Tuesday
May 24, 2016

Posts by DrBob222

Total # Posts: 52,411

Chemistry
1. Absolutely not a good idea to use different thermometers. You want the DIFFERENCE in temperature. If either thermometer reads only slightly different than the other, then that error will be the final calculation. 2. m = mols/kg solvent = 0.150/1.2 = ? Then delta T = Kf*m ...
February 19, 2016

Chemistry
Stoichiometry and Henderson-Hasselbalch equation. You have 100 mL of 0.1M NaHC2O4 = 10 millimols sodium bioxalate ..HC2O4^- + OH^- ==> C2O4^2- + H2O I..10........0........0 add..........x.............. C..-x.......-x........x E..10-x......0........x Plug the E line into the...
February 19, 2016

Chemistry-Dr.Bob 222
I copied this from Wikipedia. "The units of the pre-exponential factor A are identical to those of the rate constant and will vary depending on the order of the reaction. If the reaction is first order it has the units s−1, and for that reason it is often called the...
February 19, 2016

Chemistry
The question is somewhat confusing to me. Here is what I think the question is about. What volume of 75% (w/w) HNO3, density 1.41 g/mL is required to prepare 1 L of 0.1M HNO3. First determine the M of the 75% HNO3 starting material. That is 1.41 x 1000 x 0.75 x (1/63) = approx...
February 19, 2016

chamistry
What's with the same post five times. 24000 what?
February 19, 2016

chemistry!
You will see the solution become brownish (if the solution is water) or purple (f the solvent is hexane or carbon tetrachloride).
February 19, 2016

CHEMISTRY HELP
You had this in math. It isn't chemistry. 5.75 = 4.74 + log b/a 1.01 = log b/a 10^(b/a) = 1.01 Plug into the calculator; a/b = 10.23
February 19, 2016

chemistry
The tutors here are sharp people but few of us have the heats of solution for thousands of chemical compounds memorized. We may be able to help if you supplied that data.
February 19, 2016

Chemistry
But why don't you learn to do it right so when you have a number that isn't an even multiple, you will know how to do it. For this problem, that is 21 mols O2 x (4 mols CO2/7 mols O2) = 21 x 4/7 = 12
February 19, 2016

chemistry
63(0.691) + 65(0.309) = ? S is done same way.
February 19, 2016

Chemistry
That is correct but check my response to this question posted separately. I would strongly suggest you do it through the coefficient process so you can do it easily if the numbers are not even multiples as they were in the previous problem or in this new one.
February 18, 2016

Chemistry
How do you know which numbers goes on top and which on the bottom? Look at the units. By placing O2 on the top and C2H6 on the bottom, the mols C2H6 cancel to leave mols O2 as the unit and that's what you want. If you put mols C2H6 on top and mols O2 on the bottom, the ...
February 18, 2016

Chemistry
That is absolutely correct and your reasoning is sound. But if the numbers didn't come out so even could you do it? Here is the way itis done for ALL problems. You use the coefficients. 4.0 mols C2H6 x (7 mols O2/2 mols C2H6) = 4.0 x (7/2) = 28/2 = 14 mols O2.
February 18, 2016

Chemistry
1% w/w = 1 g coke/100 mL solution = 1 g coke/(1 g coke + 99 g H2O). Now if you knew the density you could go further but I don't see a density listed. If you wish to assume the density of the solution is 1.0 g/mL (and it should be close to that since this is such a dilute ...
February 18, 2016

CHEMISTRY PLEASE HELP APPRECIATE IT LOTS!
Most of these stoichiometry problems are worked the same way. Here is a step by step procedure. 7.) How many moles of fluorine are required to react with 12 g of sodium iodide? I already balanced it but am confused to go from here F2 + 2 NAi ---- 2 NaF + I2 12 g NaI + 2 mol ...
February 18, 2016

chem
2HgO ==> 2Hg + O2 mols HgO = 15.22/molar mass HgO Using the coefficients in the balanced equation, convert mols Hg to mols O2.
February 18, 2016

chemistry
p1v1 = p2v2
February 18, 2016

Chemistry
Yes, the data is there to calculate that. The spacing is not good since this forum messes up the spacing; however, you are given the initial concentrations for both NO and O2. Then you are given the concentrations after certain times. That allows you to know the rate in M/s.
February 18, 2016

Chemistry
So what's the rate law? I don't know the exponents but you have that you say. Rate = k(NO)^x*(O2)^y where x and y are the exponents you have determined. Look at any run in the experiment, substitute rate, (NO) and (O2), then calculate k.
February 18, 2016

chemistry
Is that 200 g of H2? Watch the typos. Is that at STP. You don't give the P or T so I'm assuming STP. mols H2 = grams/molar mass - ? Then 1 mol H2 occupies 22.4 L at STP
February 18, 2016

Chemistry
I posted the answer above. Let me know if you can't find it.
February 18, 2016

Chemistry
Do you have k1 and k2 for H2C2O4? We can't get the same answer unless we use the same values for the two constants.
February 18, 2016

Chemistry
What you've done is almost correct assuming the spacing is ok. The numbers are but some are in the wrong place. This forum doesn't do spacing very well. I'll try to improve that. .......... AgCl ==> Ag^+ + Cl^- I.........solid.....0.......0 C.........solid.....x...
February 18, 2016

Chemistry
If that is 5 g then you have only one significant figures so the answer is 0.1 and you're correct. However, the second part can't be done that way. You have assume, I suppose, that Br2 is a gas and it occupies 22.4 L/mol. If that were true your answer of 2.44 would be ...
February 18, 2016

Chemistry
see your other post above.
February 18, 2016

chemistry
See your other post above.
February 18, 2016

Chemistry
Technically any number you choose. I'm sure the author of the problem meant (but didn't say) how much HCl is need to react COMPLETELY with the 5.8 g Al(OH)3 3HCl + Al(OH)3 ==> AlCl3 + 3H2O mols Al(OH)3 = grams/molar mass = ? Using the coefficients in the balanced ...
February 18, 2016

Chemistry
If the energy is 2.93E-19/photon, the multiply by 6.02E23 to find the energy of a mole of them.
February 18, 2016

chem
C = KpP C = 4.48E-5*(760mm-23.8mm) = ? mols/L. Then ? x 44 = grams/L. Convert to g/mL.
February 18, 2016

CHEMISTRY
I would do this. 5% w/v means 5g HAc/100 mL solution which is (5/60) mols/100 and that is 5/60/0.1L or 0.0833 M. Then millimols HAc is 30 x 0.0833 = 25. So acid + base = 25 pH = pKa + log(base)/(acid) 5.75 = 4.74 + log b/a b/a = about 10.3 but you need a better answer than ...
February 18, 2016

CHEMISTRY!!!! HELP
I didn't check 2. #1 is not right but the system is correct. 1. Your calculation for molar mass of Ag2O is not right. The molar mass is closer to 231.8. You obtained that number by 1Ag + 2O and it should be 2Ag + 1 O or (2*107.9)+ 16 = about 231.8. 2. The second error is ...
February 17, 2016

Chemistry
1. Zn + 2AgNO3 ==> Zn(NO3)2 + 2Ag mols AgNO3 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols AgNO3 to mols Zn. Now convert mols Zn to grams Zn. g Zn = mols Zn x atomic mass Zn. 2. The balanced equation is as follows: (NH4)2SO4 + Ca(OH)2...
February 17, 2016

Chemistry Help please! (:
Answered above.
February 17, 2016

chemistry
D is correct
February 17, 2016

chemistry
The answer is hydrogen bonding in H2O as opposed to H2S; the best answer choice is A. Hydrogen bonding a intermolecular bonding.
February 17, 2016

chemistry
I don't think the question makes any sense. The hands are not anything. I suspect the answer the author wants is A; i.e., chemical energy drives the clock hands to move.
February 17, 2016

chemistry
CaC2 + 2H2O --> Ca(OH)2 + C2H2 mols CaC2 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols CaC2 to mols C2H2 Then grams C2H2 = mols C2H2 x molar mass C2H2. This the theoretical yield (TY). The actual yield (AY) is 13.5 grams. %yield = (AY/...
February 17, 2016

Chemistry
First determine the constant in p = Kc*C You're given p and C, solve for Kc. Then using that value for Kc, plug in M and Kc and solve for pN2.
February 17, 2016

Chemistry
pH = pKa + log (base)/(acid) You know pH, Ka is calculated from KaKb = Kw = 1E-14 and pKa = -log Ka. You know base is 0.1, substitute into the above and solve for acid. Since the problem asks for mols and grams, the easy to do this is to substitute millimols into (base) and (...
February 17, 2016

Chemistry
None of the equations are balanced.
February 16, 2016

Chemistry
The amount of NaHCO3 depends only upon the starting amount of NH3. 1. You have the equation. Make sure it is balanced. If not, balance it before going further. 2. Convert NH3 to mols. mol = M x L = ? 3. Using the coefficients in the balanced equation, convert mols MJ3 to mols ...
February 16, 2016

chemistry
There is no problem with the NaCl or the AgNO3; the problem exists because of the K2CrO4 indicator solution. In practice the pH is adjusted to between 7 and 10; NaHCO3 is usually used. At lower pH values, the CrO4^2- is converted to HCrO4^-. CrO4^2- + H^+ ==> HCrO4^- ...
February 16, 2016

chemistry
The white ppt is BaCO3. The gas given off is CO2. CO3^2- + 2H^+ ==> CO2(gas) + H2O CO2 + Ba(OH)2 ==> BaCO3(s) + H2O
February 16, 2016

Chemistry
All of the plastics in your car (and your home) are chemistry. The food you eat is chemistry. The clothes you wear are chemistry. The computer you use is chemistry. Bob Pursley is right on target. EVERYTHING is chemistry. The more you understand chemistry the more you ...
February 16, 2016

oops Semisi----Chemistry: stoich
You didn't convert 320 g O2 to mols first. mols O2 = 320/32 = 10; then 10 x 5/4 = 8.00 mols H2O formed.
February 16, 2016

oops Semisi===Chemistry
No that's not right. mols O2 = 2.50g/32 = 0.078 but you should do it more accurately. Convert to mols Fe2O3. That's 0.078 x 2/3 = approx 0.052 Then g Fe2O3 = mols x molar mass = 0.052 x 159.7 = approx 8.3.
February 16, 2016

Chemistry
Pick out iron filings with a magnet, add water. Wood ships float to the top and can be picked out. Filter what remains and the sand will be trapped in the filter paper. The salt will remain in the water. Evaporate the water to recover the salt.
February 16, 2016

chemistry
Use PV = nRT and solve for pNH3 initially. Substitute pNH3 from this calculation into the below. pNH3 is approx 1.5 but you need a more accurate number. ...........NH4HS ⇌ NH3 + H2S I.........solid....1.5....0 C.........solid.....+x....x E.........solid....1.3+x...x ...
February 16, 2016

Chemistry
.......4KO2+2CO2⇌2K2CO3+3O2(g) E.....solid..7.33E-2.solid...x Kp = p(O2)^3/p(CO2)^2 Substitute and solve for pO2 Ptotal = pCO2 + pO2
February 16, 2016

Chemistry
See your other post.
February 16, 2016

Chemistry
OK. You changed screen names BUT you also included units. Then heat is added delta H is +. When heat is produced, delta H is -. So for this _+2.4 kcal is delta H.
February 16, 2016

Chemistry, chemical change
Can't answer. You didn't include the units for the 22,000. 22,000 what? The rules are that if it is exothermic, and this reaction is because it tells you it reacts and gives off heat, then delta H is negative. So delta H = -22,000 somethings or -22 somethings. The ...
February 16, 2016

Chemistry
delta P = Xsolute*Poacetone
February 15, 2016

Chemistry
Calculate mole fraction ethylene glycol. Then Psolution = Xsolution *Po H2O You would do well to use the same screen names for your posts.
February 15, 2016

Chemistry
Do you mean NaCl or NaBr. I assume NaBr. 2Na + Br2 ==> 2NaBr mols Na = grams/atomic mass Na = ? Using the coefficients in the balanced equation convert mols Na to mols NaBr. Then grams NaBr = mols NaBr x molar mass NaBr.
February 15, 2016

chem21
2.8 g x (100 mL/27 mL) = ? or if you want to do it by proportion it is (2.8/27) = (x/100) Solve for x.
February 15, 2016

Chem
That melts the ice at zero to liquid water at zero C. Now to heat it from zero C to 60 C is q = mc*delta T. q = 30 x 4.184 x (Tfinal-Tinitial) Then add the two for the total.
February 15, 2016

Chem
4Al + 3H2SO4 ==> 2Al2(SO4)3 + 3H2 Does all of the Al dissolve? Assuming it does, then, how many mols H2 are produced? That's n = PV/RT = (480*0.427)/(8.314*300) = about ? ?mols H2 x (4 mols Al/3 mols H2) = ? = grams theoretical yield. %yield = (grams H2 produced/7.5)*...
February 15, 2016

chem
H2SO4 + 2NaHCO3 ==> Na2SO4 + 2H2O + 2CO2 mass NaHCO3 = 155.00-144.50 = 10.50 g used. mols NaHCO3 = grams/molar mass = about 0.125 If all were to be used it would produce how many mols H2O. That is 0.125 mols NaHCO3 x (2 mols H2O/2 mols NaHCO3) = 0.125 mols CO2. mols H2SO4...
February 15, 2016

@Emma---chemistry
Note that this is a limiting reagent problem.
February 15, 2016

chem
mols Cu initially = grams/atomic mass = about 0.3 but you need a more accurate answer. mols HNO3 initially = M x L = about 1.3 but see note above. Convert mols Cu to mols NO2. That's about 0.3 mols Cu x (2 mols NO2/1 mols Cu) = about 0.6 mols. Convert mols HNO3 to mols NO2...
February 15, 2016

Chemistry
This is a limiting reagent (LR) problem. You know that because amounts are given for BOTH reagents. I suppose you means HCl for HC. 1. Write and balance the equation. 2. Convert grams Mg to mols. mols = grams/atomic mass = ? 3. Convert HCl to mols. mols HCl = M x L = ? 4. ...
February 15, 2016

chemistry
1. Write and balanced the equation. 2. Convert 13.75 g Ba(OH)2 to mols. mols = grams/molar mass = ? 3. Using the coefficients in the balanced equation, convert mols Ba(OH)2 to mols H3PO4. 4. Now convert mols H3PO4 to the volume needed. M = mols/L. You have M and mols, ...
February 15, 2016

chemistry
2KClO3 ==> 2KCl + 3O2 You need how many mols O2? That's n = PV/RT. Substitute and solve for n = mols O2. Using the coefficients in the balanced equation, convert mols O2 needed to mols KClO3. Convert mols KClO3 to g KClO3 needed. That's grams = mols x molar mass = ?
February 15, 2016

Chemistry
2Al + 6HBr ==> 2AlBr3 + 3H2 4 mols Al will produce how much H2? That's 4 mols Al x (3 mols H2/2) mols Al) = ? 3 mols HBr will produce how much H2?That's 3 mols HBr x (3 mols H2/6 mols HBr) = ? This is a limiting reagent problem. The answer to how much is produced is...
February 12, 2016

Chemistry
Energy used to melt ice at zero C to liquid water at zero C. dq = mass ice x heat fusion = (10/18) x 6.02 kJ/mol = 3.34 kJ. Energy remaining to be used is 8.50 kJ - 3.34 = 5.15 kJ. Energy used to raise T of water at zero C to 100 C. q = mass H2O x specific heat H2O x (Tfinal-...
February 12, 2016

chemistry
Limestone rock contains solid calcium carbonate that can react with acid to give products. In one experiment, 1.452 g of limestone rock is pulverised and then treated with 25.00 mL of 1.035 M HCl solution. After the reaction is completed, the resulting mixture is still acidic...
February 12, 2016

Chemistry
How about this? 20Ne + 21Ne + 22Ne = 100% 20Ne + 0.26 + 22Ne = 100% and 20Ne + 22Ne = 100-0.26 = 99.74% Let x = 20Ne and 0.9974-x = 22Ne Set your equation up as usual and solve for x and 0.9974-x.
February 12, 2016

Science (1 question)
Rolling friction is the correct answer. Why not gravity. The question is about REDUCING some force. You CAN reduce the friction since the wheels are not touching the track but you can NOT reduce gravity. That is present in the same amount where ever the wheels are; i.e., above...
February 10, 2016

Chemistry 101
heat lost by granite + heat gained by H2O = 0 [mass granite x specific heat granit x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0 Substitute and solve for specific heat granite, the only unknown.
February 10, 2016

Chemestry
When the next (spoonful, pinch, spatula, etc) was placed into the solution and it did not dissolve.
February 10, 2016

Chemistry
(V1/T1) = (V2/T2) Don't forget C must be in kelvin.
February 9, 2016

AP Chemisty
.......CaSO4 --> Ca^2+ + SO4^2- I......solid......0.......0 C......solid......x.......x E......solid......x.......x Ksp CaSO4 = (Ca^2+)(SO4^2-) Now if we add a large excess of sulfate as Na2SO4, that makes SO4^2- very large, Le Chatelier's Principle says the reaction ...
February 9, 2016

Chemistry
HCl is a strong acid; therefore, it ionizes 100% which means (H3O^+)=(HCl)
February 9, 2016

Chemistry
I don't see a question here, but why not write that "weird" acid as sulfuric (or sulphuric) acid?
February 9, 2016

Chemistry
........HA ==> H^+ + A^- I....0.001.....0.....0 C......-x......x.....x E....0.001-x...x.....x Substitute the E line into the Ka expression and solve for x = (H^+) and convert to pH. Be careful, you may need to use the quadratic equation; i.e., you may not be able to call 0....
February 9, 2016

chemistry
pH + pOH = pKw; then pH = pKw - pOH
February 9, 2016

AP CHEMISTRY
Probably you worked it right and left off the exponents. The answer is 5.27E-4 bar unless that K you list is Kc and not Kp.
February 9, 2016

Chemistry
Step1. Calculate the mols KMnO4 used. mols KMnO4 = M x L = ? Step2. Using the coefficients in the balanced equation, convert mols KMnO4 used to mols Na2C2O4 needed. Step3. Then mass Na2C2O4 = mols Na2C2O4 x molar mass Na2C2O4.
February 9, 2016

Chemistry 101
a. I would convert 35 mpg to km/L. I obtained 14.88 km/L but you should confirm that. Then distance = km/L x 22 L = ? b. 1 gallon = 3.785 L. $1.99/gallon x (1 gallon/3.785 L) x 22 L = ? c. Take the km from part a, convert to miles, then 44 mi/hr x #hr = total miles Solve for...
February 9, 2016

Chemistry 101
volume Pb = mass/density You know mass in pounds, convert that to grams. There are 454.6 g Pb in one pound. You know density. Solve for volume of Pb. The volume of the Pb pushes out that much volume of the water so add 2500 mL + volume Pb in mL to find final volume of water.
February 9, 2016

Chemistry 101
1 mL = 1 cm^3 = 1 cubic centimeter = 1 cc. 7.50 cc x 7.85 g/cc = 58.9 grams. Note that cc in numerator cancels with cc in the denominator.
February 9, 2016

Chemistry 101
mass object = volume x density volume = 57.50-50.00 = ? density = given. Solve for mass object.
February 9, 2016

Chemistry 101
Convert 1" to cm 1 in x 2.54 cm/in = 2.54 cm Volume sphere = (4/3)*pi*r^3 Then density = mass/volume = ? and compare with 1.00 g/cc.
February 9, 2016

Chemistry
delta T = Kf*m You know delta T, Kf is 1.86, solve for molality.
February 9, 2016

chemistry
CaCl2 + Ca(NO3)2 ==> No reaction. CaCl2 + 2AgNO3 ==> 2AgCl + Ca(NO3)2 CaCl2 + AgNO3 + NH3 + H2O ==> Ag(NH3)2Cl + Ca(NO3)2 and you balance.
February 9, 2016

AP Chemistry
.........HF => H^+ + F^- I.......4.7E-2..0....0 C.......-x......x....x E.....4.7E-2....x....x Ka = (x^2)/(4.7E-2 - x) Solve for x = (H^+) and convert to pH. If you are having trouble obtaining the correct answer you may need to solve the quadratic; i.e., don't neglect ...
February 9, 2016

Analytical Chem
NaOH + CO2 ==> NaHCO3 or you can write CO2 + H2O ==> H2CO3, then H2CO3 + NaOH ==> NaHCO3 + H2O
February 9, 2016

Analytical Chem
NaOH absorbs CO2 from the atmosphere and pH decreases.
February 9, 2016

Chemistry
........2A(aq) <--> B(aq) I.......3.10........0 C.......-2x.........x E.....3.10-2x.......x 5.48E-5 = (x)/(3.10-2x) Clear the denominator. 5.48E-5(3.10-2x) = x 5.48E-5*3.10 - 5.48E-5*2x = x Complete the multiplication, combine terms, solve for x.
February 9, 2016

chem,i need someone to explain this definition
Suppose you have a piece of pure aluminum. That means there is no other material(chemical if you will) in that piece of Al. You may treat Al with other chemicals that will make compounds (a compound is composed of two or more elements) BUT you can not treat pure Al (an element...
February 8, 2016

Science 10
distance = 1/2 * gt^2 You know d and g, substitute and solve for t.
February 8, 2016

Chemistry
mols SO3 = grams/molar mass = ? Then M SO3 = mols/L. Let's call this about 0.0075 M but that's just an estimate. You need to do it much more accurately. mols O2 = grams/mola mass = ? Then M O2 = mols/L. Let's call this about 0.003 M. Again, you should do it more ...
February 8, 2016

chemistry
See your post on Al2(CO3)3 to see how to do this one.
February 8, 2016

Chemistry
39 g Al2(CO3)3 mols Al2(CO3)3 = grams/molar mass = ? There are 2 mols Al^3+ for every mole of Al2(CO3)3 There 3 mols of [CO3]^2- for every mole of Al2(CO3)3. There are 9 mols O atoms for every mole Al2(CO3)3
February 8, 2016

Chemistry
p1v1 = p2v2
February 8, 2016

chemistry
Please rephrase your question and/or provide more information. It isn't clear to me what you want.
February 8, 2016

Chemistry
Ptotal = p(drygas) + pH2O 750 = pdrygas + 20 Solve for p dry gas.
February 7, 2016

chemistry
I have not used the triiodide ion (I3^-) below but you may convert to that if you wish. KIO3 + 5KI + 3H2SO4 ==> 3H2O + I2 + 3K2SO4 2S2O3^2- + I2 ==> S4O6^2 + 2I^- mols KIO3 = M x L = ? mols I2 produced = 3 x that = ? mols S2O3^2- needed = 2 x mols I2 = ? Then M S2O3^2...
February 7, 2016

organic chemistry
First, determine K. Ko/a = 20/13.3 Then K = (org layer)/(aq layer) For part b. Let x = grams in org layer; then 40-x = grams in aq layer. Then (organic layer) = x/300 (aqueous layer) = (40-x)/300 K = (x/300)/(40-x)/300 Solve for x and 40-x. For part a use the same set up but ...
February 7, 2016

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