# Posts by DrBob222

Total # Posts: 54,974

AP Cemistry
I hope you saw my correction for the bath tub of water. I picked up the dH for H2O2 and not H2O. My eye sight isn't that good anymore and those little subscripts are difficult for me to see. At any rate, I think the big problem you had with that was correcting J to kJ in ...

AP Cemistry
For an ideal monatomic gas, Cp is (5/2)R. You can read about it here. In fact, several links you can get by Googling "heat capacity ideal gas" explains this better, I think, than the one I'm giving you. http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/shegas.html

chemistry
How much heat was generated. 3947.0 kJ/mol x (1.311/16.59) = q Then q = Ccal*delta T Substitute and solve for Ccal.

chemistry
Same type problem as hexane

chemistry
http://www.jiskha.com/display.cgi?id=1477618485

chemistry
Scroll down and find the post I made for Sam. Same problem. It isn't the first post you see for Sam the the one for same below that.

chemistry
heat gained by cool water + heat lost by warm water = 0 [mass warm water x specific heat H2O x (Tfinal-Tinitial)] + [mass cool water x specific heat H2O x (Tfinal0Tinitial)] = 0 Substitute and solve for Tf.

Chemistry

Chemistry
I have always used this one. Works every time. 1.02 g/mL x 1000 mL x (%/100) x (1/molar mass NaOH) = M You can do it piecemeal if you wish. M = mols/L. You know M and 1L, solve for mols. grams NaOH = mols x molar mass gives you grams solute. density of the 1 L gives you grams ...

Chemistry
2 OCl^- + 2e + 4H^+ ==> Cl2 + 2H2O 2Cl^- ==> Cl2 + 2e When you add these two you end up with twice the coefficients so divide everything by 2. I do it this way because it's easier to explain to students and then divide by 2; however, you can do it from the beginning ...

chemistry
I showed you how to do this last night Sam.

Chemistry
mass HCl needed is 1000 kg x 0.42 = 420 kg or 420,000 g HCl, then mols HCl = 420,000/molar mass HCl = ? Using the coefficients in the balanced equation, convert mols HCl to mols H2SO4. Then grams H2SO4 (at 100%) = mols H2SO4 x molar mass H2SO4 = ? Since it is only 90% pure, ...

chemistry
See your previous post. Same formula.

chemistry
q = mass C6H15 x specific heat x delta T Substitute and solve for specific heat.

chemistry
..Ba(OH)2 + 2HCl ==> BaCl2 + 2HCl mols Ba(OH)2 = 0.060 x 0.300 = 0.18 mols HCl = 0.060 x 0.600 = 0.036 mols Ba(OH)2 left = 0 mols HCl left = 0 mols H2O formed = 0.036 q = dH = mass H2O x specific heat H2O x (Tfinal-Tinitial) Then convert J to kJ. That is ? kJ for 0.036. To ...

chemistry
dE = q + w You know dE and work. Solve for q. Then q = mass gas x specific heat gas x (Tfinal-Tinitial) Substitute and solve for speific heat.

chemistry
[mass cool H2O x specific heat H2O x (Tfinal-Tinitial)] + [mass warm water x specific heat water x (Tfinal-Tinitial)] = 0 Substitute and solve for Tf.

Chemistry
mols CH4 = grams/molar mass. Then q produced = 890 kJ/mol x ? mols from above = ? Then q produced = mass H2O x specific heat H2O x (Tfinal-Tinitial)

Chemistry
No, there are two equations. The first is the ionization of HA;' HA ==> H^+ + A^- The second is the NaA. NaA ==> Na^+ + A^- In a buffer equation one usually finds use of the Henderson-Hasselbalch equation.

Organic Chemistry 1
a. mols HF = grams/molar mass = 5/20 = ? about 0.25 mols b. Then M = mols/L = 0.25 mols/0.1 L = ?

Organic Chemistry 2
I don't know that it's better either way. For a higher yield, it often means the solvent was not completely removed. Another reason is a side product is included.

chemistry
q = mass H2O x specific heat H2O x (Tfinal-Tinitial) That's q = delta H in J for 2.13 g. Then (delta H/2.13)*molar mass KClO4 = dH in J/mol. Convert to kJ/mol.

Chemistry
https://en.wikipedia.org/wiki/Electronegativity

Chemistry
(0.78*50) + (0.15*51) + (0.07*52) = ?

CHEMISTRY
H3PO4 + 2NaOH ==> Na2HPO4 + 2H2O

Chemistry
mols = grams/molar mass mmols = mg/molar mass

Chemistry
Can't do it. You can calculate molality but not molarity. If you have density you can convert molality to molarity.

oops---AP Chemistry
I picked up the dH formation for H2O2 and not H2O. Sorry about that. So other than the 23.3 C as delta T, the other big change you need to make is the conversion of J to kJ.

AP Chemistry
I would have used 23.3 for delta T but that isn't that big a deal. Makes q about 3.47E7 J. But I didn't get close to your answer for Hess's law. I have (2*H2O + CO2)-(CH4) (2*-187.8)+(-393.5) - 74.81 and I have something like 700 kJ or so. Check that if you will ...

AP Chemistry
Convert 59 F to C. Convert 101 F to C. Calculate q (heat) needed to raise temperature from Tinitial to Tfinal. Do that this way. q = mass H2O x specific heat H2O x (Tfinal-Tinitial). You will need to convert 94 gallons to liters and that to mL. The number of mL will be the ...

Chemistry
6.55 lbs x (453.6 g/lb) = ? grams. Then mols = grams/molar mass = ?

Chemistry
KSCN + Fe^3+ ==> FeSCN^2+ KSCN = 0.2 x 18/20 = 0.18 M Fe^3+ = 0.002 x 2/20 = 0.0002 M So FeSCN^2+ must be 0.0002 M You can make an ICE chart for that if you wish to see it better. ......KSCN + Fe^3+ ==> FeSCN^2+ I.....0.18...............0 add........0.0002............ C...

Chemistry
Very interesting but I don't see a question. If you wanted to know the molarity of the NaoH, you need to tell us what indicator was used; i.e.,did 1 or 2 H ions react with the NaOH?. Another point is did you mean 0.1m. That stands for MOLAL, not MOLAR.

Chemistry
ascorbic acid + I2 ==> 2I^- + dehydroascorbic acid mg ascorbic acid = 10 mL x 1 mg/mL = 10 mg. mols ascorbic acid = 0.01 g/molar mass ascorbic acid Using the coefficients in the blanced equation, convert mols ascorbic acid to mols I2. Then M I2 = mols I2/L I2

Chemistry
%B = (6*atomic mass B)/(molar mass Ca2B6O11.5H2O)]*100 = ? The way I see it you don't have two problems. The above calculates the percent B for a pure sample of the mineral. Something like 15.78% B. I wouldn't buy it.

chem
Properties like ionization energy and bond energy will be the same.

Chemistry
First, the equation you have written is not balanced. Here is the corrected version. 2C2H8O + 7O2 (g) -> 4CO2 (g) 8H2O (l) + 4012 kJ of heat energy a. You can look at this two ways. The bottom line is that 2*60.1 g alcohol releases 4012 kJ heat. So what will 1000 g release...

Chemistry
2H2 + O2 ==> 2H2O 2 mols H2 will produce 2 mols H2O; therefore, 5 mols H2 will produce 5 mols H2O. g H2O = mols H2O x molar mass H2O.

Chem 2
First, you decide which of the ionizations you need. That's Ka2 because pH of 7.6 requires pKa close to that value and that is Ka2 having a pKa of 7.21. You have two equations. Eqn 1 is pH = pKa2 + log [(B)/(A)] 7.6 = 7.21 + log [(B)/(A)] (B/A) = 2.45 and (B) - 2.45(A) ...

Chemistry
I went through the calculations quickly and obtained 3.622 which rounds to 3.62 for He. The small difference in our numbers probably comes from my obtaining 0.981 for n. I'm positive you worked it correctly.

Chemistry
Let X = mass He and Y = mass Kr. Two equations and two unknowns. eqn 1 is X + Y = 10 Then use PV = nRT and solve for n = total mols. equation 2 is (X/4) + (Y/83.8) = total mols Solve for X = grams He.

Chemistry
What's the preceding question?

Chemistry
I almost agree with you. However, if you add 241 and 18 and -379 you end up with zero and zero is neither endo nor exo so I would make that -380 so as to have a delta H = a negative number.

Chemistry
......SiO2 + 3C->SiC + 2CO a. mols SiC = 100,000 g/molar mass SiO2 = ? Look at the equation 1 mol SiO2 produces 1 mol SiC; therefore, ? mols SiO2 will produce that many mols SiC. Convert mols SiC to grams. grams SiC = mols SiC x molar mass SiC = ?. This is the theoretical ...

chemistry
Due to the spacing problem I can't tell if all is ok or not; however, I suspect most of it is. The correct answer is 0.456 M You should have divided by L and not mL. Then M = mols/L = ? above/0.080 - 0.456 mols sucrose = 12.5/342 = approx 0.0365 M = mols/L = 0.0365/0.080...

Chemistry
If you REALLY want 2.5 m (m means molal, not molar), then dissolve 2.5/4 mol HCl in 0.250 L H2O. The resulting solution may or may not be 250 mL. If you want 2.5 M (molar) and I suspect you do, then dissolve 2.5/4 mol HCl in some water and make to a total volume of 250 mL.

Chemistry
It can be anything; in the commecial product it is water.

chemistry
How many mols do you need? That's M x L = mols. Then mols = grams/molar mass. You know molar mass and mols, solve for grams.

To Mara
I have posted an answer for your question on acetone and ethanol (equimolar solutions) to equal 1000 mL. It's back on page 3 at the time I write this. Post your work if you get stuck and I suggest you repost at the top of the board. We will find it easier that way.

Chemistry
Since the melting point is above the final T you need not worry about a phase change. q = mass x specific heat x (Tfinal-Tinitial).

Chemistry
2C4H10 + 13O2 ==> 8CO2 + 10H2O mols C4H10 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols C4H10 to mols H2O. Now convert mols H2O to grams H2O with g = mols x molar mass = ?

Ap chemistry
There are 2 mols Al^3+ in 1 mol Al2(SO4)3 so (Al^3+) is twice that of the salt. There are 3 mols SO4^2- in 1 mol Al2(SO4)3 so (SO4)^2- is three times that of the salt.

Chem: pH of acids and bases
You started very well. Just go from there. There can be two Ka values because there are two H ions to dissociate. .......H2X + H2O ==> H3O^+ + HX^- I....0.320............0.......0 C.....-x..............x.......x E...0.320-x...........x.......x Now Ka1 = (H3O^+)(HX^-)/(H2X) ...

chem
The atom must become excited by absorbing energy from some source.

oops--typo--Chemistry - acids & bases
I'm sure you picked it up but that's 0.115 M from the problem and not 0.15. My typo.

Chemistry - acids & bases
Nope. You used millimols in this and you should use molarity. Ka is 1.8E-5, yes, but that is Ka = (H3O^+)(Ac^-)/(HAc) and you must substitute M and not mmols. If acetic acid is HAc, then .......HAc+ + H2O ==> Ac^- + H3O^+ I......0.15..........0......0 C......-x................

Chemistry
Look up Henry's constant for CO2 in H2O. Be careful because there may be two constants depending upon how the equation is used. I use p = KcC. Substitute and solve for C, then convert to pH.

Chemistry
7 in x (2.54 cm/in) x (1 m/100 cm)= ? meters = wavelength Then c = freq x wavlength You know c and wavelength, calculate freq

Chemistry
Take 10 mL of the 0.5 M acid and add enough water to make 30 mL

Chemistry
A = grams acetone E = grams ethanol dA = density acetone dE = density ethanol VA = volume acetone VE = volume ethanol ------------------ You want the volume to be 1000 mL; therefore, VA + VE = 1000 mL but since volume = mass/density, then A/dA + E/dE = 1000....eqn 1 Two ...

Chemistry
Separate this into the net molecular equation first. H^+(aq) + Cl^-(aq) + Li^+(aq) + OH^-(aq) ==> Li^+(aq) + Cl^-(aq) + H2O(l) To turn this into the NET ionic equation, just cancel those species that appear on both sides. So you cancel Cl^-(aq) on the left and right and ...

Chemistry
2 m^3 x (100 cm/m)^3 = ? cm^3 1E4 kg x (1000 g/kg) = ? Then density = mass in g/volume in cm^3

chemistry
All reactions reach an equilibrium. Some do so at 99.99999% complete while others are at 20% or so and others at 0.000001% or so. Reactions occur if the energy of the products is less than the energy of the reactants and the activation energy is not too high.

Chemistry
Convert 0 F to C. C = (F-32)*5/9 = ? That's approx -17.78 delta T = Kf*m 17.78 = 1.86*m Solve for molality. Then m = mol/kg solvent You have m and kg H2O, solve for mols ethanol. Finally, mols ethanol = grams/molar mass. You have molar mass and mols, solve for grams. Post ...

Chemistry
Did all of the Fe react? Then mols Fe = grams Fe/atomic mass Fe = ?

Chem
What are the units? -6.00 what? 1. dHrxn = (n*Gf products)-(n*dGf reactants). 2. dG = -RTlnK 3. Kp = pO2

Chemistry
H2 + 2OH^- ==> 2H2O + 2e Fe^3+ + e ==> Fe^2+ Multiply eqb 1 bt 1 and eqn 2 by 2, then add.

Chemistry need asap
a. The equation looks ok to me. b. mols NO = 0.5g/molar mass NO = ? mols O2 = 0.4 g/molar mass NO = ? mols H2O = 12/molar mass H2O = ? Now convert each of the mols above to mols HNO3 produced. This is a limiting reagent (LR) problem and the smaller number of mols will be ...

Chemistry
You need to proof your post and correct it.

chemistry
First line Lyman Series is transition from n2 = 2 to n1 = 1 E = Eo(1/1^2 - 1/2^2) E = 2.18E-18(1-1/4) E = 2.18E-18(1-0.25) E = 2.18E-18(3/4)

Chemistry
MO + H2 ==>M + H2O 0.090 x (molar mass MO/molar mass H2O) = 0.3975 Solve for molar mass MO, subtract 18 to arrive at atomic mass M.

Chemistry
I don't like any of the answers but 2 comes the closest, I think. What actually happens is that the atom absorbs the energy, electrons move from a lower orbit to a higher orbit THEN (and I emphasize THEN) the electron falls back to a lower level and emits electromagnetic ...

Chemistry
(1/wavelength) = R(1/1^2 - 1/2^2) Look up R. That's the Rydberg constant. It's about 1.09 E7

Chemistry
yes, E divided by h. f = E/h

Chemistry
Pick a number. You don't have T or V listed. You need those to answer.

Chemistry
2Na + 2H2O ==> 2NaOH + H2 mols Na = 0.05. g Na = mols Na x atomic mass Na = ?

BioChemistry
mols = M x L = ?

Chemistry
pH = -log(H^+) Substitute and solve.

Biochemistry
Your question is not clear to me.

Chemistry
I don't think you have enough information. How much PCl5 do you have (pressure or M)?

chemistry
(1/wavelength) = RZ^2(1/n^2 - 1/n^2) (1/wavelength) = RZ^2*(1/1^2 - 1/x^2) and solve for x. R = Rydberg constant = 1.0973732 The first n is n = 1 and the second n is n = 2; that's where the 1/1^2 and 1/x^2 come from. Z is the atomic number of the element; in this case that...

Chemistry
I don't believe this problem can be solved without using the 0.38 J/g*C as a starting point. I looked that up in a table and found the two closest elements were Zn and Cu. Basically, then, we decide which is the right one. ........M + Cl2 ==> MCl2 ....0.5007 + x .....1....

Chemistry
Cu(NO3)2(s) + H2O(l) ==> Cu^2+(aq) + 2NO3^-(aq)

chemistry
I presume the 17% means that work from the milk is 3.0 kJ/g x 390 g x 0.17 = ? kJ of work. Then plug this into work = mgh as shown in the problem and solve for h = height in meters.

chemistry
First you must determine if the Cu goes through a phase change (i.e., melting) before it reaches 337.3, (it doesn't) so q = mcdT

chemistry
Your set up looks ok but I don't get that answer when I do the math using your numbers. I get something like 50.2. By the way, I looked up Fe and found 0.444 but I assume you are using numbers supplied with the problem.

chemistry
q = [mass H2O x specific heat H2O x (delta T)] + (Ccal*delta T)

CHEMISTRY FOR ENGINEERS
Note that you will need to change A to meters; also, wave number = 1/wavelength

Chemistry
You want XNaOH = 0.03. Then 0.03 = mols NaOH/[mols NaOH +(mols H2O-mols NaOH)] If you let y stand for mols NaOH, this becomes 0.03 = y/[y+(100/18)-y] Solve for y = mols NaOH. Post your work if you get stuck.

Chemistry
I don't think you typed all of the problem/question. You get mass H2O from mass = volume x density and that will answer your posted question. However, most of these problems want to calculate delta H, usually in kJ/mol. That is done as follows: q = mass H2O x specific heat...

Analytical chemistry
A good factor to remember is 1 ppm = 1 mg/L so 1000 ppm would be 1000 mg/L So you want1000 mg (that's 1 gram) MgCO3 in a L of solution.

chemistry
1 ppm = 1 mg/L 1 ppm = 1 mg x (25/1000) = 0.025 mg/25 mL. You want 0.02 ppm so 0.02 x 0.025 = ? mg solute in 25 mL solution.

Chemistry
I don't know your problem but all you need to do is to think of any sentence starting with that "next" letter. The following won't went a Pulitzer Prize but it answers the question. Now is the time, Or any time for that matter, No matter how little or late, ...

chemistry need help
Cr^3+ + 4H2O==> CrO4^2- + 3e + 8H^+ BrO^- + 2e + 2H^+ ==> Br^- + H2O -------------------------------- Multiply eqn 1 by 2 and eqn 2 by 3, then add to obtain the complete balanced redox equation.

CHEMISTRY
a. bubbles b. rxn decreases with time c. ran how of marble chips d. 1. incrase concn HCl 2. increase surface area of chips by breaking them apart into smaller pieces.

@ b.k.---chemistry
Yes, you should use 1/50, calculate as shown above but x will be concentration and not mols. Then convert x = concentration in mols/L to mols.

Chemistry
You don't have enough information to even estimate an answer, much less obtain a real answer. Also, my crystal ball isn't working today.

Chemistry
q1 = heat need to change temperature of solid ice at -45 C to solid ice at 0 C. q1 = mass ice x specific heat solid ice x (Tfinal-Tinitial) q2 = heat needed to change solid ice at 0 C to liquid water at 0 C. q2 = mass ice x heat fusion water. Total q = q1 + q2

Chemistry