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September 21, 2014

Posts by DrBob222


Total # Posts: 43,903

chem
ascorbic acid is C6H8O6. mols ascorbic acid in 100 g is mol = grams/molar mass = 100/176.12 = ? There are 6 C atoms/mol acid, 8 H atoms/mol acid, and 6 O atoms/mol acid. mols C is 6x that. mols H is 8x that. mols O is 6x that.
July 20, 2014

chem
See your other post above.
July 20, 2014

science
I can't find anything on the web that gives a rate of solution for caster sugar. But all sites agree that caster sugar dissolves quickly.
July 20, 2014

chemistry
Sure. If the experimental value is less than the actual value the percent error is negative. If the experimental value is larger than the actual value the percent error is positive. But most (at least many) people use the absolute value of the error when reporting in which ...
July 20, 2014

Chemistry
Sorry but I don't understand the question.
July 20, 2014

Chemistry
The pure element is zero. All elements in their standard state are zero.
July 20, 2014

Chemistry
NOPE. T is not 2.3, that's delta T for the experiment. The initial T is 23.1 so that must be the T of the methane when it's added to the bomb or 294.25K and that gives n = 0.0112 or about 11.2 millimoles.
July 20, 2014

Chemistry
I don't know the context of the problem but your 979 kJ/mol appears to be right if you have the number of significant figures correct. Does the problem say anything about "about 10.0 millimoles" methane? You have P, V, R, and T and you can calculate n. If I can ...
July 20, 2014

chemistry clearly step by step
I agree the problem makes no sense. I have brought this up before to Ken; m stands for molal while M sands for molar.
July 20, 2014

Chemistry
How much 2.5M HNO3. CaO + 2HNO3 => Ca(NO3)2 + H2O This is an acid/base reaction but in terms of the several types I think you are looking for double displacement.
July 20, 2014

Chemistry
I think I remember that dH I found on the web was 890 kJ/mol for dHcomb. I used that to calculate how much CH4 I had to start with and that's when I discovered you probably made a typo with that 10.0 mols you posted then. This problem is q for combustion is 4.319 kJ/mol x ...
July 19, 2014

Chemistry
I thought I did this for you a couple days ago and found you made a typo on the moles (instead of millimoles) CH4. What's giving you trouble?
July 19, 2014

chemistry
Why are you having trouble with this? pH = -log(H^+) Plug in pH, solve for H and use that and the last equation to solve for OH, then compare. (H^+)(OH^-) = Kw = 1E-14.
July 19, 2014

chemistry
dHrxn = (n*dHproducts) - (n*dHreactants) dSrxn = (n*dSproducts) - (n*dSreactants) Then dGrxn = dHrxn - TdSrxn If dGrxn is - the products are favored. Show your work if you gets stuck.
July 19, 2014

chemistry
dSrxn = (n*dSproducts) - (n*dSreactants)
July 19, 2014

chemistry
See your posts above.
July 19, 2014

chemistry
See your post above.
July 19, 2014

chemistry step by step for me. Thank a lot
Is that 2m HNO3 or 2M HNO3?
July 19, 2014

math
4^8 = 6.5536E4 6.5536E4*8 = ?
July 19, 2014

chemistry
The acid is one of the pair with more H. The base is the one of the pair with fewer H. You name it; it can be a solvent.
July 18, 2014

chemistry
5.4% v/v means 5.4 mL/100 mL so in 435 mL solution there will be 5.4 x (435/100) = ? or (x/435)*100 = 5.4%
July 18, 2014

chemistry
Yes. That should be 10g solute.
July 18, 2014

chemistry
4% m/v means 4g solute/100 mL solution. So in 250 mL you would have 4 x 250/100 = ? Or another way is (x/250 mL)*100 = 4%
July 18, 2014

chemistry
a. Nope, that won't do it. M = mols/L solution. mols = grams/molar mass 335 mL = 0.335 L b. I'm confused by the question since HCl is a gas and not a liquid. So we need the density of the solution if that's what it is.
July 18, 2014

chemistry
I see your post below.
July 18, 2014

chemistry
You're right, it's probably wrong. If you will post the problem and your work I'll find the trouble.
July 18, 2014

chemistry
I assume all are gases. I assume initial H2O is 0. Initial (NO) = 0.100/2 = 0.050M Initial (H2) = 0.200/2 = 0.100M Initial (N2) = 0.0800/2 = 0.0400M ........2NO + 2H2 ==> N2 + 2H2O I......0.05...0.10....0.04..0 C......-2x....-2x....+x....+2x E...0.05-2x.0.10-2x.0.04+x..2x ...
July 18, 2014

chemistry
This is a bit out of my league but here is what I found on the web. There are other sites if you Google structure factor. structure factor
July 18, 2014

chemistry
1 amu = 1.6605E-24g
July 18, 2014

Math
698 miles x (1 gallon/18 miles) x (4 pts/gallon) = ?
July 17, 2014

Science
I assume the 30 degrees is the angle to the normal; also I assume you are neglecting the effects of the container holding the honey. n1*sin 30 = n2*sin 19.5 n1 is 1 for air. Solve for n2.
July 17, 2014

Chemistry
Didn't Bob Pursley do this for you? http://www.jiskha.com/display.cgi?id=1405592944
July 17, 2014

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

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