Sunday
October 26, 2014

Posts by DrBob222


Total # Posts: 44,734

Chem
15% by mass means 15 g in 100 g solution. We can use the above and convert to 24.88 g if you wish OR I think the easiest way to do this is to substitute into the equation for percent mass. method 1. 15g x (24.88/100) = approx 3,7g method 2. (X g solute/g solution)*100 = % (X/...
October 13, 2014

chemistry
wavlength = h/mv You know wavelength but change that to meters, you know h and mass electrons, solve for v. Substitute v into KE = 1/2 mv^2
October 12, 2014

CHEM
mols LiI = grams/molar mass = ? m - mols LiI/kg solvent = ?
October 12, 2014

chemistry
I'm sure you meant Pb(NO3)2 Pb(NO3)2 + MgCl2 ==> PbCl2 + Mg(NO3)2 The key to this problem is knowing that PbCl2 is a ppt. First you must determine which is the limiting reagent. mols Pb(NO3)2 = M x L = approx 0.06 mols MgCl2 = M x L = approx 0.04 If we used 0.06 mols Pb...
October 12, 2014

chemistry
Look at the problem with KHP. All of these are essentially the same. Step 1 is mols standard solution (the one with BOTH M and L) Step 2. Use the coefficients in the balanced equation to convert mols of what yu have to mols of what you want. Step 3. Use the definition of M = ...
October 12, 2014

Organic Chemistry
What did you use to prepare the pentyl chloride. An acid. The NaHCO3 was to neutralize the excess acid.
October 12, 2014

chemistry
KHP + NaOH ==> NaKP + H2O mols KHP = grams/molar mass The rxn is 1:1; therefore, mols NaOH = mols kHP. Then M NaOH = mols NaOH/L NaOH
October 12, 2014

chemistry
This is a limiting reagent (LR) and you know that because values are given for BOTH reactants. Al2S3 + 6 H2O -> 2 Al(OH)3 + 3 H2S mols Al2S3 = grams/molar mass = ? mols H2O = grams/molar mass = ? Convert mols Al2S3 to mols H2S Convert mols H2O to mols H2S It is likely these...
October 12, 2014

chemistry
1 ppm = 1 mg/L 270 ppm = 270 mg/L Convert that to mg/400 mL. 270 x (400/1000) = ? mg in 400 mL Change to grams.
October 12, 2014

Chem Lab Help- Check Urgent
That doesn't help much. Is this an extraction? Do you know anything about the unknown? Is it an acid? base? ester? anything else other than it's an unknown? Is this a qual experiment. A quant experiment?
October 12, 2014

Chem Lab Help- Check Urgent
What are you doing? Solvent for what. What are you measuring?
October 12, 2014

Chemistry
Repost if you still have trouble but remember I need what you're using for pKa2 if I'm to come up with the same answer you have.
October 12, 2014

Chemistry
No, I disagree. You aren't necessarily bad at solving buffer problems, you are bad about not following instructions. Of course it's wrong. You didn't follow my instructions. Step 1. Use the equation 7.2 = pKa2 + log b/a where b is base and a is acid. You will need ...
October 12, 2014

Chemistry
pH = pKa + log(base)/(acid) pH = 7.2 pKa is pKa2 for H3PO4 base is HPO4^2- acid is H2PO4^- and you want 1 M buffer which means a + b = 1 First you determine the values of a and b. You need two equations. The first one is 7.2 = pKa2 + log b/a Solve for b/a The second one is a...
October 12, 2014

chem science
The measured melting point probably will be lower than it should be because not all of the mercury in the bulb is subject to expansion/contraction due to the temperature of the liquid. As you have described the post you are measuring the temperature of the water.
October 12, 2014

Chemistry
sp3
October 12, 2014

CHEMISTRY
Just below, I responded to a similar question by Matt suggesting this is a poor question. The only correct answer I think is that the percent error will increase and surely that is too simple an answer. The error will increase, meaning it will be an error mor than perfect ...
October 12, 2014

Chemistry
mols KCl = grams/molar mass = approx 0.0025 mols KCl in 25.0 g H2O at that depth but that's an estimate. How much volume is the 25.0g? That's mass = volume x density and v = m/d = 25.0/1.071 = ? and convert to L. Then = M = mols/L
October 12, 2014

chemistry
You didn't express your post very well but I think you have H2SO4 and are adding one of the four to it. If the light dims (and in fact it will go essentially out if you add to the exact equivalence point) Ba(OH)2 this will form BaSO4 and that is insoluble. So the answer is...
October 12, 2014

chemistry
I assume you meant 0.0520 M Cl^-. You want mols Cl^- = M x L = approx 0.12 but that's just an estimate. Then mols CaCl2 = 0.118/2 since 1molecule of CaCl2 supplies 2 Cl^- ions. g CaCl2 = mols CaCl2 x molar mass CaCl2.
October 12, 2014

Chemistry
I have used this. density x 9.8 x height(m) = 101.325 kPa So if height is 6 ft (1829 mm) density is about 5.6 or so. Check that out. Here is a good site. http://hyperphysics.phy-astr.gsu.edu/hbase/pflu.html'\ But don't stop there. Click on the manometer link at the ...
October 12, 2014

Chem
I don't think the problem is stated very well. You know without any reasoning that the percent error will increase. Surely this isn't the answer you want. It appears to me that you want an answer that is based on the final result. If all of the alum is not dissolved, ...
October 12, 2014

chemistry
mols HCl = M x L = ? mols NaOH = M x L = the same q = mass H2O x specific heat H2O x Tfinal-Tinitial). This is q for the water and calorimeter. If you want the calorimeter by itself you must look up the heat neutralization and adjust for that.
October 12, 2014

chemistry
I don't see a question here.
October 12, 2014

Chemistry
mols in 25.4g Ca = grams/molar mass = approx 0.6 but that's an estimate. mols C = approx 0.6 g C in 0.6 mols = approx mols x atomic mass.
October 12, 2014

CHEMISTRY
You're there. Since 24/1 is the EW for LiOH, then 24 g LiOH in 1L solution will be 1 N. (also 1 M) b. Same for H3PO4. Dissolve 98/3 g H3PO4 in a little water and make to the 1L mark with water to prepare a 1 N solution of H3PO4. Technically you need the reaction being used...
October 12, 2014

CHEMISTRY
This is just a dilution. mL x % = mL x % 250mL x 70% = ?mL x 100%
October 12, 2014

CHEMISTRY HELP
mols C6H12O6 = grams/molar mass = ? Then m = molality = mols/kg solvent. You know kg solvent and mols, solve for m. Then delta T = Kf*m and solve for dT, then subtract from 0 to find new freezing point. OR, delta T = Kb*m and solve for dT then add to 100 to find the new ...
October 12, 2014

Chemistry
Didn't I do this for you last night? Go back and try to find it. Post gain at the top of the page is you still have trouble.
October 12, 2014

chemistry
I worked this above at your later post.
October 12, 2014

chemistry
Zn + 2HCl ==> H2 + ZnCl2 mols Zn = mass/atomic mass Zn. I would use 690.5/65.38 = ? 1 mol Zn = 1 mol H2; therefore, ? mols Zn = same mols H2. When you know the size of the balloon or something about the volume of each balloon you can finish the problem.
October 12, 2014

chemistry
You need to clarify the problem. I think you are asking to calculate (Fe^3+) which you have mixed 1 mL of 0.00050 M FeCl3 with 9 mL of 2.0 M HCl. This is just a dilution problem. You have diluted 1 ml Of the FeCl3 with 9 mL of the HCl solution. Assuming the volumes are ...
October 12, 2014

Chemistry
We can't draw mechanisms/diagrams/pictures on this forum. I suggest you look at google. I'm sure there is on on the web. Try this site. I see some electrons being pushed. If this does'nt help use google. https://www.google.com/search?q=mechanism+aldehyde+fehling%...
October 12, 2014

To Twaha---chemistry
What you have posted is pure blarney. First error: 300 mL solution equals 5 g MgCl2 and not 0.5. The problem says 300 mL solution and 5.0 g MgCl2. Second error: you are trying to base molarity on solution/grams and it should be mols/L solution. The correct solution is as ...
October 11, 2014

chemistry
mols MgCl2 = grams/molar mass Then M = mols/L solution
October 11, 2014

CHEMISTRY
% by mass = grams solute/100 g solution or (X/600)*100 = 5.5 X = 600*0.055 = 33 g solute. You can prove that if you wish to know you're right.(33/600(*100 = right! 5.5% So how much is water and how much is solute. (If 33g is the solute, then 600-33 = ? must be H2O)
October 11, 2014

CHemistry
The molecular equation is Fe(NO3)3 + 3NaOH ==> Fe(OH)3 + 3HNO3 You can add the phases if you wish. net ionic equation is Fe^3+(aq) + 3OH^-(aq) ==> Fe(OH)3(s)
October 11, 2014

Chemistry
There's an easier way to do this but I don't have it yet so here is the long way. 1/wavelength = RZ^2(1/n^2 - 1/n^2) Solve for wavelength. R = 1.0973E7 Z = 4 The first n^2 in the formula is 1 The second n&2 in the formula is 0 So 1.0973E7*4^2((1-0) and that gives you 1...
October 11, 2014

Chemistry
2 mols Mg will produce 2 mols MgO. 2 mols MgO x molar mass MgO = grams MgO
October 11, 2014

Chemistry
2Li3PO4 + 3Ca(NO3)2 ==> Ca3(PO4)2 + 6LiNO3
October 11, 2014

Chemistry
If you just want to melt the ice and not heat up the country side you would need (grams ice x heat fusion) You will need to convert 20 L ice to grams and you can do that with density in which grams = volume x density. Look up heat fusion and multiply.
October 11, 2014

AP Chemistry
I don't think #1 is right so I believe you should rethink your other answers although I didn't look at them after #2. My reason for this response is I assume the procedure went something like this. (initial mass alum - final mass alum) = loss in mass and that is mass ...
October 11, 2014

CHEMISTRY
V2O5 + 2H2 ==> V2O3 + 2H2O
October 11, 2014

CHemistry
pKsp = 9.74 = -log Ksp Ksp = 1.82E-10 .............AgCl ==> Ag^+ + Cl^- I............solid....0.......0 C............solid....x.......x E............solid....x...... 0.1 The 0.1 for Cl^- comes from the problem Ksp AgCl =1.82E-10 = (Ag^+)(Cl^-) 1.82E-10 = (x)(0.1) Solve for ...
October 11, 2014

Chem lab
As well as what you've come up with.
October 11, 2014

Chem lab
You need to tell us what experiment you did and how you went about it.
October 11, 2014

chemistry
Two simple ways: 1. The blue or green color of the original solution is still there or 2. Let the Cu(OH)2 ppt settle and add 1-2 drops to the supernatant liquid at the top of the container and see if more ppt forms.
October 11, 2014

Chem
Total mols = mols O2 + mols N2 = 1.58 + 0.420 = ? You divided mols/molar mass to find X and that isn't right. XO2 = nO2/total mols. XN2 = nN2/total mols Then you can find partial pressure of each this way. pO2 = XO2*Ptotal pN2 = XN2*Ptotal
October 11, 2014

Chem
When you post a problem like this it does little good unless you post the constants you are using too. We are likely to use the wrong set in our book and the answer we come up may not agree with yours but both could be right with the constants we've used. As it turns out ...
October 11, 2014

Chem
I don't agree with that.I would have carried the 24.6 out another place and rounded later. That part is ok and I obtained 24.63 L; however, if you use P(Mm)= dRT you never need to go through the volume calculation since it isn't in the final equation. You just plug in ...
October 11, 2014

chemistry
This is a limiting reagent (LR) problem. You know that when amounts have been given for BOTH reactants. I'll use abbreviations alco + acetic ==> acetate + H2O mols alco = grams/molar mass mols acetic = grams/molar mass Using the coefficients in the balanced equation, ...
October 11, 2014

Dav public school
The R group donates electrons to the O atom making it more negative which makes it harder to release a hydrogen atom.
October 10, 2014

chem
(v1/T1) = (v2/T2) Don't forget to use T in kelvin.
October 10, 2014

Chemistry URGENT!!
The smallest anion probably is H^-. I'm not sure you can say what the largest anion (or cation) is since complex ions can carry a - or + charge and these can get large. It would be complicated to even try to calculate the diameter of those things. For example Fe(CN)63- or ...
October 10, 2014

chem
There is a short way and a long way to do this. Here is the long way. Use PV = nRT and solve for n = mols H2 gas in the 50.0L container. You don't have a T listed so make up one and use it throughout the problem. Use PV = nRT and solve for n = mols O2 in the 25.0 L ...
October 10, 2014

Chemistry
Probably H^+. That's just a bare proton while the other elements have electron shells. Even He^2+ should larger than a H^+.
October 10, 2014

Chemistry
HClO4 + NaOH ==> NaClO4 + H2O mols HClO4 = M x L = ? Using the coefficients in the balanced equation (they are 1:1), convert mols HClO4 to mols NaOH. Now M NaOH = mols/L. You know mols and L, solve for M
October 10, 2014

Conversion again (3 question finish-up)
You may want fractions because you thought you had a sure fire way to work these problems on your last post. I have posted a response there since your 0.114 fraction IS equal to 57/500 but 57/500 is NOT the fraction for the problem of 10 ft/min to mph.
October 10, 2014

Conversion again (3 question finish-up)
You need to learn how to do the conversions. I'll show you how to do the first one. You want to convert m/min to km/sec Let's work on the m to km first. There are 1000 m in a km. That 1000 m/km is a conversion factor. Therefore, 0.85 m x factor = km. Now plug in the ...
October 10, 2014

chemistry
mols C2H5OH = grams/molar mass. Use density to convert mL to grams. mols H2O = grams/molar mass. Use density to convert mL to grams. Then XC2H5OH = nC2H5OH/total mols XH2O = nH2O/total mols pH2O = XH2O x PoH2O,/sub> pC2H5OH = XC2H5OH x PoC2H5OH Ptotal = pC2H5OH + pH2O
October 10, 2014

Chemistry
2C2H2 + 5O2 --> 4CO2 + 2H2O I assume the T is constant. Use PV = nRT. Plug in P = 145 atm V = 7.00 L N = ? R = 0.08206 T = not given but I would use any convenient number, say 300. Solve for n of O2. Use n and the equation to convert to mols C2H2, plug that n back into PV...
October 10, 2014

chem 12
The answer isn't 18 g/s; it's 18 g/10 seconds and problem asked for grams in 10 seconds.
October 10, 2014

chem 12
0.75 mols/min x(1 min/60 s) x 10 s = approx 0.12 mols C12H22O11 in 10 s. You get 12 times that C so you have 0.12 x 12 = approx 1.5 mol C and that x atomic mass C = grams. Remember those first numbers are approximations so you should recalculate from the beginning.
October 10, 2014

chem 12
See my response above but I don't think the answer is 18 g/s.
October 10, 2014

Conversion
Yes, 0.114 is 57/500 but 57/500 is not the right fraction. The answer really is 0.1136364 which rounds to 0.114 mi/hr. I don't know how you arrived at 57/500. The lowest fraction is 15/132.
October 10, 2014

College chemistry
mols Cl^- = M x L = ? Using the coefficients in the balanced equation, convert mols Cl^- to mols Cr2O7^2- and that is mols Cl^- x 1/6 = ? The M Cr2O7^2- = mols/L. You know M and mols, solve for L and convert to mL.
October 10, 2014

Chemistry
C3H8 + 5O2 ==> 3CO2 + 4H2O dHrxn = (n*dHf products) - (n*dhf reactants) Then convert dHrxn from 44g (1 mol in the equation above) to 19.0g. ? = dHrxn x 19.0/44 If you carry the sign over from the first calculation you will get the correct sign for the smaller amount.
October 10, 2014

Chemistry
H should be H2. FeClO4 should be Fe(ClO4)2 Fe + 2HClO4 ==> Fe(ClO4)2 + H2 This equation you wrote is balanced but the predominate product isn't Fe(ClO4)3. 2Fe(s) + 6HClO4 (aq) --> 3H2 (g) + 2Fe(ClO4)3
October 10, 2014

chemistry
heat lost in melting ice + heat gained by H2O from melted ice + heat lost by water @ 25C = 0 heat lost by melted ice = mass x heat fusion = 15 x heat fusion. heat gained by H2O from ice = mass x specific heat H2O x (Tfinal-Tintial) = 15 x specific heat H2O x (Tfinal-0) heat ...
October 10, 2014

chemistry
In round numbers the pH is 5.0. You dilute the base along with the acid and by the same amount; therefore, the ratio of base to acid stays the same and the pH doesn't change. Dilution has no effect on the pH of a buffer but of course we all know that has limitations.
October 10, 2014

Chemistry
So c = f*w. f = frequency in Hz w = wavelength in m c is speed of light in m/s
October 10, 2014

Chemistry
See your post above.
October 10, 2014

chemistry
mols = grams/atomic mass Al.
October 10, 2014

Chemistry
https://www.google.com/search?q=calorimeter+pictgure&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=sb
October 9, 2014

chemistry
mols Mg from MgBr2 = M x L = ? mols Mg from Mg(Ac)2 = M x L (Mg) in final solution = total mols Mg/total L solution.
October 9, 2014

chemistry
I don't think so.
October 9, 2014

Pharmacy Tech
(15 g/2000 mL) x 100 = ?%w/v and this assumes the solution is 2000 mL and not more than that. Technically I can't do this calculation unless you gave a density.
October 9, 2014

Chemistry
NaOH + HA --> NaA + H2O mols NaOH = M x L = ? mols HA = same since the ratio of acid to base is 1:1 (look at the coefficients) mols HA = grams/molecular weight. You know mols HA and grams HA, solve for molecular weight.
October 9, 2014

Chemistry
The pH of the solution will be determined essentially by the formic acid because it is the stronger of the two. I would do an ICE chart for HCOOH and solve for H^+, then convert to pH.
October 9, 2014

chemistry
mols KOH = grams/molar mass = ? mols HCl = M x L Which is in excess. How much is the excess. If H in excess, (H^+) = mols/L solution. If OH in excess, ((OH^-) = mols/L. Then pH = -log(H^+) if H^+ is in excess. If OH is in excess it is pOH = -log(OH^-), the pH + pOH = pKw = 14...
October 9, 2014

chem
You didn't give an equation.
October 9, 2014

chemistry
2HNO3 + Ca(OH)2 ==> Ca(NO3)2 + 2H2O mols Ca(OH)2 = M x L = ? Convert mols Ca(OH)2 to mols HNO3 using the coefficients in the balanced equation. M HNO3 = mols HNO3/L HNO3
October 9, 2014

Chemistry
I don't see a pressure or a density. Use PV = nRT assuming you have a pressure somewhere and solve for = number of mols. Then find the density of liquid N2 at that temperature (I don't know what K| stands for) and use volume = mass/density.
October 9, 2014

Chem 2
mols urea = grams/molar mass mols H2O = grams/molar mass Xurea = nurea/total mols from above. XH2O = nH2O/total mols. PH2O = Xurea*PoH2O Lowering is Plowering = XH2O*PoH2O
October 9, 2014

Chemistry
Use the HH equation. pH = 4.80 pKa = 4.74 Solve for the ratio of (base)/(acid). That is equation 1. The second equation is (base) + (acid) = 0.15 Solve these two equations for (base) and (acid), then convert to mL by using the dilution formula of mL1 x M1 = mL2 x M2 mL1 x 1M ...
October 8, 2014

Organic Chemistry
You've said it funny. Do you mean it is 0.1g benzoic acid + 0.1 of X and 0.1 g of Y? If so then mols = g/molar mass = 0.1g/molar mass benzoic acid which is about 122. If that isn't what you meant and the mass benzoic acid is 0.3 g, then 0.3/122 = mols benzoic acid.
October 8, 2014

incomplete---chemistry

October 8, 2014

Chem Help Please!
mols NaOH needed = M x L = ? Then grams = mols x molar mass = ? Weigh out the NaOH, add to a volumetric flask, add some water, swirl to dissolve all of the solid, make to the mark of the flask, mix thoroughly. Same for HCl.
October 8, 2014

Chemistry
mols = grams/molar mass
October 8, 2014

chemistry
There are 6.02E23 molecules in 1 mol so there are 0.07 x 6.02E23 molecules in 0.07 mols. Since there are 5 O atoms in 1 molecule of N2O5, # O atoms will be 5x the number of molecules N2O5.
October 8, 2014

Chem
2K + Br2 ==> 2KBr mols K = 2/atomic mass K = about 0.05 mols Br2 = 2/molar mass Br2 = about 0.012 Convert mols K to mols Br2. That's about 0.05 x (1 mol Br2/2 mols K) = about 0.05 x 1/2 = about 0.025. Do you have that many mols Br2? NO, so Br2 is the limiting reagent.
October 8, 2014

o-chem
ethyl 4-aminobenzoate is an ester. The NaOH cleaves the ester and forms CH3CH2OH and the sodium salt of 4-aminobenzoic acid. Then the addition of HCl replaces the Na^+ with a H^+ to form the 4-aminobenzoic acid
October 8, 2014

Chemistry
There are some rather large molecules that have something other than C. Si, for example.
October 8, 2014

Chemistry
C, H, and O atoms hooked together in different numbers and in different arrangements.
October 8, 2014

Chemisty
Right so far. Find mols Ag2S, convert to mols NaNO3, convert to g NaNO3 and stick in the % formula. %NaNO3 = (mass NaNO3/mass sample)*100 = ?
October 8, 2014

Chemistry
mols NO3^- in KNO3 = M x L = ? mols NO3^- in Mg(NO3)2 = 2*M x L = ? M NO3^- = total mols/total L solution
October 8, 2014

chemistry
mols K3Fe(CN)6 = M x L = 1E-3M x 0.100 L = ? Then grams = mols x molar mass = 1E-4 x 329.24 = 0.032924 g The NaNO3 provides only the 100 mL volume. In the end you will have a solution that is 1E-3 M in KeFe(CN)6 and also 0.2 M in NaNO3
October 8, 2014

Chemistry
The N-H stretching is not there in the dimethyl compound because the H atoms are missing on the -NH2 portion.
October 8, 2014

Chemistry
The general gas law is PV = nRT. n = grams/molar mass which makes this come out to be PV = gRT/M and this can be rearranged to P = gRT/MV where M is molar mass or P*M = gRT. Substitute and solve for M = molar mass. I get about 21 but you need a more accurate number than that ...
October 8, 2014

Chemistry
2Ag2O ==> 4Ag + O2 PV = nRT Ptotal = pO2 + pH2O 760 = pO2 + 26.7 pO2 = 760-26.7 and convert to atm. Solve for n = mols O2 and don't forget to convert T to kelvin. Then ? mols O2 x (2 mols Ag2O/1 mol O2) = ? mols O2 x 2/1 = ?? Ag2O Convert mols Ag2O to grams. g = mols x ...
October 8, 2014

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