Sunday
May 24, 2015

Posts by DrBob222


Total # Posts: 49,010

Chemistry
grams = mols x molar mass.
March 12, 2015

Chemistry
Convert to mols. mols = grams/molar mass. Then find the ratio of the mols to each other with the smallest number being 1.00. The easy way to do that is to divide the smaller mols by itself and divide the other number by the same small number. Round to the nearest whole number ...
March 12, 2015

Chemistry
USUALLY we call the larger quantity the solvent and the smaller quantity the solute. Also if it's a solid and a liquid we usually call the solid the solute and the liquid the solvent. I would call the methanol the solute and water the solvent. The solution is the methanol ...
March 11, 2015

WHY CANT I POST URL'S?
I see someone should give you a lesson in reasoning. You're assumption is that all of us work at some college. 99% are retired teachers who do this volunteer work for the fun of it and because we want to help students who want help. Good luck to you.
March 11, 2015

WHY CANT I POST URL'S?
I don't believe the answer by Smartie will get it. Writeacher and I gave you the straight scoop.
March 11, 2015

WHY CANT I POST URL'S?
The webmaster gives that ability to those tutors who have passed the test of time with many many right answers and no wrong answers. You're probably new to this site so you don't have that benefit. If you want to keep posting answers and you do a VERY good job (and you...
March 11, 2015

chemistry
It takes 80 calories to melt a grams of ice. Therefore, 5400 cal = mass ice x 80 Solve for mass ice.
March 11, 2015

chemistry
The volume of solid H2O (ice) is higher than the volume of the liquid. Applying pressure will cause the reaction shown to shift to the side that occupies the lower volume. That is the liquid side so the solid melts.
March 11, 2015

Chemistry
........H2O ==> H^+ + OH^- I.......liquid..0......0 C.......liquid..x......x E.......liquid..x......x Substitute the E line into Kw for H2O and solve for x = (H^+) then convert to pH.
March 11, 2015

chemistry
I agree with all of this.
March 11, 2015

chemistry
I disagree with part of the statement but not all of it. It is exactly true that NaCl dissociates into two particles and CaCl2 into three; THEREFORE, it WOULD be more effective to use CaCl2 for the melting of ice. The fact that it raises the boiling point more, which is true, ...
March 11, 2015

chemistry
You need more info than that.
March 11, 2015

CHEMISTRY HELPPPP!!!!!!!!!
a. The one with the lowest Ea. b. k = -Ea/RT. Do that for uncatalyzed. Do that for W surface. Compare the k values.
March 11, 2015

Chemistry 2
Why not show your work for the ICE table and let us see what you need to do. Otherwise we're just guessing what you've done. It appears that you need Kc = (C)/(A)(B)^2 (Note: you don't have the squared term) Then you have x, and I assume the rest of ICE table. If ...
March 11, 2015

chemistry
The colligative property equation is delta T = i*Kf*m where i is the van't Hoff factor. It is the number of particles. NaCl ionizes to two particles. CaCl2 ionizes to three particles. So which will have the greater effect, everything else being the same.
March 11, 2015

Science
I agree
March 11, 2015

Science
I agree.
March 11, 2015

chem
PV = nRT
March 11, 2015

Chemistry
It picks up H2O from the atmosphere and changes to KOH. K2O + H2O --> 2KOH
March 11, 2015

Chemistry HW!!!
Too many questions on one post. 1. 0.50M x (75 mL/375 mL) = ? if you can make a 0.50M CaF2 solution. I didn't think it was that soluble. 2. Use the dilution formula. mL1 x M1 = mL2 x M2
March 11, 2015

chemistry
Right on all except what you do for atoms. You are right that each molecule oxygen contains two atoms of O so doesn't it stand to reason that O atoms will be twice O molecules.
March 11, 2015

Chemistry
The pH is determined by the hydrolysis of the salt. SO3^2- + HOH ==> HSO3^2- + OH^- so it will be basic.
March 11, 2015

Chemistry
CuSO4.xH2O ==> CuSO4 + xH2O g H2O = g hydrate - g salt = 1.11g mols CuSO4 = grams/molar mass = ? mols H2O = grams/molar mass = ? Now find the ratio of mols H2O to mols of 1 mol CuSO4 and round to the nearest whole number.
March 11, 2015

Chem
Kc for rxn 2 is 1/Kc for rxn 1.
March 11, 2015

Chemistry
You are right on the money!
March 11, 2015

Chemistry
I do them this way. 3.65E8 Pa x (1 kPa/1000 Pa) = 3.65E5 kPa. Then there are 101.325 kPa in 1 atm; convert to atm. Finally there are 760 torr in 1 atm. Convert to torr.
March 11, 2015

Chemistry
You know a mole of CO2 weighs 44g and has a volume of 22.4 L at STP. density = mass/volume.
March 11, 2015

Chemistry
What numbers are you using? Show your work and let me see if I can spot the error. Does this question have anything to do with radioactivity?
March 10, 2015

Science Help Please
I don't like any of the answers to #1 because long and high are relative terms. I know what a radio wave is but there are long radio waves and short radio waves. There are low frequencies and ultra high frequencies. Remember that c = 3E8 m/s (a constant) = wavelength x ...
March 10, 2015

Chemistry
Acids react with carbonates to produce H2O and CO2 + a metal salt of the acid CuCO3 + 2HCl ==> H2O + CO2 + CuCl2
March 10, 2015

chemistry
I don't see a question.
March 10, 2015

Chemistry
HCl + NaOH ==> NaCl + H2O
March 10, 2015

Chemistry
I'm sure these definitions are in your text/notes. For solubility remember like dissolves like; therefore, ethanol is soluble in water since both contain OH groups. Water is a polar compound and polar ionic compounds dissolve in polar solvent.
March 10, 2015

Chemistry
HCN + KOH ==> KCN + H2O mols HCN = ? mols KOH = ? How much HCN formed? How much HCN left over. Use the Henderson-Hasselbalch equation to solve for pH. Post your work if you get stuck.
March 10, 2015

Chemistry
mL1 x M1 = mL2 x M2 250 x 0.2 = mL2 x 2.5 Solve for mL to take of the 2.5 M stuff.
March 10, 2015

Chemistry
[Fe(NO3)3] = 0.00200M x (5.0 mL/10.0 mL) = ? (KSCN) = 0.00200 x (5.0 mL/10.0 mL) = ? (FeSCN)^2+ = 0 Did you try inserting these numbers into the M1V1 - M2V2 equation the prof gave you in the problem. That will give you the same numbers I have above. Try it.
March 10, 2015

chemistry
mols = grams NaCl/molar mass NaCl You know grams and molar mass, solve for mols. Now use the definition of M. M = mols/L You know M, you know mols, solve for L and convert to mL.
March 10, 2015

Chemistry
Calculate mols needed (mols = M x L) and convert to grams. g = mols x molar mass. Then you need to get the language straight as to how this is put together.
March 10, 2015

Chemistry
Vinegar comes in several different percent acetic acid; the most popular are 4% and 5% and this is w/w %.
March 10, 2015

chemistry
HClO + KOH ==> KClO + H2O At the beginning you have pure HClO. .......HClO ==> H^+ + ClO^- I.....0.150......0......0 C........-x......x......x E...0.150-x......x......x Substitute the E line into the Ka expression and solve for x = H^+ and convert to pH. After reaction: ...
March 10, 2015

CHemistry
The pH at the equivalence point is determined by the salt of the titration. The salt is methylamonium chloride and its the MeNH3^+ ion. Here is the hydrolysis. The concn of the salt at the equivalence point is 0.140/2 - 0.07 .......MeNH3^+ + H2O ==> H3O^+ + MeNH2 I.......0....
March 10, 2015

Chemistry
Suppose you make up some numbers. 100 mL HAc x 0.1M = 10 mmols HAc. 100 mL HCl x 0.05 = 5 mmols HCl AS IONS. Adding 100 mL x 0.1M NaOH AS IONS I think will react predominately with the HCl leaving 10 mmols HAc and 5 mmols NaOH. That will produce 5 mmols NaAc and leave 5 mmols ...
March 10, 2015

Chemistry
You're adding HCl to the buffer solution of part 1. question 1 gives NaAc = 0.10M and HAc = 0.20M You are taking 100 mL; theefore, millimols NaAc = base = 0.1 x 100 = 10. mmols HAc = acid = 0.20 x 100 = 20. You are adding 28.8 mL x 0.035 = about 1 millimols HCl. ............
March 10, 2015

chemistry
This is a limiting reagent (LR) problem and you know that because amounts are given for BOTH reactants. You may want to locate the arrow keys on your computer and use them. Fe2O3(s) + 3CO(g)--> 2Fe(s) + 3CO2(g) mols Fe2O3 = 35.0 mols CO = 41.5 Use the coefficients in the ...
March 10, 2015

chemisty
Rules for oxidation state. http://www.chemteam.info/Redox/Redox.html C in CH4, H is +1 and there are 4 so total charge on 4 H is +4. Since the molecule is zero, C must be -4 C in benzene, C6H6 H is +1. 6*+1 = +6. Since benzene is 0 charge, then 6 C must be -6 and EACH C must ...
March 10, 2015

Chemistry
You didn't give Kf for the copper ammine complex. Be sure to look it up in your text/notes. mols CuCO3 = approx 0.979/123 = about 0.008 but you need to redo this, as well as all of the other calculations. And be sure to find the Kf for Cu complex in your text; texts often ...
March 10, 2015

chemistry
See the H2SO4/NaOH problem.
March 10, 2015

chemistry
H2SO4 + 2NaOH ==> Na2SO4 + 2H2O mols NaOH = mols x L = ? Use the coefficients in the balanced equation to convert mols NaOH to mols H2SO4. Then M H2SO4 = mols H2SO4/L H2SO4. You know M and mols, solv eof L; convert to mL if desired.
March 10, 2015

chemistry
See your other limiting reagent problems.
March 10, 2015

science
(CO) = 1.40/molar mass CO = approx 0.05 mol and 0.05mol/1.41L = estd 0.03M (H2O)= 1.4/molar mass H2O = approx 0.078 mols and 0.078mol/1.61L = 0.05M (H2) = 1.4/molar mass H2 = approx 0.7 mols and 0.7 mol/1.61L = 0.4M You need to do these more accurately as well as those that ...
March 10, 2015

Chemistry
For 1 use the Henderson-Hasselbalch equation to calculate pH. 2. Set up an ICE chart. The I line is what you start with in problem 1, the C line is what you're adding from problem 2, the E line is to be calculated and plugged into the HH equation and solve for the new pH. ...
March 10, 2015

chemistry
I don't know what the problem is asking. The word composition seems out of place with the rest of the problem.
March 10, 2015

chemistry
We don't do all of your homework for you. The idea is to help so you can do it yourself. The problem with CaO to CaCO3 is worked the same way as this problem. You try it. I'll be more than happy to check your work and answers. Also, if you don't understand ...
March 10, 2015

Chemistry
See this post and the answer to it. http://www.jiskha.com/display.cgi?id=1425953308
March 10, 2015

Chem
Did you try the solution I posted last night?
March 10, 2015

chemistry
CaO + CO2 ==> CaCO3 mols CaO = grams/molar mass = ? Use the coefficients in the balanced equation to convert mols CaO to mols CaCO3. Now convert mols CaCO3 to grams. grams = mols CaCO3 x molar mass CaCO3
March 10, 2015

chemistry
You plug the numbers into the rate expression. rate = k*A*B If you double A and double B then rate goes up by 4. Or the longer way is to make up a number for k, A and B. Let's make them easy and call k = 1, A = 2 and B = 3 so rate1 = 1*2*3 = 6 Now lets double A and double ...
March 10, 2015

Chemistry
Isn't this just a P1V1 = P2V2 problem? You have V1 liters gas at STP and you want it to go to 2E7 L at P of 22 atm. You want to solve for V1.
March 10, 2015

Chemistrhy 110
How many moles do you want? That's mols = M x L = ? Then mol = grams/molar mass. You know molar mass and mols, solve for grams.
March 10, 2015

Chemistry
The definition: M = mols/L You can get mols by mols NaOH = grams NaOH/molar mass NaOH
March 10, 2015

Chemistry Need Help
No, you have diluted 25.0 mL of 1.50M NaOH to 50.0 mL total volume so (Na^+) is now just 1/2 what it was. 1.5 M Na^+ x 25/50 = ?
March 10, 2015

Chemistry
(H2S) = mols/L = 0.46 mol/4.6L = 0.1M ............2H2S ==> 2H2 + S2 I............0.1......0.....0 C............-2x......2x....x E..........0.1-2x.....2x....x Substitute the E line into Kc expression and solve for x, then 2x = (H2)
March 9, 2015

chemistry
This is a limiting reagent problem (LR) and I work these the long way. Na2O + H2O ==> 2NaOH mols Na2O = grams/molar mass = ? mols H2O = grams/molar mass Using the coefficients in the balanced equation convert mols Na2O to mols NaOH. Do the same for mols H2O to mols NaOH. It...
March 9, 2015

Science (Chemistry)
Your 64 cc is now right but you reported the mass to three places. You're allowed only two because you have two in 2.7 g/cc. Here is a link about significant figures. http://www.chemteam.info/SigFigs/SigFigs.html That means your 172 (I obtained 172.8 which rounds to 173 to...
March 9, 2015

AP Chem
The HH equation uses pKa. Don't have pKa? Remember to convert Kb to pKb, then pKa + pKb = pKw = 14
March 9, 2015

AP Chem
When 0.025 L of 2M WHAT is added to it. Use the Henderson-Hasselbalch equation and set up an ICE chart with it. If you will show your work I can help you through it.
March 9, 2015

Chemistry
I disagree with C.
March 9, 2015

science
And I still don't like any of the answers but I think A is the one to choose. All of the other choices are nonsense.
March 9, 2015

CHEM
(P1V1/T1) = (P2V2/T2) Remember T must be in kelvin.
March 9, 2015

chemistry
I disagree. Look up the definition in your text/notes.
March 9, 2015

Chemistry
I have two questions. 1. What dos netball mean? 2. What results do you have that are supposed to help you answer this question?
March 9, 2015

chemistry 30
C2H4 + 3O2 ==> 2CO2 + 2H2O dHrxn = (n*dHf products) - (n*dHf reactants). You can look up the values for dHformation in your text or notes.
March 9, 2015

Chemistry
Well, it's a regular stoichiometry problem if you work it the long way. I can do that and you can see how the two fit together. The problem says all gases at the same conditions but they don't say what those conditions are so I'll just assume everything is at STP ...
March 9, 2015

Chemistry
2CO + O2 ==> 2CO2 When all gases and at the same T and P, one may use a shortcut in which volumes may be used as if they were mols. 0.677 L CO + (2 mols O2/1 mol CO) = L O2 gas needed.
March 9, 2015

chemistry
See your other post above but this one is not eligible for the shortcut. Convert g KClO3 to mols. mols = g/molar mass = ? Then convert mols KClO3 to mols O2 Use PV = nRT and convert mols CO2 to L CO2 at the conditions listed.
March 9, 2015

Science
You will produce the number of mols H2 that you have mols Zn. You don't have mols Zn anywhere in the problem.
March 9, 2015

Science
I don't like any of the choices for question #1 but you've probably picked the best answer of the lot. (But it isn't anything to brag about. :-( I agree with all of the others. Good work.
March 9, 2015

chemistry
More information is needed.
March 9, 2015

chemistry
I need more information than that.
March 9, 2015

chemistry
What reaction?
March 9, 2015

chemistry
37.8 x 1/2 = g carbs 37.8 x 1/2 = g fat g carbs x 4 kcal/g = ? g fats x 9 kcal/g = ? Total kcal = kcal from carbs + kcal from fats.
March 9, 2015

biochemistry
Use the Henderson-Hasselbalch equation, substitute pKa for CH3COOH and (CH3COOH) for acid, solve for base, then convert to grams. Post your work if you get stuck.
March 9, 2015

biochemistry
Use the HH equation and substitute for acid and base, solve for pH. Post your work if you get stuck.
March 9, 2015

chemistry
I don't buy all of this. .0324*2/2=0.0346 mols MnI2 I don't know how you did this but 0.0324 x 2/2 should be 0.0324. 0.26315*2/13=0.020242 mols F2 0.2631 x 2/13 = 0.0404 so MnI2 is the LR. right? F2 =LR .0202 mols MnF3x112g/mol MnF3=2.26g MnF3
March 9, 2015

chemistry
This is a limiting reagent (LR) problem and you know that because an amount is given for each reactant (in this cse 10 g each). 2MnI2(s) + 13F2(g)--> 2MnF3(s) + 4IF5(l) mols MnI2 = grams/molar mass = ? mols F2 = grams/molar mass = ? Using the coefficients in the balanced ...
March 9, 2015

Chemistry, pH
It's 1.78E-10. Why are you confused. 14-4.25 = 9.75 = pOH Then pH = -log(OH^-) -9.75 = log OH^- OH^- = 1.78E-10 OR OH^- = 10^-pOH OH^- = 1.78E-10
March 8, 2015

Chemistry, pH
Remember this. pH + pOH = pKw = 14 You know pKw and pH, solve for pOH. Then pOH = -log(OH^-), substitute and solve for OH^-.
March 8, 2015

chemistry
NaOH + HCl ==> NaCl + H2O mols NaOH = M x L = 1.0 x 0.5 = 0.5 mols HCl = M x L = 0.025 x 2 = 0.05 So HCl is the limiting reagent. q = mass H2O x specific heat H2O x (Tfinal-Tinitial) Find q. That is q/0.05 mol H2O. Convert to kJ/mol This is the right way to do it but I don...
March 8, 2015

typo--Chemistry 30
That first terms of [mass Ag x Hvap] should be a negative term. I omitted the - sign in front of it.
March 8, 2015

Chemistry 30
heat produced by solidification + heat lost by Ag cooling + heat gained by calorimeter water = 0 [mass Ag x Hvap] + [mass Ag x specific heat Ag x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0
March 8, 2015

chemistry
Good luck!!
March 8, 2015

chemistry
copper(II) chloride means it is coper chloride with the copper having a valence of 2. The old names were cuprous chloride for CuCl and cupric chloride for CuCl2. This new way is a way of telling you that it is copper with +2 and not copper with +1. lead(II) oxide is the same ...
March 8, 2015

chemistry
I responded to your question and I asked if you knew the four types of chemical reactions? yes or no. And what do you not understand?
March 8, 2015

chemistry
See your other post above.
March 8, 2015

chemistry
You start by knowing the types of chemical reactions. Do you know what they are? synthesis single replacement decomposition double replacement.
March 8, 2015

Physics
How can you say it any more precisely. You jump up in the moving plane, you come down in the same spot from which you jumped.
March 8, 2015

Chemistry
mols C = 3.0/12 = ? mols O = 8.0/16 = ? Find the ratio of the two to each other with the smallest number being 1.00. The easy way to do that is to divide both numbers by the smaller of the two. That will give you whole numbers with the smallest being 1.0
March 8, 2015

chem
M make it easier to do. Start M Na2S = 0.474 New M Na2S after dilution = 0.474 x (40 mL/300 mL) = ?M Na2S Since there are 2 Na ions for each molecule of Na2S, then (Na^+) will be just twice that of Na2S.
March 8, 2015

chem
Is this 0.474m or 0.474M? I assume you know there is a difference between the two.
March 8, 2015

chemistry
Zn + 2HCl ==> ZnCl2 + H2 mols Zn = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols Zn to mols H2. Then mols H2 gas x 6.02E23 molecules/mol H2 = ? # molecules H2 gas.
March 8, 2015

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