Thursday
July 31, 2014

Posts by DrBob222


Total # Posts: 43,225

chemistry
mols CaCl2 = grams/molar mass M = mols CaCl2/L soln

Chemistry
I think you're right about A. Wouldn't you need to work to make KE into PE? C. To evaporate H2O you must add heat so that must be endo. D. If you burn a piece of wood that is combustion. It gets hot, right? So that must be? E. When water freezes it is exothermic. No, I...

Chemistry
And you think what? and why?

Chemistry
Under some circumstances the last one COULD be right but I agree with your answer. I obtained 32.5 L of the gas at STP and most reactions will occur if there is an excess of reagent and the conditions are right.

Chemistry
I think the problem is this. I believe you have calculated N for N2O5 correctly. That's N2O5 LEFT. Then 1-N = mols N2O5 that decomposed to form O2, take 1/2 that and convert to V using PV = nRT If I do that I obtain 6.76 which rounds to 6.8L. I don't remember but I may...

Chemistry
I agree with all of the answers given by Bob Pursley. The correct choice from your list is #8. You haven't entered the correct choice; i.e., 8.

Chemistry
(HCHO) = (H2) = (CO) = 1 mol/2L = 0.5 M add (HCHO) = 2/2 = 1.0M add (CO) = 1/2 = 0.5M ..........HCHO(g) --> H2(g) + CO(g) E........0.5M........0.5M.....0.5M add.......1.0M..........0......0.5M Substitute the E line into Kc expression and calculate Kc. #2. a. Since the syste...

chemistry
Take enough solution to have 1 mol total. That means you have 0.15mol H2SO4 and 0.85 mol H2O. Convert H2O to grams which is 0.85 x (18 g H2O/mol H2O) = approx 15 Then m = mol/kg solvent m = 0.15/0.015 = ? estimated.

Chemistry
I don't see any products. Heat formation of what? Just type normally, we know what should be a subscript.

Chemistry
All of these are acid/base reactions. B. CH3CH2NH2 + HBr ==> CH3CH2NH3^+ + Br^- or as a compound CH3CH2NH3Br

Chemistry
Wouldn't this be ln(No/N) = kt You know No and k, t is given but change so k and t are in the same units. Solve for N = mols N2O5 at end of 20 hours, then take 1/2 that for mols O2 and use PV = nRT to calculate volume O2.

Chemistry
Yes, A is correct. C is worded funny and I don't know what it means but it could be true depending upon how it is interpreted.

Chemistry
Right. C is correct. NH3 is the base.

Chemisty
MgSO4 + BaCl2 ==> BaSO4 + MgCl2 BaSO4 ppts. Net ionic is SO4^2-(aq) + Ba^2+(aq) --> BaSO4(s)

Chemistry
You had a problem almost like this that Bob Pursley helped you with. You ant 11.5 g pot benzoate so the reaction must produce a theoretical yield of 11.5g/0.71 = ? Then mols K benzoate = ?/molar mass K benzoate Convert to mols tolune, then g tolune = mols x molar mass toluene.

Chemistry
ln(No/N) = kt No = 4.73E-4 N = ? k = in the problem t = 24 hours changed to min since k in in min.

Chemistry
See your post below.

Chemistry
phosphate tetrahedral in shape; therefore is non-polar. SO3 is trigonal planar which makes it non-polar.(see http://www.tutor-homework.com/Chemistry_Help/Molecular_Geometry/049_Sulfur_Trioxide_SO3.html) NO2- is trigonal planar electronic geometry but molecular geometry is bent...

Chemistry
I posted an answer under the other screen name of Gloria then erased it after reading your responses to this question because I misinterpreted the question as wanting an answer of ionic or covalent. I think all of your answers are correct. I assume you can answer the other pos...

Chemistry
See other post under Dory

Chemistry
That's density 32 g what. mass = volume x density If that density is right, substitute that and volume and solve for rmass.

Chem
I have consulted with a friend who is an organic chemist and he tells me all of these are acid/base reactions. Hence for part B CH3CH2NH2 + HBr ==> CH3CH2NH3^+ + Br^- or you may want to write that as CH3CH2NH3Br. That is the salt but is ionic and ionizes as I have it above.

Trigonometry, can someone check this please
I agree with Steve. I think you have mis-labeled the diagram. The distance AB is 120m and that is the hypotenuse of the triangle and not the base.

Chemistry
The systematic name is butan-1-ol

Chemistry
Just the name butanol USUALLY means n-butanol or 1-butanol (that is, with the OH on the terminal C)

Chemistry. HELP.
I do these the long way. mols O2 = 25/22.4 = estimated 1+. g ethanol = m = vd = 50.0 x 0.789 = estimated 40 g, then mol = g/molar mass = estd 40/46 = estd 0.9 C2H5OH + 3O2 ==> 2CO2 + 3H2O Convert mols O2 to mols CO2 using the coefficients in the balanced equation. 1+mol O2 ...

chemistry
You know ALL compounds are zero. Ca is +2 each. 3*2 = 6+ You know O is -2 each. 8*-2 = -16 Since everything must add to zero, then +6 +(-16) + 2P = 0 -10 + 2P = 0 2P = 10 P = +5 each

chemistry
This is akin to asking us to write a term paper for you. I'll get you started. Air conditioning. Compressor compresses gas in outside unit, liquid flows to cooler, liquid evaporates and cools in the process, a fan blows across the coils that are now quite cold and the cool...

Math
The slope is y/x y = 23-8 = 15 x = 15-4 = 11

check my arctan please
right. 4.8 degrees.

Chemistry
The long way of doing this is to look up the reduction potentials of each. Zn^2+ + 2e ==> Zn has a reduction potential of -0.763 and you want the reverse of that which is Zn ==> Zn^2+ + 2e E = +0.763 and do likewise for Ag ==> Ag^+ + e E = -0.8 Now look up, in success...

chemistry
mL acid x M acid = mL base x M base

check my set up please
yes

check my set up please
I believe your set up finds the height of the tower. The line of sight to the BASE of the tower is 34 meters by measurement. The line of sight to the TOP of the tower is cos 72 = 34/x

chemistry
Well, to be a smart aleck, I would say it's 5.6g/950 mL since you didn' specify %, M, m, or what. If you want molarity, M, then mols KOH = grams/molar mass and M = mols/L solution.

physical chemistry
Decomposition how? If you want 2H2O2 ==> O2 + 2H2O, then dHrxn = (n*dHo products) - (n*dHo reactants)

Chemistry
You need a mass of NaCl. Then mols NaCl = grams/molar mass = ? Finally, mols Na^+ = mols NaCl x 6.02E23 mols Cl^- = mols NaCl x 6.02E23 # particles will be the sum of #Na^+ + #Cl^-

Chemestry
Redox equations are balanced by a procedure. Others are balanced by inspection which is just another word for trial and error. If you will post an equation you want balanced (not a made up one but a real one) I can show you how to do it.

Analytical Chemistry
You don't have a clear question. How many mL is a question, of course, but to do what? And is that m or M. I assume you know there is a difference.

chemistry
CH3OH ==> 2H2O mols CH3OH = grams/molar mass = approx 0.2 but that's only an estimate. mols H2O = 2x that from the coefficients. molecules H2O = mols H2O x 6.02E23 = ?

Chemistry
Coordination number has slightly different meanings depending upon how it is used. One is in crystallography and the other is in complex formation. Here is a site that you can read about both. http://en.wikipedia.org/wiki/Coordination_number Basically, coordination number in c...

chemistry
I can help with specific questions about this process, chemically, but you must write your paper. This is a discussions question that basically has little to do with chemistry but a lot to do with politics and society and the human side of radioactive decay, including its use ...

Chemistry
mL1 x M1 = mL2 x M2 56mL*1.93M = mL2 x 0.9M mL2 = approx 120 mL (which is the total volume). So you must have added 120-56 = ? and that is assuming that the volumes are additive.

Chemistry
c = p*K For O2, c = 1.3E-3 mol/L*atm x (0.2) and for N2, c = 6.8E-4 mol/L*atm x (0.8). Add to find total mols, then XO2 = nO2/total mols XN2 = nN2/total mols.

Chemistry
plasma etching wet etching oxidation vapor deposition

Chemistry
What do you need help with?

Chemistry
I would do this. Convert 0.135m to ?M first. Take 1000 mL of 0.135m, it will contain 0.135 mols KF. How many grams is that? That's 0.135 x molar mass KF = about 7.8g(but that's an estimate and you should redo this and all of the other calculations that follow for they ...

Chemistry
Do you mean 0.135m or do you mean 0.135M?

Chemistry
18% w/w means 18g NH4Cl/100 g solution. mols NH4Cl = grams/molar mass = ? Convert 100 g solution to L using density; then M = mols/L.

Chemistry
7.9 x (5.9/100) = ?

Chemistry
1.55 g/mL x 1000 mL x 0.65 = 1007.5 g H2SO4. mols H2SO4 = grams/molar mass mass solution = 1.55 x 1000 = 1550. mass H2O = 1550-1007 = ? molality = mol H2SO4/kg H2O

oops--Chemistry
Do you have a 6.25m or a 6.25M solution? Mathmate's answer and definition is for 6.25M. The correct answer for 6.25m is below. m is molality and the problem states molality (not molarity). molality = mols solute/kg solvent. 6.25m means 6.25 mols NaOH/kg solvent. g = mols x...

Physics
I think you will get faster service if you don't switch change names.

chem
Ptotal = pO2 + pCO2 + pN2 Ptotal must be in torr if the others are in torr. 1 atm = 760 torr.

chem
(P1V1/T1) = (P2V2/T2) Remember T must be in kelvin.

rounding
No.If that is 146.627 FEET (you don't have the unit) then 147 is rounded to the nearest foot. To the nearest 0.1 foot it must be 146.6 feet. Why must it be a whole number?

chem
This is a "simple" stoichiometry problem. Here is the format for solving all of these. 1. Write and balance the equation. CS2 + 3O2 ==> CO2 + 2SO2 2. Convert what you have (in this case mL O2) to mols. The problem doesn't say it is a standard conditions but it...

chem
Use PV = nRT and solve for n = mols of gas, then n = grams/molar mass and solve for g.

chem
Use PV = nRT n isn't given but n = grams CO2/molar mass CO2

chem
All of these gas law problems stem from the same formula of (P1V1/T1) = (P2V2/T2) The four or five preceding this post are variations of this formula.

chem
See the next post up.

chem
See two posts up.

chem
See three posts up.

chem
See four posts up.

chem
(V1/T1) = (V2/T2)

chem
(V1/T1) = (V2/T2) Remember T must be in kelvin. Standard T is 273K

chem
P1V1 = P2V2. If you eneter P1 in atm then P2 will be in atm and you will need to convert to torr. Or you can convert 2.93 atm to torr (1 atm = 760 torr) initially and the final P will be in torr.

chem
I don't understand the question.

chemistry
See your earlier post.

chemistry
Use P1V1 = P2V2. Since no "real" value is given for P1 you can assign any convenient number for P1, then 16 times that will be P2 and work the problem OR you can simply subsitute 16*P1 for P2.

simplify the expression
What do you mean they don't match? 14^-4 = 1/(14^4) = 2.6E-5

how would i set this up?
Draw a figures, then side opposite angle is 1 ft and horizontal is 12 ft so tan angle = 1/12.

chemistry
Convert 50.0 mL ethanol to mass using mass = volume x density. I obtained approximately 50 x 0.789 = about 40g but that's an estimate only as are all of the other numbers. You need to go through the calculations yourself. mols ethanol = 40/molar mass = about 0.87 mols O2 =...

chemistry
22% by mass means 22 g solute/100 g solution. How many mols in 22g? That's 22/342 about 0.064 mols which is an estimate as are all of the other calculations that follow. You should recalculate each for yourself. So we have 0.064g solute/100 g solution. Use the density to c...

oops--chemistry
I posted the answer then re-read the problem and saw I had not included energy to remove that 50 mL H2O at the boiling point. Therefore, I deleted that post. Here is the complete answer. energy to melt ice + energy to raise melted ice to 100 from zero C + energy to raise 100 g...

chemistry
Follow the instructions I gave. Actually there are two final temperatures and that's why I said to work the problem in steps. The FIRST final T which I've listed as Tfinal is the final T of the ice water + 100 C water. The ice melts and lowers the temperature of the 10...

chemistry
I would do this is steps. First, determine the mass of the ice. mass ice = volume ice x density ice at 0C. You will need to look up the density at 0C. Then [mass H2O x heat fusion] + [mass melted ice x specific heat H2O x (Tfinal-0)] + [mass H2O @100 x specific heat H2O x (Tfi...

Chemistry
Ptotal = pH2 + pH2O Ptotal = 99.8 kpa pH2O = 2.33 kPa. PH2 = ?

Chemistry
PV = nRT. You don't have n but n = grams/molar mass.

chemistry
I would like to know how much ice and how much liquid water @ 100 C you have? I haven't thought through the problem and that info may or may no be needed; however, it would make me feel better to have that info.

chem
1 mole of anything contains 6.02E23 molecules. Convert 19.0 g MgCl2 to mols. mol = grams/molar mass. Then convert that many mols to molecules MgCl2 (use #1 as a template if needed). Then you notice there are 3 atoms for each molecule so 3x molecules gives you atoms.

chem 2
Were are parts B, C, and D. Rxn is (add the two half cells below) Cr(s) ==> Cr^3+ + 3e Ag^+ + e ==> Ag(s) -------------------- Cr(s) + 3Ag^+ ==> 3Ag(s) + Cr^3+

chemistry
I'm guessing the reaction is something like this and I'm assuming there is enough Ag to complete the reaction although I don't know what "amount AgNO3 used was unchanged" means. Cu(s) + 2Ag^+ ==> 2Ag(s) + Cu^2+ mols Cu = grams/atomic mass mols Ag = 2 x...

Science
That isn't a good answer.

Chemistry
I agree

Chemistry
k = 0.693/t1/2 Solve for k and substitute into the below equation. ln(No/N) = kt No = 12.0 mg N = ? mg k = from above t = 13.5 hrs

Science (Please check!)
If it is a stove top burner and you set the pan on it, the heat is transferred by conduction.

Chemistry II
There is no way to answer this question without some kind of rate equation.

ALGERBRA
-7*5 = 5*91X -35 = 455X X = ?

College Algebra
That's what I would do first.

Chemistry
P1V1 = P2V2

Chemistry
http://www.jiskha.com/display.cgi?id=1401311215

Science
http://www.jiskha.com/display.cgi?id=1401311215

chemistry
Do you mean 2.10 M? If so then pOH = -log(2.10) and pH + pOH = pKw = 14 With pOH and pKw you can solve for pH.

chemistry
It COULD be right but as far as I know that is no such compound as NaHClO3. NaClO3 is sodium chlorate. HClO3 is chloric acid. I don't know of anything with the formula NaHClO3.

chemistry
I don't see a question here.

chemistry
If you say so. I don't see a question.

science
Is this a question? If so it isn't clear; please rephrase it.

Chemistry
PV = nRT n = grams/molar mass = 23.0/207 = ? Remember T must be in kelvin.

Chemistry
I know it is exothermic because I've been there and done that and I know it gets hot. You can look up delta G of products and reactants in tables and calculate delta Grxn BUT those values are based on knowing both delta H and delta S so I don't think that is a legitima...

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