Thursday
February 26, 2015

Posts by DrBob222


Total # Posts: 47,261

Chemistry
I agree it is a little confusing as to exactly what they want. In particular the pH range of the average range is confusing but I would go with the average percent or (0.057+0.084)/2 = about 0.0705%. I would start with 100 mL of solution and that will contain 100 x 0.000705 = ...
February 3, 2015

Acidity of different concentrations
Yes and yes. Yes, the concentration affects the pH and the pH of a stronger acid will have a lower pH.
February 3, 2015

Chemistry
q = mass ethanol x specific heat ethanol x (Tfinal-Tinitial)
February 3, 2015

Organic Chemistry TLC Chromatography
I don't know how this fits into TLC chromatography but here is what I would do. 5.6 mL x 0.95% = mL x 85% mL = 6.2588 mL is what you can make. So you take 5.6 mL 95:5 ethyl acetate and add pure ethyl acetate to make 6.2588 mL total. Check it. You have 5.6 mL x 0.95 = 5.32 ...
February 3, 2015

Chem Uni. Urgent!!!
I re-iterate that the percent recovery is not 50%.
February 3, 2015

Chem Uni. Urgent!!!
So you had in that 1g of stuff you started with 1 x 0.85 = 0.85g acetanilide; 1 x 0.14 = 0.14g NaCl; 1 x 0.01 = 0.01 g charcoal. Wouldn't the theoretical yield = 0.85 g acetanilide. That's what you would get if you had 100% yield? right? I might argue that percent ...
February 3, 2015

Science
Yes.
February 3, 2015

Science
Did you not understand "conserved"? When mass is conserved it is neither gained nor lost. When momentum is conserved it is neither gained nor lost. I copied the following from Wikipedia. "The law of momentum conservation can be stated as follows. For a collision...
February 3, 2015

Science
Isn't momentum conserved? If D is correct then the system gained momentum and it can't do that.
February 3, 2015

Chimstery
1. Write and balanced the equation. 2. Convert mass Fe to mols. mols = grams/molar mass = ? 3. Using the Coefficients in the balanced equation, convert mols Fe to mols CO. 4. Now convert mols CO to g. g = mols x molar mass. Print this page. This four step procedure will work ...
February 3, 2015

chemistry
The problem doesn't say so but implies you want the dH, dS, dG FOR THE REACTION. 1. You have the equation, balanced it. 2. dHrxn = (n*dHf products) - (n*dHf reactants) 3. dSrxn = (n*dSf procuts) - (n*dSf reactants) 4. Then dGrxn = dHrxn - TdSrxn. Substitute and solve for ...
February 3, 2015

Physical Science
Ms. Sue is right. All of these units show up on Google.
February 3, 2015

science subject
We can't draw structures on this forum. Your best bet is to google them.
February 3, 2015

Chemistry
I don't follow everything you've done. There are 4 atoms to the face centered unit cell. mass unit cell = (197 x 4/6.02E23) = ?grams. volume unit cell = mass/density = ? cc cubed root V = ? = a cm Then a(2)^1/2 = 4r and solve for r = ? in cm. I obtained 1.44E-8 cm = 1....
February 3, 2015

science 1 question
Yes, D.
February 3, 2015

Chemistry
Thank you for showing your work. You have done everything exactly right EXCEPT you have one more step to go through. Your answer is ln p1 = 4.613. Find the number for which ln p = 4.613 and it is about 100.7 which rounds to 101 mm. :-)
February 3, 2015

chemistry
Yes, again thanks for showing your work. It really helps spot the problem quickly. I which more students would do that. It would make it easier for them but they don't want to take the time it takes to type it out. Which makes us take the time to type it which means we ...
February 3, 2015

chemistry
Thanks for showing your work. It helps spot the problem which is that you should have substituted 29 for 29%. The 100 is in the formula to convert that 0.29 to 29% or 29 = 100(x/40). You can omit the 100 and use 0.29 = (x/40) In other words, your answer is just 100x to small. ...
February 3, 2015

chemistry
What's the problem? dG = dH-TdS The usual mistake made by students is they don't recognize that dH is in units of kJ/mol BUT dS in in units of J/mol. One of them must be converted to the other.
February 3, 2015

chemistry
core electrons 15-5 = ?
February 3, 2015

chemistry
Test for what? to show what?
February 3, 2015

chm
Like dissolves like. KBr is a polar compound; it won't dissolve in non-polar solvents. And your "think" makes no sense; similar solute???
February 3, 2015

chm
Please don't change screen names. mols glucose = grams/molar mass mols methanol = grams/molar mass Total mols = mols glucose + mols methanol mole fraction methanol = nmethanol/total mols. psoln = Xmethanol*Pomethanol For the difference, what about interactions between ...
February 3, 2015

chm
See your other post with a different screen name. Do you think posting under different screen names will get different answers?
February 3, 2015

chm
Please don't change screen names. m = mols/kg solvent mols = grams/molar mass. 1.143 g/mL x 1000 mL = 1143 g = mass solution 10.0% of that is H2SO4 = 1143 x 0.100 = 114.3 g is H2SO4. mols H2SO4 = grams/molar mass = ? mass H2O = 1143-114.3 = 1028.7 Then m = mols/kg = ? You ...
February 3, 2015

General Chemistry
The first question makes no sense due to typos (and I think parts have been omitted). The second one is ...........SrCO3 ==> Sr^2+ + CO3^2- I..........solid.....0........0 C..........solid.....x........x E..........solid.....x........x Substitute the E line into Ksp ...
February 3, 2015

Chemistry
C = Q/dT C = 3871/44.9 = ? J/C
February 3, 2015

Chemistry
delta T = Kf*m You know delta T (it's 20C), and Kf, solve for m. Then m = mols/kg solvent. You know m and kg solvent (1 kg), solve for mols. Then mols = grams/molar mass You know mols and molar rmass, solve for grams.
February 3, 2015

chem
Can't you use the Clausius-Clapeyron equation. ln(p2/p1) = dHvap(1/T1-1/T2)/R You have p1 = 1 atm with T1 = 373 and you have p2 and listed. Solved for T2 in K. Convert to C is needed.
February 2, 2015

chem
See your other post.
February 2, 2015

science
Yes. Mass doesn't change. The weight changes with the gravitational force.
February 2, 2015

Are there even any physics tutors here???
You may be right but I think Ms. Sue and I were simply pointing out that at least two profs were around in the last couple of hours. You are right, however, that many question, many of them physics and math, go unanswered.
February 2, 2015

Are there even any physics tutors here???
Reiny answered one at 10:20 P.M.
February 2, 2015

chemistry
Use the HH equation.
February 2, 2015

chemistry
Why don't you show your work and let us find the error? M = 0.85 mols/2L = 0.425M ........Br2 + Cl2 ==> 2BrCl I.....0.425..0.425.....0 C.......-x.....-x......2x E.....0.425-x.0.425-x..2x Go from there.
February 2, 2015

chemistry
Thanks for showing your work. Your work looks ok and the substitutions look ok. I think the trouble may be the number of s.f.. If I round a to 1.6E3 (2 s.f.) and add to b rounded to 3 s.f. of 6.96E3 and add to c rounded to 2 s.f. of 1.1E3, I get 9.66E3 which rounded gives 9....
February 2, 2015

physical science
To produce what?
February 2, 2015

chm
I might make that 3.38 M to 3 s.f.
February 2, 2015

chm
I disagree with Damon's answer. 1.105 g/mL x 1000 mL x 0.30 x (1 mol/98g) = 3.4 M
February 2, 2015

chemistry
You must be trying to measure the volume of a Pb cube but it isn't clear to me how you're doing it.
February 2, 2015

Chemistry
Use the Arrhenius equation. Remember to convert kJ/mol to J/mol Use k1 for k1 and 6.5*k1 for k2. That way k1 cancels and have just the ratio.
February 2, 2015

Chemistry
Fe2O3 + 3CO--> 2Fe + 3CO2
February 2, 2015

Chemistry
Convert 14.56 inches to meters. Convert 10.92 inches to meters. Then meters x meters = square meters.
February 2, 2015

Chemistry
mass = volume x density
February 2, 2015

Organic Chemistry
This makes absolutely no sense to me.
February 2, 2015

Inorganic Chemistry
I may have missed something here but it appears this site has all of the rules. It may be painstaking to apply the rules but I don't think I need to do it for you. http://en.wikipedia.org/wiki/Slater%27s_rules
February 2, 2015

Chemistry
I expect that is diprotic acid. The problem doesn't say but I assume the phenolphthalein end point will titrate BOTH H ions. mL x N x mew = grams where mew is milliequivalent weight. Substitute and solve for mew. Convert to equivalent weight. Then equivalent weight = molar...
February 2, 2015

chemistry
Is that 1.489 g/cc? Because the solid has a higher density that 1.489 g/cc.
February 2, 2015

chemistry
I showed you how to do this last night. What's the problem? Show your work if you want help in getting through it.
February 2, 2015

chemistry
A straight solubility product problem and one almost the same as the TlCl problem.
February 2, 2015

chemistry
Ag2CrO4/BaSO4/TlCl. All of the problems are done the same way. I won't work these for you but I shall be happy to help you through them if you tell us exactly what is troubling you with this type problem.
February 2, 2015

Chemistry- sig figs
The rule I follow is to round the 0.2748 to 0.2750 and the 5 rule that says to round to the even number which rounds to 0.28 to two s.f. However, I don't know if the mathematicians agree with this. I see examples all over the net that would round this to 0.27. Perhaps a ...
February 2, 2015

chemistry
Your best bet is to google it. You will find more information about Cu than you ever wanted to know. It is a solid with "copper" color.
February 2, 2015

science
I suppose #3 is considered the right answer but many people have little faith in those regulations and the ability of the nuclear industry to carry out those regulations.
February 2, 2015

Chemistry
Write and balance the equation. Then dHrxn = (n*dHf products) - (n*dHf reactants)
February 2, 2015

oragnic chemistry
92.0g x (1 lb/453.6g) = ? Note g unit cancels with g unit (one in the numerator and one in the denominator thus getting rid of the unit you don't want) and this leaves only the one unit of lb which is what you want.
February 2, 2015

chemistry
mols = grams/molar mass
February 2, 2015

Chemistry
You need to do better than this. I can't tell the difference between questions and answers. In fact, I'm not sure of the question. With regard to the last one, the KClO3 is the decomposition. The Zn and HCl is a single replacement and the Fe and S rxn is synthesis.
February 2, 2015

Chemistry
Usually smaller.
February 2, 2015

Science
You don't? Why does the floor hold you up(that is, why don't you sink into the floor?). Because the floor is pushing back with the same force you are pushing(standing) down. When you sit on a chair the chair pushes you up with the same force you are pushing down. If it...
February 2, 2015

Science
For every action and there an equal and opposite reaction.
February 2, 2015

Science
What's doing the aciton? The arms and legs. What is reacting? the water pushes back.
February 2, 2015

Science
See your previous question.
February 1, 2015

Thermodynamics
T final is the same for both. Tinitial for Al is T it started; Tinitial for H2O is T it started.
February 1, 2015

Thermodynamics
heat lost by Al shot + heat gained by H2O = 0 [mass Al x specific heat A x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0 Substitute all of the numbers and solve for Tfinal.
February 1, 2015

Chemistry
By itself you don't. Usually 15% by mass means 15g solute/100 solution. In that case, then 15 g/molar mass solute = mols solute.
February 1, 2015

chemistry
mols TlCl = grams/molar mass = ? mols Then M = mols/L = approx 0.04 but you need to do it more accurately. ........TlCl ==> T.^+ + Cl^- I.......solid....0.......0 C.......solid....x........x E.......solid....x........x Substitute the E line into the Ksp expression and solve...
February 1, 2015

chemistry
No ppt. There are essentially three reasons for a reaction to occur. 1. A ppt is formed 2. A gas is formed. 3. A slightly ionized substance si formed. KCl, Na2SO4, K2SO4 and NaCl all are soluble so #1 will not occur. 2. None of the four possibilities is a gas so #2 will not ...
February 1, 2015

chemistry
If a ppt forms it must be because Ksp is exceeded. The only slightly soluble material is the possibility of CaSO4. Therefore, you must determine Qsp for the solution and see if Ksp is exceeded. (Na2SO4) in final solution is 0.004 x (100/600) = approx 6.67E-4 (CaCl2) in final ...
February 1, 2015

Science
right
February 1, 2015

Science
momentum is mv. The higher mass makes it harder to start or stop.
February 1, 2015

Chemistry
15% w/w = 15 g H2O2/100 g solution. mass = volume x density. You know mass and density, solve for volume in mL and convert to L. mols H2O2 = grams/molar mass, then M = mols/L solution.
February 1, 2015

Chemistry
OK, we'll assume that is m and 0.267 molal KIO3. 0.267m means 0.267 mols KIO3/1000 g solvent. 0.267 mols KIO3 x molar mass KIO3 = grams KIO3 = approx 57 g but you need to that more accurately as well as the calculations that follow. Then total solution is g KIO3+ 1000g ...
February 1, 2015

Chemistry
Is the m or M?
February 1, 2015

Chem
mols solute = grams/molar mass. No molar mass; can't work the problem.
February 1, 2015

Science
Let's let L be long wings; s for short wings. So we have Ls and ss So the combinations are Ls; Ls; ss and ss. The two Ls will be long and the ss will be short wings which looks like 50% to me.
February 1, 2015

chemistry II
acetic acid is HAc HAc + KOH ==> KAc + H2O mols KOH = M x L Look at the coefficients. mols HAc = mols KOH Then M HAc = mols HAc/L HAc
February 1, 2015

chemistry
H2C2O4 + 2NaOH ==> Na2C2O4 + 2H2O mols H2C2O4 = M x L = ? mols NaOH = 2x mols H2C2O4 (look at the coefficients) M NaOH = mols NaOH/L NaOH You know M and mols, solve for L NaoH.
February 1, 2015

Chemistry
I assume you mean M^2+ ions. Also I assume the 0.150 mol M(NO3)2 solid does not change the volume of the solution. You do this in two steps. .....M^2+ + 4CN^- ==> M(CN)4^2- I..0.150...0.840.........0 C..-0.150..-4*0.150......+0.150 E....0......0.240........0.150 What we ...
February 1, 2015

Chemistry
......Ba3(PO4)2 ==> 3Ba^2+ + 2PO4^3- I.....solid..........0..........0 C.....solid..........3x.........2x E.....solid..........3x.........2x Ksp = (Ba^2+)^3(PO4^3-)^2 Substitute the E line into Ksp expression and solvle for x. That gives you the solubility of the solid.
February 1, 2015

Not a subject for course-off topic question
Writeacher gave you the best advice. On this subject of thanking teachers I never thanked some of the best and caring teachers I had and I've regretted it time after time. Some I stayed in contact with and thanked them MANY years later. Some I stayed in contact with but ...
February 1, 2015

chemistry
Yes, that's what it is. Don't forget to include the liquid H2O in the reactants.
February 1, 2015

chemistry
See your sucrose question.
February 1, 2015

chemistry
I can't tell the difference between your answers and those on the question.
February 1, 2015

science answer fast please!
I don't think so. Molecules are a combination of atoms so if it's just one of a kind we call it an atom and not a molecule.
February 1, 2015

chemistry
Do you have a question?
February 1, 2015

science
Technically speaking graphite is not an element. Carbon is an element and graphite is pure carbon. Graphite is just another form of carbon. Graphite is an allotrope of carbon; diamond is another allotrope of carbon. http://en.wikipedia.org/wiki/Allotropes_of_carbon
February 1, 2015

chem
I wonder if your typing is just VERY bad or if you don't know better. amstrong must be Angstrom, spectra line should be spectral line, bama series must be Balmer series and I have no idea what R = 109766rcm is. lander must be lambda and Li2 doesn't exist. Assuming you ...
February 1, 2015

chemistry
ln(No/N) = kt No = 99.8 N = 78.2 k = solve for this t = 25 hours Then k = 0.693/t1/2 Solve for t1/2 You probably do better to write I-131.
February 1, 2015

chemistry
See your other post below.
January 31, 2015

Chem
k = 0.693/t1/2
January 31, 2015

chemistry
dHrxn = (n*dHf products) - (n*dHf reactants)
January 31, 2015

chemistry
Add equation 1 to the reverse of equation 2, then divide the final equation by 2. When reversing an equation change the sign of dH. When dividing an equation by 2 divide dH by 2. When adding equations add dH values for each.
January 31, 2015

chemistry
dHrxn = (n*dHf products) - (n*dHf products) dHrxn = -127 = (n*dHf .....etc) Substitute and solve for dHf CaC2 which is the only unknown in the equation.
January 31, 2015

chemistry
Thank you for showing your work. I don't see anything wrong with your set up or the numbers. Always check to see that you used the correct value from the tables. I suspect the problem is one of significant figures. I think the answer is -2512 kJ. -1.574E3 - 0.4836E3 = -2....
January 31, 2015

To Morgan---Chemistry
If you had shown your work instead of answers we could have seen at a glance what the problem was. As it is you must check your work against mine below. I recognize this as one of the answers I gave you a couple of days ago. You have made errors in q1, q2 and q2*. I didn't...
January 31, 2015

chemistry
Use the HH equation, then convert pH to H^+.
January 31, 2015

chemistry
millimols HCOOH = mL x M = approx 65 but you need to do all of these calculations more accurately. mmols HCOONa = base pH = pKa + log (base)/(acid) Substitute and solve for (base) in millimols. Change to mols, then g = mols x molar mass. You know mols and molar mass
January 31, 2015

chemistry
You have doubled the reaction; wouldn't the new enthalpy change be just twice as much.
January 31, 2015

Chemistry
What's the /\H = 90?
January 31, 2015

Pages: <<Prev | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | Next>>

Members