Thursday
April 24, 2014

Posts by DrBob222


Total # Posts: 41,906

Chemistry
You're STILL using 0.0821 for R and I distinctly remember saying when you use P in kPa R must be 8.314. To make things a little easier you could have changed to 0.946 L also. P actually is 56.66 but rounding to 56.7 should be ok. n = PV/RT n = 56.7*0.946/(8.314*308) n = ab...

Chemistry
The percentages just tell you how much Na2CO3 and NaHCO3 you start with. 1 x 0.62 =0.62g Na2CO3. 1 x 0.38 = 0.38g NaHCO3. I will estimate from here but you confirm and use better accuracy. It makes the fractions come out better. mols Na2CO3 = 0.62/106 = 0.00585 mols NaHCO3 = 0...

Chemistry
Your numbers don't look all that bad except you are using the wrong R. The value of 0.08206 is used with p in atm. When you use kPa R is 8.314. I would have used 0.946 for 1 qt to L (the easy way to do the conversion is to go to Google, type in "1.00 quart to" wi...

Chemistry
Why don't you show your work and let us find the error? You can play hide and seek with these problems all day long.

Chemistry
Knowing the formulas won't do much good if you don't know how to use them. It is important to use the right units. Looking at the last problem for which you posted your work, see if my correction helps you in the others. If post specific questions, show your work, and ...

Chemistry
Show your work. Probably you aren't following my instructions OR I goofed somewhere.

Chemistry
So do the steps.

Chemistry
Use it. Are you looking for a hand out? We try to help, we try not to do.

Chemistry
use it

Chemistry
630 mL = 0.630 L; right. 20 C is 20+273 = 293K; right. 0.75atm x 0.630L = n*0.08206*293 n = 0.0196 mols. I suspect you just punched in the wrong numbers or hit the wrong button somewhere on your calculator. Also you quit when you had n. Then n = grams/molar mass 0.0196 = g/32 ...

Chemistry
Show your work and let us find the error. A common error is not using kelvin for temperature. Also remember volume must be in L

Chemistry
n = grams/molar mass Then PV = nRT R in 0.08206 L.atm/mol.K gives P in atm atm x 760 = p in torr 1 atm = 14.7 psi

Chemistry
Use mols each gas in PV = nRT and solve for p. Then Ptotal = pN2 + pO2 + pHe

Chemistry
(P1/T1) = (P2/T2)

Chemistry
P1V1 = P2V2

Chemistry
Use PV = nRT and solve for n = number of mols gas. Then n = grams/molar mass and solve for grams.

Chemistry
A = log 1/T Use A1 = kc1. Substitute A1 and c1 and solve for k. Then A2 = kc2. Substitue A2 and k and solve for c2.

Chemistry
a. 2.00E-3 x (5.00/total volume) = ? b. 2.00E-3 x (4.03/total volume) = ?

Chemistry please help
Your question is somewhat lengthy and sorta runs in circles; however, I assume the question boils down to why are you using the average. I think the answer is this. You may use individual titrations, calculate EACH run for molarity (or whatever you're calculating) and afte...

chem
2000 lbs Hg x (453.6 g/lb) = ? grams Hg = approx 9.07E5 2HgO ==> 2Hg + O2 + 90.8 kJ/mol 90.8 kJ/mol x (9.07E5/2*molar mass HgO) = ?

Lab/Chemistry
See you post above under a different screen name. Don't screw things up by using different screen names.

chem
C5H12 + 8O2 ==> 5CO2 + 6H2O mols pentane = grams/molar mass Using the coefficients in the balanced equation, convert mols pentane to mols H2O Now convert mols H2O to grams. g = mols x molar mass.

Chem
One at a time. See Cr2S3. How did it get that formula? I use the "cross charge" method which means Cr must be 3 and S must be 2.i ignore the charge of + and -; I figure the cation will be + and the anion will be -. CrI3. Cr must be 3 and I must be 1. This method won&...

Chemistry
pH = pKa + log (In^-)/(HIn) Using pKa and pH of 4.00, you can solve for (In/HIn) Remember the ratio must be at least 10:1 to change color (or 1:10 depending upon how you look at it).

Chemistry
mols KOH = grams/molar mass M KOH = mols/L solution M (OH^-) = mols KOH since the KIOH is 100% ionized. pOH = -log(OH^-) Then pH + pOH = pKw = 14. You know pKw and pOH, solve for pH.

Chemistry
Look at your KOH problem.

Chemistry
Look at the KOH problem.

Chemistry
All of these problems are similar.

Chemistry
HNO3 is 100% ionized.

Chemistry
1 kg = 1000 g mols NaOH = 1000 g/molar mass = ? Then M = mols/L solution. Solve for L solution.

chemistry
I worked this for you yesterday. Go back and find the post.

Chemistry
delta T = Kf*m Substitute and solve for m m = mols solute/kg solvent Substitute and solve for mol solute. mols = grams/molar mass. You know grams and mols, solve for molar mass. Then (empirical molar mass)*x = approx molar mass. Solve for x and round to whole number.

chemistry
from what? If s/he produced it from shoe leather I would call it a phenomenal percent yield. If from 45 g Na2CO3 it is only 100% yield.

chemistry
mols KI = grams/molar mass Then M = mols/L solution.

Chemistry
(NaOH) = 0.190M x (1.90 mL/1500 mL) = ?

CHEM
I can't draw Lewis structures on this forum; I suggest you google Lewis structure xxx where xxx is the molecule and look at those diagrams. You can count the non-bonding electrons.

CHEM
Molecular means largely covalent. PCl3 covalent but LiBr ionic CCl4 covalent but KOH ionic NaH ionic and CaF2 ionic I don't think any of them are.

Chemistry 1150
heat lost by warm water + heat gained by cool water = 0 [mass warm water x specific heat water x (Tfinal-Tinitial)] + [mass cool H2O x specific heat H2O x (Tfinal-Tinitial)] = 0 Solve for Tfinal. Watch the units.

Science
heat lost by warm water + heat gained by cool water = 0 [mass warm water x specific heat water x (Tfinal-Tinitial)] + [mass cool H2O x specific heat H2O x (Tfinal-Tinitial)] = 0 Solve for Tfinal.

Chemistry
See your other post.

Chemistry
Yes, 0.206 mol HCl remaining is exactly right; however you went around the barn to work the problem. Here is an easier way. Let's say you've already determined that FeS is the limiting reagent. So 0.223 mols FeS x (2 mols HCl/1 mol FeS) = 0.446 mols HCl used. 0.652 mol...

chemistry
CH4 is not. CF4 is not CH3F is. All three molecules are tetrahedral shapes. The C-H bonds are slightly polar BUT the tetrahedral shape is symmetrical and the individual bond polarities cancel so the overall polarity is zero for the molecule. Same argument for CF4. However, for...

chemistry
I would have answered that k2o is unknown. I agree that K2O is potassium oxide.

chemistry
You must want the head of solidification which is the heat fusion. For H2O that is 80 cal/grams

Chem
Yes, CaF2 is calcium fluoride.

Chemistry
empirical formula mass = about 12 + 1 + 35.5 = 48.5 (CHCl)x = 290.8 x*48.5 = 290.8 x = approx 5.996 which we round to 6 so the formula is (CHCl)6 or C6H6Cl6

chemistry
g C = 2.20g CO2 x (atomic mass C/molar mass CO2) = about 0.6g g H = 0.4g H2O x (2 atomic mass H/molar mass H2O) = 0.044 g O = 1.00g - g C - g H Note: you need to redo all of this more accurately than I've done them. Convert to mols mols C = 0.6/12 = about 0.05 mols H = 0.0...

AP Chemistry
You could work out each one? right?

College Chemistry
And I have no intention of working this problem BUT I certainly can tell you where to start. You ALWAYS start by writing and balancing the equation. H2O2 + KMnO4 ==> a. You have density and grams KMnO4 solution, convert g to mL. b. You now have mL and molarity KMnO4, mols =...

Chemistry
mols NaOH = M x L = ? 1 mol NaOH = 2 mol ascorbic acid g ascorbic acid = mols x molar mass %asc = (g asc/mass sample)*100 = ?

Chemistry
See your post above.

Chemistry
First off, remember HI is a strong acid; i.e., it ionizes 100%. Therfore, (H^+) = (HI). mols HI = grams/molar mass M HI = mols HI/L solution (H^+) = (HI) pH = -log(H^+) 5 is done the same way since HNO3 is a strong acid also. I should point out it is stated incorrectly. The wa...

chem
How about 0.040 since the ratio is 1 mol HCl to 1 mol NaOH.

chemistry
..........PCl5 --> PCl3 + Cl2 E.........217.......13.2 13.2 Kp = pPCl3*pCl2/pPCl5. Substitute the E line into Kp expression and solve for Kp. Cl2 added. Total P = 217 + 13.2 + 13.2 = 243.4 New total P = 263 Cl2 added = 263-243.4= 19.6 torr New Cl2 = 19.6 + 13.2 = 32.8 torr ...

CHEMISTRY - SCIENCE
mols I2 = grams/molar mass Solve for mols I2. Use density to convert 130 mL propane to grams. m = mols solute/kg solvent

Chemistry
When a blank is used the spectrophotometer is made to read 100% with the blank inserted (you may make it read A = 0 which is the same as 100%T). So if you set the unit to read 100%T (0 Absorbance) with the blank, what will it read if you next insert a dilute Cr solution. We do...

Science
When a reaction occurs it is exothermic if heat is released and endothermic if heat is absorbed. What that means is that in exothermic reactions the reaction flask gets hot. For example, if you pour gasoline into a container and light it it burns giving off a flame and heat. F...

chem
[x/(x+314)]*100 = 42 Solve for x, then check it.

Chemistry
Count the electrons and look up the atomic number on the periodic table. But it's an excited atom not in the ground state.

Chemistry
Ca(OH)2 solid in H2O. Saturated solution. Ca(OH)2 + 2HCl ==> CaCl2 + H2O Ca(OH)2 suspension. Saturated solution. Add HCl. The New ionic rxn is 2OH^- + 2H^+ ==> 2H2O. H2O is very weak electrolyte. Rxn goes to completion forming H2O. That reduces the OH^- in solution forci...

chemistry
Jin? Abby? Use PV = nRT and calculate n to reduce the pressure to that indicated, then n = grams/molar mass. You know n and molar mass, solve for grams.

chemistry
Here is how you do it if you find that information. delta T = (39.9-normal f.p.) = Kf*m Substitute and solve for m = molality m = mols solute/kg solvent Substitute and solve for mols solute. mols solute = grams solute/molar mass solute. You know mols and grams, solve for molar...

chemistry
I don;t know what 81.2 kg/mol means for a Kf. I don't know the normal freezing point of biphenyl.

chemistry
Read your question and rephrase it to take care of the errors. You surely don't mean calculate mass. The mass is given. And you don't give the normal freezing point so we don't know delta T. And that 81.2 kg/mol? Kf is usually given in C/m.

chemistry
How many mols did yu start with? That's mols NH4NO3 = grams/molar mass Now convert mols NH4NO3 to mols H2O using the coefficients in the balanced equation. Do the same for mol O2 and the same for mols N2. Add mols to find total mols, then use PV = nRT to solve for pressure.

Chemisry
Atomic number = 16 from the periodic table. # p = 16. # e = 16 S^2- must have two more electrons. #p + #n = mass number. You know #p and mass number, calculate #n.

Chemistry
1s2 2s2 2p6 3s2 3p3 Count the electrons; that's the atomic numbr and you didn't need to write the electron configuration to do that. You can count from the problem. C. Count the p. D.total protons must = total electrons E. Can you find them?

Chemistry
2N^2 = ?

Chemistry 192
Ni is 1s2 2s2 2p6 3s2 3p6 3d8 4s2 Remove the 2 4s electrons to make the 2+ ion. Now you do Br. Write the neutral atom then add an electron to the outside shell.

chemistry
unk = 10/19.6 = approx 0.5 mL/min He = 10/5.05 = appxox 2 mL/min (2/0.5) = sqrt(M/4) Square both sides. (4/0.25) = M/4 Now solve for M.

chemistry
10.0 mL H2O2 x 1.01 g/mL x 0.03 = ? g O2. mols O2 = g/molar mass Then use PV = nRT to solve for volume O2 at the conditions listed.

chemistry
This is a limiting ragent problem. I know that because amounts are given for BOTH reactants. When dealing with gases and the T and P remain the same, one can take a short cut ans use volume directly as if volume = mols. It saves a little time. a. Calculate volume butane formed...

Chemistry
There may be better, faster. and easier ways to do this but this is a fast write up, too. I can't do flow diagrams on this forum so take what I write and turn it into a flow diagram. Add NaOH (but not a huge excess) to ppt Al, Fe and Ni. Ca is in the filtrate. To the ppt, ...

chemistry
I don't think so.

Science
A. Same results as what? B. Compare the density of two materials; i.e., Al and Au. Al is about 2.7 g/cc and Au is close to 20 g/cc. So th same mass of Al occupies much more space. Why. Because of the spaces between Au atoms are not th same as spaces between Al atoms. C. Some o...

Biochemstry
You don't make sense. base/acid would equal the same as what? base/acid you calculate from pH = pK2 + log (base/acid) and B/A = approx 0.8 and I did that for you which makes base = about 0.8*A You slipped some decimal points. 0.085/0.5L = 0.17 BUT you make sure that 0.085 ...

Biochemstry
KH2PO4 + KOH ==> K2HPO4 + H2O mols KH2PO4 = 11.7/136.08 = about 0.086 Therefore, base + acid = 0.086 (but you need to do it more accurately). 7.10 = 7.21 + log (base)/(acid) B/A = about 0.8 B+A = about 0.086 Solve the two equations simultaneously for B and A. That will give...

CHEMISTRY - SCIENCE
[x g solute/(x g solute + 314 g H2O)]*100 = 42 Solve for x

newton law science
f = ma You know f and you know m, solve for a.

chemistry
heat lost by Fe + heat gained by Au = 0 [mass Fe x specific heat Fe x (Tfinal-Tinitial)] + [mass Au x specific heat Au x (Tfinal-Tinitial)] = 0 Solve for Tfinal.

chem
Just use the dilution formula. mass1 x %1 = mass 2 x %2 Substitute and solve.

Chemistry
0.240g = mss Cu + S compound -0.192g = mass Cu --------------- 0.048 g = S added to the Cu %Cu = (mass Cu/mass total)*100 = ? Take a 100 g sample. mols Cu = grams/atomic mass Cu mols S = grams/atomic mass S Find the ratio of Cu to S with the smaller number being 1.00 Post you...

Science
No. I would go with a; however, it begs the question of "lower than what"? My assumption is lower than fresh water. The freezing point of salt water depends ONLY upon the number of dissolved particles (NaCl, MgCl2, etc.); i.e., how much other stuff is dissolved in it.

Science
If x is doubled it will be 2x. If the price is $4.00 doubling will be $8.00

Chemistry
CuO + H2 ==> Cu + H2O mols CuO = grams/molar mass Using the coefficients in the balanced equation, convert mols CuO to mols Cu. Then g Cu = mols Cu x atomic mass Cu.

Chemistry
You need to find the arrow key on your computer and use it. --> or ==> or >>>>. Using the coefficients in the balanced equation, convert mols each to mols Fe(OH)2. 3.70 mols Fe x (1 mol Fe(OH)2/1 mol Fe) = 3.70 mols Fe. 6.95 mol NiO(OH)2 x (1 mol Fe(OH)2/2 mo...

Chemistry
2KOH(aq)+H2SO4(aq)→K2SO4(aq)+2H2O(l) mols H2SO4 = M x L mols KOH = 2*mols H2SO4 M KOH = mols KOH/L KOH

Chemistry
My vote is with Damon. Ag^+ is silver ion. P^3- is the phosphide ion. For example, Mg3P2 is magnesium phosphide. Mg3N2 is magnesium nitride, etc.

Chemistry
What's a cold alkali? Alkalies are bases and as far as I know there is no difference between a cold one and a hot one other than the rate at which they react.

Chemisty
4Fe + 3O2 ==> 2Fe2O3 mols Fe2O3 = grams/molar mass Using the coefficients in the balanced equation, convert mols Fe2O3 to mols Fe in the equation. You want grams Fe? Convert mols Fe to g. g = mols Fe x atomic mass Fe. Note that the grams 6.52 O2 is not relevant.

Chemistry
5.00 g = initial mass -3.943 g after heating ------- 1.057 g = mass H2O driven off in heating mols H2O = 1.057/18 = about 0.0587 mols CuCl2 = 3.943/134.5 = about 0.0293 Find the ratio and round to whole numbers with the smaller number being 1.00 0.0293/0.0293 = 1.00 0.0587/0....

chemistry
PV/T = k = constant Volume of the tires are essentially constant although they can give a little. Friction between tires and pavement causes heat to be generated. If V is to stay essentially the same, then P must go up if T goes up in order keep k the same. The heavier the loa...

Chemistry
Zn(CN)2 ==> Zn^2+ + 2CN^- .....................+ .....................H^+ .....................v .....................v .....................HCN Note that the added H^+ form HCN with the anion and that forces the solubility equilibrium t the right which increases the solubi...

General Chem
How many mols do you want? That's M x L = ? Then mols = grams/molar mass You know mols and molar mass, solve for grams.

Chemistry
Yes because not all of the lines have the same intensity.

chemistry
See your other posts under other screen names.

chemistry
Show what you can do and explain where you stop and what yu don't understand. I can help you through but you need to get involved other than just posting questions.

chemistry
What do you think and why?

Chemistry
Sara? Jan? Whomever? The ones that ionize 100%.

careers in mathematics and physical sciences
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