Thursday
February 26, 2015

Posts by DrBob222


Total # Posts: 47,263

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

Science
I think your answer is right; the frequency changes as the fire truck goes by. However, I have a problem with the statement that the pitch changes from high to low as the fire truck passes by. As the fire truck comes toward you the frequency increases; after the fire truck ...
January 21, 2015

Science
right
January 21, 2015

Chemistry
This a two equation problem that you solve simultaneously. Here are the two equations. Let x = g CH4 and y = g C2H6 ---------------- equation 1 is x + y = 5.00 g You get the second equation by converting grams of CH4 to grams CO2 and grams C2H6 to grams CO2 and make the total ...
January 21, 2015

chem
3.80E25 H2O molecules x 2 = # H atoms in water molecules. 5.80E24 NH4 molecules x 4 = # H atoms in NH3 molecules. Sum is total H atoms in both sets of molecules.
January 21, 2015

Analytic chemistry
mols HgO = grams/molar mass = ? Using the cofficients in the balanced equation, convert mols HgO to mols OH^- then convert that to mols HClO4. Finally, M HClO4 = mols HClO4/L HClO4
January 21, 2015

Chemistry (Acid-Base)
This may not be the easiest way but it's what I would do. First, calculate (H^+), (butanoate), and (butanoic acid) in the 0.1 M solution at pH of 4.00. Then since I like to work in grams with these things I would convert the butanoic acid part into gram and for any number ...
January 21, 2015

AP Chemistry
No, your equation looks ok to me. I think what you need to do is to convert dG and dH from so many kJ/mol to so many kJ/4.88 g H2. To do that dG = -237.2 kJ/mol x (4.88 g/4*atomic mass H) = ? dH = -285.8 kJ/mol x (4.88 g H2/4*atomic mass H) = ? Then dG = dH - TdS You have dG ...
January 20, 2015

Chemistry
It depends upon the hydrolysis of the salt. For anions, such as CN^- in Ca(CN)2, the CN^- is hydrolyzed as follows: CN^- + HOH ==> HCN + OH^- so the solution is basic because it frees up OH^-. What about Ca^2+. It USUALLY is considered as not hydrolyzing. NaHPO4 is similar...
January 20, 2015

chemistry
You write two equations and solve them simultaneously. First equation is let x = mass NaCl and y = mass CaCl2 ---------------------- equation 1 is x + y = 12.42 The second equation you get by converting x and y to grams AgCl For NaCl(x) that is x(mm AgCl/mm NaCl) where mm is ...
January 20, 2015

AP Chemistry
Change feet to meters. Find volume in m^3. length x width x height = ? m^3 12.8 ug/m^3 x ? m^3 from above = total ug Be. Convert ug Be to g Be and convert that to mols Be. mols Be = grams Be/atomic mass Be. Then there are 6.022E23 atoms in 1 mol Be. Post your work if you get ...
January 20, 2015

Chemistry
This is a limiting reagent problem. There are other ways to do this but I like this method. Basically you work three stoichiometry problems. I will assume you will use P for phosphorus (and not P4) and P2O5 for the oxide (and not P4L10) You will need to adjust the equation if ...
January 20, 2015

AP Chemistry
..........CaF2 --> Ca^2+ + 2F^- I.........solid....0........0 C.........solid....x........2x E.........solid....x........2x The easy way to do this is to convert g/L to mols/L and go from there. mols/L = 0.0167/molar mass CaF2. Then Ksp = (Ca^2+)(F^-)^2 Ksp = (x)(2x)^2 = 4x...
January 20, 2015

AP Chemistry
Technically the CN- really is 0 initially and 2x + 0.065 at equilibrium. ......Ni(CN)2 ==> Ni^2+ + 2CN^- I.....solid........0.......0 C.....solid........x.......2x E.....solid........x.......2x Then ......KCN --> K^+ + CN^- I........0.065.....0......0 C.......-0.065....0...
January 20, 2015

Chemistry
mols NH3 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols NH3 to mols H2o Convert mols H2O to grams H2O at 100% yield. g H2O = mols H2O x molar mass H2O. Then g H2O @100%yield x 0.0611 = g H2O produced at 6.11% yield.
January 20, 2015

Chemistry
Answered above.
January 20, 2015

chemistry
28 days is 2 half lives. Start P-32 = 100% 1st half life = 1/2 that or 50% left 2nd half life = 1/2 that or 25% left.
January 20, 2015

Chemistry
Which salt?
January 20, 2015

chemistry
Please read your post and note how ridiculous it reads. The answer is that it produces zero mols NaHCO3. You start with NaHCO3. Let's suppose you asked instead to calculate the mols NaHCO3 NEEDED to react with 0.4 mols H2SO4. That's the old trick of using the ...
January 19, 2015

Earth Science
Which is why I wrote "all but b could be chosen"
January 19, 2015

Earth Science
I would chose softness as the answer for 3. All of the sites list color, luster, fracture, cleavage, hardness, streak,etc. Although we may think we know how soft a mineral is if we know the hardness, softness is not something that is measured. For #1 I agree that the answer ...
January 19, 2015

Chemistry
The easy way to do this is to work in g and A units. You know 0.5g sample x 0.240E-2 = 1.2E-3 g Cu. You know the ratio of A unit is 0.250 vs 0.6; therefore, 1.2E-3 g Cu x (.260/0.6) = ? g Cu in the unknown. To calculate molar absorptivity use A = ebc. Technically I don't ...
January 19, 2015

Chemistry
I have several issues with a). That's 1.694 mg CoSO4; when you convert that to 0.001694 that is now g/mL and not mg. Second where you have 1*10^-6 mol you threw away the other 3 places. The 1.695 is to four places and you should have 4 places in the answer. So 1.694E-3 g/...
January 19, 2015

Chemistry
Answered below twice and one time with much more information.
January 19, 2015

chemistry
mol fraction N2 = mol N2/total mols. and if you want mol fraction of the others it is XAr = mols Ar/total mols XO2 = mols O2/total mols.
January 19, 2015

chemistry
Didn't I do a similar one for you yesterday. Find total mols gase Find mole fraction (XN2) of N2. Then pN2 = XN2*Ptotal.
January 19, 2015

Chemistry
Yes to both. The weak acid and its salt (or the weak base and its salt) do not have to be the same concentration. It is best if they are because that gives you the best possible buffering capability but any reasonable values will work. Of course a VERY SMALL value for one of ...
January 19, 2015

Chemistry
I answered the similar question below. You want a weak acid and a salt of the weak acid OR a weak base and a salt of the weak base. I see no reason why this would not be a reasonably good buffer. Why don't you try it. I'll get you started. 100 mL x 0.1M HF = 10 mmols ...
January 19, 2015

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