Friday
August 29, 2014

Posts by DrBob222


Total # Posts: 43,390

science
http://www.education.com/science-fair/
August 19, 2014

to shohanur--science
I gave you the mechanism to answer this question in an earlier post but you had to figure it out. You need to learn to think instead of waiting for someone to give you the answer.
August 19, 2014

math
A = 100s B = 10s C = 1s A*B*C = 30 B+C = A C=3 Solve simultaneously.
August 19, 2014

Physical science
You know that one(1) mole of any gas at STP occupies 22.4L. So # mol x 22.4 L/mol = ? L
August 19, 2014

oops--typo--Science
That Fe should be F2. Sorry about that
August 19, 2014

Science
2 atoms N for every molecule N2. 1 mol occupies 22.4 dm^3; therefore, mols F2 = 50 dm^3 x (1 mol/22.4 dm^3) = ? # atoms = twice that. b.Which F2? I assume F-19 Calculate mols F2 as above. Then remember there are 19 nucleons in 1 molcule Fe. There are two F atoms/molecule so ...
August 19, 2014

Science
Frankly, I don't like any of the answers but I agree with Steve, D is the best choice of those listed. I would like to see at least a course or two in "boatsmanship".
August 19, 2014

science
density = mass/volume v = same mass steel is larger. What does that do to the density?
August 19, 2014

chemistry calculations
Note that the coefficients in this equation are a, b, and c, and those have a value of 1 in this instance.
August 19, 2014

Chemistry
Constant P? (V1/T1) = (V2/T2) Remember T must be in kelvin.
August 19, 2014

Chemistry
A = abc and we will call a*b = k, then A = kc You know A = 0.118 You know k is 19.4 Solve for c in mols/L
August 19, 2014

CHEMISTRY
I don't think H2SO4 and S2 will react. In any event, what you have is not balanced and I think the products you show can't be right. Do you have a question about this?
August 19, 2014

maths
4 x 35 cm = ? cm
August 19, 2014

4th grade math
100 + where she is now.
August 18, 2014

maths
Neither. But 2.300 megameters will do it. That's the same as 2.300E6 m.
August 18, 2014

maths
What are your choices? 2300 km = 2.300E3 km, 2.300E6 m, etc. or miles, light years,?
August 18, 2014

Cost
cost + 0.5*cost = 81.00 cost = ?
August 18, 2014

algebra
A = # adult tickets C = # child tickets ----------------- A+C = 2000 4A + 2C = 6400 Solve the two equations simultaneously for A and C.
August 18, 2014

chemistry
mols KCl = grams/molar mass M = mols KCl/1.30 dm^3
August 18, 2014

chemistry
You want to use the van't Hoff equation You can find it here. http://en.wikipedia.org/wiki/Van_%27t_Hoff_equation
August 18, 2014

chemistry
mol = M x L You know mols and M, solve for L.
August 18, 2014

chemistry
Although some of the HNO3 gives H2 gas most is reduced to NO. I have never heard of the "partial method" but my best guess is that it is the same as the half reaction method. Zn ==> Zn^2+ + 2e HNO3 +3e + 3H^+ ==> NO + 2H2O ------------------------ Multiply the ...
August 17, 2014

chemistry
total mols = M x L = ? grams = mols x molar mass = ? Then % = (grams/50)*100 = ?
August 17, 2014

Chemistry
You should type the problem from scratch. You also need to know the volume of the NaOH. Then mols NaOH = M x L = ? mols acid (if monoprotic) = mols NaOH Then M acid = mols acid/L acid.
August 17, 2014

incomplete--chemistry

August 17, 2014

chemistry
mols = grams/molar mass
August 15, 2014

chemistry
1. n = mols of gas = 1.12/22.4 = ? n = grams/molar mass. You have grams and n, solve for molar mass. Then vapor density = molar mass/molar mass H2 = molar mass/2.016 = ? 2. See #1.
August 15, 2014

chemistry
You need to determine k, the rate constant and I would do it this way. ln(No/N) = kt No = 10 N = 90 k = solve for this t = 5 days. Then knowing k, redo ln(No/N) = kt No = 100 N = Solve for this. k from above t = 20 days
August 15, 2014

Math
You can do it the hard way with 1+2+3+4+5+6+7+8+9+10+.........31 = ?
August 14, 2014

Math
let x = #motorcycles and y = # cars ----------------- x+y = 48 motors 2x + 4y = 136 tires Solve the two equations simultaneously for x and y
August 14, 2014

science
Perform a mixed melting point; i.e., mix the unknown with pure benzoic acid and determine the m.p. If the unknown is benzoic acid the mixed m.p. will be 122.5 +/- a little depending upon how pure the unknown sample and pure benzoic acid are. If the mixed m.p. is lowered ...
August 14, 2014

science (chemistry)
You mix in fibers from the filter paper with the sample.
August 14, 2014

chemistry
I assume this is in a closed container so that the H2 gas can be captured. 2Al(s) + 6HCl(aq) ==> 3H2(g) + 2AlCl3(aq) Kc = (H2)^3*(AlCl3)^2/(HCl)^6
August 14, 2014

physical chemistry
Set up an ICE chart with P = pressure NH3 initially. Total P at equilibrium is 10 atm. If it is 96% dissociated, then you lose 0.96P NH3, form 1/2 that for N2 and form 3/2 that for H2. ...........2NH3 ==> N2 + 3H2 I...........P......0......0 C........-0.96P...0.48P..1.44P E...
August 14, 2014

science help
See your post below.
August 13, 2014

science
I can help you with chemistry but biology is not my bag.
August 13, 2014

Chemistry
Read the volume on the graph at the equivalence point, take half that volume, look on the graph and find the pH at that 1/2 volume point, that will give you the pH at the half way point and that will be pKa. Convert to Ka. What you are doing is using the Henderson-Hasselbalch ...
August 13, 2014

Chemisty
Here is a good web site. http://www.elmhurst.edu/~chm/vchembook/213organicfcgp.html Here is the line you should focus on. Amide > Acid > Alcohol > Ketone ~ Aldehyde > Amine > Ester > Ether > Alkane
August 12, 2014

Chemistry
Post your work if you get stuck and we can help you through it.
August 12, 2014

maths
7 boxes x (d dollars/r boxes) = ?
August 11, 2014

maths
You can put 3 1/3rds in one row and you have 3 rows. 3*3 = ?
August 11, 2014

chemistry
2NaOH + H2SO4 --> Na2SO4 + 2H2O mols NaOH = mols x L = ? mols H2SO4 = 1/2 mols H2SO4 (look at the coefficients in the balanced equation). M H2SO4 = mols H2SO4/L H2SO4
August 11, 2014

chemistry
grams = mols x molar mass
August 11, 2014

chemistry
grams = mols x molar mass
August 11, 2014

College Chemistry II
This looks like a rather complete discussion. http://www.pwtag.org/researchdocs/Used%20Ref%20docs/52%20Carbondioxide%20in%20water%20equilibrium.pdf
August 10, 2014

chemistry
mols KI = grams/molar mass = ? Then M = mols/L solution
August 10, 2014

College Chemistry II
I think the trouble is two-fold. 1. I believe you are trying to calculate Ksp and not solubility or S. 2. You have not taken into account the increased solubility due to the acidity. Your equations look good. But notice the following. ..........ZnCO3 ==> Zn^2+ + CO3^2- and ...
August 10, 2014

chemistry
Here is the rule to follow. 1. Move the decimal to the immediate right of the first digit other than a zero. In this case that is 3.0 2. Add x 10. In this case that would make it 3.0 x 10 3. Count the number of places from the original placement of the decimal to the new ...
August 10, 2014

Chemistry
Thanks. The last answer is the one you want. When a gas is evolved in a closed system, the system eventually reaches equilibrium so the forward and the reverse reactions occur but the system as a whole does not change from the equilibrium point. When the system is open, the ...
August 8, 2014

Chemistry
What are you studying? The following answer assumes you are studying reasons for a reaction to go to completion. When one or more products are a gas the reaction is shifted to the right and it goes to completion. Reactions go to completion for one of three reasons: 1. A gas is...
August 8, 2014

Chemistry
I'm not sure where you're headed with this but I'm guessing that K for liquids where M is used for the concentration is no problem for you but if a gas is involved you don't know how to handle it. For example, in the reaction A(aq) + B(aq) ==> C(aq), Keq = (...
August 8, 2014

Chemistry 2
It looks ok to me but you don't need all of those intermediate numbers.
August 8, 2014

Chemistry
a. This isn't all inclusive but you would want the food all the mice ate to be the same, living conditions (temperature and humidity), exercise, etc. b. http://chemistry.about.com/od/chemistryterminology/a/What-Is-The-Difference-Between-Control-Group-And-Experimental-Group...
August 8, 2014

chemistry
If it took more alkali (28 mL vs 25 mL HNO3), then the acid was more concentrated than the alkali.
August 7, 2014

chemistry
If you performed this experiment why don't you know the color before and after?
August 7, 2014

Chemistry
This is a limiting reagent (LR) problem. 1a. Using the coefficients in the balanced equation, convert mols CH4 to mols of CO2. 1b. Do the same for mols O2 to mols CO2. 1c. It is likely that these two values for CO2 will not be the same; the correct value in LR problems is ...
August 7, 2014

Chemistry
I have interpreted the problem differently from Bob Pursley so my answers differ. First, the pure acid is what molarity? 1.42 x 1000 x 0.70 x (1/63) = 15.8M Then use c1v1 = c2v2 15.8M x 2 mL = 1M x v2 v2 = about 15.8 x 2/1 = about 31.6 mL = total volume v2 which means you add ...
August 7, 2014

Physical chemistry
I think the trouble you are having is knowing what vapor density is. vapor density = molar mass gas/molar mass H2. vapor density N2O4 = molar mass N2O4/molar mass H2 = 92.011/2.016 = 45.64 vapor density NO2 = molar mass NO2/molar mass H2 = 46.0055/2.016 = 22.82 The ratio is 2:...
August 7, 2014

Chemistry
I think you've made two errors in calculation. If I use 420 kPa and 0.5 L volume with T 800K I solve for n = PV/RT and I obtained your value x 10. Then if I use c = n/v that's n/0.5L = Your value divided by 1000. I think your data are good; I think your calculations ...
August 7, 2014

Chemistry
First, forget what I told you. You are titrating KH2PO4 with HCl. KH2PO4 + HCl --> H3PO4 + KCl You notice (which is what I didn't notice when I first read the problem) that 10 mL of 0.1M KH2PO4 is exactly neutralized (neutralized may be the wrong word) by 10 mL of 0.1M ...
August 7, 2014

Chemistry
Use the Henderson-Hasselbalch equation.
August 7, 2014

chemistry -repost
A couple of points. 1. Did you mean "occurs quickly, a flash of light creates an I2 concn ......? so that the rate law is rate = k(I)^2 for 2I ==> I2 2. I have been unable to use this to obtain 1.0E-6 but I have close to that. 3. I will look at it again if you will ...
August 6, 2014

Dance
high kickers hot kickers
August 5, 2014

Chemistry
PV = nRT Solve for n = number of mols, then n = grams/molar mass. You know n and grams, solve for molar mass.
August 5, 2014

Organic Chemistry
Is this to show your answer? I would agree with OH^- to H2O to H3O^+ but I don't know what H3O- is. And I don't understand part b.
August 4, 2014

Science(check answers)
I agree with 2 and 3 but I don't see questions 4,5,6.
August 4, 2014

chemistry
I am far from an organic chemist but I would think it would hydrolyze to form salicylic acid and acetic acid. I don't know if the SA would decompose after that or not.
August 4, 2014

Ochem
%v/v = (volume eugenol/total vol)*100 = 4.42 total volume = 30 mL; therefore, 0.0442 = (volume eugenol/30) volume eugenol = 0.0442*30 = ? but I would have done it in grams from the beginning and used density to convert to mL. (m eug/mH2O) = (peug*164/pH2O*18) (m eug/30) = (4*...
August 4, 2014

Chemistry
See below
August 4, 2014

Chemistry
See your post below.
August 4, 2014

Chemistry
You didn't give any volumes. First, determine the volume for the equivalence point. HN3 + KOH ==> KN3 + H2O mL HN3 x M HN3/mL KOH = mL KOH needed to reach the equivalence point. Then divide the titration into segments as follows: a at the beginning, c at the equivalence...
August 4, 2014

Chemistry
dS = nRT*ln(Vfinal/Vinitial)
August 4, 2014

Chem
P is 155/760 = ? if you are using R = 0.08205 and T is 273+339 = ? That gives you (NO)in mols/L and you plug that into the rate law to calculate [delta(NO)/delta T] and convert that back to mm Hg using P = MRT (remember you will get atm and atm x 760 = mm Hg)
August 4, 2014

Chem
Your post said you didn't know how to derive the formula. I did that for you. Do you have an answer for the problem? I assume so since this is a study guide.
August 4, 2014

Chem
Could this be as follows: PV = nRT with P in atm, V in L, n = mols and R and T usual.' P = n(RT)/V Since n/V = mols/L that is M so p = MRT.
August 4, 2014

chemistry
1.0 x 10^-7 WHAT?
August 4, 2014

Science (Physics)
I = E/R
August 3, 2014

Science
1/R = 1/R1 + 1/R2 + 1/R3 Plug any value into R and calculate it.
August 3, 2014

Physics
I = E/R
August 3, 2014

Physics
See your post above with the 3 ohm and 6 ohm R
August 3, 2014

chemistry
The corrected equation is as follows and I've balanced it as well: 2KNO3 + H2SO4 = K2SO4 + 2HNO3 mols H2SO4 needed = 2 mols KNO3 x (1 mol H2SO4/2 mol KNO3) = 2*1/2 = 1 mol H2SO4 needed. g H2SO4 = mols H2SO4 x molar mass H2SO4. b. 5 mols H2SO4 x (2 mol HNO3/1 mol H2SO4 = 5 ...
August 3, 2014

chemistry
For what reaction?
August 3, 2014

Chemistry
a. Na is the limiting reagent. You should verify that. mols Na = 5/23 = about 0.22 but that's an estimate. [386 kJ/(2*23g)] x 5 = kJ heat released. b. 5 g Na = about 0.22 mols Na and that will produce 0.22/2 = about 0.11 mols H2. Use PV = nRT to solve for V in L. If you ...
August 3, 2014

chem
OK. I will assume the Ksp for CaSO4 is about 1E-4. The values I can find on the web aren't quite that but it makes the problem a little easier. Since you can't find it in your tables, I assume the problem is saying that 1.00 g CaSO4 is soluble in 1 L solution. If that ...
August 3, 2014

chem
Right, however, look in the tables in your text (usually in the back in the appendix) and you will find Ksp (solubility products) listed. Those are the numbers I need. Why can't I look them up? I can but tables don't agree and I want to use the same numbers you must use.
August 3, 2014

chem
What Ksp values are you using for BaSO4 and CaSO4?
August 3, 2014

Chemistry
Not quite. If you use Kb for NH3 = 1.8E-5 then pKb = -log Kb = about 4.74 and since pKa + pKb = pKw = 14, then pKa = 14-4.74 = 9.26. Your tables may give a different value for Kb NH3 but most show 1.8E-5 or 1.75E-5
August 3, 2014

Chemistry
The base is NH3. The acid is NH4^+. a. With a strong acid it's the base that uses it; i.e., NH3 + H^+ ==> NH4^+ b. With a strong base it's the acid that uses it. NH4^+ + OH^- ==> NH3 + H2O c. So we start with 100 mL of the buffer. millimols NH3 = mL x M = 100 x ...
August 3, 2014

Chemistry
Jason, have you worked with the Henderson-Hasselbalch equation?
August 3, 2014

Chemistry
After you go through the equilibrium the second time you end up with M COCl2. You know M = mols/L. You know M from your calculation and you know L (10L) so mols = M x L = ? = n and use PV = nRT to solve for pressure. No, you don't go through the Kp thing because there is ...
August 3, 2014

Chemistry
You solve the equation. mols Cl2 = 2.60/71 = 0.0366 M Cl2 = mols/L = 0.0366/10 = 0.00366 M CO = 0.00366 Kc = (COCl2)/(CO)(Cl2) 1.23E3 = [(x)/(0.00366-x)^2] 1.23E3*(0.00366-x)^2 = x 1.23E3*(0.00366-x)(0.00366-x) = x and go from there. x = 0.0023 I believe although I've ...
August 3, 2014

Chemistry
These numbers are estimates so you need to go through and recalculate all of them. (Cl2) = mols/L = 2.60/71/10 = about 0.004M (CO) = 0.004 (actually closer to 0.00366). ..........CO + Cl2 ==> COCl1 I.....0.004..0.004.......0 C........-x.....-x.......x E.....0.004-x.0.004-x...
August 3, 2014

Chemistry
Reason it out. The ideal gas law is PV = nRT If you keep V, R and T constant, then P is proportional to n so larger n values will increase P.
August 2, 2014

Chemistry- practice question
qrxn is -8537.4 J q/gram = -8537.4/0.47 = ? q/mol = -8537.4/0.47g)*(24.3 g/mol) x (1 kJ/1000 J) = -441.4017 kJ/mol but if that 0.47 g Mg is correct you're allowed only two significant figures.
August 1, 2014

Chemistry
(P1V1/T1) = (P2V2/T2)
August 1, 2014

chemistry
mols compound = grams/molar mass = ? M = mols/L solution = mols/0.142 L = ?M. That x 1000 = mM.
August 1, 2014

science
mols CH4 = grams/molar mass = ? mols O2 = g/molar mass = ? mols SO2 = g/molar mass = ? total mols = mols CH4 + mols O2 + mols SO2 XCH4 = mols CH4/total mols pCH4 = XCH4*Ptotal
July 31, 2014

Chemistry
If you are satisfied that dG is ok, then set up the ICE chart. .......H2O ==> H^+ + OH^- I......1.0.....0......0 C......-p......p......p E......1.0-p...p......p Then Kp = pH^+ * pOH^-/pH2O and substitute the E line into Kp expression and solve for p. Then use p to calculate...
July 31, 2014

science
density = mass/volume
July 31, 2014

Chemistry / help
I really don't understand why you are having trouble with this? It appears to me the answer should be obvious to you. Tell me what you don't understand and we can go through it. But let me give you some food for thought. 1. Can you place a cube of ice (a solid) in a ...
July 31, 2014

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

Search
Members