Monday
October 20, 2014

Posts by DrBob222


Total # Posts: 44,571

chemistry
For mole fraction, X CsBr. mols CsBr = from the problem mols H2O from the problem = grams/molar mass Then X CsBr = mols CsBr/total mols. mass % CsBr is grams CsBr/100 g solution.
September 8, 2014

chemistry
m = mols solute/kg solvent You know m and kg solvent; solve for mols solute. Then mols solute = grams/molar mass You know mols solute and molar mass, solve for grams.
September 8, 2014

chemistry
mass % is grams solute/100 g solution. 12.8% w/w is 12.8g NH3/100 g solution. mass = density x volume. You know 100 g solution and density of the solution; solve for volume of the solution. Convert g NH3 to mols NH3. g/molar mass = mols. Then M = mols/L solution. m = mols ...
September 8, 2014

Biology Help
Enzymes speed up the rate of conversion from reactants to products by lowering the activation energy needed for the reaction to occur.
September 8, 2014

chemistry
There are 453.6 g in 1 lb and 1000 g in 1 kg. There are 12 inches in 1 foot There are 2.54 cm in an inch. There are 100 cm in a m.
September 7, 2014

Chemistry
volume of water = 58.5 mL volume cubes = 2.0 x 2.0 x 2.0 = 8 cc = 8 mL. new volume in BOTH graduated cylinders is 58.5 + 8 = ? No, I didn't err. Both Pb and Al have the same volume so the water levels will be the same when both are submerged.
September 7, 2014

Science
Usually that is applied to a statement when facts are enough to back up the explanation but it makes sense with the information we have. Then we stay that is a tentative explanation because in the future we may find we need to tweak the explanation.
September 7, 2014

science
A hypothesis becomes a theory if the experimental details fit. Then theories become laws with time (sometimes the theory must be tweaked to make it fit new data)
September 7, 2014

chemistry
Most of your questions are about conversions. What is your main problem with these? You need to learn how to do them yourself. If you will explain in detail perhaps we can set you on the right track.
September 7, 2014

chemistry
See your other post.
September 7, 2014

chemistry
1A = 1E-8 cm
September 7, 2014

Chemisty 132
Didn't I do this earlier? (or at least one just like it)
September 7, 2014

chemistry
E = hc/wavelength
September 7, 2014

chemistry
You don't need us to do this for you. Punch in the numbers and that's it.
September 7, 2014

Chemistry
232 amu x (1 g/6.022E23 amu) = ? For d there are 1E-8 cm = 1 A and 1E-9 nm = 1 m
September 7, 2014

chemistry
See your post above.
September 7, 2014

chemistry
volume = (2.04 cm)^3 density = mass/volume
September 7, 2014

questions- - -a level chemistry
1. Is the 0.78 atm the partial pressure to start or after equilibrium is established? 2. What's the new Kp (or Kc) at 350K? I suggest you repost the question at the top of the page and include the information in answer to the questions 1 and 2.
September 7, 2014

Chemistry
q1 = energy released on vapor cooling from 93 C to 78.3 C q1 = mass ethanol x specific heat ethanol vapor x (Tfinal - Tinitial) note: Tf is 78.3 and Ti is 93.0. q2 = energy released on changing from vapor at 78.3 to liquid at 78.3 q2 = mass ethanol x heat vaporization q3 = ...
September 7, 2014

Young Harris College
You do this in steps. q1 = energy needed to heat solid ice from -30 C to solid ice at 0 C. q1 = mass ice x specific heat ice x (Tfinal-Tinitial) where Tf is 0 and Ti is -30 C. q2 = heat needed to change the phase at zero C from solid ice to liquid water. q2 = mass ice x heat ...
September 7, 2014

Chemistry
$155 x (1 kWh/0.129) x (1 J/2.78E-7 kWh) = ?
September 7, 2014

chemistry
I would look at B as the incorrect one.
September 7, 2014

Chemisty 132
So this in steps. Within a phase the formula is q = mass x specific heat x (Tfinal-Tinitial). For example, to heat liquid H2O from zero C to 100 C use q = mass x specific heat x (100-0) = ? At a phase change (from ice to liquid at the melting point or from liquid to steam at ...
September 7, 2014

CHM
I have spent a lot of time looking for a site to which I could refer you to for this question but to no avail. So here is my best educated guess and the reasoning. I think volumetric pipets are #1 in accuracy. They require only one measurement reading (when the pipet is full...
September 7, 2014

Chemistry
mols CO2 = 0.0489. Using the coefficients in the balanced equation, convert mols CO2 to mols NaHCO3. Then convert g NaHCO3 to mols; as g = mols x molar mass
September 7, 2014

Chemistry
1.60M x (59.9/208) x [134/(134+111)] = ?
September 7, 2014

Physical Science
What's the density?
September 7, 2014

Chemistry- urgent!
You need to know the rules for significant figures. Here is a good site. Study it carefully. http://www.chemteam.info/SigFigs/SigFigs.html For 15: All multiplication and division. The s.f. rule is the final answer can have as many s.f. as the LOWEST number involved. All of ...
September 7, 2014

analytical chm
I don't know to which methods you refer. You weigh it once, heat, weigh again, and repeat until constant weight.
September 7, 2014

Chemistry (concentrations)
I think Mr. Pursley hit a 6 instead of a 5 and meant 2*12.6 = 25.2 ppt Cl^-.
September 7, 2014

chemistry
2KBr ==> 2K + Br2
September 7, 2014

Organic chemistry
I assume NaCl does not ionize when dissolved in glucose. mols NaCl = grams/molar mass. Subsittute and solv for mols NaCl. Then m = molality NaCl = mols/kg solvent Substitute mols from above and kg solvent is 0.200 kg, and solve for m. Then delta T = Kf*m You have Kf for ...
September 7, 2014

chemistry
I think I would look at B is the incorrect one.
September 7, 2014

chemistry
Is that an all gaseous reaction? If so change in volume will have no effect on the equilibrium.
September 7, 2014

chemistry
I really don't know how to answer this because the answers are confusing. A is not true for certain. B. The electron configuration is 1s2 2s2 2p4 and that 2p4 would make it a true statement; however, I don't think that is the answer wanted. Oxygen has 6 electrons in n...
September 6, 2014

Chemistry
We can't place bars over anything. #2 has no zeros but I guess you could rewrite it as 42ssss and all of the zeros (represented by s) are non-significant zeros. I would rewrite 1 as 8.04sE3 where s stands for the non-significant zero. #3 can be written as 0.00000470 or s....
September 6, 2014

chem help plz
Convert 125 km to miles. I get about 77.7 miles but you should confirm that. 77.7 mi/day x 7 days/week = about 544 miles but that's approx. You should redo all of the math before and after this sentence. 544 miles x (1 gal/22.0mi) approx 24.7 gallons. 24.7 gallons x (1 L/0...
September 6, 2014

Chemistry
Here are two good sites. The first one tells you how to do s.f. and the other is the definition of decimal place. http://www.chemteam.info/SigFigs/SigFigs.html https://www.google.com/search?q=what+is+a+decimal+place&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=...
September 6, 2014

ANALYTICAL CHM
Align the eye EXACTLY in line with the bottom of the meniscus (to avoid parallax) and read the bottom of the meniscus. I use my finger placed just below the meniscus on the outside of the buret so that my finger image is reflected off the bottom of the meniscus. That allows me...
September 6, 2014

ANALYTICAL CHM
http://chemed.chem.purdue.edu/genchem/lab/equipment/pipet/error.html http://chemed.chem.purdue.edu/genchem/lab/equipment/buret/error.html
September 6, 2014

CHEM 1A
This is a limiting reagent (LR) problem and I work these the long way and probably not at all like your prof does. But here goes. mols Ca = 6.87/atomic mass Ca = approx 0.171 which you have. mols O2 = 4.58/32 = approx 0.143 ( you used the atomic mass of O and not the molar ...
September 6, 2014

chemistry
For the impure Cu the rxn is Cu ==> Cu^2+ + 2e. anode At the pure Cu the rxn is Cu^2+ + 2e ==> Cu(s) cathode
September 6, 2014

chemistry
a. At the anode you have 2Cl^- ==> Cl2 + 2e. b. What do you think the Cl2 will react with?
September 6, 2014

Chemistry
It isn't right and your gut should tell you that. How can you have an acid solution with a pH greater than 7. Remember 7 is neutral so a pH of 7.70 means your acid solution is basic and that can't be. Where are you in chemistry? If it is not beginning chemistry there ...
September 6, 2014

Chemistry
Convert 1.25 lb Hg to grams. That's 1.25 lb Hg x (453.6 g/lb) = ? grams Hg. Then mass = volume x density. You know mass and volume, solve for density.
September 6, 2014

Chemistry
Pb(NO3)2 + 2HCl ==> PbCl2 + 2HNO3 mols Pb(NO3)2 = grams/molar mass = ? Then convert mols Pb(NO3)2 to mols PbCl2. That's a 1:1 conversion. Then mols PbCl2 x (6.02E23 molecules/mol) = ?
September 6, 2014

Chemistry
Because they are soluble in water.
September 6, 2014

Chemistry
Specific gravity of Pb is 11.34 but I didn't get that from the problem.
September 6, 2014

Chemistry
You will need the density of Au, then volume = mass/density Substitute mass from the problem and density you have to find volume. Then volume Au + 10.10 mL = new volume of the ethanol in the graduated cylinder.
September 6, 2014

Chemistry
volume of Au cube is 3 x 3 x 3 = 27 cc New volume reading for water level will be 27 + 5.75 = ?
September 6, 2014

chemistery
Surely, if you tell us what you don't understand about them. Most of us, however, aren't prepared to write a chapter or two or three.
September 6, 2014

thcs do can
CuCO3 + FeSO4 ==> FeCO3 + CuSO4
September 6, 2014

chemistry
I'm not familiar with the compound CaClF but my best educated guess is that it's an ionic compound and has no bond angle. Or did you just forget to write the compound in the question?
September 6, 2014

chemistry
You posted this same question yesterday. You need to expand the question a little. What topics? periodicity of columns, periodicity of rows, trends in boiling points, trends in melting points, trends in ionic/covalent behavior, etc,
September 6, 2014

Chemistry
kg N washed away is 1250 kg x 0.1 x 0.15 = ? kg. That x 1E6 is mg N. 0.165 ft^2/s = 4.7 L/s (by the way that's liter and not litter; it's a volume not a litter of puppies). concn = mg/4.7 for concn after 1 s but I'm unsure of the time involved. It seems to me that ...
September 6, 2014

oops==P.E
Here is the site. http://www.scienceprofonline.com/genetics/ten-human-genetic-traits-simple-inheritance.html
September 5, 2014

P.E
What does your book say? What do your notes say? Here a site for you to read.
September 5, 2014

P.E
I don't agree with you.
September 5, 2014

Chem
number of protons. Look at the atomic number. The atomic number is the number of protons in the nucleus of the atom. For example, Na will have 11. What about electrons. The number of electrons in the neutral atom is the same as the number of protons in the nucleus. Therefore, ...
September 5, 2014

chemistry
You must have meant PV/nR = T PV = nRT is that P = 36 atm or some other unit. is that V = 8.6L or some other unit? So n = PV/RT = 36*8.6/(0.08*200).
September 5, 2014

chemistry
I don't know how to write the lamda symbol;I will call it L. Then if hvL = mv2, then L = mv2/hv = mv/h
September 5, 2014

chemistry
74.0 g = mass dish+mass salt+mass water -52.5 g = mass dish + mass salt -----------------========== 21.5 g = mass water Note that if you subtract equation 2 from equation 1 the number is 21.5 g and the mass dish + mass salt cancel leaving mass water.
September 5, 2014

chemistry
Maybe forever because I don't know how you get the temperature to 156 C because all of the fluid would boil away at just over 100 C. But we'll not worry about that; I assume this is just a made up problem and the author of the problem didn't think about that. So ...
September 5, 2014

6th grade math
I don't understand the problem. 26, 17, 15, 6, -19, -20. Yes, -19 is a larger number than -20.
September 5, 2014

chemistry
You have the problem spelled out so well, why not just use d = m/v or v = m/d = 550 g/1.10 mL = ? mL.
September 5, 2014

CHEM 1A
On the right track but not quite right. You may have just mislabeled your numbers. 51,800 g O2 is what you want. mols O2 = 51,800/32 = 1618.7 MOLES O2 (not grams) needed. Convert that to mols KNO3 by multiplying by 4/5 = 1295 mols KNO3 and you have that labeled right. Then ...
September 5, 2014

chemistry
I would do this. pH = 5 means (H^+) - 1E-5 M. mols (H^+) in flask A = M x L = 1E-5*0.1 = 1E-6. So to make a pH = 7 we must exactly neutralize the acid to give pure H2O which has a pH of 7.00. So we need exactly 1E-6 mols OH^- in flask B and that in 100 mL (0.1L) is (OH^-) = 1E...
September 5, 2014

Chem
Your post is confusing? Are you calling buttermilk and butterfat the same? You drank 3L milk x 0.0236 = 0.0708 L buttermilk in that 3L. For the second part, grams = volume x density volume buttermilk you drank is 3L = 3000 mL and it is 2.36% buttermilk, then in 3L you drank ...
September 5, 2014

physical chemistry
I don't know what a concentration quotient is. What does it say in your text/notes? If you are talking about the formation constant for FeSCN, look through the experiment and note those areas where an measurement error may have occurred.
September 5, 2014

Chemistry
Doesn't this depend upon how these are broken down? H2O + CO2 <--> H2CO3 <-->H^+ + HCO3^- <--> H^+ + CO3^2- How many reactions is that? Is it one or three or six? Not a very good question in my mind; i.e., the question isn't very well defined. And we ...
September 5, 2014

Chemistry
I assume 872 nM is 872 nanomolar which would make it 872-9M or 8.72E-7M. The problem states that OH is ADDED UNTIL the OH^- is 8.72E-7M. Now, since (H^+)(OH^-) = 1E-14 Plug in OH and solve for H. I get 1.15E-8 M and convert that to pH.
September 5, 2014

Chemistry
No. What you have drawn is not an isomer of C2H2 for it doesn't have the formula of C2H2 but C4H8.
September 5, 2014

CHEM
A valence electron is an electron in the outside shell. Br has 7, S has 6, Na has 1. Look at the group of the periodic table in which the electron is found. That often tells you the number of valence electrons. I don't know how your are supposed to handle a "...
September 5, 2014

Analytical CHM
This site will provide information for you. http://fclass.vaniercollege.qc.ca/~direnzom/Laboratory%20Notes%20-%20Equipment.pdf
September 5, 2014

Analytical CHM
I don't know if this will help or not. http://avogadro.chem.iastate.edu/msds/i2.htm
September 5, 2014

pharmacy math
(15g/2000)*100 =
September 5, 2014

Chemistry
1 mol CO2 has a mass (molar mass) of 44 g. right? 1 mol CO2 contains 6.02E23 molecules. right? ergo
September 4, 2014

chemistry
(200 m/21 s) x (1 km/1000 m) x (60 s/min) x (60 min/hr) = ?
September 4, 2014

physical science
density = mass/volume Substitute and solve.
September 4, 2014

chemistry
What kind of percent? volume percent, mass percent, --- If you want volume percent, then %N2 = (volume N2/total volume)*100 = ?
September 4, 2014

chemistry
http://en.wikipedia.org/wiki/D%C3%B6bereiner%27s_triads
September 4, 2014

Chemistry
mols naphthalene = grams/molar mass = ? molality = m = mols naphthalene/kg solvent Then delta T = Kf*m and solve for delta T. Subtract from the normal freezing point to arrive at the new freezing point.
September 4, 2014

chem
volume = l x w x h Substitute and calculate volume Then density = mass/volume =?
September 4, 2014

Chemistry
density = mass/volume mass = 6.8 g volume = 9.30-7.1 = ? Round the answer to two significant figures.
September 4, 2014

Bio Chem
pH = pK2 + log (base)/(acid) 9.0 = 10.33 + log b/a solve for b/a which is equation 1 but b and a will be mols and no concentration. The second equation is a + b = 0.75L x 0.100M = ? mols Solve the two equations for b and a and convert mols to grams from mols = grams/molar mass
September 4, 2014

chemistry 101
I did this for you last night before I went to bed; what's the problem? When you keep getting the wrong answer the BEST thing you can do is to show your work. That way we aren't fumbling in the dark.
September 4, 2014

chemistry
topics? The elements are Be, Mg, Ca, sr, Ba, Ra
September 4, 2014

chemistry
no equation. no rate constant. no nothing here.
September 4, 2014

biology
That means that the system is not stagnant; i.e., all of the parts of the system are changing from one form to another but the overall percentages don't change with time. Let me give you an example in chemistry (since I'm a chemist). It's similar to equilibrium. In...
September 3, 2014

Chemistry
This is a redox equation. Fe^2+ probably is oxidized to Fe^3+. C2O4^- probably is reduced to CO2. H2O2 probably is reduced to H2O Here is everything you wanted to know about redox equations. http://www.chemteam.info/Redox/Redox.html
September 3, 2014

SCIENCE:BIOLOGY>
If you will copy your post and indicate your answer NEXT TO THE QUESTION, I shall be glad to check them. 1 is done this way. 6.5 hr/day for 5 day = 32.5 hrs There are 60 minutes in an hour There are 60 seconds in a minute. Put all of that together in the form of dimensional ...
September 3, 2014

chemistry
The "type" depends upon how you want it classified. It is a double replacement (some call it double displacement) reaction. It also is a precipitation reaction since BaSO4 is insoluble. The net ionic equation is Ba^2+(aq) + SO4^2-(aq) ==> BaSO4(s) The Na and NO3 ...
September 3, 2014

Chem Help Please!!!
We can't draw diagrams (graphs or equipment set up) on this forum but here is a site that goes into this in detail. This is only one of many; if you don't find something here go to Google and type in "separation toluene and cyclohexane by distillation" ...
September 3, 2014

chem
See my response below to another post. I found values for kcal per grams glucose of 3.35 to 3.8. I have always used 4 as an average. Using 4 kcal/g you have g glucose in 2700 mL at 4g/100 mL you have infused 4 x (2700/100) = ?g glucose. Then kcal = 4 or whatever your notes/...
September 3, 2014

chemistry
rate = k(NO)^2(Br)
September 3, 2014

chemistry
I have always used 4kcal/g carbohydrate. Probably that's an average and glucose may not be "average" but based on that the answer is 3 g x (2900/100) = g glucose infused = about 87g. Then 4 kcal/g glucose x 87g glucose = ? kcal I found on the web numbers from 3.3...
September 3, 2014

math
I agree
September 3, 2014

math
He meant to measure out 60 which would have left 40 in the graduated cylinder. But he left 45 there which is 5 mL more than intended. %error =(5/60)*100 = ?
September 3, 2014

Math. HELP!
$1(#hd) + $2(#ham) = $48
September 3, 2014

math
(ab)^3/[(3a)^2*b] a^3*b*3/(9a^2*b ab^2/9
September 3, 2014

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