Monday
November 24, 2014

Posts by DrBob222


Total # Posts: 45,580

chemistry
(NH4)2Cr2O7 → Cr2O3 + N2 + 4H2O .....2.5...................x........[1.0g] The Law of conservation of mass tells you that you don't lose anything. 2.5 = mass Cr2O3 + 1.0 mass Cr2O3 = ?
October 14, 2014

chemistry
I don't see a question here.
October 14, 2014

science
q = mass Cu x specific heat Cu x ((Tfinal-Tnitial) use q = 90,000 J. Use mass Cu as 2000g specific heat comes out in J/g*C
October 14, 2014

Chemistry
You would expect the reactive to go up as you go down the table because that last outside electron is further and further away from the nucleus. Reactivity should be Li<Na<K<Rb<Cs<Fr. Look at the melting points for Li about 180 Na about 98 K about 63 You can see...
October 14, 2014

Science Please Check!
I agree with both of your choices. I don't know if you've seen this or not but a way to remember and/or identify a carbohydrate is that they are just that; i.e., a CARBO (meaning C) and HYDRATE (meaning water or H2O) glucose and fructose are C6H12O6. That's 6C and ...
October 14, 2014

Science
for what?
October 14, 2014

Physical Science- Math skills
Rachel obtains 14/10 = 1.4 g/mL whereas she should obtain 14/9 = 1.555 which I would round to 1.6 g/mL if she had measured the volume correctly.
October 14, 2014

Chemistry
Convert 0.935 inches to cm. Use (4/3)*pi*r^3 to find the volume of the sphere in cubic centimeters. Use mass = volume x density to find the mass Then mols = grams/atomic mass.
October 14, 2014

Chemsitry
q needed to raise T of ice at -24.3 to zero is q1 = mass ice x specific heat ice x (Tfinal-Tinitial). We don't know mass ice yet but this equation would look like this. q1 = mass ice x 2.01 x [0-(-24.3)] = mass ice x 48.84 = 48.84m q2 = heat needed to melt ice at zero to ...
October 14, 2014

chem
Ptotal = pO2 + pH2O You want p in atm? Convert 23.8 torr to atm. 0.8 atm = pO2 + (23.8/760) Solve for pO2. You want p in torr? Convert 0.8 atm to torr 0.8*760 = pO2 + 23.8 Solve for pO2.
October 14, 2014

chem
(V1/T1) = (V2/T2) Remember that T must be in kelvin.
October 14, 2014

chem
I agree.
October 14, 2014

chem
Note the correct spelling of celsius. Use (V1/T1) = (V2/T2) Remember T must be in kelvin
October 14, 2014

chem
Use PV = nRT P in atm and T in kelvin
October 14, 2014

Chemistry
I am terribly confused but I can make the following comments. The molar absorptivity is USUALLY given in mols/L and that's the way it is tabulated in reference tables; however, your 0.225 is ok as long as you show the units that go with it as you've done. Then for the ...
October 14, 2014

Chemistry
No. pKa is 3.86 I think. I looked it up on the web and I've posted the way to work the problem earlier. If you are parsing the question, the problem is asking for mols Mg(OH)2 required to produce a pH of 4.0 from that solution of lactic acid. Looking up pKa is just a part ...
October 14, 2014

Chemistry
I assume you meant CaCl2 but I can't answer with the data listed. stable to what? -36 what?
October 14, 2014

Chem Help Please!
This site does not have drawing capability.
October 14, 2014

chemistry
2S2O3^2- + I2 ==> S4O6^2- + 2I^- mols S2O3^2- = M x L = ? mols I2 = 1/2 that (look at the coefficients in the balanced equation) M I2 = mols I2/L I2.
October 14, 2014

Chem---DrBob222
First I'm not an organic chemist. When I took organic it was all memory work. Now it is all mechanisms. So I think I remember it's 3o > 2o > 1o but I can't tell you why. Here is a site that may help you. http://www.masterorganicchemistry.com/2012/08/08/...
October 14, 2014

chem
This is a Ksp problem with a common ion of Pb from the Pb(NO3)2. ..........Pb(IO3)2 ==> Pb^2+ + 2IO3^- I.........solid.........0........0 C.........solid.........x........2x E.........solid.........x........2x Pb(NO3)2 is 100% dissociated. ........Pb(NO3)2 ==> Pb^2+ + ...
October 13, 2014

Science
I found a web site that said average size was 6 micrometers diameter; 3 mm is 3 micrometers so if that was radius it would be about right.
October 13, 2014

Science
I don't know the answer to the question but there are no units on a. Isn't 3 mm and 0.003 m the same thing? So it can't be b or c and you KNOW it isn't 3m. So it must be 0.003 whatever unit you omitted.
October 13, 2014

chemistry
No. You calculate the time in seconds and convert to ns. 1O^9 ns = 1 s
October 13, 2014

chemistry
I don't think you or I have the equipment to calculate the speed of light. It is 3E8 m/s Convert 2462 mi to meters then 3E8 m/s x # sec = 2462 converted to m. The conversion factor is 1 mile = 1609.34 meters.
October 13, 2014

Chemistry 30
dHrxn = (n*dHf products) - (n*dHf reactants) Look up delta H formation in tables (usually in the back of your text but also on the web), plug into the above and calculate.
October 13, 2014

AP Chem
OK. What you want is delta H for the equation of NH3 + HCl ==> NH4Cl You get that by taking the equation for reaction 1 and adding the reverse of the equation for reaction 2 as shown below. But before I do that I want to point out that equation 2 is not correct. Perhaps you...
October 13, 2014

AP Chem
It appears to me that you haven't posted all of the information or at least I don't know what's going on. Is this an experiment you are conducting? I don't understand what you have determined; ie., the "theoretical enthalpy changes of each reaction." ...
October 13, 2014

chemistry
Usw PV = nRT and solve for n = number of mols air. Then n = grams/molar mass. Solve for grams. Don't forget T must be in kelvin.
October 13, 2014

chemistry
The buffer starts with 4 mL x 0.01 = 0.04 mllimols HA and 3 mL x 0.01 = 0.03 millimoles A^- ........HA + OH^= --> A^- + H2O I......0.04..0.......0.03..... add........0.002-------------- C....-0.002.-0.002.+0.002............. E...0.038....0.....0.032.......... So you have 0....
October 13, 2014

Chemistry
Look up the pKa for lactic acid. You have 200 x 0.15M HL(lactic acid) = 30 millimols HL. Set up an ICE chart. You have 30 mmols HL and zero OH^- and zero L^-. You want to add NaOH to it to form the L^- and take away from the HL while doing that. ...........HL + OH^- ==> L...
October 13, 2014

Chemistry
See your post later (above).
October 13, 2014

Chemistry Equation
H2SO4 --> H^+ + HSO4^- (100%) HSO4^- ==> H^+ + SO4^2- There is no k1. k2 = (H^+)(SO4^2-)/(HSO4^-) CO3^2- + H^+ ==> HCO3^- kb1 = (HCO3^-)/(H^+)(CO3^2-) HCO3^- + H^+ ==> H2CO3 kb2 = (H2CO3)/(H^+)(HCO3^-)
October 13, 2014

chemistry pH
At the beginning you have 0.29 M LiOH. That ionizes 100% so (OH^-) = 0.29M pOH = -log(OH^-); solve for pOH,then pOH + pH = pKw = 14. YOu know pKw and pOH solve for pH. To start we have 25 mL x 0.29 M = approx 7 millimols LiOH but you need a better answer on this as well as all...
October 13, 2014

chemistry
BOH = weak base BOH + HCl ==> BCl + H2O So the pH at the equivalence point will be the pH of a solution of the salt, BCl. The B^+ will be hydrolyzed to form B^+ + HOH ==> BOH + H^+ Ka for B^+ = (Kw/Kb for BOH) - (H^+)(BOH)/(B^+) (Kw/4.0E-9) = (x)(x)/(0.110-x) and solve ...
October 13, 2014

chemistry
I answered this below earlier. If you don't understand something in my response you're welcome to ask for clarification but posting again just means you want someone to do the work for you.
October 13, 2014

Chemistry
Call Ascorbic acid just HA. HA + NaOH ==> H2O + NaA mols vitamin C (HA) = grams/molar mass = 0.500/molar mass mols NaOH required = same since the ratio in the equation is 1:1. Then M NaOH = mols NaOH/L NaOH. You have M NaOH and mols NaOH, solve for L NaOH and convert to mL.
October 13, 2014

chemistry
C'mon. Look up the properties of H2 gas and O2 gas and liquid water and you will know the answer.
October 13, 2014

College Chemistry lab
Did you have a standard concn of Fe and you have an absorbance for that? Or do you the the absorptivity or extinction coefficient?
October 13, 2014

chemistry
In all of my years I have never heard of NaNO3 being referred to as saltpeter. KNO3 yes but not NaNO3. One web site where I looked just now lists EITHER NaNO3 or KNO3 (or other nitrates); another lists just KNO3. Just a side note. NaNO3 + H2SO4 ==> NaHSO4 + HNO3 dHrxn = (n*...
October 13, 2014

Chemistry
I have searched diligently and can't find what FA stands for; however, I did find that FA 1 or FA2 ........FA 7 are codes used to label solution or solids on exams. As I understand it the code for the chemical is on the label and if needed the chemical is identified in the...
October 13, 2014

chemistry
It's a base. It accepts a proton (or two protons).
October 13, 2014

chemistry/math
See your other post above.
October 13, 2014

chemistry/math
Plug into the definition of M. M = mols/L. You know mols and M, solve for L
October 13, 2014

chemistry
This is a limiting reagent (LR) problem. You know that when values are given for BOTH reactants. Mg(OH)2(s) + 2HCl(aq) MgCl2(aq) + 2H2O(l) mols HCl = M x L = approx 0.038 but you need a better answer than that estimate. mols Mg(OH)2 = approx 0.05 Convert mols HCl to mols MgCl2...
October 13, 2014

Chemistry
Not quite. ammonium chloride is NH4Cl. potassium sulfate is K2SO4. Is this a trick question. There is no reaction, just a mixing of the ions. Is this an aqueous solution? If solids: NH4Cl(s) + K2SO4(s) ==> No reaction If aqueous solutions: NH4Cl(aq) + K2SO4(aq) ==>NH4^+(...
October 13, 2014

Chemistry 101
3NaOH + H3PO4 ==> Na3PO4 + 3H2O mols NaOH = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols NaOH to mols Na3PO4. That's ?mols NaOH x (1 mol Na3PO4/3 mols NaOH) = ? mols NaOH x 1/3 = ? mols Na3PO4. Steps for solving stoichiometry ...
October 13, 2014

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

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