Thursday
October 23, 2014

Posts by DrBob222


Total # Posts: 44,667

chemistry
I will assume you are using concentrated HNO3. With concd HNO3 the reduction product is NO2; with dilute HNO3 the reduced product is NO. Cu + 4HNO3 ==> Cu(NO3)2 + 2H2O + 2NO2 mols Cu = grams/molar mass = approx 0.0063 but you need to do it and the calculations that follow ...
September 18, 2014

Physical Science
I see this problem this way. Perhaps another tutor will look at it too. dE = q+w -103 = q + w If the evaporator coils lose 54 kcal that is -54 from the coils(exothermic at the coils) which makes it + 54 kcal to the heat pump. Then -103 = 54 + w w = ?
September 18, 2014

CHEMISTRY
Put the problem into apples (or oranges) and see if that doesn't help. The mass of an apple is 100 grams. Using the unit factor method, calculate how many apples you have if they weigh 500 grams? (100 g/apple) x # apples = 500 g Solve for # apples = 500/100 = 5 PROOF: 100g...
September 18, 2014

chemistry
http://en.wikipedia.org/wiki/Phthalic_acid
September 18, 2014

chemistry
Mo2O3 has mass 15.27g % Mo in Mo2O3 = (2*95.94/239.88)*100 = about 80% but you should do that more accurately. Out of a 15.27g sample, 15.27 x 80% = about 12.2 g Mo and the rest is oxygen. If you started with 12.2 g Mo there must be 12.2 g in the new oxide which means oxygen ...
September 18, 2014

Chemistry
mols NaOH = M x L = ? mol HCl = mols NaOH (look at the coefficients in the balanced equation) Then M HCl = mols HCl/L HCl.
September 18, 2014

general chemistry I
5 drops H2O x (0.05 mL/drop) = 0.25 mL Then (0.25/1.00)*100 = 25% error. The others are done the same way. The purpose of this problem is to demonstrate that an absolute error (in this case one of 0.25 mL) is a larger percentage of the small pipet than of a larger pipet. For ...
September 18, 2014

Chemistry
1.763E-24 g/e x #e = 5.6g
September 18, 2014

science, chemistry
Not the correct spelling of celsius. Use PV = nRT and solve for n. V = pi*r^2 and convert to L.
September 18, 2014

chemistry
This is a limiting reagent(LR) problem. N2 + 3H2 ==> 2NH3 mols N2 = grams/molar mass = 8/28 = approx 0.29 but you need to do all of these calculations yourself and do them more accurately than my estimates. mols H2 = 10/2 = 5 Convert mols N2 to mols H2. That's 0.29 mols...
September 18, 2014

Chemistry
If it isn't too concentrated, rub it between your fingers. Bases have a "slick" feeling. Too concentrated and it may burn your fingers.
September 18, 2014

Chem---DrBob222
For C=C there are four electrons between each C atom. But don't count the bonds or electrons as a way of calculating the oxidation state. Counting the electrons is a way to calculate the formal charge on the atom but that isn't the same thing as oxidation state.
September 18, 2014

Chem---DrBob222
If you go with what I did the oxidation number for each C is 3 1/3 just as I posted. This whole process is just a matter of book keeping. H can have +1 or -1 and we stay out of trouble if we assign +1 in most cases unless we know the compound is a hydride such as NaH or CaH2. ...
September 18, 2014

Chem
You must know how to do parts of this or have some ideas about how to proceed. Let's hear your thoughts and a rationale for why you have those thoughts.
September 17, 2014

oops- - Chem
Steve made two typo but othrwise the problem is ok. Just follow the steps but not the numbers. That should be 28.3g/(2.5) = ?
September 17, 2014

chemistry
The solubility is 0.029g/10 mL or 0.0029g/1 mL so there will be 73.53 times that in 73.53 mL. right?
September 17, 2014

Chemistry
1. If this is a beginning chemistry question the answer is that KCl doesn't do anything to the pH. In advanced courses you will learn that the activity coefficient has an effect and the pH will decrease slightly. 2. Since KOH ionizes 100% it will produce OH^- and that will...
September 17, 2014

AP Chemistry
You want how many mols? That's M x L = mols. Then mols = grams/molar mass. You know molar mass and mols, solve for grams. Dissolve that many g CuSO4.5H2O in some water and make to exactly 300 mL with distilled water.
September 17, 2014

physical science
80 miles x (1 km/0.6214 mi) = ?
September 17, 2014

Physical Science
No but mostly because volume is not measured in grams but in cc or cm^3. volume = mass/density = 3800 g/10 g/cc = 380 cc
September 17, 2014

chemistry
1a. Actually, I don't think it advisable to prepare a slightly more concd solution of KMnO4. I know why this as been broached and that's probably because KMnO4 is not pure straight out of the bottle and because it is reduced to MnO2 when prepared; however, my ...
September 17, 2014

Chem
This programing recognizes one space and ignores after that. I would assign H as +1 each for a total of +7 for H. I would assign N a +3 for a total of +3 for N That leaves -10 for C (to make zero for the compound which it must be) which makes EACH H -3 1/3.
September 17, 2014

CHEMISTRY
The answer in the data base/text/whatever must be wrong. I get 1.93965 which I would round to 1.94 to 3 s.f.
September 17, 2014

CHEM
If CP is cyclopentadienyl you should know that we can't draw structures on this forum. If it's a compound between carbon and phosphorus I know little about it but it appears that can't be the right formula.
September 17, 2014

Physical Science
q = mass spoon x specific heat spoon x (Tfinal-Tinitial)
September 17, 2014

chemistry
I worked a similar problem (just different numbers) yesterday. Look at the chemistry posts to find it. I must leave now and can't do this but I'll be back this afternoon.
September 17, 2014

chemistry
3g CaCl2/0.5 L = 6/L = 0.6g/dL dilute 10 mL to 1000 mL; new concn is 0.6g/dL x (10/1000) = 6E-3g/dL mols = 6E-3/111 = approx 5.41E-5 mols in 6E-3g CaCl2. Then 5.41E-5 mol/dL = 5.41E-4 mol/L - 5.41M. I've estimated here and there; you should go through the math yourself ...
September 17, 2014

REACTION KINECTICS
At 600. Take 100 mols as an arbitrary number. .......CH3CH3CH3 ==> CH3CH=CH2 + H2 I.......100............0..........0 C........-x............x..........x E......100-x...........x..........x Ka = 0.104 = (x)(x)/(100-x) Solve for x for mols = x, then (x/100) = fraction ...
September 17, 2014

Physical Science
Calculate the new pressure with P1V1 = P2V2 The pressure had to decrease if the volume increased. See Boyle's Law
September 16, 2014

chem
Is that 3.00 cmcm a typo and you meant to write 3.00 cm on an edge. mass = volume x density volume = (3.00)^3 = 27 cc density = 8.90 g/cc Substitute and solve for mass in grams.
September 16, 2014

chemistry
CaCO3 + 2HCl ==> CaCl2 + H2O + CO2 You list no data; therefore, no calculations are possible showing loss CO2 or anything else. Please be advised, also, that we can't draw/sketch graphs on this forum.
September 16, 2014

Scientific Method
I would design and implement an experiment before collecting data.
September 16, 2014

Chem-Extraction Lab
Caffeine is too soluble in dichloromethane. You could do a mixed melting point with pure caffeine and the product you think is caffeine.
September 16, 2014

Bio Chem
pH = pKa + log (base)/(acid) pH = 4.87 pKa = 4.87 Therefore, 4.87 = 4.87 + log (base)/(acid) and (base)/(acid) = 1 which means (base) = (acid) If you lower the (H3O^+), that raises the pH so let's substitute a higher number for pH, say 5.87 and see what happens. 5.87 = 4....
September 16, 2014

Organic chem Extraction of caffeine from tea
You may be thinking of suspension or emulsion.
September 16, 2014

Chemistry
The molar mass (molecular weight/molecular mass) is Pb = 207.2 I = 126.9 PbI2 is (207.2 + 2*126.9) = ?
September 16, 2014

chemistry
1 meter = 6.21E-4 miles. 0.11 m/s x (6.21E-4 mi/meter) = ? mi/second 0.11 m/s x (6.21E-4 mi/m) x ? seconds = 5 hrs x (60 min/hr) x (60 s/min)
September 16, 2014

Science! Help!
I agree
September 16, 2014

science
You didn't give the density of water but I suppose we can assume it is 1.0 g/mL. I would NEVER taste it even though some one told me it was alcohol or water. :-). I would carefully smell it. OK so you want to utilize the densities. Place an ice cube in the liquid. If the ...
September 16, 2014

Science
Less mass makes it easy to get off the ground with an airplane. Which plane will weigh less, one made of Al or one made of Cu?
September 16, 2014

Science
I would expect the less dense Cu metal to float on the more dense liquid Hg, at least until the Cu was dissolved. (Many metals (including Cu) will form an amalgam with Hg.)
September 16, 2014

Chemistry
You made a typo in the equation; it should be Pb(NO3)2 + 2NaI ==> PbI2 + 2NaNO3 (should be NO3 and not NO2 with NaNO3. Also, note that you don't put quantities in the equation line. This is a limiting reagent (LR) problem. You know that because amounts are given for ...
September 16, 2014

Science
I agree
September 16, 2014

Chemistry
Area swimming pool is pi*r^2 and that x h is the area of a cylinder. That gives you cubic feet. Let's call that 1000 cubic feet. 1 gallon = 0.134 cubic feet. 7.58 gallons/min x (0.134 ft^3/gallon) = about 0.8 ft^3/min 0.8 ft^3/min x ?min = 1000 ft^3 Solve for min
September 16, 2014

Chemistry
28 strides x (41 in/stride) x (1 m/39.37 in) x (1 km/1000m) = approx 0.03 km in 10 seconds. 0.03 km/10 sec x ?sec = 5 km Solve for seconds ?sec x (1 min/60 sec) = ?min
September 16, 2014

Chemistry Urgent Help Please!
Extraction Sublimation if it's the right kind of sample.
September 16, 2014

chemistry
(Independent variable) causes a change in (Dependent Variable) and it isn't possible that (Dependent Variable) could cause a change in (Independent Variable). I think your are right.
September 16, 2014

OChem
You can make the problem easier by choosing to dissolve 29.1 g acetanilide in 100 mL solvent at 60 C. Then you cool it to O c and it will dissolve 3.53g. How much do you recover? That's 29.1-3.53 = ? grams recovered. What percent is that? That's (?g/29.1)*100 = ?%
September 16, 2014

chemistry
I assume this is 14.5% by mass (w/w), That means 14.5 g/100 g solution. So 14.5g CaCl2 dissolved in (100-14.5)g H2o = what you want.
September 16, 2014

chemistry
mols CO2 needed = grams/molar mass = approx 7.9 but I've estimated. You need to do it more accurately as well as all of the numbers that follow. Using the coefficients in the balanced equation, convert mols CO2 to mols C3H8. That's 7.9 mols CO2 x (1 mol C3H8/3 mols CO2...
September 16, 2014

chemistry
I don't understand the question.
September 16, 2014

chemistry
Here is how you do a and b. a. HNO3 is a strong acid; i.e., it ionizes 100%. Therefore, HNO3 ==> H^+ + NO3^- amd H^+ = 0.01 Then pH = -log(H^+) = -log(0.01) = -(-2) = 2 b. Ba(OH)2 is a strong base and ionizes 100% as in Ba(OH)2 ==> Ba^2+ + 2OH^- In a above you had only 1...
September 16, 2014

chem
I would convert 2.19E-9 to mols and call that No. Then N = initial mols - 1.07E15, and put that into ln(No/N) = kt. You know No, N, and t. Solve for k.
September 16, 2014

chem 2
Pether = Xether*Po ether Palc = Xalc*Po alc Ptotal = pether + palc I assume you know how to get Xether and Xalc. Xether = mols ether/total mols. Xalc = mols alc/total mols.
September 16, 2014

chemistry
25B is a typical acid/base reaction 26.HBr is an acid; H2O is a base. The fact that it doesn't normally go in reverse means that the HBr is a stronger acid than H2O. That is, H2O is pulling a H^+ from H^+ to make it H3O^+ so H2O (adding a proton is a Bronsted base) so it&#...
September 16, 2014

Chem Extraction of Caffeine from Tea
Did you extract with ether? That, or whatever solvent you used, is quite volatile and you must vent it. The more you shake it, especially at the beginning, the more vapors are trapped.
September 16, 2014

Analytical Chem
Yes but there is an easier way to do it. Let S = solubility Zn(CN)2==> Zn^2+ + 2CN^-,then + H^+ =>HCN ..solid....S.......2S Ksp = (Zn^2+)(CN^-)^2 For HCN ==> H^+ + CN^- You should confirm all of this. Ka = 6.2E-10 = (H^+)(CN^-)/(HCN) If pH 2.39 then (H^+) = about 4E-3...
September 16, 2014

Chemistry 400/ Chem 1A
excess mol ethanol x molar mass ethanol = grams ethanol in excess
September 15, 2014

Chemistry 400/ Chem 1A
mols KMnO4 = grams/molar mass = approx 0.033 but you need to this and all of the calculations that follow more accurately. mols ethanol = approx 0.05 Convert mols KMnO4 to mols H2SO4. That's 0.033 x 6/4 = 0.05 Convert mols ethanol to mols H2SO4. That's 0.05 x 6/5 = 0....
September 15, 2014

chem
Calculate the neutron:proton ratio. For 48K it has 29N and 19P N/P = 1.5 79Br has 44N and 35P with N/P = 1.26 32Ar has 14N and 18 P with N/P = 0.77 Here is a graph of #neutrons vs #protons. 32Ar is far below the band of stability. 48K is above 79Br look relatively close; I ...
September 15, 2014

Chemistry
mols Al = g/atomic mass = approx 3.06 but you should do this more accurately (as well as all of the other calculations below. I estimate.) Convert to mols O2 using the coefficients in the balanced equation. That's 3.05 x (3 mols O2/4 mol Al) = 2.29 Do you have that much O2...
September 15, 2014

chemistry
mols = M x L Only KCl has Cl^- so that has been diluted from 57.0 mL to 57.0+57.0 + 56.0 = 170 mL. New concn is 0.325 x (56.0/170) = ? Another way is to find mols Cl^-. That is M x L = 0.325 x 0.057L = ? Then M KCl = mols KCl/L solution = (0.325*0.057)/(0.056+0.057+0.057)
September 15, 2014

chemistry
I've been waiting on you to show some work and that hasn't happened yet. Please indicate your answers and why you think that is the answer.
September 15, 2014

chemistry
q = mass x specific heat x (Tfinal-Tinitial)
September 15, 2014

chemistry
17% is h1 35% is 83 Then 48% is 84 (0.17)*81 + (0.35)*83 + (0.48)*84 = ?
September 15, 2014

chemistry
See above.
September 15, 2014

Organic Chemistry
http://www.youtube.com/watch?v=vheqX9W8bf4
September 15, 2014

chemistry
b
September 15, 2014

chemistry
Don't run the numbers together. 1s2 2s2 2p6 3s2 3p2 = ? Add the electrons and that must the be atomic number of the element on the periodic table.
September 15, 2014

chemistry
Wouldn't the answer be obvious if you took the different between F and F; i.e., the electronegativity of F is 4.0 so 4.0-4.0 = 0 and that's < 0.5, right? You can calculate, just for the fun of it, the others. EN H is 2.1 EN K is about 0.8 or 0.9 (you can look it up...
September 15, 2014

chemistry
According to the Arrhenius theory: The acid is the one with the H^+. The base is the one with the OH^-. OR Accoarding to the Bronsted-Lowry theory: The acid is the one that donates a proton. The base is the one accepting a proton
September 15, 2014

Chem
41. q = mass H2O x specific heat H2O x (Tfinal-Tinitial) 42. 100 C is the boiling point for H2O. If you add more heat to water at 100 C it will start to boil. It will continue to boil until all of the water has evaporated. The temperature of the pot will not go above 100 C ...
September 15, 2014

chemistry
I shall be happy to critique what you write.
September 15, 2014

Chemistry
Thanks for showing your work. I think your error is in the last step. If I divide 100/4E-19 I get an answer like 25E+19 or 2.5E20 Check that out.
September 15, 2014

Chemistry
E of 1 photon = hc/wavelength E of 1 photon x # photons = 100 J
September 15, 2014

Chemistry
I don't know what you're doing wrong with your calculator but you need to find out and get it under control. 162/4.53E20 = approx 40E-20 or 4E-19 (I think the actual number is 3.57E-19). (both numbers wrong). My final answer comes out to be about 5.6E-7 m which is ...
September 15, 2014

Chemistry
I think the error is in the exponent.
September 15, 2014

Chemistry
If you will show your work perhaps I can find it as in the other laser problem.
September 15, 2014

Chemistry
1 watt = 1 J/s 15 watt = 15 J/s 15 milliwatts = 15 millijoules/s =0.015 J/s 0.015 J/s x (60 s/min) x (60 m/hr) x (3 hrs) = ? total Joules This E is for 4.53E20 photons so total J/4.53E20 = energy in J/1 photon. Then E in J/photon = hc/wavelength. Solve for wavelength.
September 15, 2014

Chemistry
Go to Google, type in mass proton. Or look in your text/notes.
September 15, 2014

Chemistry
wavelength in m = h/mv h is Plancks constant m is mass proton in kg v is velocity in m/s
September 15, 2014

Chemistry
Go to Google and type in mass electron. I think it is 9.08E-31 kg but you should confirm that.
September 15, 2014

Chemistry
dX*dp = h/4*pi dp is change momentum = m*v; therefore, 4*pi*dX*m*V = h Substitute 4, pi, dx = 611E-12, m is mass electron in kg, h is Planck's Constant, solve for V
September 15, 2014

Organich Lab Help Please!!!!!!!!
I think you're ok if the assumption that the volumes are additive is ok but I don't know about that. Having said that, I don't know of any other way of approaching the problem. If I were making up the problem I would have made the aq layer the top on a and the ...
September 15, 2014

Organich Lab Help Please!!!!!!!!
I went through this last night and you've corrected at least one of the problems. What is your trouble now? Explain in detail. Based on my calculations I would think the aqueous layer would be on the bottom for a. How can you test it. You have the mixture in a sep funnal, ...
September 15, 2014

Chemistry: Please Help!!
39. KE = 1/2*m*v^2. As the more energetic molecules of water (from the sweat) leave due to evaporation, the average energy of the remaining molecules is decreased and lower energy means lower T. Another way of saying the same thing is that energy to help the molecules escape (...
September 15, 2014

Chemistry: Please Help!!
37. Look up the density of H2O versus temperature. I believe the maximum density is at 4 C; therefore, 4C should be the temperature of water at the bottom. right? 38. I might take issue with the statement. The water flows from the outside of the root to the inside of the plant...
September 15, 2014

Chemistry
B is not likely. There is no driving force for N2 and H2O to react but I don't base that prediction upon the polarity of the molecules themselves. Diving forces for reactions are 1. formation of a precipitate (insoluble material). 2. formation of a gas (one is already a ...
September 15, 2014

Chemistry
P1V1 = P2V2 Substitute and solve for the unknown.
September 15, 2014

Pure Chemistry
P1V1 = P2V2
September 15, 2014

chemistry
mass = volume x density mass = 10 mL x 2.5 g/mL = ?
September 15, 2014

chemistry
There are 10^9 nm in 1 m. 0.002 m x (1 m/10^9 nm) = ?
September 15, 2014

Chemistry
yes
September 15, 2014

Analytical CHM
I did this for you yesterday, in detail. KHP + NaOH ==> KNaP + H2O mols KHP = grams/molar mass = 0.8/molar mass KHP = approx 0.0039 but you need to do this step as all that follow more accurately as I've estimated. Step 2. Convert mols KHP to mols NaOH using the ...
September 15, 2014

Chemistry
All you ever wanted to know about charge balance: http://ramsey1.chem.uic.edu/audrey/chem222/assign_docs/fall_12/mass_charge_ANS.pdf All you ever wanted to know about mass balance. http://mimoza.marmara.edu.tr/~zehra.can/CHEM209/6.%20Mass%20Balance%20Charge%20Balance.pdf both...
September 15, 2014

Chemistry
566 kJ/2 mol x 0.750 mols = ?
September 15, 2014

Organich Lab Help Please!!!!!!!!
You have posted this for the last day or two. One reason you don't have an answer is that you don't say what the ethylene bromohydrin is mixed with. You say mixed with 100 mL OF WHAT? Second reason is when I look up ethylene bromohydrin on google I find the density is ...
September 15, 2014

chemistry
(3.92/gallon)x (13.5 gallons/week) x (1.5 weeks) = ?
September 14, 2014

chemistry
mols Ag in 6.00g = grams/atomic mass mols Cu = 1/2 mols Ag (from the coefficients in the balanced equation) Then g Cu = mols Cu x atomic mass Cu
September 14, 2014

Chem 1
What's the temperature of the water when the bottle is first filled. Let's say it is such that the density of the watrer is 1.0 g/mL. If the problem doesn't tell you it can't be solved exactly. If density i8s 1.0 g/mL, then the mass of the water is 1,700 grams...
September 14, 2014

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