Wednesday
October 1, 2014

Posts by DrBob222


Total # Posts: 44,171

Science
The refractive index and whether the medium is more or less dense
July 17, 2014

Math
What's the problem? What's the question? You want a formula for what?
July 17, 2014

science
http://www.wisegeek.com/what-is-cardiovascular-homeostasis.htm http://www.mhhe.com/biosci/genbio/maderbiology/supp/homeo.html http://www.ehow.com/about_6326540_cardiovascular-system-maintain-homeostasis_.html
July 17, 2014

Chemistry
I assume your 0.907 is from 4.319kJ/C x (2.1C) = 9.07 kJ/10 mol = 0.907 kJ/mol. But you must correct for the wire and I don't think you've done that. The equation is CH4 + 2O2 ==> CO2 + 2H2O + heat When they say thermochemical reaction they may want dH = -? since it...
July 16, 2014

chemistry
2Na + Cl2 ==> 2NaCl Convert mols Na t mols NaCl. That's 3.0 mols Na x (2 mols NaCl/2 mols Na) = 3 mols NaCl g NaCl = mols NaCl x molar mass NaCl = about 175g (estimated). That is the theoretical yield(TY). The actual yield (AY) is 145.8. Note that the TY above is ...
July 16, 2014

Science
KE = 1/2(m)(v^2) KE = 1/2 * 60 * 3^2 = ?
July 16, 2014

Chemistry
Don't you have some information about the increase in temperature?
July 16, 2014

math
let x = time it takes to walk home. (3/4)*x = 18 Solve for x.
July 16, 2014

math
Ms Sue gave you the answer worked out. If you want to do it algebraically, let x = the number, Then (x^4) + 4 = 26*10 Solve for x.
July 16, 2014

math
b = Bob's age now t = Tom's age now -------------- age now is b = 3t age in 12 years for t is t+12 = 15 Therefore, t now is 3 (that's 15-12 = 3) b age now is 3*3 = 9
July 16, 2014

Math
Is my face red. Circumference, which is what you want, is pi*diameter. I, unfortunately, gave you the formula for the area of a circle. Bad! I get an "F" for the day.
July 16, 2014

Math
If the diameter of the wheel is 45 cm then the radius is 45/2 = 22.5 cm and the circumference is pi*r^2. When the wheel makes one full revolution it will have traveled the circumference of the wheel.
July 16, 2014

math
One side is now 4*3 = 12 and the other side is 3*3 = 9 so the new perimeter must be 12+12+9+9 = ? The original perimeter is 3+3+3+3 = ? Now compare.
July 16, 2014

Chemistry
I assume you men 270 molal. 270 m means 270 mol/kg solvent. g NaCl = 270 x 58.5 (apprx) = estimated 16000 g (you need to go through the entire problem and redo the math; I've estimated all of these numbers. The mass of the solution is 1000 g solvent + 16000 g NaCl = about ...
July 16, 2014

CHEMISTRY
1)If we dissolve 0.03 mols HF in 1L H2O, we have prepared a solution that is 0.03M in HF. However, since HF is a weak acid, it dissociates(partly) in solution to HF + H2O ==> H3O^+ + F^- and the HF present as the molecule is decreased to 0.027M. 2) Any amount of HF in any ...
July 16, 2014

CHEMISTRY
For the second question and increase in the forward direction increases OH in the HPO4 rxn and that decreases pH. For the CO3^2- rxn the increase in the forward rxn decreases pH because H3O^+ is being used. For the initial post I don't know what you're asking.
July 16, 2014

math
Would that be 20*21/2 ?
July 15, 2014

chemistry
[275 mL/(725+275)] x 100 if you want it is %volume.
July 15, 2014

Science
I don't buy A. For example, I might observe that my clothes are wet and explain by saying I walked home in the rain. However I could have gotten wet by taking a shower with my clothes on. So I don't think just any explanation can go with just any observation.
July 15, 2014

Chemistry
I think the easy way to do b is to convert everything to millimols and use that to construct an ICE table. I think this way is easier than converting everything to final M. mmols HBz = mL x M = 250 x 0.125 = 31.25 mmols Bz^ = 250 x 0.147 = 36.75 mmols HCl added = 15.3...
July 15, 2014

Chemistry
Are you sure about part a? I think an error is starting with 0.45M formic acid. Wouldn't you need to start with more formic acid to end up with 0.45M? If you used the HH equation for part b you should have come up with 3.64 and you're a long way from that. I used 3.75 ...
July 15, 2014

Chemistry
I thought we did all this yesterday. You worked the formula on your own and I showed you how to do the molar mass and molecular formula.
July 15, 2014

Chemistry
The procedure looks ok but the numbers don't.You must be punching the wrong buttons. The 0.00485 is really 0.004855 and I would round that to 0.00486 M (and that's M and not m) = 0.000198 x 1.92 = 0.000381 and molar mass is 0.242/0.000381 = ? Check my work.
July 15, 2014

Chemistry
You're right so far. 5.41E6 J = 5.41E3 kJ. molar mass Glauber's salt is 322 so here is what you have. 322 g salt absorbs 74.4 kJ. So how many g will it take to absorb 5.41E3 kJ. That will be 322 x (5.41E3 kJ/74.4 kJ) = ? g of the salt.
July 15, 2014

Chemistry
q = mass air(in g) x specific heat air x delta T Solve for q (which is delta H) Convert to g of the salt to give that delta H.
July 15, 2014

Chemistry
Glacial acetic acid is about 17.5M mL1 x %1 = mL2 x %2 mL1 x 17.5 = 120 mL x 25% mL 1 = ?
July 15, 2014

Chemistry
10% by volume means 10mL ethanol/100 mL solution. You want 150 mL so 10 mL ethanol x (150/100) = ? mL ethanol required.
July 15, 2014

chemistry
mols NaOH = M x L = ? mols vinegar = mols NaOH M vinegar = mols vinegar/L vinegar = ?
July 15, 2014

chemistry
You may be thinking that the double bond makes it a trigonal planar structure but when ethylene (with double bonds) is polymerized the double bond is broken and polyethylene consists of single bonds and that makes it tetrahedral. :-)
July 14, 2014

Chemistry
heat lost by Fe + heat gained by H2O = 0 [mass Fe x specific heat Fe x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0 Substitute the numbers and solve for Tfinal H2O You may need to look up specific heat Fe and H2O if they aren't given in the ...
July 14, 2014

Chemistry
Nope. Liquid CAN'T be right. If you pour 100 mL water into a 100 mL container it is filled. If you pour the same volume f 100 mL water into a 500 mL container is will NOT be filled. So liquid can't be right. The answer of liquid is NOT using common sense. You KNOW the ...
July 14, 2014

Chemistry
I really wonder about this science bug with some. Many questions, like this one, is just common sense. Think this through and you'll have the answer. If you pour 100 mL water(a liquid) into a 100 mL beaker will it fill it? Will that same 100 mL water fill a 500 mL ...
July 14, 2014

science
http://www.webelements.com/ Scroll down the table to find these elements and compare with the elements above them.
July 14, 2014

chemistry
mL1 x %1 = mL2 x %2 350 x 15 = mL x 9
July 14, 2014

Chemistry
121J/c/313 = ? J/g*C
July 14, 2014

Science
I believe the answer is B. Here is an example of weighing by difference and why it is a good method. Let's assume we know the mass of can accurately as 10g and a tennis ball accurately as 5 g. Now we use a scale in which we can't adjust the zero. Let's suppose at ...
July 14, 2014

CHEM
I'm assuming that 6.0m is a typo and you meant 6.0M.(There is a difference). mL1 x M1 = mL2 = M2 mL1 x 6.0M = 110 mL x 0.500M
July 14, 2014

Chemistry
A factor converts any unit to any other unit. The factor used depends upon which unit you have and which unit you want. For example. A. There are 10 mm to 1 cm so the conversion factor is 10mm/1cm or you can write it the other way as 1 cm/10mm. 8.43 cm x factor = ? mm Now we ...
July 14, 2014

Chemistry
No, if pi = MRT then M = pi/RT M = 0.00543/(0.08205*301) = about 0.000220M or mols/L. M = mols/L mols = M x L = 0.000220*1.37L = about 0.000301 mols = grams/molar mass or molar mass = grams/mols = 0.325/0.000301 = ? Note, however, that even if what you proposed were correct ...
July 14, 2014

Chemistry
pi = MRT pi = 4.13 torr/760 = ? atm M = unknown R = 0.08205 T = 28 + 273 = ? Solve for M in mols/L You know M and L, solve for mols. Then mol = grams/molar mass. Youj know grams and mols, solve for molar mass. NOTE: In the future it would help if you would show what you know ...
July 14, 2014

Chemistry
Since the empirical formula mass is about the same as the molecular formula mass then the molecular formula is the same as the empirical formula.
July 14, 2014

Chemistry
Yes, empirical formula is C3H2N10. Empirical formula mass is 178. (3*12) + (2*1) + (10*14) = 178 The approximate molar mass is given by the boiling point elevation. delta T = Kb*m 1.84 = 2.53*m m = about 0.7 but you need to go through this and all other calculations. I've ...
July 14, 2014

Chemistry
I don't see a question here.
July 14, 2014

Chemistry
Then Xunk = mols unk/total mols. 0.2 = [(23.71g/Y)/(23.71Y)+(0.281)] and solve for Y = molar mass unknown. I made a typo in the above. It should be 0.2 = [23.71/Y/(23.71/Y)+ (0.281)]. First the numerator = 0.2*denominator. 23.71/Y = [0.2*(23.71/Y) + (0.281)] 23.71/Y = (4.74/Y...
July 14, 2014

Chemistry
pEtBr = XEtBr*PoEtBr 319.7 = X*400 XEtBr = about 0.8 (estimated) see last post. Xunk = 1-about 0.8 = about 0.2 mols unk = 23.71/molar mass or 23.71/Y. mols EtBr = 30.64/109 = about 0.281 Then Xunk = mols unk/total mols. 0.2 = [(23.71g/Y)/(23.71Y)+(0.281)] and solve for Y = ...
July 14, 2014

Chemistry
0.218M means 0.218 mols CH3COOH/L solution. g CH3COOH = 0.218 x molar mass = approx 13g but you should redo this and all of the other calculations that follow. I've estimated everything. From density, mass = volume x density = 1000 mL x 1 g/mL = 1000 grams. So 1000g = mass...
July 14, 2014

CHEMISTRY
delta H is - according to the rxn as written. delta S is - according to the rxn as written If dG is +, then TdS is more + than dH. I guess that means dS is more negative than dH but it's the TdS TERM that counts.
July 14, 2014

CHEMISTRY
When you ask which direction the rxn will shift I think you must say "if T is added" or "if P is increased" or some other variable is changed. Perhaps you are asking which direction is spontaneous?
July 14, 2014

CHEMISTRY
See the above about my trouble with the word shift. 1. products higher S than reactants. dS = + 2. reactants higher S than products. dS = - 3. products higher S than reactants. dS = + 4. reactants higher S than products. dS = -
July 14, 2014

CHEMISTRY
All of this looks good to me except for the last part. Since the number of significant digits is 4 (at least I'm calling 3900 as 4 because I assume it is 3900.) then that 2.99 is really 2.997 ( or if not 4 s.f. for 3900 then it would be 2.997 and round to 3) which makes ...
July 14, 2014

CHEMISTRY
How much of this do you know how to do. Show your work and let me go through it.
July 14, 2014

chemistry
The ammonium ion (NH4^+) is hydrolyzed according to this equation. NH4^+ + H2O ==> H3O^+ + NH3 (H3O^+) = acidic
July 14, 2014

CHEMISTRY
Why do you have the problem identifying the conjugate pairs? The pair consists of the one with more H and the one with less H. And for CO3^2- it should be obvious not to pick H2O as its conjugate pair.
July 14, 2014

CHEMISTRY
How are we going to do that? Then we have B::N and there are too many electrons around the central atom.
July 14, 2014

CHEMISTRY
pi = iMRT i is 1 for the four listed so it all depends upon M. Which M gives the largest pi?
July 14, 2014

chem
heat produced by burning 9.69g C6H6 is 5.69 mJ/mol x (9.69/molar mass C6H6) = ? MJ. Convert to J. Then J = mass H2O in g x specific heat H2O x (Tfinal-Tintial) and solve for Tf.
July 13, 2014

chem
How much heat was evolved in the combustion? That's 3209.0 kJ/mol x (1.829/159.29) = q = ? Then q = Ccal*delta T. Solve for Ccal.
July 13, 2014

Chemistry
Assuming you are using an indicator, you stop when the indicator changes color from its acid color to its base color.
July 13, 2014

Chemistry
That 5.67% m/v means 5.67 g glucose/100 mL blood; therefore, 5.67g glucose x (5,200 mL/100 mL) = ?
July 13, 2014

Fun time
1.55 g/mL x 3000 mL = ? The mass of the H2SO$ in that 3.0L is 1.55 g/mL x 3000 mL x 0.65 = ?
July 13, 2014

Chemistry
I agree
July 13, 2014

Chem 1120
Yes and no. You have Kc given in the problem. All you need to do is to substitute Kc into the Kp = Kc*(RT)^delta n and solve for Kp and you're done. The only thing changing I2 from solid to gas changes is delta n. For I2(g) ==>2I^-(g) delta n will be 2-1 = 1
July 13, 2014

Chem 1120
Kp = Kc(RT)^delta n. BTW, isn't I2 a solid. Then does I2 go in the denominator.
July 13, 2014

Chemistry
1___________ 2__________ 3_________ 1__________ Mix the two and you have 3_________ 1___________ 2__________
July 13, 2014

Chemistry
Yes. If that 1.1 is 1.1 and not 1.10 atm, then 0.71 is right. If it is 1.10 you should have one more place in your answer.
July 13, 2014

Chemistry
Two points. If T is to 4 places I would use R as 0.08205 although that won't make much difference. The other one makes more difference. P is 1.1 atm in the problem and not 1.
July 13, 2014

Chemistry
no. If you obtained two different answers why did you pick that one? You know something must be wrong. How did you get V = 24.7 L. If I plug those numbers into V =nRT/P I don't get that. But I do obtain a number that agrees with the formula I gave you.
July 13, 2014

Chemistry
The general gas formula of PV = nRT can be modified to P*molar mass = density*R*T
July 13, 2014

Chemistry
n = mols gas = 0.155/22.4 = ? n = grams/molar mass. You know n and grams, solve for molar mass.
July 13, 2014

Chem
1170.0 kJ/42.75 x #g = 191.9 kJ
July 13, 2014

Science
Probably not D.
July 13, 2014

Chemistry
This question makes no sense.
July 13, 2014

chemistry
and your answer?
July 13, 2014

Science
And your answer is?
July 13, 2014

Science
And your answer?
July 13, 2014

science
When you cut a bar magnet in two you end up with two smaller bar magnets. You don't get a monopole.
July 12, 2014

science
To get a sonic boom in air the "jet" must travel faster than the speed of sound in air. For air that is about 343 m/s. The "jet" fish would need to travel faster than the speed of sound in water. At 25C the speed of sound in fresh water is about 1497 m/s or...
July 12, 2014

science
In general, the speed of sound with wind is speed in still air + speed of wind. So shouting with the wind at your back means the speed is increased; shouting with the wind in your face means sound to your front is decreased speed.
July 12, 2014

babysitting
It doesn't sound like that to me but I'll take your word for it. However, you still listed no choices.
July 12, 2014

no choices--babysitting
This is baby sitting?
July 12, 2014

chemestry
E = R(1/n^2 - 1/n^2) R = 1.097E7*(1/4 - 1/25)
July 12, 2014

exam
CH4 + 2O2 ==> CO2 + 2H2O dHfrxn = (n*dHf products) - (n*dHf reactants) dHf rxn = -780 kJ/mol Substitute the others and solve for dHf CO2
July 12, 2014

CHEMISTRY
Did I miss something here? If the solubility of KClO3 is 10g/100g H2O and you add 15 g KClO3 to 100 g H2O, then it will dissolve 10 g KClO3 and the other 5g KClO3 will be unaffected. Of course the solution is saturated after the water has dissolved all it can.
July 12, 2014

CHEMISTRY
What do you mean by embedded. Do you mean you dissolved 15g or you added 15g KClO3.
July 12, 2014

CHEMISTRY
1. 1% means 1g I2/100 g solution = 10g I2/1000g solution = 10g I2/(10g I2+ 990g ethanol) 2. mol I2 = grams/molar mass 3. m = mols/kg solvent = ? You can convert to M if you know the density of the solution.
July 12, 2014

chemistry
Will alter the enthalpy of what?
July 11, 2014

science
http://en.wikipedia.org/wiki/Reflection_%28physics%29
July 11, 2014

Surds
(a+b)^2 = a^2 + ab + b^2
July 11, 2014

CHEISTRY
Do you know the order of the reaction?
July 11, 2014

Chemistry
LiOH(s) + H2O(l) ==> Li^+(aq) + OH^-(aq) dimeNH(l) + H2O(l) ==> dimeNH2^+(aq) + OH^-(aq)
July 11, 2014

science
What's the Law of Inertia say? That an object in motion tends to stay in motion until acted upon by an outside forcew. The car is traveling at 50 km/hr so the dummy, the car seats, the belts, the steering wheel and everything in the car is also traveling at 50 km/hr. When ...
July 11, 2014

science
You can read all about "clocks in rocks" here. http://www.sciencecourseware.com/virtualdating/files/1.0_ClocksInRocks.html I shall be happy to critique your summary explanation.
July 11, 2014

chemistry
C6H12O6 ==> 2C2H5OH + 2CO2 mols glucose = grams/molar mass = estimated 0.5 Using the coefficients in the balanced equation, convert mols glucose to mols ethanol. That is 0.5 x (2 mols ethanol/1 mol glucose) = 0.5 x 2 = 1 mol ethanol produced. Then g ethanol = mols x molar ...
July 11, 2014

science
mols H2SO4 = grams/molar mass Then M = mols H2SO4/L solution. Note: 100 mL = 0.100 L.
July 11, 2014

electric circuit
Probably 6 cells in series to give 12 v, then 6 sets of those (36 cells total) in parallel.
July 11, 2014

Clincal
I don't see a question here.
July 11, 2014

chemistry
Please read and rephrase. It makes no sense as is.
July 11, 2014

chemistry
See your other post above.
July 11, 2014

Chemistry
mL1 x M1 = mL2 x M2 mL1 x 17.8 = 250 x 2.00M Add some distilled H2O to the 250 mL volumetric flask, then pipet the value of mL1 of the 17.8M H2SO4 into the 250 mL flask adding concentrated H2SO4 cautiously. Add distilled H2O to the mark and mix thoroughly.
July 10, 2014

chemistry
1 in^3 = 16.38 cc 13.4 in^3 to cc = ? 1 lb = 453.59 grams 5.14 lb to grams = ? Then d = mass/volume
July 10, 2014

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