Sunday
December 4, 2016

Posts by DrBob222

Total # Posts: 53,737

Chemistry
mass = volume x density. mass Zn = 1 x density Zn (you will need to look that up). mass Cr = 1 x density Cr. Look up density Cr also. Then subtract to find mass difference.
November 9, 2016

Chemistry
Mg + 2HOH ==> Mg(OH)2 + H2 mols Mg = grams/molar mass = ? Using the coefficents in the balanced equation, convert mols Mg to mols H2O Then grams H2O = mols H2O x molar mass H2O = ?
November 9, 2016

Chemistry
CaCl2 + Na2SO4 ==> CaSO4 + 2NaCl mols CaCl2 = M x L = ? Convert to mols Na2SO4. That is ?mols CaCl2 x (1 mol Na2SO4/1 mol CaCL2) = ?mols CaCl2 x 1/1 = ? Then M Na2SO4 = mols/L. YOu know M and you know mols, solve for L and convert to mL.
November 8, 2016

Chemistry
% w/w = (grams solute/grams solution) x 100 = ?
November 8, 2016

chemistry
What is your main problem with this question? Do you know what these compounds are? How they react with water?
November 8, 2016

Chemistry
Why don't you look up the Law of conservation of mass and see what it means?
November 8, 2016

chem 15
1 ppm = 1 mg/L; therefore, 175 ppm = 175 mg CaCO3/L. Convert to grams Ca ions. Convert to mols Ca M = mols Ca/L solution.
November 8, 2016

chem 15
%w/w = (mass solute/mass solution)*100 = ?
November 8, 2016

Chemistry
Check your post. Are you sure that is lead(IV) acetate and not lead(II) acetate. The ppt will be lead(II) chloride, PbCl2, and not PbCl4.
November 7, 2016

Chemistry
You make a set of standards (solution of known concentration of the molecule/ions you want to determine), run them through the same procedure you will use on the unknowns, then measure the absorbance of each. Plot A on the y axis and mg/mL on the x axis. That is your ...
November 7, 2016

Chem
Should be As^3-. Those extra electrons repel each other and the other electrons in the outside shell and that causes the ionic radius to be larger.
November 7, 2016

chemistry
Not so. mols P4 = 20/molar mass P4 = ? mols Pbr3 = ?mol P4 x (4 mols PBr3/1 mol P4) = ? For grams Br2, it isn't 2.93. mass Br2 = volume x density = 50 mL x 2.93 g/mL = ? Then mols Br2 = g/molar mass = ? Convert mols Br2, as above, to mols PBr3 . The smaller number will be ...
November 7, 2016

Weird question science
Right, but I don't know that it's such a weird question.
November 7, 2016

chemistry
mass = volume x density or vol = mass/density vol Au + vol Ag = total vol Let x = mass Au then 9.35-x = mass Ag (x/19.3) + (9.35-x)/10.5 = 0.654 Solve for x = mass Au, then x/19.3 = vol Au.
November 7, 2016

chemistry
See your other post above. We appreciate it when you use the same screen name; we can help you better and faster that way.
November 7, 2016

chem
1 = -log (H^+) so for pH 1, (H^+) = 0.1M and for 1 L of that, mols HCl = M x L = 0.1 x 1 = 0.1 mol. 2 = -log (H^+) (H^+) = 0.01 M and mols HCl = 0.01M x 1 L = 0.01 mols. Then 0.1 mol HCl - 0.01 mol HCl = 0.09 mols HCl to be removed. 2HCl + CaCO3 ==> CaCl2 + H2O + CO2 mols ...
November 7, 2016

Chemistry
Is this just a "I wonder what would happen if" from a bunch of kids sitting around at night with nothing to do except thing up absurd questions.
November 6, 2016

Chemistry
1. Write the balanced equation. C2H5OH + 3O2 ==> 2CO2 + 3H2O 2. Convert 760 g ethanol to mols. mols = grams/molar mass = ? 3. Using the coefficients in the balanced equation, convert mols ethanol to mols CO2. That's ?mols ethanol x (2 mols CO2/1 mol ethanol) = ? 4. ...
November 6, 2016

Chemistry
You're right that C = 4.22E-5 M. So M x L = mols = 4.22E-5 mol/L x 2E-3 L = mols X in that final 2 mL sample that was measured. But that also is the mols in that 300 uL taken from the original sample. Convert to grams. That is g = mols x molar mass = ? That gives you grams...
November 6, 2016

chemistry
You need to look up the solubility of NaCl in water at 80 C, then assign saturated, unsaturated, supersaturated
November 6, 2016

Chemistry
2H2O ==> 2H2 + O2 mols H2O = 4.307/18 = ? mols O2 = ?mols H2O x (1/2) g O2 = mols O2 x molar mass O2 = ?
November 5, 2016

Chemistry
Same problem as above. Just different numbers.
November 5, 2016

@ Steve--typo I think---chem.
I agree with almost all of your work. I also would agree that working it as a math problem is a lot easier than as a chemistry problem. I did it as a chem problem because it was labeled chem. While the mols Ar = 1.2 it is 1.2 both in the initial mixture as well as the final ...
November 5, 2016

chem.
Steve has worked this as a math problem (because he is a math person). I assume the title of chemistry for the question you may want to work it as a chemistry problem. Do it this way. BTW, I agree with Steve's answer EXCEPT for the 1.5 mols. If mols Ar are 1.2 in the ...
November 5, 2016

Chemistry
Since Sn ==> Sn^2+, then if M Sn^2+ is 0.65, so mols Sn^2+ = M x L = 0.65 x 0.023 = ? and same mols Sn to have started the process. Then g Sn = mols Sn x atomic mass Sn = ?
November 5, 2016

chemistry
CaCO3 + 2HCl ==> CaCl2 + H2O + CO2 mols CaCO3 = grams CaCO3/molar mass CaCO3 = ? mols CaCl2 = mols CaCO3 since 1 mol CaCO3 produces 1 mol CaCl2. Then g CaCl2 = mols CaCl2 x molar mass CaCl2 = ?
November 5, 2016

Chemistry Solutions
Your post just isn't clear. I can prepare almost any number of mL from 59 g NaOH but of WHAT concentration. Do you mean to start with 59 g NaOH and ask how many mL of 19.4M NaOH can be prepared from that? If so then mols NaOH in 59 g = grams/molar mass = 59/40 = 1.475 mols...
November 5, 2016

chemistry
0.025 mg = 25E-3 g Pb. mols Pb = grams Pb/atomic mass Pb. 1000 mL H2O x 1.00 g/mL = 1000 g = 1 kg. molality = mols Pb/kg H2O
November 5, 2016

chemistry
p = mv
November 5, 2016

chemistry
wavelength = h/mv
November 5, 2016

Chemistry
(P1V1/T1) = (P2V2/T2)
November 5, 2016

Chemistry
Also we assume that all of the ice melts. q1 = heat needed to raise T of cube at -13.3 to zero C. q1 = mass ice x specific heat ice x (Tfinal-Tinitial) q2 = heat needed to melt ice at zero C to liquid water at zero C. q2 = mass ice x heat fusion. q3 = heat needed to raise T of...
November 4, 2016

chemistry
Use PV = nRT. You know P, V, R and n. n = grams/molar mass. Solve for T (in kelvin).
November 4, 2016

chemistry
There is no reaction. Look up the solubility of these. KNO3 is soluble Ba(C2H3O2)2 is soluble. Now look at the possible products if they react as double displacement. KC2H3O2 is soluble and Ba(NO3)2 is soluble. Neither of the possible products is a gas. Neither is a weak ...
November 4, 2016

Chemistry 101
I don't know the details of the experimental set up.
November 4, 2016

chemistry
1000 is the volume of the solution. Since you want M, that means you want mols solute/L solution. 1000 is volume of solution. 1000 mL x density in g/mL = grams solution. 1000 x g/mL x (%/100) = grams solute. 1000 x g/mL x (%/100) x (1/molar mass solute) = M where grams solute/...
November 4, 2016

Tricky Math Question
My two year old calculator gives an answer of "invalid".
November 4, 2016

chemistry
That's right. Count the electrons and there are 57 but the configuration is not right for La.
November 4, 2016

chemistry
You need to know the rules. Here is how you do it. The rules are: n = 1,2,3 etc in steps of whole numbers. ell (I can't write the script l) is 0, 1, 2, etc in steps of whole numbers but never more than n-1. or less than 0 mell = -ell to + ell in steps of whole numbers (...
November 4, 2016

chemistry
First, what is the M of the 70% HNO3. That's 1.36 g/mL x 1000 mL x 0.70 x (1/63) = ? M1 Then M1 x mL1 = M2 x mL2 M2 is 0.250; mL2 = 1000 mL, solve for mL1.
November 4, 2016

Chemistry
I don't see a question here.
November 3, 2016

Chemistry
https://en.wikipedia.org/wiki/Elimination_reaction
November 2, 2016

Chemistry 11
g Cu(NO3)2 = 3.9 g H2O = 5.0-3.9 = 1.1 mols Cu(NO3)2 = 3.9/187.5 = 0.0208 mols H2O = 1.1/18 = 0.0611 You want n mols H2O/1 mol Cu(NO3)2 So 1 mol Cu(NO3)2 = 0.0208/0.0208 = 1.000 n mols H2O = 0.0611/0.0208 = 2.94. Round that to a whole number of 3.0 Formula is Cu(NO3)2*3H2O
November 1, 2016

chemistry
(62.9298*0.6909)+(x*0.3091) = 63.546 Solve for x.
October 31, 2016

Chemistry
Assume any gram size you wish; i.e., say 5g He and 5g Xe (that is 50% by mass). Then n He = grams/atomic mass = ? n Xe = grams/atomic mass = ? total mols = ? XHe = nHe/total mols and XXe = nXe/total mols. Use PV = nRT and solve for total P of the system usig total mols. Then ...
October 29, 2016

Chem
Use PV = nRT
October 28, 2016

Chemistry
First, calculate M NaOH. mols NaOH = grams/molar mass = ? M = mols/L = mols/0.1 L = ? That gives you the (NaOH) and that is the same as the (OH^-) Now, pOH = -log(OH)^- and pH + pOH = pKw = 14. Calculate pH from this.
October 28, 2016

Chem
NaN3 ==> Na + 3/2 N2 Use PV = nRT. n = grams NaN3/molar mass NaN3. Convert that to mols N2 and plug that into PV = nRT; Solve for V. Then work = pdV and the sign will be negative since the system is doing work in the expansion.
October 28, 2016

Is this homework dump?==chemistry
I've answered enough of these. You've shown no work, no thought, no nothing. I'll be glad to help but no more freebies with me doing all of the thinking.
October 28, 2016

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 ...
October 28, 2016

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
October 28, 2016

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.
October 28, 2016

chemistry
Same type problem as hexane
October 28, 2016

chemistry
http://www.jiskha.com/display.cgi?id=1477618485
October 28, 2016

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.
October 28, 2016

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.
October 28, 2016

Chemistry
See your earlier post.
October 28, 2016

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 ...
October 28, 2016

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 ...
October 28, 2016

chemistry
I showed you how to do this last night Sam.
October 27, 2016

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, ...
October 27, 2016

chemistry
See your previous post. Same formula.
October 27, 2016

chemistry
q = mass C6H15 x specific heat x delta T Substitute and solve for specific heat.
October 27, 2016

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 ...
October 27, 2016

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.
October 27, 2016

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.
October 27, 2016

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)
October 27, 2016

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.
October 27, 2016

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 = ?
October 27, 2016

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.
October 27, 2016

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.
October 27, 2016

Chemistry
https://en.wikipedia.org/wiki/Electronegativity
October 27, 2016

Chemistry
(0.78*50) + (0.15*51) + (0.07*52) = ?
October 27, 2016

CHEMISTRY
H3PO4 + 2NaOH ==> Na2HPO4 + 2H2O
October 27, 2016

Chemistry
mols = grams/molar mass mmols = mg/molar mass
October 26, 2016

Chemistry
Can't do it. You can calculate molality but not molarity. If you have density you can convert molality to molarity.
October 26, 2016

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.
October 26, 2016

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 ...
October 26, 2016

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 ...
October 26, 2016

Chemistry
6.55 lbs x (453.6 g/lb) = ? grams. Then mols = grams/molar mass = ?
October 26, 2016

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...
October 26, 2016

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.
October 26, 2016

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
October 26, 2016

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.
October 26, 2016

chem
Properties like ionization energy and bond energy will be the same.
October 26, 2016

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...
October 26, 2016

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.
October 26, 2016

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) ...
October 26, 2016

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.
October 25, 2016

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.
October 25, 2016

Chemistry
What's the preceding question?
October 25, 2016

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.
October 25, 2016

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 ...
October 25, 2016

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...
October 25, 2016

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.
October 25, 2016

Chemistry
It can be anything; in the commecial product it is water.
October 25, 2016

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.
October 25, 2016

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.
October 25, 2016

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).
October 24, 2016

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 = ?
October 24, 2016

  1. Pages:
  2. <<Prev
  3. 1
  4. 2
  5. 3
  6. 4
  7. 5
  8. 6
  9. 7
  10. 8
  11. 9
  12. 10
  13. 11
  14. 12
  15. 13
  16. 14
  17. 15
  18. Next>>