Tuesday
January 17, 2017

Posts by DrBob222

Total # Posts: 53,873

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

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.
October 24, 2016

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) ...
October 24, 2016

chem
The atom must become excited by absorbing energy from some source.
October 24, 2016

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.
October 24, 2016

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................
October 24, 2016

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.
October 24, 2016

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
October 24, 2016

Chemistry
Take 10 mL of the 0.5 M acid and add enough water to make 30 mL
October 24, 2016

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 ...
October 24, 2016

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 ...
October 24, 2016

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
October 24, 2016

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.
October 24, 2016

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 ...
October 24, 2016

Chemistry
Did all of the Fe react? Then mols Fe = grams Fe/atomic mass Fe = ?
October 23, 2016

Chem
What are the units? -6.00 what? 1. dHrxn = (n*Gf products)-(n*dGf reactants). 2. dG = -RTlnK 3. Kp = pO2
October 23, 2016

Chemistry
H2 + 2OH^- ==> 2H2O + 2e Fe^3+ + e ==> Fe^2+ Multiply eqb 1 bt 1 and eqn 2 by 2, then add.
October 23, 2016

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 ...
October 23, 2016

Chemistry
You need to proof your post and correct it.
October 23, 2016

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)
October 23, 2016

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.
October 22, 2016

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 ...
October 22, 2016

Chemistry
(1/wavelength) = R(1/1^2 - 1/2^2) Look up R. That's the Rydberg constant. It's about 1.09 E7
October 22, 2016

Chemistry
yes, E divided by h. f = E/h
October 22, 2016

Chemistry
Pick a number. You don't have T or V listed. You need those to answer.
October 22, 2016

Chemistry
2Na + 2H2O ==> 2NaOH + H2 mols Na = 0.05. g Na = mols Na x atomic mass Na = ?
October 22, 2016

BioChemistry
mols = M x L = ?
October 22, 2016

Chemistry
pH = -log(H^+) Substitute and solve.
October 22, 2016

Biochemistry
Your question is not clear to me.
October 22, 2016

Chemistry
I don't think you have enough information. How much PCl5 do you have (pressure or M)?
October 22, 2016

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...
October 21, 2016

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....
October 21, 2016

Chemistry
Cu(NO3)2(s) + H2O(l) ==> Cu^2+(aq) + 2NO3^-(aq)
October 21, 2016

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.
October 21, 2016

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
October 21, 2016

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.
October 21, 2016

chemistry
q = [mass H2O x specific heat H2O x (delta T)] + (Ccal*delta T)
October 21, 2016

CHEMISTRY FOR ENGINEERS
Note that you will need to change A to meters; also, wave number = 1/wavelength
October 21, 2016

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.
October 21, 2016

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...
October 20, 2016

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.
October 20, 2016

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.
October 20, 2016

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, ...
October 20, 2016

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.
October 20, 2016

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.
October 20, 2016

@ 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.
October 20, 2016

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.
October 20, 2016

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
October 19, 2016

Chemistry
That's my answer also.
October 19, 2016

Chemistry
I worked this for someone just a day or so ago but I can't find it. Here is a summary. This is a limiting reagent (LR) problem and you know that because amounts are given for BOTH reactants. N2 + 3H2 ==> 2NH3 mols N2 = grams/molar mass = ? mols H2 = grams/molar mass...
October 19, 2016

Chemis6
C6H12O6 → 2C2H5OH + 2CO2 mols ethanol needed = grams/molar mass Using the coefficients in the balanced equation, convert mols ethanol to mols glucose Now convert mols glucose to grams. g = mols x molar mass = ? Post your work if you get stuck.
October 19, 2016

Chemistry
PCl5 ==> PCl3 + Cl2 Is this 100% reaction or must you use the Keq (which you don't list).
October 19, 2016

Chemistry
Here is a similar problem. Just change the numbers. http://www.jiskha.com/display.cgi?id=1442613787
October 19, 2016

Chemistry
See your post above.
October 19, 2016

Chem
Bob Pursley worked this problem for you that I saw this A.M. Look for it. Click on bob Pursley's answers and you can find it.
October 19, 2016

chemistry
The answer by Ashley is correct but the equation is not. Here is the correct equation. Zn + 2HCL-->ZnCl2 + H2
October 19, 2016

Science
distance = rate x time 500 mi = 500 mi/hr x time. Solve for time in hours.
October 19, 2016

Chemistry
for f.p. delta T =i*Kf*m i = 3 for Na2SO4 m you have look up Kf. Subtract delta T from 0 C to find new f.p. for b.p. delta T = i*Kb*m look up Kb. You have m and i, add delta T to 100 C to find new boiling point.
October 19, 2016

chemistry
[mass Pb x specific heat Pb x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0 The only unknown here is Tfinal
October 19, 2016

chemistry
See your previous post. Same kind of problem. Post your work if you get stuck.
October 19, 2016

chemistry
Wouldn't you think N2 < NO2 < KCl?
October 19, 2016

beginning algebra
Plug in 1 for x and solve for y. Plug in 2ffor x and solve for y. Plug in 3 for x and solve for y. Need more? Plug in a number for x or y and solve for the other.
October 19, 2016

Chemistry
(V1/T1) = (V2/T2)
October 19, 2016

Chem
It helps us help you better when you use the same screen name. You didn't do that but see your other post above.
October 19, 2016

chemistry
KCl + Br2 = no reaction
October 19, 2016

chemistry
no reaction. Cl2 and KBr is yes, Br2 and KCl none.
October 19, 2016

chemisty
1 mol of atoms contains 6.02E23 atoms.
October 18, 2016

chemi
See your other post.
October 18, 2016

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