Friday
October 24, 2014

Posts by DrBob222


Total # Posts: 44,711

chemistry
I may have missed something but I don't think this problem has been posted correctly. If I start with 20 mL CO and no mL CO2 it will form 20 mL CO2. If I start with no CO and 20 mL CO2 it will have 20 mL CO2 after the spark. I don't see how you can get less than 20 if ...
August 21, 2014

chemistry
40% w/w HCl means 40g HCl in 100 g solution. That is 40g HCl in (40g HCl + 60g H2O). mols HCl in 40 g = 40/about 36.5 = about 1.1 but you need a more accurate number. Then m = mols/kg solvent = 1.1mol/0.060kg solvent = ?m. I think you need density to determine the molarity but...
August 21, 2014

chemistry
? means I assume you can do what comes before the ? g = mols x molar mass. You want to know grams Co(NO3)2. You know mols Co(NO3)2. You can look up the molar mass Co(NO3)2. So to obtain grams (which you must do to solve the problem) you take mols (0.471) from above and ...
August 21, 2014

chemistry
0.471 m means 0.471 mols Co(NO3)2 in 1 kg solvent. How many g Co(NO3)2 is 0.471 mols? That's g = mols x molar mass = ? = approx 86 grams Co(NO3)2 Total mass of the solution then is approx 86 + 1000 = approx 1086g total. % = (g solute/total grams solution)*100 = ?
August 21, 2014

chemistry
Didn't you understand the NaOH answer? Wouldn't this be answered the same way.
August 21, 2014

Chemistry
1.50 g NaHCO3 in 17.1 g H2O. So in 100, there is 1.50 g NaHCO3 x (100/17.1) = approx 9 but you need to do it more accurately. % NaHCO3 = (g NaHCO3/total g)*100 = (9/109)*100 = ? %H2O = (gH2O/total g)*100 = (100/109)*100 = ?
August 21, 2014

chemistry
7.06% w/w NaOH means 7.06g NaOH in 100 g solution. So in 187 g there will be 7.06g NaOH x (187/100) = ? or if you want to do it by the factor method it is 187 g solution x (7.06g/100g) = ?
August 21, 2014

physical science
When each is acting on the same line in the same direction then the forces will add to be 5N + 7N = 12 N.
August 21, 2014

chemistry
I do limiting reagent problems the long way. There are shorter ways to work this problem but I think they are more difficult to explain. H2 + Cl2 ==> 2HCl mols H2 = grams/molar mass = 3.56/2 = 1.78 mols Cl2 = 8.94/71 = 0.126 Using the coefficients in the balanced equation, ...
August 21, 2014

science
We need more information. Are the resistors in series or parallel. How many resistors.
August 21, 2014

General Physical Science
volume in cc = 65 cm x 45 cm x 80 cm = ? Assuming the density of the water is 1.00 g/cc, then mass = volume x density There are 1000 g in 1 kg.
August 21, 2014

oops--physical science
That's 1024 km/11.5 = ? km/hr which works out to be about 55 mph. No speeding ticket today. :-)
August 21, 2014

chemistry
if heated produces iron (II) sulfide
August 21, 2014

chemistri
5.20% w/w means 5.20 g Cu(NO3)2 in 100 g solution. 1. Convert 5.20g to mols. mols = grams/molar mass. 2. Convert 100 g solution to mL using density. mass = volume x density or volume = mass/density = 100g/1.48 and convert mL to L. 3. Then M = mols from step 1/L from step 2
August 20, 2014

physical science
Half a lap is 25 meters. So the distance is 25 m. Where did s/he end up? 25 m from where s/he started. So the displacement is 25 m. I don't know the context of the problem but there could be a + or - sign for the displacement.
August 20, 2014

physical science
I agree
August 20, 2014

Chemistry
Dream big. Use PV = nRT You know P, V, R (0.08206) and T (use T in Kelvin = 273+c). Solve for n. Then mols = n = grams/molar mass. YOu know grams and mols, solve for molar mass and look it up on the periodic table. Post your work if you get stuck but explain what you don't...
August 20, 2014

Chemistry
I think you're allowed only 3 significant figures so I would round that to 108, Look through your problem and make sure no temperature was given. I must leave the house. Back in about an hour.
August 20, 2014

Chemistry
Good. Now use the coefficients in the balanced equation to convert mols O2 to mols C2H2. That is 38.38 mols O2 x (2 mols C2H2/5 mols O2) = 38.38 mols x 2/5 = about 15 but you can clean up the numbers. Now use the smaller tank and PV = nRT and solve for P. P = ? V = 3.50 L n = ...
August 20, 2014

Chemistry
I didn't work it for you but I gave you the three steps to solve it. It isn't easy to help if you don't tell me what you don't understand. Three steps. Copied from above. 1. PV = nRT for the 7 L tank for O2 @ 135 atm and solve for n. 2. Use the equation to ...
August 20, 2014

Chemistry
PV = nRT for the 7 L tank for O2 @ 135 atm and solve for n. Use the equation to convert mols O2 to mols C2H2. Use PV = nRT and n mols C2H2 and solve for P in the smaller tank.
August 20, 2014

MATHH#2
y = 2x+5 y = 3x ----------- Substitute 3x for y in equation 1. 3x = 2x+5 x=5 Then put x in equation 2 for y = 3x or 3*5 = 15
August 20, 2014

organic chemisrty
I looked the melting points up on the web. Assuming you meant cis-2-butENE and not cis-2-butane(I don't know what this is). I found 2-butyne to have the highest m.p. @ -32 C
August 20, 2014

organic chemisrty
What in the world is cis-2-butane?
August 20, 2014

biology
Did you see this? http://utahscience.oremjr.alpine.k12.ut.us/sciber00/7th/cells/sciber/levelorg.htm
August 19, 2014

chemistry
If the concd H2SO4 is 100%, then 1.84 g/mL x ?mL = 33.5g Solve for ?mL.
August 19, 2014

Quantitative reasoning
Let a = administrators Let f = faculty Let s = students ----------------- a + f + s = 26 5s = a s+5 = f solve for s,a,f.
August 19, 2014

math
(1/10) x 200 = 20 or 0.1 x 200 = 20
August 19, 2014

math
See your other post.
August 19, 2014

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

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

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