Monday
April 27, 2015

Posts by DrBob222


Total # Posts: 48,535

chemistry
2Li + 2H2O ==> 2LiOH + H2 mols LiOH = grams/molar mass = ? Look at the coefficients. It takes 2 mols H2O to produce 2 mols LiOH; therefore, mols H2O = mols LiOH
February 18, 2015

Chemistry
Example: CH4 + 2O2 ==> CO2 + 2H2O 16 + 64 = 44 + 36 What do you think? Are atoms conserved? That is, do you have the same number of atoms on each side? Is mass conserved? That is, do you have the same number of grams on each side?
February 18, 2015

chemistry
Probably none. I don't recall H3PO4 decomposing to form H2 gas.
February 18, 2015

science
Use the Henderson-Hasselbalch equation.
February 18, 2015

Organic Chemistry
You want the solubility expressed as g/mL. So 1.0g/300 mL = 0.333 g/100 mL. Right? And 1.0 g/17 mL is 1/17 = about 0.06 g/mL or approx 6 g/100 mL. Then Ko/a = approx 6/0.333 = about ? in which Ko/a is the partition coefficient of organic/aqueous.
February 17, 2015

chemistry
I answered your earlier post below.
February 17, 2015

chemistry
Anytime amounts are given for BOTH reactants you know it is a limiting reagent (LR) problem and the first thing you must do is determine the LR. mols (NH4)2CrO4 = M x L = ? mols Cr(NO3)3 = M x L = ? Using the coefficients in the balanced equation, convert mols EACH one into ...
February 17, 2015

Chemistry
I believe this is 3% w/w which means 3g H2O2/100 g solution. mols H2O2 = 3/molar mass H2O2 in 100 g solution. 2H2O2 ==> 2H2O + O2
February 17, 2015

AP Chemistry
I think 8.72 is the correct answer.
February 17, 2015

chemistry
different radii different charge on ions different volumes among others.
February 17, 2015

AP CHEM
mols Ba(OH)2 = M x L = ? mols OH in Ba(OH)2 = 2x that = ? mols Naoh = m x L = ? final (OH^-) = total (OH^-)/total L
February 17, 2015

chemistry
You would have done well to write the full question. I assume you are mixing 20.00 ml of a 50% saturated solution of BaCO3 (with the given Ksp) with 20.00 mL of 0.0100 M Na2CO3 although you don't say what the solutions are. Next, I understand the first sentence that you ...
February 17, 2015

chemistry
See your other post.
February 17, 2015

chemistry
mols H3PO4 ==> M x L = ? Use the coefficients in the balanced equation to convert mols H3PO4 to mols Ba(OH)2. Now M Ba(OH)2 = mols Ba(OH)2/L Ba(OH)2. You know mols and M, calculate L.
February 17, 2015

chemistry
2LiOH + H2SO4 ==> Li2SO4 + 2H2O mols LiOH = M x L = ? Using the coefficients to convert mols LiOH to mols H2SO4. Now M H2SO4 = mols H2SO4/L H2SO4
February 17, 2015

science
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/grnhse.html
February 17, 2015

PNU
I would convert 288 pm to cm, then cube that to obtain the volume in cc. Next, mass = volume x density = ? Next, (atoms/unit cell)x molar mass/6.02E23 = mass from previous step. Solve for molar mass. Then mols = 208g/molar mass 1 mol contains 6.02E23 atoms; how many atoms in ...
February 17, 2015

Chemistry and physics
I think it is two fold. First the Fe filings are heated to an incandescent point, then the combination of Fe and S to produce Fes is an exothermic reaction and that produces the red orange glow with Fe until the all of the reaction has taken place.
February 17, 2015

Chemistry
You haven't worded the question very well; I assume that 6.843 g/mL is the density. Therefore, you have the density and volume and you want to calculate the mass. mass = volume x density You have volume and density, substitute and calculate mass.
February 17, 2015

science
mols HCl = M x L = ? mols HNO3 = M x L = ? M final = total mols/total L (H^+) = final M pH = -log(H^+) (H^+)(OH^-) = Kw = 1E-14
February 17, 2015

Chem
You did an experiment? What did you observe.What pairs of ions did you use?
February 17, 2015

chemistry
Convert 0.88 g CO2 to CaCO3. That's 0.88 x (molar mass CaCO3/molar mass CO2) = ?g CaCO3 Then % CaCO3 in sample = (?g CaCO3/mass sample)*100 = ?
February 17, 2015

chemistry
Intermolecular forces, primarily dispersion forces and induced dipole-induced dipole forces increase as the atomic mass and size increases.
February 16, 2015

Chemistry
Suppose we (you and I) are making hamburgers. You're cooking the meat and I'm toasting the buns. I can toast buns at the rate of 1 whole buns/min. You can cook a pattie in 10 minutes. What determines the number of hamburgers we can make in an hour. You of course. You ...
February 16, 2015

chemistry
heat to water = q = mass H2O x specific heat H2O x (Tfinal-Tinitial). You don't know q or Tfinal. But you can calculate q this way, then solve for Tfinal. The problem tells you that burning 1 mol carbon to produce CO2 gas gives 393.5 kJ of heat. How many mols do you have? ...
February 16, 2015

chemistry - dilution factor
I don't think so and that's one reason I don't use the factor. I'm never sure we're all on the same page with dilution factor. If the graph you are reading from gives you the concn in the SAMPLE BEING MEASURED, then you KNOW that the concn in the undiluted ...
February 16, 2015

chemistry - dilution factor
Yes, the dilution factor is 4 in 5 or 0.8. Frankly, I don't use the factor as such but read the quantity from the graph of A vs conc, which gives you the concn in the diluted sample. Then concn in diluted sample x 5/4 = concn in original sample
February 16, 2015

chemistry
Yes and if that's all the question wants you're ok. However, most questions like this want kJ/mol or kJ/gram (in this case mol or g of NaOH).
February 16, 2015

Chemistry
Noble gases are non-metals; however, astatine is not a noble gas. It is a halogen. Most articles I have read emphasize that there is some evidence for it to be a metal, some as a non-metal, and some as a metalloid. Most also emphasize that with such limited data we can only ...
February 16, 2015

Chemistry
You're right but I don't quite understand why you ask such a question. Halogens are non-metals (all of them are non-metals) Non-metals must be non-metals (or they wouldn't be called that).
February 16, 2015

science
d = rt or r = d/t speed one way = 5000/15.5 = ? speed other way = 5000/14.5 = ? average speeds and round to three significant figures. I get 333.7 which I would round to 334 m/s. 344.83 = sound with wind -322.58 = sound against wind 22.25 = 2w wind = 22.25/2 = 11.1 m/s
February 16, 2015

chemistry
mass H2O = last weighing - first weighing volume = 60 mL density = mass/volume
February 16, 2015

Science
c = f*w So as f goes up, w goes down. Yes, c is the correct answer.
February 16, 2015

Science
right again.
February 16, 2015

Science
Mrs. Sue and Ms. Sue are not the same person according to their IP addresses.
February 16, 2015

chemistry
mols C = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols C to mols CH4. ?C x (1 mol CH4/2 mols C) = ? mols CH4. Convert mols CH4 to grams by g = mols CH4 x molar mass CH4 = ? g CH4. This is for 100% yield. But you will get only 83.0% of that ...
February 16, 2015

Chemistry
Use the coefficients in the balanced equation to convert anything to anything. 17.7 g H2O x (1 mol C3H8/4 mols H2O) = 17.7 x 1/4 = ? mols C3H8. Then g propane = mols propane x molar mass propane.
February 16, 2015

I am so lost
delta T = Kf*m Substitute delta T (6.60-3.98), Kf (20.00) and solve for m = molality m = mols/kg solvent. You know m and kg solvent (0.005818); solve for mols mols = grams/molar mass. You know mols and grams, solve for molar mass.
February 16, 2015

science
You need to clean up your post. Does she drop the stone or throw the stone.
February 16, 2015

Chemistry
Is that 3% w/w or 3% w/v. I will assume 3% w/v 3% w/v means 3g KCl in 100 mL solution. You want 1500 so 3 x 1500/100 = 45 g and you're right.
February 16, 2015

chemistry
pi = MRT Substitute and solve for M = molarity Then M = mols/L. You know M and L, solve for mols Then mols = grams/molar mass. You know grams and mols, solve for molar mass
February 16, 2015

I am so lost
See your post above.
February 16, 2015

Chemistry
The way I read the problem it is a hydrolysis problem. NH4^+ + H2O ==> NH3 + H3O^+ and you want the NH3 (ammonia, not ammonium) to be 5 ppm. Note that 5 ppm is 5E-3g/L and convert to mol/L and work the problem to see M NH4Cl. Then convert that to g NH4Cl in 300 gallons. The...
February 16, 2015

chemistry
http://www.jiskha.com/index.cgi?
February 16, 2015

chemistry
Ptotal = pCO2 + pH2O Ptotal is what you want. You know pCO2 is 740. Look in your text/notes and find the vapor pressure of H2O at 25 c. That is the pH2O. Calculate Ptotal.
February 15, 2015

chemistry
...........Sr(OH)2 --> Sr^2+ + 2OH^- I..........solid........0........0 C..........solid........x........2x E..........solid........x........2x Substitute the E line into the Ksp expression and solve for x = (OH^-), then convert that to pOH then to pH.
February 15, 2015

Chemistry
And what's that got to do with Kc?
February 15, 2015

chemistry
mols HNO3 = grams/molar mass M HNO3 = mols HNO3/L solution pH = -log(HNO3)
February 15, 2015

Chemistry
I assume you are talking about fractional distillation. The higher boiling materials have higher molar masses.
February 15, 2015

Chemistry
You don't have the information here. It must be is another part of your experiment.
February 15, 2015

chemistry
k = 0.693/t1/2 Then ln(No/N) = kt No = 100 N = 10 k from above. Solve for t in days.
February 15, 2015

chemistry
So use the Arrhenius equation and calculate it.
February 14, 2015

chemistry
100/2^n = 3.50 Solve for n = number of half lives. half life = 15.0 days/n = ? k = 0.693/t1/2
February 14, 2015

chemistry
1/2^10 = ?
February 14, 2015

Chemistry
1.0326g CaCO3 x (molar mass Na2CO3/molar mass CaCO3) = grams Na2CO3. % purity = (grams Na2CO3/mass sample)*100 = ?
February 14, 2015

Chemistry
I'm skeptical that this reaction produces elemental Cu.
February 14, 2015

chemistry
dE = q+w so if w is zero dE = q. Which of those reactions produces the least work. Hint: Which reactions have a gas produced; which does not? A gas does work against the atmosphere when expanding.
February 14, 2015

chemistry
k = 0.693/t1/2
February 14, 2015

chemistry
I don't see any way to calculate concentration. You have grams and you can get mols, but mols/L = ? rate = d(C2H2)/time.
February 14, 2015

chemistry
mass = volume x density. mass = 786 mL x 1.028 g/mL = ? Round to 3 s.f.
February 14, 2015

chemistry
My guess is that this is a problem to test your ability to report ONLY the right number of significant figures. density = mass/volume. Calculate the answer then round to two s.f.
February 14, 2015

chemistry
I can't decipher the question.
February 14, 2015

Chen UNi
You can't balance this. No S on the right.
February 14, 2015

chem uni
Al2???
February 14, 2015

PLEASE CHEM
Ag^+ + e ==> Ag H2O+ NO2^- ==> NO3^- + 2e + 2H^+ Multiply equation 1 by 2 and equation 2 by 1 then add the two for the complete equation.
February 14, 2015

Chemistry
Look before you leap. I worked this an hour or more ago.
February 13, 2015

chemistry
MgF2 ===> Mg + F2 ..........1.66..2.56 ..........1.29....x (1.66/1.29) = (2.56/x) Solve for x and convert to grams.
February 13, 2015

Chemistry
Use (P1/T1) = (P2/T2). You assumed that doubling the T would double the P. It works that way but you must use the right T. You may not use T in C; convert to kelvin. K = 273 + C
February 13, 2015

Chemistry
1.20 x (75.0/248) x [124/(124+111)] = ?
February 13, 2015

Chemistry
#3 fits best for the answer to 3.
February 13, 2015

Chemistry
I notice #1 and #2 are the same question. I remember them being diffferent when I answered this last night. I assumed a wavelength of 590 nm and with that assumption #2 is worked right and the answer is right. Some of those numbers you used in #1 are not in the problem. I ...
February 13, 2015

Chemistry
What's the wavelength for #1 and 2?
February 13, 2015

Science
Close and good reasoning; the flaw is that the principle quantum number (n = 1,2,3,etc) is the same for any one row and although the orbitals within the n level do have different energies, the main reason is #4. I think the "clue" in #5 is the word "primary"...
February 13, 2015

chemistry
What do you need help with. These conversion factors are all over the web.
February 13, 2015

chemistry
See your post above.
February 13, 2015

Chemistry
molar mass CH3OH = 32 molar mass ethanol = 46 molar mass isopropanol = 60 longer chains, more complicated molecules, high intermolecular forces. I would expect enthalpy vap to follow the same trend.
February 13, 2015

Chemistry
Use the Clausius-Clapeyron equation. You know dHvap. Use P1 = 101.325 with T1 = unknown normal boiling point. P2 and T2 I assume are in the data/plot.
February 13, 2015

Science
1.Infrared radiation has wavelengths ranging from about 800 nm to 1 mm. What is the frequency of radiation of wavelength 970 nm? Answer in units of s−1 Convert nm to m and use c = f*w. c is speed of light in m/s, solve for f(requency) and substitute for w(avelength).<...
February 12, 2015

science
400/170 = 2.35 so he weighed 2.35 times more on Jupitor. The alien, must hve weighed 2.35 times less on earth.
February 12, 2015

AP Chemistry
ok, on the assumption that the + H really means endothermic then PCl5(g) + heat ==> PCl3(g) + Cl2(g) All of your answers are correct IF the system is endothermic.
February 12, 2015

AP Chemistry
I didn't look at #1 because I'm not sure what it says, particularly the Ho part. Ho to me means standard conditions for thermodynamics heat formation tables and those tables are for 25C or 298K. This reaction is at 500 C which doesn't agree with my understanding of...
February 12, 2015

AP Chemistry
In somewhat unorthodox language Le Chatelier's Principle says that a system in equilibrium tries to undo what we do to it. For #2 write it has follows: PCl5(g) ==> PCl3(g) + Cl2(g) + heat 1. If we add heat the reaction shifts so as to use up heat. Since moving to the ...
February 12, 2015

AP Chemistry
Thanks for showing your work. It helps us spot the problem. The set up for Kc is correct but the answer is not. I get something like 3.317E-2 (and I know that's too many significant figures) for Kc. My best quickest guess is that you're punching in x instead of divide ...
February 12, 2015

chemistry
mols p-a = grams/molar mass mols aceta = mols p-a g aceta = mols aceta x molar mass aceta That is the theoretical yield.
February 12, 2015

chemistry
I would think too much water would cause too much solubility loss of the product.
February 12, 2015

Chemistry
S is an element. Fe is an element. When they react both change completely because a chemical reaction has taken place and a compound has been formed. The product has none of the physical properties (all are solid of course) or chemical properties.
February 12, 2015

chem
This is a limiting reagent (LR) problem and you know that because amounts are given for BOTH reactants. CaCO2 + 2HCl ==> H2O + CO2 + CaCl2 mols CaCO3 = grams/molar mass mols HCl = grams/molar mass Using the coefficients in the balanced equation, convert mols CaCO3 to mols ...
February 12, 2015

chemistry
small negatively charged
February 12, 2015

chemistry
Do you have choices? It sounds that you do from the "the two experiments"....
February 12, 2015

Chemistry
Post your work if you get stuck.
February 12, 2015

Chemistry
Use the Arrhenius equation.
February 12, 2015

chemistry
Do you mean the expressions for Kc and Kp. Without numbers, there is no way to calculate the value of either. 2SO2(g) + O2(g) ↔ 2SO3(g) Kc = (SO3)^2/(SO2)^2(O2) Kp = p^2SO3/p^2SO2*pO2 2NH3(g) + H2SO4(l) ↔ (NH4)2SO4(s) S(s) + H2SO3(aq) ↔ H2S2O3(aq) Same ...
February 12, 2015

geluksdal secondary school
# protons = atomic number--that whole number usually in bold black print on the periodic table. # protons + # neutrons = mass number--that isn't on the periodic table but usually is in the problem. #p + #n = mass # and rearrange to For example, 17Cl35 is chlorine with 17 ...
February 12, 2015

chemistry
Set up an ICE chart. .........HCOOH + H2O --> H3O^+ + HCOO^- I.......0.424.............0........0 C........-x...............x........x E.....0.424-x.............x........x Substitute the E line into the Ka expression for HCOOH and solve for x = (H3O^+), then convert that to...
February 12, 2015

Chemistry
If the density of the object is less than that of water it will float; if the density of the object is greater than that of water it will sink.
February 12, 2015

Chemistry 2
And you know what about this? The definitions are % w/w = grams/100 g solution m = mols/kg solvent M = mols/L solution X = mols solute/total mols.
February 12, 2015

Chemistry
a) dGorxn = -RTlnK Solve for K. Remember dG is in Joules, R is 8.314, T in kelvin. b) If you mean dG, then go with the below. dG = dGo + RTlnQ
February 12, 2015

Chemistry
You don't have units on all of the numbers.
February 11, 2015

CHEMISTRY
150 Cal = 150 food calories. Sugar has 4 food Cal/g. 150 Cal/4 = about 35 or so g sugar
February 11, 2015

chem
mols AlCl3 = M x L = ? mols Cl^- = 3x that There are 6.02E23 Cl^- in 1 mol Cl^-.
February 11, 2015

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