Thursday
July 24, 2014

Posts by DrBob222


Total # Posts: 43,171

Chemistry
zero or very low

Chemistry
Take equation 1 and add it to the reverse of equation 2 and add that to the reverse of 1/2 equation 3. When reversing dH, change the sign. When taking 1/2 equation, also take 1/2 dH.

chemistry
Q = coulombs = amperes x seconds Q = 0.680A x 20m x (60s/m) = ? = about 816 96,485 coulombs will deposit (63.54/2)g Cu. You have 816 coulombs; therefore, 63.54/2 x (816/96,485) = about 0.3g if I punched the right buttons.

Underwater explosion
Other tutors may wish to weigh in on this question but I think the answer is yes IF the timing is just right and the compressed air force can be sustained long enough.

Chem
This is an example of a back titration; i.e., the KI/KIO3 produces I2, the I2 reacts with some of the vit C, the excess I2 is titrated with thiosulfate. 6H^+ + I^- + IO3^- ==> 3I2 + 3H2O Then vitC + I2 ==> 2I^- + vitCx mols IO3 added initially = M x L = 0.025 x 0.01988 =...

chemistry
The question isn't exactly clear; it isn't clear that it is the greatest amount of acid per grams antacid or per mol antacid. H^+ + OH^- ==> H2O So the one with the largest OH per mol will neutralize the most acid. That is Al(OH)3. And you don't capitalize every...

chemistry
Wouldn't that be 100g/5 dm^3 = 20g/dm^3

Chemistry
No, the problem says to write the equilibrium constant expression. Nothing about finding the value of K.

Chemistry
What is your problem with these. Keq expressions are the same. K = (products)^x/(reactants)^y and raise each substance to the power indicated by the coefficient.

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

chemistry
mols acetic acid = grams/molar mass, then M acetic acid = mols/L

chemistry
M = mols/L

chemistry
See your post above.

Chemistry
Yes you do exactly what you have outlined. I would look at change in C and change in O for n. If we see ethanol as C2H6O and assign oxiatioin states of -2 for O and +6 for 6H, that makes 2 C in ethanol as -4. On the right the 2C are +8 so the change in e is 12. We can check th...

chemestry
I suggest you google these terms.

Chemistry
Same process. Write the balanced equation. Convert g CO2 to mols with mols = grams/molar mass. Use the coefficients to convert mols CO2 to mols HCl. Then M HCl = mols HCl/L HCl.

Chemistry
Na2CO3 + 2HCl ==> 2NaCl + H2O + CO2 mols Na2CO3 = M x L = ? Using the coefficients in the balanced equation, convert mols Na2CO3 to mols HCl. Then the defintion of M HCl = mols HCl/L HCl. You know M and mols, solve for L.

science
L1 x %1 = L2 x %2 ?L x 0.8% = 0.5L x 9% ?L = ?

what is the answer
Set up a ratio and proportion. (feet/shadow) = (feet/shadow) (8.1/24.3) = 20.1/x) Solve for x.

chemistry
The temperature at which water boils at high altitudes is lower than the temperature it boils at lower altitudes. Therefore, when cooking on a high mountain the water may boil 98 instead of 100 C so you should boil it (less, more). 2. Water boils when water boils. Turning up t...

Chemistry
NOPE. You changed SO4^2- on the right to S2O4^2- and you can't do that. Also you have the e on the wrong side. Other than that it is ok. 2OH^- + SO3^2- ==> SO4^2- + 2e + H2O

Chemistry
I shall be glad to help you through this but you need to learn to do these yourself. I do these the looong way. The first step is to determine the oxidation step of each element. I will help you here. S on the left is +4 and on the right is +6. Add electrons to the appropriate...

chemistry
It will take mass H2O x heat vaporization to turn the 30g into steam at 100 C.

Chemistry
This one is right. If you haven't already do so go back and look at the sulfite ==> sulfate because the one is not right.

Chemistry
I think the trouble you are having is caused by not putting the charges in. That H on the right should be 4H^+. The MnO4 on the right should be MnO4^-. When you do that the e need on the right is not 8 but 3 so the charge on the left is zero and on the right is (-1+4-3) = zero...

Chemistry
Again you need to learn to do these. Mn on the left is +4 and on the right is +7. Cu on the left is 2+ and on the right is zero. Balance the electron change first. Mn on the left goes to Mn on the right with ? change of e. Cu on the left goes to Cu on the right with ? change i...

CHEMISTRY
I worked this for you yesterday.

Chemistry
mols malic acid = grams/molar mass M = mols/L solution.

Chemistry
I worked it using the numbers you provided and came up with the same answer you did of 0.963 so there is nothing wrong with your math. The problem is that the reduction potential of Ni is not 0.26. It is -0.26.

chemistry
I don't believe you didn't know how to do any of this. 1. delta Tb = impure b.p.- pure b.p. 2. delta T = Kb*m Substitute and solve for m. 3. Isn't the mass given in the problem. Convert to kg. 4. m = mols/kg solvent. You know m and kg solvent, solve for mols

chemistry
See your post above.

chemistry
I suggest you read these things before you post them. You provided absolutely no information other than it is in the introductory information. But I don't see any introductory information.

Chemistry
You say you've looked up these values. My values won't be the same as yours because I'm using an old book but they will be close. Here is how you do the first one. Cr==> Cr^3+ + 3e You look in your table and find this potential. It will be listed "backwards...

chemistry
(H3O^+) = (A^-)

chemistry
pH = -log(H3O^+) 4.95 = -log(H3O^+) -4.95 = log(H3O^+) Another way of writing this is (H3O^+) = 10^-4.95 Solve for (H3O^+)

chemistry
An interesting problem. Three equation and three unknowns but we can work it around with just two since these are related. Let X = mass BaO and Y = mass CaO and mm stand for molar mass. ---------------- eqn 1 is X + Y = mass whatever that may be. Convert to sulfates and you ha...

chemistry
Mg + 2HCl ==> MgCl2 + H2 mols Mg = X mols H2 produced = X (look at the coefficients; 1 mol H2 produced for 1 mol Mg used) Volume = mols*22.4L/mol volume 22.4X liters.

to Bob P--Chemistry
I've gone cross eyed with these large numbers but I don't believe H and O balance in your equation.

Chemistry
2C60H87O23N12P +173O2 ==>120CO2 + 72H2O + 24HNO3 + 2H3PO4 Check this carefully. mols biomass = grams/molar mass Using the coefficients in the balanced equation, convert mols biomass to mols CO2. Now convert mols CO2 to grams. g = mols CO2 x molar mass CO2

chemistry
pH = -log(H^+)

Chemistry
The easiest way to do these problems is in parts and you need three formulas to do it. q at a phase change; i.e., solid to liquid or liquid to gas. For solid to liquid (melting point) it is q = mass solid x heat fusion. For liquid to gas (boiling point) it is q = mass liquid x...

CHEMISTRY
I worked this for you last night. Did you look at that?

chemistry
I believe you forgot the coefficients (e.g. 8). 8CH4 ==> C8H8+ 12H2 dGfrxn = (n*dGfC8H8 + n*dGfH2)-(n*dGfCH4) 620.735 = [(1*214.417) + (12*0)] - (8*dGfCH4) 620.735 = 214.417 + 0 - 8x Solve for x.

Chemistry
dH = mass H2O x specific heat H2O x (Tfinal-Tinitial) This will give you the enthalpy change for the reaction as stated in the problem and that is for 0.05g P. Generally these problems don't want that; they want the enthalpy change per mol but this problem doesn't ask ...

chemistry
I suppose you are to use M and m as the same. 0.121g/100 gH2O = solubility. mol N2O = 0.121/60 = approx o.002 and 0.002/0.1kg solvent = 0.02m p = KcC 1 atm = Kc*0.02 Kc = 1 atm/0.02 = 50 atm/m p = KcC 1.600 = Kc from above *C Solve for C in molality and convert to g/100 if des...

Science
In warmer climates the winters are warmer. The moisture from a hot shower is in the form of vapor (gas); however, it could be a liquid if it hasn't had time to completely vaporize and the water droplets are still visible (and you can feel those droplets on the skin).

Chemistry
mols H2SO4 = M x L = approx 0.1 mols NaHCO3 = M x L = approx 0.05 2NaHCO3(aq) + H2SO4(aq) ==>Na2SO4(aq) + 2H2O(l) + 2CO2(g) This should get you started. Post your work if you get stuck and clearly explain what you don't understand.

Chemistry
m = mols/kg solvent 2.0 = mols/3.5 Solve for mols, then mol = grams/molar mass. You know m and molar mass, solve for grams.

Chem Check Please!!!
I don't agree with 4. I agree with 5 and 6.

Chem Check Please!!!
I don't agree with 2. I agree with 3.

Chem Check Please!!!
I don't agree with #1.

Chemistry
I think Ni is initial N. and Nf is final N so the electron is making the transition from N = 1 to N = 2 so this is an absorption but the formula I list is for emission. That won't change frequency or wavelength but it will change the sign of E. delta E = R(1/1 - 1/4) where...

Chemistry
Take 100 g sample for 58.5g C 4.1g H 11.4 g N 26.0 g O Convert to mols. I'll use approximations. 58.5/12 = 4.875 4.1/1 = 4.1 11.4/14 = 0.814 26/16 = 1.625 Now find the ratio in small whole numbers with the smallest number being 1.00. The easy way to do that is to divide al...

General Chem 2
2Al^3+ + 6I^- ==> 2Al(s) + 3I2(s) dGo = -nFEo n = 6

Chemistry - Science (Dr. Bob222)
x = 2 y = 1 How did I do that? V on the left has a oxidation state of +5 and on the right it is +4. S on the left is +4 and on the right is +6. V has changed by 1e S has changed by 2e So V couple must be multiplied by 2 and S couple by 1 to make each lose/gain 2 electrons.

Chemistry
mols = grams/molar mass

Chemistry - Science (Dr. Bob222)
Thanks. I just didn't think the 50% could be right. The concept behind disproportionation is that an element in an "intermediate" oxidation state (in this case Cu^+ is halfway between Cu below it and Cu^2+ above it) can "react with itself" if the potent...

chemistry - Science
I would do this. Calculate g Zn that goes into solution and g Cu that are deposited from solution. Coulombs = amperes x seconds = ?. 95,485 coulombs will use (65.4/2)g Zn and deposit (63.5/2)g Cu. Calculate g Zn used, convert to mols, and add to the 0.1 mol already there. Calc...

chemistry - Science
See your other post.

Chem Check Please!!!
2 is ok 3 is ok I don't agree with 4.

Chem Check Please!!!
1. Cris, I don't agree with C as an answer. Here is the way you keep these straight. Just remember the definition of oxidation and reduction. Oxidation is the loss of electrons. Reduction is the gain of electrons. The substance oxidized is the reducing agent. The substance...

chemistry
By the way, it's past my bed time but I'll be around tomorrow.

chemistry
87 is right. 37 and 50 are right Check your numbers for PEN. You can't possibly get 74 something. 50 x 1+ is about 50. 37 x 1+ = about 37 and add in a pinch for electron mass and you have AT LEAST 50+37+pinch = 87. And it can't be less than 86.909187 because it LOSES m...

chemistry
I can't follow what you've done. I have mass p + mass N + mass e = 87.723173 and that - 86.909187 = 0.813986 amu and that converted to kg = 1.3516563E-27 kg. Let me know if we are on the same page to this point and please show your work for as far as you are and we can...

chemistry
How would you answer these and why?

Chemistry
d2sp3 but obviously those atoms without d orbitals are not eligible for this.

chemistry
You can deposit 196.97/3 = approx 66 g Au with 96,485 coulombs of electricity. So how much will be required to deposit 19.7g 96,485 x (19.7/66) = approx 29,000 coulombs. coulombs = amperes x seconds. Substitute coulombs and seconds and solve for amperes. Note those numbers I u...

Chemistry
TiO2 + 2C ==> 2CO + Ti We don't need to make any corrections for molar mass and kg if we keep everything in kg. kg mols C = 14.0/12 = approx 1.17 kg mols TiO2 = 44.0/79.88 = approx 0.5 Using the coefficients in the balanced equation, convert kg mols of each to kg mols o...

Science
I'm not positive how to answer this. Certainly b and d are not driven by humans and can be eliminated. Global warming, c, is attributed to human impact so that's a definite yes. A is the one I'm unsure about. The greenhouse effect is the name we have given to gases...

CHEM 101
We can't draw pictures, structures, diagrams, etc on this forum.

chemistry
CaCO3 ==> CaO + CO2 mols CaCO3 = grams/molar mass. Using the coefficients in the balanced equation, convert mols CaCO3 to mols CO2. Now convert mols CO2 to grams. g = molls x molar mass.

chemistry chem science
time in seconds is 35 min x (60 seconds/min) = ? amperes = 160 mA = 0.160 A. Calculate Q = # coulombs = amperes x seconds. Then you know that 96,485 coulombs will deposit 112.4/2 grams Cd (that's molar mass Cd/valence). (112.4/2)g Cd x ?coulombs from above/96,485 = ?

chemistry
Instead of someone just giving you the answers, I would like to know what it is you don't understand.

Chemistry 1
The highest freezing point will be the one with the smallest delta T and that will occur for the material with the smallest number of particles; i.e., highest van't Hoff factor x molality or i*m A. 0.1M KCl im = 2*0.1 B. 0.05M NaCl im = 2*0.05 C. 1M AlPO4 im = 1*3 D. 0.1...

chemistry
(P1V1/T1) = (P2V2/T2) You don't need to use moles of gas if you use this formula. Notice that you have no initial volume and no actual final volume (just twice the initial). I would pick a convenient number (any number) for V1 and multiply that by 2 for V2.

Chemistry
2NaOH + H2SO4 ==> Na2SO4 + 2H2O mols H2SO4 = M x L = ? Using the coefficients in the balanced e4quatioin, convert mols H2SO4 to mols NaOH. Now M NaOH = mols NaOH/L NaOH. You know mols and M, solve for L NaOH and conert to mL if you wish.

Chemistry
mols C2H5OH = grams/molar mass m = mols/kg solvent

Chemistry
C2H8 + 5O2 ==> 2CO2 + 4H2O When working with gases we can use a shortcut in which we use L as if L = mols. Then we make the conversion form mols propane to mols O2 as usual. ?L O2 = 3.8 L C3H8 x (5 mols O2/1 mol C3H8) = 3.8 x 5 = ?

Chemistry
delta T = i*Kf*m 2 = 1*Kf*0.5 Solve for Kf.

chemistry
You know we can't draw pictures on this forum but the half reactions are MnO4^- + 3e + 2H2O ==>MnO2 + 4OH^- NO + 4OH^- ==> NO3^- + 3e + 2H2O I have written the MnO4^- as a reduction an the NO as an oxidation so as to keep the electrons on opposite sides. I think you ...

questions
When the car burns fuel (either gasoline or diesel) it combines with oxygen and under the best of conditions would produce CO2 and H2O. However, with the heat of the engine (due to the combustion that is necessary to power the car) some carbon monoxide, NOx which is NO, NO2, a...

Chemistry- is this correct?
To two significant figures, yes. If that 0.30 was really 0.300 (and you just omitted a zero) then you could have 3 s.f. and that would be 0.125M. As posted, however, 0.13 is right.

To JJ
Your problem is somehow intertwined with another and I can't post an answer there. Solve the problem by applying the dilution formula of mL1 x M1 = mL2 x M2

chemistry
Don't you have a graph or a table that gives you solubility at various temperatures?

Chemistry
You want 5L of O2. And if you could get 100% yield from the reaction you could calculate how much NaNO3 would be required to produce 5L O2. However, the problem says the reaction is only 78.4% yield so we must start with more NaNO2 so that at the end with just 78.4% yield we w...

Chemistry
2NaNO3 ==> 2NaNO2 + O2 5L O2 at 78.4% yield would need to be 0.784 = 5/x and x = about 6.4 6.4L at STP = ? mols mol = 6.4L/22.4L = approx 0.29 Convert mols O2 to mols NaNO3. That's 0.29mol O2 x 2 mol NaNO2/1 mol O2) = approx 0.57 mol NaNO3. Then g NaNO3 = mols x molar m...

chemistry
Use PV = nRT. T must be in kelvin. I don't know what 0.01m is. If you mean for that to be 0.01 mols, that will be n

Chemistry
M = mols/L. 0.142M NaI = 0.220 mols NaI/ L solution. Solve for L.

Chemistry
mL1 x M1 = mL2 x M2

Chemistry
Let's call this BNH2 to save some typing. ..........BNH2 + HOH --> BNH3^+ + OH^- I........0.223.............0.......0 C.........-x...............x.......x E.......0.223-x............x.......x But you know x = 9.7E-6. Evaluate 0.223-x and substitute into the Kb expressio...

chemistry
Please clarify the question. What is 5.75gmolecules?

chemistry
.........NH4HS(s) ==> NH3(g) + H2S(g) I........solid.........0........0 C........solid.........x........x E........solid.........x........x Kc = (NH3)(H2S) 1.8E-4 = x^2 x = 0.013M. Does this exhaust the 5.00 g NH4HS? 0.13 mols/L x 3L = 0.040 mols H2S and 0.040 mols NH3. How...

typo--Chemistry
Specific heat is 4.184 and not 4.194. I typed it right in the equation but wrong above that.

Chemistry
It would have helped if you had re-posted the question; however, I found it and here is the response I made. heat lost by pebble + heat gained by water = 0 heat lost by pebble = 532.1 J heat gained by water = mass H2O x specific heat H2O x (Tfinal-Tinitial) Set q = heat gained...

Science
I think this is nonsense but the answer probably is B. That's the only one of the four that doesn't have the same thing on the right that's on the left.

Chemistry
I expect the difference in #1 is that I didn't read anything on the calculator but kept everything in until the final answer.

Chemistry
I agree with #2. For #1 I obtained 1.1E-11

Chemistry
If you have used the screen name Sha in the last day or so I worked this problem earlier. I may be able to find it if you didn't.

Chemistry
You made a typo in th equation. It should be CH3NH2 + HOH ==> CH3NH3^+ + OH^- I obtained 2.9E-2 for OH^- but we may not have used the same Kb. I used 5E-4.

Chemistry
NH4^+ is the only one hydrolyzed. You know NO3^-, Cl^- and K^+ are not hydrolyzed BECAUSE those hydrolysis products would be STRONG acid/bases. For example, Cl^- + HOH ==> HCl + OH- or K^+ + HOH ==> KOH + H^+ and that doesn't happen. Why NH4^+? BECAUSE it forms a WEA...

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