Tuesday
September 23, 2014

Posts by DrBob222


Total # Posts: 43,936

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

CHEMISTRY
How much voltage do you need? How much can you get from these two materials? Look up the Eo values and calculate.
July 10, 2014

CHEMISTRY
Here is a simplified activity series table. A metal will displace any metal ION BELOW it in the activity series; i.e., Al will displace Cu^2+ but Cu will not displace Al^3+. 2Al + 3Cu^2+ ==> 3Cu(s) + 2Al^3+ Cu^2+ + Al^3+ ==> no reaction. http://www.cod.edu/people/faculty...
July 10, 2014

CHEMISTRY
Look up the standard reduction potentials for I2, Br2, and Al^3+. Then set them up on a sheet of paper something like this, along with H2. ..........................Eo vs SHE Br2 + 2e --> 2Br^-..........1.07 I2 + 2e --> 2I^- ...........0.54 2H^+ + 2e --> H2...
July 10, 2014

CHEMISTRY
See the activity series question.
July 10, 2014

CHEMISTRY
By definition, reduction occurs at the cathode.
July 10, 2014

CHEMISTRY
You obtain the electrolysis products of H2O and not Al.
July 10, 2014

CHEMISTRY
It's an arbitrary standard and an arbitrary number.
July 10, 2014

CHEMISTRY
I wouldn't say they contained H2O but I agree they are moist. Compared to a wet cell; however, relatively speaking the dry cells are dry.
July 10, 2014

CHEMISTRY
You repeated my line but didn't answer if this was a made up problem or not. I don't like that answer until I have more information about the question.
July 10, 2014

CHEMISTRY
I wonder if this is a made up problem? Sn^2+ + 2e ==> Sn E = -0.14 Cr --> Cr^3+ + 3e E = ? ---------------------- Ecell = -0.60 then Cr must be -0.46 written as an oxidation so as a reduction it would be +0.46 but that isn't what it gives in the tables.
July 10, 2014

chemistry
What numbers do you have?
July 10, 2014

Chemistry
Some picky points. n N2 I obtained 0.007279 so I rounded to 0.00728. For n O2 I obtained 0.00436 I obtained 0.0029 for mols N2 just as you did; however, it is done by 0.0036 x 2/3 and not 3/2. Finally,(this is not so picky) the problem asks for mL so you should convert your 0....
July 9, 2014

Chemistry
almost. n = 0.0079? Why did you throw away the 1 on 0.00791. You have three places in yur other numbers; you should keep three for the answers. Then if I multiply 0.00791 x 16 I get 0.1265678 which rounded to 3 s.f. is 0.127grams CH4.
July 9, 2014

Chemistry
Change -15F to degrees C. That's approximately -26 Then delta T = Kf*m approx 26 = 1.86*m solve for molality. m = mols/kg solvent = mols/1kg You have m and kg, solve for mols. Then mol = g/molar mass. You have molar mass and mols, solve for g
July 9, 2014

CHEMISTRY
H2 gas at a pressure of 1 atmosphere bubbled over "black platinum" in a 1 M solution of H^+ is arbitrarily set at zero. Black platinum is platinum with a fine coating of extremely small particles (granules) of Pt. That surface apparently gives better reproducibility ...
July 9, 2014

CHEMISTRY
3 M+1...M+2...M+3 Then the two half reactions are M^2+ ==> M^+3 + e M^2+ + e ==> M^1+ then add the two half rxns --------------- 2M^2+ ==> M^3+ + M^+
July 9, 2014

CHEMISTRY
Just think of an example of an element in a compound with the element at its max oxidation state. For example take SO3 where S is +6. It CAN'T be oxidized any further (if this is the max) to go to S7 or S8 or higher) but it can go down to something like SO2 or S or H2S. So...
July 9, 2014

CHEMISTRY
You don't think so or you don't know so. Did you check it? I checked it and all atoms appear to balance. I even found a site in which someone did a lot of work to do it with half reactions. Here it is if you are interested. The numbers match those from another site ...
July 9, 2014

CHEMISTRY
It's not simple but here is what I found on the internet. I don't vouch for its authenticity. 10[Cr(N2H4CO)6]4[Cr(CN)6]3 + 1176KMnO4 + 1399H2SO4 = 35K2Cr2O7 + 420CO2 + 660KNO3 + 1176MnSO4 + 223K2SO4 + 1879H2O
July 9, 2014

CHEMISTRY
I'm confused by your use of the terms reactant/products side. From the original question I thought that was a compound and if it is a compound there is no reason why you can't have an element exhibiting two different oxidation states. In coordination compounds that is ...
July 9, 2014

CHEMISTRY
I would start this way. This is a zero charged compound so the cation must be +3 and the anion part must be -4. We know CN is -1. I always go with +1 for H and -2 for O unless I know better. A value of +4 for C is always a good choice (unless it interferes with my +1 for H ...
July 9, 2014

CHEMISTRY
right. 3KIO3 + 2KMnO4 + H2O ==> 3KIO4 + 2K^+ + 2OH^- + 2MnO2 but that is not the usual way of doing it. Usually we have an ionic equation or a molecular equation but a mixed is not wrong (unless your prof says to write a molecular equation in which case you will have points...
July 9, 2014

CHEMISTRY
Actually, there is nothing wrong with having a "mixed" equation in which you have both molecules and ions. However, in your case you added 5K^+ on the left and you added only 3K^+ on the right. So in changing from the ionic to the molecular equation your molecular ...
July 9, 2014

CHEMISTRY
I think the answer is no but you just didn't finish. You added 5K^+ on the left. 3 of those on the right go with 3KIO4 and the other two go with 2KOH
July 9, 2014

CHEMISTRY
Here is a step by step of what I do for half reactions. This is the LONG way of doing it but I use it for two reasons: 1. It requires the student to know oxidations states. 2. The same procedure is used for acid OR basic solution. And I'm going to omit the spectator ions; ...
July 9, 2014

chemistry
You don't give the density of the solution so I have no way of knowing what the final volume. You also don't give any units for the 190^3 for water. If we assume units are cc If we assume the volumes are additive (and you can make that assumption since the volume of ...
July 9, 2014

chemistry
You must have a reaction in mind. You can't get PbCl2 from MgCl2 without some reaction.
July 9, 2014

chemistry
HNO3 + KOH ==. KNO3 + H2O mols HNO3 = M x L = 2.5 x 0.1 = 0.25 mols KOH = 2.55 x 0.1 = 0.255 Since the reaction is a 1:1 ratio, the HNO3 is the limiting reagent and 0.25 mols H2O will be produced. g H2O = mols H2O x molar mass H2O = ?
July 8, 2014

pharmacy calculations
I answered this for you earlier.
July 8, 2014

ph
I'm not a pharmacist but if that means take 250 mg every 8 hours for 7 days, the total dose is 250 mg/dose x 3 doses/24 hrs x 24 hours/1 day) x 7 days = ?
July 8, 2014

questions
So you want 15 tablets for 1/2 the month (30/2 = 15 days) and another 15/2 day supply so that is 15 + 7.5. You dispense 15 + 8 = 23 tablets unless you want to cut one of the tablets into two. I don't know if you are allowed to cut tablets or not. If so then you want 22.5 ...
July 8, 2014

Chemic
mL1 x %1 = mL2 x %2 mL1 x 98% = 50 mL x 5% Solve for mL 1. Add that amount to 50 mL volumetric flask and make to the mark with distilled H2O.
July 8, 2014

CHEMISTRY
You're right. I turned it around. Sorry about. Just reverse everything and you will have that half reacted. For KPb(OH)3 the cation is K^+ and the anion is Pb(OH)3^- So I would write PbO2 ==> Pb(OH)3^- I assume this is a basic solution. Pb is +4 on the left and +2 on ...
July 8, 2014

CHEMISTRY
In acid solution.? 2H^+ + ClO^- + 2e ==> Cl^- + H2O In basic solution? H2O + ClO^- + 2e --> Cl^- + 2OH^- The way to learn this is to do them. Looking at what someone else has done won't get it. If you will share what your problem(s) is/are in doing these perhaps I ...
July 8, 2014

Chemistry
Yes, and if your prof is picky about the number of significant figures you whould round that to 514 mL. You are limited to 3 from the 325 to start.
July 8, 2014

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