'll check you ...
April 14, 2015

Chemistry
Tim, this is just like the problem you posted below which Jundy answered incorrectly but I followed up. What is it you don't understand about limiting reagent problems? We need to get you so you can work all of these yourself.
April 14, 2015

chemistry
I don't understand the problem. Can you give an example or two for n and A.
April 14, 2015

Chemistry
NaOH + H2SO4 ==> NaHSO4 + H2O You have 0.1M x 50 mL = 5 millimols H2SO4. Therefore, to reach the first equivalence point you must titrate 5 millimols (another 5 millimols will be needed to titrate the second H). So you will need 50 mL of 0.1M NaOH to titrate that first H ...
April 14, 2015

Science
momentum is mass x velocity. The wrecking ball is MUCH heavier than the tennis ball; therefore, it does much more damage when it hits the wall.
April 14, 2015

chemistry
PV = nRT and solve for n = number of mols. Then n = grams/molar mass. You know molar mass and n, solve for grams.
April 14, 2015

Chemistry
I don't believe Junday into account the 85 grams of each reactant. mols SO2 = 85/64 = about about 1.3 mols H2S = 85/34 = about about 2.5 Calculate LR from that and I believe the LR is H2S. Check it out.
April 14, 2015

Chemistry
Many thanks for showing your work. It helps me spot the problem right off. BTW, I assume this is a monoprotic acid. Your error is in step 2. 1.78 mmols NaOH is correct. That means mmols HA is 1.78. You took 25 mL for that titration and M = mmols/mL; therefore, 1.78 mmols/25 mL...
April 14, 2015

Chemistry
q = mass metal x heat fusion. You know q and heat fusion, solve for mass metal.
April 14, 2015

Science
E = 2.18E-18*Z^2(1/16 - 1/36) Note this goes from 4 to 6 so energy must be absorbed.
April 14, 2015

Science
See your last post. Also, just what do you mean by value? size, length, width, energy, just what kind of value?
April 14, 2015

Science
You have posted many questions in the last week or so but never any thoughts about the answer. You need to start telling us what you think the answer is or exactly what you don't understand.
April 14, 2015

chemistry
Volume of 1 atm? I might believe 1 L but not 1 atm for volume.
April 14, 2015

Science
d although I don't like the word decay following gamma. Gamma rays are the result of decay of the parent atom.
April 14, 2015

Chemistry
mass in grams = volume x density Then convert grams to pounds. There are 453.6 grams in one pound.
April 14, 2015

Science
1/wavelength = R(1/9 - 1/25) Then E = hc/wavelength. OR E = 2.18E-18(1/9 - 1/25)
April 14, 2015

Science
Convert amu to kg, then E = mc^2
April 14, 2015

Science
How many days in a month? Use 30? 50/30 = 1.67 months in 50 days k = 0.693/t1/2 and substitute k into the below equation. I used 1.67 months. ln(No/N) = kt. No = 100 mg N = ? solve for this k from above. t = 5 months
April 14, 2015

Chemistry
5500 kJ. 40.6 kJ/mol x # mol = 5500 kJ. Solve for mols H2O Convert mols H2O to grams. Convert, using density, grams H2O to L H2O.
April 14, 2015

chemistry
0.25 x ((5/2/3/2) = 0.25 x (2.5/1.5)= ?
April 14, 2015

Chemistry
I note that many of these are the same type. Learn to work one and you know how to work all. If you will kindly start over with the first one of your choice, tell us exactly what you don't understand about it, perhaps we can help you through it. Then we can proceed to the ...
April 14, 2015

Chemistry
PV = nRT and solve for n = number of mols. Then n = grams/molar mass. You know n and grams, solve for molar mass. Identify the gas from that. Remember some gases are diatomic.
April 14, 2015

Chemistry
You need to work on this post. It's willy nilly. No sense.
April 14, 2015

Chemistry
pKa = -log Ka. Solve for Ka. Then..........HA ==> H^+ + A^- I.............1.......0.....0 C...........-.375...0.375..0.375 E...........0.625...0.375..0.375 Substitute the E line into the Henderson-Hasselback equation and solve for pH.
April 14, 2015

chemistry
(V1/T1) = (V2/T2) Remember all Ts must be in kelvin.
April 13, 2015

science
http://en.wikipedia.org/wiki/Agonist
April 13, 2015

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