Wednesday
April 23, 2014

Posts by DrBob222


Total # Posts: 41,901

chemistry
This is a limiting reagent (LR) problem. I know that becsuer amounts are given for BOTH reactants. 2H3PO4 + 3Ca(OH)2 ==> Ca3(PO4)2 + 6H2O 1. mols H3PO4 = M x L = ? Do the same for mols Ca(OH)2. 2a. Using the coefficients in the balanced equation, convert mols H3PO4 to mols ...

chemistry
The idea of predicting which is ionic, which covalent, which polar covalent depends upon some man made definitions and how to interpret them. Look up the value for the electronegativity (EN) for each element. If the difference is about 1.9 or so it is about 50% covalent/50% io...

Chemistry
(P1/T1) = (P2/T2)

Chemistry
See your other post.

chemistry
4. mols = grams/molar mass 5. At what pressure? If you mean standard pressure of 760 mm Hg then you need to remember that 1 mol of gas occupies 22.4 L at STP 6. Take a 100 g sample which will be 36.2g Al 63.8g S. Convert these to mols by mols = g/atomic mass. 36.2/27 = about 1...

chemistry
volume of sphere = (4/3)*pi*r^3 Plug into mass = volume x density I assume you either have or can look up the other information.

Chemistry
The correct name for the ionic compound Al2Se3 is? I would name this aluminum selenide but some might prefer the name aluminum triselenide. The correct name for the ionic compound Fe2Se3 is? I would name this iron(III) selenide; some may prefer iron(III) triselenide. the Roma...

Science
I suppose one should ask WHICH experiment by Lavoisier but I agree with your answer.

AP Chemistry- Equilibrium
MgCl2 + 2NaOH ==> Mg(OH)2 + 2NaCl millimols MgCl2 = 10.0 x 0.18 = 1.8 mmols NaOH = 20.1 x 0.56 = about 11.3 but you should do these more accurately. The remaining steps are approximations too. 1.8 mmols MgCl2 will use 3.6 mmols NaOH and form 1.8 mols Mg(OH)2. The solubility...

AP Chemistry- Equilibrium
See your other post.

chemistry
AgOH ==> Ag^+ + OH^- Mg(OH)2 ==> Mg^2+ + 2OH^- Ksp Mg(OH)2 = (Mg^2+)(OH^-)^2 Ksp AgOH = (Ag^+)(OH^-) Calculate (OH^-) in a saturated solution of Mg(OH)2. That is .........Mg(OHO2 ==> Mg^2+ + 2OH^- I........solid........0.......0 C........solid........x.......2x E........

chemistry
I would go with d but you should know how to do these.

Science
I agree.

Science
For NaOH, this is 100% dissociated; therefore, (OH^-) = (NaOH) OH^- = 2 M pOH = -log(OH^-) pH + pOH = pKw = 14. You know pOH, solve for pH. The H2SO4 isn't as simple as it lookis. If you are an advanced student, (0.39+x)/(0.39-x) = k2 for H2SO4. Solve for x and evaluate 0....

Science
See your post above.

chemistry
Did you finish your post? I would write for this particular compound Tl2Te3 which I would name thalium(III) telluride

physical science
Mass is the same no matter where. Weight is greatest on planet with largest G and smallest on planet with smallest G.

physical scief = nce
f=ma or a = f/m = 10/1 = ?

Chemistry HELP
With 1:2.24 you can't round to 1:2. Multiply by a whole number until you get two whole numbers (or at least to close whole numbers). 1:2.24 2:4.48 3:6.72 4:8.96 which I would round to 4:9 for the formula C4H9. Having done that I don't know what to do except look at you...

Chemistry
How many moles do you want? That'x M x L = ? Then mols = grams/molar mass.

Chemistry
CaCO3 ==> CaO + CO2 mols CaCO3 = 0.01 mol. You get 1 mol CO2 for each mol CaCO3; therefore, you can produce a maximum of 0.01 mol CO2. How many grams is that? g CO2 = mols CO2 x molar mass CO2.

Chem
Does this reaction go to completion or do you have a Keq?

Chemistry
N2 + 3H2 ==> 2NH3 mols NH3 = grams/molar mass = 42800/17 = ? Using the coefficients in the balanced equation, convert mols NH3 to mols H2. Now convert mols H2 to grams. g = molx x molar mass.

chemistry
I need clarification. Group I and II are cations, not anions.

chemistry
5.13 g CO2 x (1 mol CO2/44g) x (1 mol C/1 mol CO2) = ? and I don't believe that is 0.117 2.10g H2O x (1 mol H2O/18) x (2 mol H/1 mol H2O) = ?

science
BC: d = rate x time 40,000 = 2500*t t = 8 hours for the first half. 40,000 = 1000*t t = 20 hours for the second half. Total time = 28 hours. There are ways to go here. The first is to see if half the time (14 hours) at the FC speeds will come up more or less than 40,000. d = r...

Chemistry
K3PO4(s) ==> 3K^+(aq) + PO4^3-(aq) I don't know the level of chemistry for you, but I assume you're not expected to know that the PO4^3- ion will hydrolyze in H2O as PO4^3-(aq) + HOH(l) ==> HPO4^2-(aq) + OH^-(aq)

Science
In a perfect world I suppose I agree with you. Although it isn't part of the problem, remember that preservation means from all influences, not just those by man.

Chemistry (Analytical) followup
I assume this is the CaC2O4 problem. If the pH is reduced to 2, that makes the H^+ MUCH larger (by a factor of 10,000,000 which is really MUCH larger) and the solubility of the CaC2O4 is increased significantly. The reason is that you add a competing reaction (actually two rea...

Chemistry
In this case yes. If 48% w/v, that means 48g HBr/100 mL solution so 4.6 mL will have 48 g HBr x (4.6 mL/100 mL) = ? g and that gives grams in the volume you want which can be convert to mols by mol = g/molar mass. The problem with w/w is that you have no way of knowing how muc...

Chemistry
I don't believe it can be done without the density. I think 48% w/v can be done without density but not w/w.

Chemistry
You want to calculate the molarity of the H2O2. 35% w/w means 35 g H2O2/100 g solution. Since mass = volume x density, then volume = mass/density = 100g/1.14 = about 87.7 mL. mols in 35 g = 35/about 34) = about 1 mol M = mols/L = about 1/0.0877 = ? Then mols in 0.8mL = M x L. ...

Chemistry
Is that 10 mL of the 0.2M H3PO4 added to 250 mL H2O to make 260 mL solution? If you titrate the entire solution, which seems unlikely, then you will have H3PO4 ==> NaH2PO4 + H2O mols H3PO4 = 0.010L x 0.2M = 0.002 mols NaOH required = 0.002 since 1 mol H3PO4 = 1 mol NaOH. Th...

Chemistry (Analytical)
I'm assuming that at a pH of 9 the H^+ will not increase the solubility over that of a saturated solution of CaC2O4. ............CaC2O4 ==> Ca^2+ + C2O4^2- I............solid......0........0 C............solid......x........x E............solid......x........x Ksp = (Ca...

chemistry
I'm not sure what you mean by a dry solution. Certainly there are many but I don't think any of them apply here. Do you mean 135 mL of 0.120 M NaNO3 in a solvent. Do you want 1 L of solution. You want how many mols? That's M x L = ? = 0.135 x 0.120 = ? Then mol/L =...

Chemistry
14% (that's v/v) means 14 cc ethanol/100 cc wine so 750 cc wine x (14 cc ethanol/100 cc wine) = about 105 cc ethanol. 14 units x (10 cc ethanol/unit) = 140 cc ethanol 140 cc ethanol x (1 bottle/105 cc ethanol) = ? bottles

Chemistry
You might get an average out of this. http://en.wikipedia.org/wiki/Carbon-13_NMR

Chem
It's Mg and MgCl2. 1.5 g Cl x (molar mass Mg/2*atomic mass Cl) = ?

Science
2 is right. For 1, use the same f = ma you did in #2.

Chemistry
I would go with Br, Si, Cd.

Havlicek
PV = nRT. You know n, R, T, and V. Solve for P. Use PV = nRT again, plug in P from above and solve for V with the new conditions.

chemistry
So the new pressure is 101 + (100 x 51/10.2) = ? Then P1V1 = P2V2

Chemistry
%Oxygen = (3*16/molar mass KClO3*100 = ? about 39%

Chemistry
Along those lines, yes. The calculation is complicated by the fact that NaCl ionizes completely into two ions while the dextrose isn't ionized at all. With NaCl you must use pi = i*nRT where i is 2 for NaCl. For dextrose i = 1. So I would calculate M NaCl and M dextrose, f...

Chemistry
You are. mols NaCl = 0.9g/58.44 = ? ?/0.1 = M

Chemisty
I understand. I know you don't think I answered your question but I did the best I could without enough information. You must define accuracy. How accurate is "an accurate result"? Is that 1 ppt, 1%, 10% 50%, just what. From your response I assume you weighed the...

Chemisty
The question is far to general. How much accuracy do you want? What size buret are you using? Assuming you are using a 50 mL buret and you dilute the raw acetic acid by a factor of 100, it will take about 3.1 g NaHCO3 for an accuracy of better than 1 part per thousand variatio...

Chemistry
q for ice at -20 to ice at 0. q = mass x specific heat ice x delta T (dT = 20). q to melt the ice is q = mass ice x heat fusion. q to heat from zero to 95. q = mass H2O x specific heat H2O x dT and dT = 95. Then sum the q values.

Chemistry
This is a limiting reagent (LR) problem. I know that because amounts are given for BOTH reactants. 2K | i2 ==> 2kI mols K = grams/molar mass mols I2 = grams/molar mass Using the coefficients in the balanced equation, convert mols K to mols KI. Do the same for mols I2 to mol...

Chemistry
pBr2 = ? n = 0.960 R = 0.08206 T = 273 + 1000 = 1273K p = nRT/V = (0.960)*0.08206 x 1273/1 = 100.28 BUT I said that was approx and you should go through it with more accuracy. I would round that to 100. pH2 = (1.28*0.08206 x 1273/1 = 128.49 with the same recommendation. I woul...

Science
1 is C. 2 I don't know, 3 I don't understand the choices, 4 is A.

Chemistry
See Damon's response above.

asap science
Buoyancy pushes an object upward.

Chemistry
What exactly is your problem in doing this?

Chem (Specific Heat)
q = mass x s.h. x (Tfinal-Tinitial) 7.74E3 = 75.0 x s.h. x (125-10) Solve for s.h.

chemistry
This take a LOT of typing. Exactly what do you understand and not understand?

Chemistry
0.038 mol FeCl2 x (1 mol K2Cr2O7/6 mol FeCl2) = mols K2Cr2O7. Then M = mols/L so L = mols/M = Then multiply by 1000 to convert to mL.

chemistry
I didn't get 177 mL. mols KMnO4 = grams/molar mass mols Na2C2O4 = mols KMnO4 x (5 mols ox/2 mol MnO4) = ? Them M Na2C2O4 = mols/L Solve for L and convert to mL.

Chem 2
delta T = i*Kf*m for freezing point, subtract 0 C - delta T. i for Na2SO4 = 3 delta T = i*Kb*m for boiling point add delta T + 100 = ?

chemistry
Us the dilution formula of L1 x M1 = L2 x M2 1.64L x 4.95M = ?L x 2.58M ?L = ?

AP chem
Five separate problems can take a long time. Exactly what do you understand (and not understand)?

Chemistry
3.566 XeF4 x (atomic mass Xe/molar mass XeF4) = g Xe

Chem
The only way this can be done that I know of is to have at hand a calibration curve for sugar solutions. If you have such a curve (% sugar on one axis and density on the other) you can read % sugar from the graph. I'm a little surprised that the density is < 1.00g/cc al...

Chemistry
You can't do this? Look up the atomic masses to five or more places for each element (a periodic table or the web) and find the sum.

Chemistry
See your post above.

General Chemistry
If the intermolecular force is greater the vapor pressure will be less because the molecules must have more kinetic energy to escape as a vapor.

Chemistry
I would look in a text for periodic trends and find my answer there.

Chemistry
See your other post.

Ap Chemistry
does not or will not goes in the blank.

chemistry
(18.9 kJ/0.5g) x (1 cal/4.184 J) = ?

AP Chemistry
I don't get it. If it has pH of 7.4 at neutralization why would anything need to be added to neutralize it? BTW, 25 mL of what M of what?

Science
d

Chemistry AP
Several steps to this problem. Here is an outline. 1. Use the HH equation and solve for the ratio of base/acid; i.e., sodium benzoate to benzoic acid. Then convert that to percent of each. 2. Use the percents to calculate a van't Hoff factor. That is 2*%base + 1*%acid = to...

Chemistry
Piece a cake. Check out the site for balancing equations. 4HCl + 3As2O3 + 4NaNO3 + 7H2O --> 4NO + 6H3AsO4 + 4NaCl http://www.chemteam.info/Redox/Redox.html

Chemistry
q = mass H2O x specific heat H2O x (Tfinal-Tinitial)

chemistry
(0.325/0.482)*100 = ?

Chemistry
3Mg + 2H3PO4 ==> 3H2 + Mg3(PO4)2 mols H3PO4 = grams/molar mass. Using the coefficients in the balanced equation, convert mols H3PO4 to mols Mg. Then convert mols Mg to grams. g = mols Mg x atomic mass Mg.

Chemistry
Note that 1 mol SA = 1 mol aspirin and 1 mol SA = 1 mol acetic anhydride. Therefore, 75 mol SA will produce 75 mols aspirin. Then g aspirin = mols x molar mass. 75 mol SA will use 75 mol acetic anhydride; g = mols x molar mass.

chemistry
Please explain what your problem is here. It seems to me that if you've seen a bunsen burner operate you should know the answer to 1 & 2. If you haven't seen one in operation you should. For 3,5,5,6. Aren't these described in some detail in your lab manual or you c...

chemistry
Yes, R is 8.314 Then P1 goes with T1 and P2 goes with T2. Delta H is 557.0 kJ/mol but you should use 557,000 in the formula;i.e., convert to J/mol.

chemistry
Use the Clausius-Clapeyron equation

gwagwa
KE = 1/2*m*v^2

sciene(HELP)
I answered this below. Go back and read your posts to see if there is a response before posting again.

chemistry
and 5.

chemistry
and 4.

chemistry
triplicate

chemistry
duplicate

chemistry
See this. http://www.jiskha.com/display.cgi?id=1391564392

science(CHECK ANSWERS)
I don't think A is the right answer. A is absorbing sunlight for photosynthesis but that is being trqansformed into chemical energy in which CO2 and H2O form glucose. B is absorbing EM to form heat and that is thermal energy, C. The solar panel is absorbing EM and making e...

Chemistry
pi = nRT pi = 821/760 Substitute R and T (remember T must be in kelvin) and solve for n. Then n = grams/molar mass. You know n and grams, solve for molar mass. M = mols/L solution.

Chemistry
But this is what you started with, not what the prof gave you as an unknown. The most likely reason for >100% recovery, as I've already said, is not drying the samples sufficiently so you weigh all of the sample plus some extra water. And you had to dry three samples; i...

Chemistry
I'm glad to know you omitted those last steps. Do you know what the actual percentages are. If we knew that we could make some educated guesses about why may have gone wrong although that won't answer either of the two question posed.

Chemistry
I don't think your professor will buy either argument you gave above. The mass of NaCl will not change and SiO2 won't absorb into the atmosphere. Frankly, I don't understand how this separates the CaCO3. Did you omit a step? In the process you give the CaCO3 and Si...

Chemistry
First, I don't know what process you used for separating the components. One common error is this type lab procedure is not drying each and that always contributes to greater than 100% recovery. If you care to type in the procedure you used perhaps I can help with the othe...

ap chemistry
a. Use the Henderson-Hasselbalch equation.

ap chemistry
Approach this problem as in the NH3/HCl problem below and see where you are on the titration curve. Post your work if you need addition assistance.

ap chemistry
millimols HCl = 34 x 0.2 = 6.8 mmols NH3 = 29 x 0.05 = 1.45 ..........HCl + NH3 ==> NH4Cl I.........6.8...1.45......0 C........-1.45.-1.45.....+1.45 E.........5.35...0........1.45 If you look at the numbers you will notice that the titration with HCl has neutralized all of ...

Chemistry
I don't know that you can except in some circumstances. First, most gases are not very soluble (some exceptions are NH3, SO2, SO3 etc) so unless it reacts with water and is quite soluble, you don't expect it to be a gas. Most liquids are not soluble in H2O unless they ...

ap chemistry
Substitute into the HH equation.

ap chemistry
Use the HH equation and solve for Ac. pH = pKa + log (Ac/HAc) 5.027 = 4.744 + log Ac/0.5 Now convert M Ac to grams.

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