Sunday
March 29, 2015

Posts by DrBob222


Total # Posts: 47,990

chemistry
mols urea = grams/molar mass = ? mols H2O = 100 g/molar mass = ? Total mols = nurea + nH2O mole fraction H2O = XH2O XH2O = nH2O/total mols psolution = XH2O*PoH2O
January 27, 2015

Chemistry
Use the coefficients in the balanced equation to convert anything to anything. 7.2 mol Fe x (3 mols O2/4 mols Fe) = 7.2*3/4 = ?
January 27, 2015

physics --chemistry
zero. Work is force x distance. d is zero, force x zero = zero.
January 27, 2015

chemistry 116
heat lost by Cu + heat gained by H2O 0 [mass Cu x specific heat Cu x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0 Substitute and solve for Tfinal
January 27, 2015

chemistry
If that is 58 J/C, the specific heat is 58/126 J/g*C.
January 27, 2015

college chemistry
The HNO3 and NaOH exactly neutralize each other to produce H2O. The remainder can be calcualted by the Henderson-Hasselbalch equation pH = pKa + log (base)/(acid) base is CH3COONa acid is CH3COOH pKa is 4.74
January 27, 2015

chemistry
For #2, use the HH equation and solve for the ratio base/acid
January 27, 2015

chemistry
This is a limiting reagent (LR) problem since amounts are given for BOTH reactants. AgNO3 + NaBr ==> AgBar + NaNO3 mols AgNO3 = M x L = ? mols NaBr = M x L = ? Convert mols AgNO3 to mols AgBr Convert mols NaBr to mols AgBr. It is likely the two values will not agree which ...
January 27, 2015

chemistry
1 mol ascorbic acid reacts with 1 mol I2 so the ratio is 1:1. mols ascorbic acid = grams/molar mass = ? mols I2 = mols ascorbic acid from the equation. M I2 = mols I2/L I2.
January 27, 2015

chem
4NH3 + 3O2 ==> 2N2 + 6H2O dHrxn = (n*dHf products) - (n*dHf reactants)
January 27, 2015

chemistry
See your other post.
January 27, 2015

chem
Yes, it's what I meant but 284 isn't the right answer if that is 284 J/min. Punch those numbers into the calculator again and remember the answer should be in kJ.
January 27, 2015

chem
Assuming the fluid is H2O and not ethylene glycol, then q in joules = mass H2O x specific heat H2O x (Tfinal-Tinitial) and I would substitute 17,000 g for mass H2O
January 27, 2015

chem
For #1 you didn't list the choices. 190 = 4.51 x Z x (315.7-21.3) and solve for Z. For #2, your numbers are ok but you have too many significant figures.
January 27, 2015

chem
I think so but you have too many significant figures. If your prof is picky about s.f. s/he will count off points.
January 27, 2015

chem
CH4 + 2O2 --> CO2 + 2H2O So you get 686 kJ for 13.7 g CH4. How much heat will you get for 1 mol (16 g)? Thats 686 kJ x 16/13.7 = ? kJ
January 27, 2015

Chemistry
The ice at zero is to melt and remain at zero. So the heat fusion must be enough to lower the liquid water from 45.0 to zero C. How much heat must be removed from the water. That's q = mass water x specific heat H2O x (Tfinal-Tinitial). That gives you q in J. Now convert ...
January 26, 2015

chem
A radius of 124 pm means a diameter of 248 pm and that is 2.48E-7 mm. So #atoms x (2.48E-7 mm/1 atom) = 1.75 mm Solve for # atoms.
January 26, 2015

Science
q = 146 cal = mass Pb x specific heat Pb x (Tfinal-Tinitial)
January 26, 2015

chemistry
q = mass H2O x specific heat H2O x (Tfinal-Tinitial)
January 26, 2015

chemistry
http://www.sciencebuddies.org/science-fair-projects/project_variables.shtml
January 26, 2015

Science
http://www.sciencebuddies.org/science-fair-projects/project_variables.shtml
January 26, 2015

Chemistry
It appears to me that you have calculate the mass of one molecule of Al(OH)3 or one formula unit. Some take that to mean the mass of 1 molecule. 1. Perhaps you want the mass of 1 mol which is about 78g. 2. Perhaps you have a problem with the number of significant figures in ...
January 26, 2015

chemistry
You have serious problems with your equation. I suspect while transcribing this from your homework paper to this site you read part from one line and part from another line. What you wrote will not occur. Did you mean Pb(NO3)2 + 2KI ==> PbI2 + 2KNO3
January 26, 2015

Chemistry
Look in your text/notes for this procedure. I can type it up, probably, if I want to spend 30 minutes typing. ;-). If you have some specific questions about the procedure I shall be happy to help. Basically you want to do this. 1. Calculate the approximate amount of H2SO4 you ...
January 26, 2015

science
You're right on.
January 26, 2015

science
C'mon. READ IT and you can be through with it.
January 26, 2015

science
Then you didn't bother to read the first two/three paragraphs. The answer jumps out at you.
January 26, 2015

science
http://en.wikipedia.org/wiki/Passive_transport
January 26, 2015

science
http://en.wikipedia.org/wiki/Passive_transport
January 26, 2015

Chemistry
It does. heat = q = mass x specific heat x (Tfinal-Tinitial)
January 26, 2015

Chemistry
120 x 4 is not 48. Correct that, then the sum will be different, too.
January 26, 2015

Chemistry
Looks ok to me.
January 26, 2015

chem
The most massive; i.e., the largest molecule.
January 26, 2015

chemistry
You want 800 ppm Na w/v which is 800 mg Na/L or 80 mg Na/100 mL. Convert 80 mg Na to ?mg Na2Cr2O7.2H2O That will be 80 mg x (molar mass Na2Cr2O7.2H2O/2Na) = ? mg Na2Cr2O7.2H2O to weigh out.
January 26, 2015

Science
%NaCl(w/w) = [36/(36+100)]*100 = ? %acetone(v/v) = [20/20+480)]*100 = ?
January 25, 2015

chem
mass = volume x density
January 25, 2015

chemistry
0.55 x 78 = ?
January 25, 2015

chemistry
The equation you have as d must be multiplied by 3. You've already added 1 d rxn as 44, add 2*44 more and you will have it.
January 25, 2015

Chemistry
Both are important but I would like to hear your thoughts instead of answering the question for you.I shall be happy to critique your thoughts.
January 25, 2015

chemistry
%K = (mass K/mass K2SO4)*100 = ? For masses use atomic and molar masses.
January 25, 2015

chemistry
density = mass/volume You have the mass metal given. Volume = 27.1-25.0 = ? That's because of the Law of Impenetrability which says that two objects can't occupy the same volume at the same time. So when the Pb was placed in the graduated cylinder the water level ROSE ...
January 25, 2015

chemistry
2Mg + O2 ==> 2MgO BUT air also contains N2 and at the elevated temperature of burning Mg it also combines with N2 as 3Mg + N2 ==> Mg3N2. So when you weigh the MgO you actually are weighing mostly MgO but with some Mg3N2. Since O2 and N2 don't weigh the same and since...
January 25, 2015

Science
Gavity? Friction?
January 24, 2015

chemistry 116
824 gallons x approx 3.8 L/gallon = approx 3000 L (but you need to use a better factor and not estimate as I've done. Then 3000 L has a mass of about 3000 g. q = mass H2O x heat vaporiation = ? Note: If you use 40.7 kJ/mol you must use mass H2O in mol(which means convert ...
January 24, 2015

chemistry 116
It helps us help you if you don't change screen names as in Alex and Daniel. 1.80% means 1.8 g/100 g solution. If the density of the solution is 1.0 g/mL, then that is 1.8 g/100 mL or 18g/1000 mL = 18 g/L. Convert 18 g to mols to convert to mols/L = M.
January 24, 2015

chemistry 116
Use PV = nRT and solve for n = mols Cl2. Then grams = mols x molar mass = ?
January 24, 2015

chemistry help
The complete freezing point depression method or the complete boiling point elevation method SHOULD include the van't Hoff factor which is the moles of particles in the solution. For molecular solids, the van't Hoff factor is 1, for ionic solids it is the number of ...
January 24, 2015

chemistry
That looks good to me.
January 24, 2015

chemistry 113
See your previous post. c = fw Substitute and solve for w. I assume the error interval is what you are allowed and still get credit for the answer. It must be a data base you are using to key in the answer.
January 24, 2015

chemistry 113
c = fw c = speed of light in m/s f = frequency w = wavelength in m. Substitute and solve for w in m and convert to nm.
January 24, 2015

chemistry 113
How many mols do you need? That's M x L = ? Convert mols to grams. g = mols x molar mass.
January 24, 2015

chemistry 113
Add the atomic masses of the atoms in FeCl2.4H2O. I don't know the connection to the error interval with this question but +/- 2 g/mol sounds large to me.
January 24, 2015

chemistry
5E6J = mass Fe x specific heat Fe x (Tfinal-Tinitial)
January 24, 2015

Science
I'm not a biochemistry and have never worked with dGo' but it appears to me from reading that dGo' = dGo + RTln[(H^+)/(H2O)] and since H^+ = 10^-7 and (H2O) = 55.5 you calculate that part of it and add to dGo to solve for dGo'.
January 24, 2015

chemistry
Either look up the heat combustion of ethene or go to the delta Hformation stables and look up CO2, H2O, and ethene. Then dHrxn = (n*dHformation products) - (n*dHformation reactants)
January 23, 2015

chemistry
This is another LR problem. Look at the last problem to see the process used. For mols of solutions, mols = M x L = ? while that of solids is mols = grams/molar mass. When you find the mass PbCl2 that is the theoretical yield. Then yield is % yield = (actual yield/theoretical ...
January 23, 2015

chemistry
I do these limiting reagent (LR) problems the long way. There are shorter ways to do them. 2Na + Br2 --> 2NaBr mols Na = grams/atomic mass = ? mols Br2 = grams/molar mass Using the coefficients in the balanced chemical equation, convert mols Na to mols NaBr. Do the same for...
January 23, 2015

chemistry
1 mol contains 6.2E23 so 2 mols contain ....., 3 mols contain ......, 4 mols contain ..... and 5 mols contain .....?
January 23, 2015

Chemistry
Generally as phosphate. You can ppt PO4^3- from an ammoniacal solution with Mg^2+ as MgNH4PO4. This is then fired in a furnace to form Mg2P2O7, magnesium pyrohosphate. That is the final weighing form. This is a typical gravimetric analysis.
January 23, 2015

chemistry
2-pentene
January 23, 2015

chemistry
How many mols do you have? That's M x L = mols KBr. Convert to grams. g = mols x molar mass
January 23, 2015

chemistry
Gas particles are in constant random motion. They impinge on the inner walls of the vessel; that force exerts pressure inside the vessel.
January 23, 2015

Chemistry
mols ZnI2 in final solution is mols ZnI2 = M x L = 0.50 x 12.0L = 6.0 mols. That also = mols in the 1.00 L taken for dilution to the 12.0 L. This 6.0 mols in the 1.00 L taken for dilution came from 2.5 L of the original; therefore, the original solution must have had 6.0 x 2.5...
January 23, 2015

chemistry
In the right concentrations they could be.
January 23, 2015

Chemistry
I remember that 1 ppm = 1 mg/L and since 1L has a mass of 1000g (at least for dilute solutions) that will be 1 mg/kg. You have 19.353g or 19353 mg/kg so you must have 19,353 ppm. You should be able to take it from here. Let's see if that checks out. ? ppm = (g solute/g ...
January 22, 2015

Science
I don't like the question. If the chemical composition remains the same then the question MUST be true. I would rather it be said as "In a physical change the chemical composition remains the same." The inclusion of all of that other stuff makes it confusing to ...
January 22, 2015

Science
right
January 22, 2015

Science
Right on both.
January 22, 2015

Chemistry
HCl + NaOH ==> NaCl + H2O mols NaOH = M x L = ? mols HCl = mols NaOH and you know that from the 1:1 ratio in the balanced equation. Then M HCl = mols HCl/L HCl.
January 22, 2015

Chemistry
See your other post.
January 22, 2015

Chemistry
.......H2C2O4(aq) ==> H^+ + HC2O4^- I.......285...........0......0 C.......-x............x......x E....0.285-x..........x......x Substitute the E line into the Ka1 expression for H2C2O4 and solve for (H^+), then pH = -log(H^+). I assume that the (H^+) is largely due to that...
January 22, 2015

science
It may be argues that degrees C work many times, especially when we are subtracting two temperatures, but degree K is the unit we usually use.
January 22, 2015

science
What's wrong with degrees C or degrees K?
January 22, 2015

Chemistry
HNO3 + NaOH ==> NaNO3 + H2O mols HNO3 = M x L = approx 0.0025 mols NaOH = M x L = approx 0.0035 excess NaOH available is approx 0.001mols M NaOH = mols/L = 0.001/0.045 = approx 0.02M You need to redo all of these calculations since I've estimated. Then poH = -log(OH^-) ...
January 22, 2015

Chemistry
See your other post.
January 22, 2015

chemistry
None of the answers are correct. There is no SO4^2- produced. By the way, you use the caps key for correct sentence structure which I applaud; do the same for correct chemical formula structure. It makes a difference. CO is carbon monoxide Co is cobalt co is the abbreviation ...
January 22, 2015

Science
The molecules in each beaker have lost kinetic energy (on average) and the average speed of the molecules is less than 25 or 40.
January 22, 2015

Chemistry
Use the Henderson-Hasselbalch equation. base is sodium acetate. acid is acetic acid.
January 22, 2015

Chemistry
mL x N x mew = grams tartaric acid. mew = milliequivalent weight of tartaric acid = molar mass/2 = ? grams from above is in 5.00 mL. Convert that to g/L.
January 22, 2015

Chemistry
HCl + NaOH ==> NaCl + H2O mols HCl = M x L = ? mols NaOH = mols HCl (from the coefficients--they are 1:1) Then M NaOH = mols NaOH/L NaOH. M = ?
January 22, 2015

Chemistry/Math
For #1 your digits are right but not the s.f. You are allowed only 2 places (because of the 1.5) so your answer should be 4.3E3 For #2, I think you keyed in 4.61E-3 instead of 4.61E3. The answer is 9.0377E6 and you are allowed 3 places so that should be rounded to 9.04E6.
January 22, 2015

physical science
0.40 s
January 21, 2015

Chem
Are these two monatomic gases? X + 2Y ==> XY2 doesn't work.Not 2 volumes XY2. Are these diatomic gases? X2 + 2Y2 ==> 2XY2 looks ok.
January 21, 2015

Chemistry
I posted earlier how to solve this problem (the b part). Show your work
January 21, 2015

. 8th grade math
Or use chemistry. 42 H2 x (1 mol N2/3 mol H2) = 42 x 1/3 = 14. Check the NH3 production. 42 H2 x (2 mol NH3/3 mol H2) = 42 x 2/3 = 28.
January 21, 2015

chemistry
Convert 1 gallon to L; i think that's 3.786 L but you should confirm that. 1.25 g/mL x 3,786 mL x 0.3830 = ? g H2SO4.
January 21, 2015

chemistry
If you take 1 mol of the mixture, g N2 = 0.4mol x 28 g/mol = ? g N2 g H2 = 0.6mol x 2 g/mol = ? g H2. density = total g/22.4 L = ? g/L.
January 21, 2015

chemistry
I don't know what you next motive is but I suggest this for your next move. And note that I've corrected your equation for the typos. C6H12 + 9O2 ==> 6CO2 + 6H2O First determine what the limiting regent is. mols cyclohexane = 32/84.2 = about 0.38 mols. mols O2 from ...
January 21, 2015

Chemistry
mass = volume x density
January 21, 2015

chemistry
See your post above. Same formula.
January 21, 2015

Chemistry (Re-post)
Calculate mols Co initially. Calculate mols EDTA in 50 mL of the EDTA solution. Subtract mols EDTA - mols Co which gives mols excess EDTA. Then M EDTA = mols/L. Substitute and solve L.
January 21, 2015

Chemistry
%N = (mass N/mass NH4NO3)*100 = ?
January 21, 2015

Chemistry
q1 = heat released in moving T of steam from 114.5 C to 100 C. q1 = mass steam x specific heat steam x (Tfinal-Tinitial) q2 = heat released by condensing steam at 100 C to liquid water at 100 C. q2 = mass steam x heat vaporization/condensation q3 = heat released by cooling ...
January 21, 2015

Science
Yes, false. If the net force is 0 N, the forces are balanced. The object would move it forces were not balanced.
January 21, 2015

chemistry
mols gas on left = 6 (for 1 mol propane) and 7 on the right. Vi then is 6 and Vf is 7 W = -p*delta V or -p(Vf-Vi)
January 21, 2015

Science
I don't agree with B. http://www.thenakedscientists.com/forum/index.php?topic=35188.0
January 21, 2015

Science
I agree
January 21, 2015

Science
I agree
January 21, 2015

Science
I understand that but I wanted to clear the air.
January 21, 2015

Pages: <<Prev | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | Next>>

Members