Friday
December 19, 2014

Posts by DrBob222


Total # Posts: 46,144

To Brooke--your posts below
I have posted responses to your question on propane/butane and the Fe/Al problem below. They are about a page down from this post.
October 17, 2014

Equilibria
........Cu^2+ + 4NH3 ==> Cu(NH3)4^++ I.......0.1M....1.0M.......0M C......-0.1M...-0.4M......+0.1M E........0?.....0.6M.......0.1M What I usually do is to recognize that with a Kf of 2.1E13 the reaction goes far to the right and you have formed essentially all of the ...
October 17, 2014

chemistry
Read your post and correct.
October 17, 2014

chemistry
A little long but not that complicated. Use PV = nRT and solve for n = total number of mols C3H8 + C4H10. You have P and R but not T and V. I would use convenient numbers for those two and you can do that since the SAME numbers will be used in the CO2 part of the problem. ...
October 17, 2014

chemistry
This is much like the C3H8/C4H10 problem but perhaps a little easier to follow. First I would conver the H2 gas in the PV = nRT formula and solve for n = number of mols. I obtained 0.00139 mols H2 gas at the conditions listed. I didn't know how far to carry the decimal; I ...
October 17, 2014

Chemistry
That equation will tell you how to dilute it. But you still must have the amount of the SrCl2 used. Let's say you used 100 mL, then 100mL x 4.7M = 45000 mL x M Solve for M of the 45 L material.
October 17, 2014

Chemistry
Sr WHAT? How much of that Sr whatever was used. mL1 x M1 = mL2 x M2
October 17, 2014

CHEMISTRY
formula units = mass/formula unit mass formula units = 1.90/60.08 =?
October 16, 2014

chemistry
Note: L is liters; the second celsius is not correct. Use (V1/T1) = (V2/T2) Remember to change T to kelvin.
October 16, 2014

chemistry
That makes it easier. Use mL1 x M1 = mL2 x M2 385*0856 = mL2 x 4.93 Solve for mL2. Directions then would be, measure out mL2 volume of 4.93M solution and add enough water to make 385 mL. The final solution will be 0.856 M.
October 16, 2014

chemistry
I assume you know the difference between 0.856 m and 0.856 M. Is this really m or should it be M?
October 16, 2014

chemistry
H2 + Cl2 ==> 2HCl This is a limiting reagent (LR) problem. You know that because amounts are given for BOTH reactants. mols H2 = grams/molar mass = ? mols Cl2 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols H2 to mols HCl. Do the same ...
October 16, 2014

Chemist - Grade 9 - Urgent.
I'm interested in what kind of trouble you are having answering this question. Ba and Sr are in the same column.
October 16, 2014

science help
Of course.
October 16, 2014

science help
Protons have a +1 charge. Electrons have a -1 charge. If the atom is to be neutral the number of protons MUST be the same as the number of electrons.
October 16, 2014

science help
I agree with A.
October 16, 2014

Ions and octet rule
Look on the periodic table for element #31. The number of protons is 31. If it were neutral it would have 31 electrons; since it has a +3 charge it must have 3 fewer electrons.
October 16, 2014

chemistry
3; i.e., 8,5 and 1. You can write that as 8.51E4 to show that.
October 16, 2014

Chemistry
Balance the equation between Fe(II) and Cr2O7^2-. Frankly, I am not familiar with the term "equivalent to xx mL of yy M" something else. I assume that means that xx mL of yyM was used to titrate it to the equivalence point. If that is it, then Convert mols Cr2O7^2- ...
October 16, 2014

Chemistry
2KClO3 ==> 2KCl + 3O2 dH = -78 kJ or you could write KClO3 ==> KCl + 3/2 O2 dH = -39 kJ/mol
October 16, 2014

big oops--chem
I forgot to tell you that you must convert the 4100 J to L*atm. Divide by 101.325.
October 16, 2014

chem
W = pdV. If the gas is expanding it does work on the surroundings; therefore, W = -4100. -4100 = -2*(V2-V1)
October 16, 2014

chemistry
I am too. Ammonium bromide is a solid and without the density the volume can't be calculated. Since you know 6.022E23 molecules is one (1) mol, you know you have 3.85E24/6.022E23 = ? moles. Then g NH4Br = mols x molar mass = ? Finally, density = mass x volume. You know ...
October 16, 2014

Chemistry
Here is a good diagram and this diagram is for an endothermic reaction and the reaction as shown is endothermic. https://www.google.com/search?q=activation+energy+vs+reverse+activation+energy&client=firefox-a&hs=b6F&rls=org.mozilla:en-US:official&channel=sb&tbm=isch&tbo=u&...
October 16, 2014

Chemistry
These problems are worked the same as a stoichiometry problem. That is, 0.5 mol Fe/10s = 0.05 mol/s, then convert to Fe2O3 by 0.05 mols/x x (1 mol Fe2O3)/2 mols Fe) = 0.025 mol Fe2O3/s.
October 16, 2014

Chemistry
Yes, 3 is a heterogeneous reaction. So is 2.
October 16, 2014

Chemistry
I don't see a reaction 3a. I see a reaction 3 and that one heterogeneous. So is 2. I think the reaction rate will increase for BOTH 2 and 3 although I think 3 is less so than 2.
October 16, 2014

chemistry
2Al ==> Al2(SO4)3.K2SO4.24H2O The above isn't fully balanced but I've balanced the only part that matters. mols Al = grams/molar mass = approx 0.0074 Using the coefficients in the equation convert mols Al to mols of alum. That's 0.0074 x (1 mol alum/2 mol Al) = ...
October 16, 2014

Chemistry
O2 + 2H2 ==> 2H2O This is a limiting reagent (LR) problem. You know that when amounts are given for BOTH reactants. mols O2 = grams/molar mass = approx 0.18 but you need a more accurate answer for this and all of the calculations that follow. mols H2 = 12.0/2 = 6 Using the ...
October 16, 2014

Chemistry
Fe(NO3)2 + 2OH^- ==> Fe(OH)2 + 2NO3^- Then Fe(OH)2 + heat ==> FeO + H2O mols Fe(NO3)2 = mols x L = ? mols FeO = mols Fe(NO3)2 (look at the equation; 1 mol Fe(NO3)2 = 1 mol FeO) Then g Fe) = mols FeO x molar mass FeO.
October 16, 2014

Chemistry
Mn(NO3)2 + 2KOH ==> Mn(OH)2 + 2KNO3 mols Mn^2+ = M x L = ? mols Mn(OH)2 = 2x mols Mn^2+.(look at the equation; it is 2 mols KOH for 1 mol Mn(NO3)2. Then M KOH = mols kOH/L KOH. You know mols KOH and M KOH, solve for L KOH and convert to mL.
October 16, 2014

chemistry
heat lost by Al + heat gained by water = 0 (mass Al x specific heat Al x (Tfinal-Tinitial) + (mass H2O x specific heat H2O x (Tfinal-Tinitial) = 0 Substitute and solve for Tf of the Al and H2O.
October 15, 2014

chemistry
S + O2 ==> SO2 q = Ccal x delta T q = 2.03 kcal/c x 1.17 = ? That q is for 1.07. To find per grams it is q/1.07 = ? kcal/g And q/1.07 x molar mass S gives kcal/mol.
October 15, 2014

Analytical Chem
I think the pH comes from the reaction of citric acid with NaOH. That is a buffer. ...........H3C + NaOH ==> NaH2C + H2O I..........0.3...0..........0 add..............0.7........... C.........-0.3..-0.3.........0.3 E...........0.....0.4........0.3 pH = pKa3 + log (base)/(...
October 15, 2014

Chemistry
%H in the BxHy = (g H/mass sample)*100 g H atoms (0.540 x 2/18)= about 0.0600 and %H atoms = (0.06/0.492)*100 = about 12% but you should be more accurate than that on all calculations that follow. Since the only other element is B, then B must be 100%-12% = about 88% Now take ...
October 15, 2014

chemistry
How did you make isoamyl bromide? What procedure did you follow?
October 15, 2014

Chem
delta T = Kb*m So which will give the largest delta T? Since m is the same it must depend on Kb?
October 15, 2014

chemistry
E is the only correct one. However, your statements don't match the answers. Potassium sulfate is K2SO4 and ammonium nitrate is NH4NO3. Another error is ammonium sulfate is (NH4)2SO4.
October 15, 2014

Chemistry
mols CO2 at STP = 3L/22.4 = ? mols O2 molecules = same since there is 1 O2 in 1 CO2. Then 1 mol contains 6.02E23 molecules.
October 15, 2014

Chemistry
I think the secret is how you search google. I have found that to find calculations that I type in "how to calculate Ksp" without the quotation marks and I get several sites showing Ksp work.. That will usually bring up a calculations page (or several of them) and I ...
October 15, 2014

Chemistry
1 mol CH4 has 6.02E23 molecules 1 mol H2O has 6.02E23 molecules so 1 mol CH4 has same number molecules as 1 mol H2O. mols methane = g/molar mass = 32/16 = 2 mol CH4. That has 2*4 = 8 mols H atoms. mols H2O vs CH4; You must multiply mols H in H2O by 2 to get mols H in CH4. So 2...
October 15, 2014

CHEMISTRY
OK. Remember that compounds must add up with oxidation states to zero; ions must add up to the charge on the ion. So Cr on the left is + 6 EACH and on the right is 3+.(O is -2 and there are two of them which makes -4 total so Cr must be +3 to leave a -1 charge on the CrO2^- ...
October 15, 2014

CHEMISTRY
Tell me what you know to do and I can go from there. Do you have a system; there are two or three available and all of them work very well. Let me know the system too so I won't switch systems on you.
October 15, 2014

typo--Chemistry
I hit the - sign instead of the = sign. you have 20*0.2 = 4 g CaCO3 to start.
October 15, 2014

Chemistry
Do you know how to work a stoichiometry problem if you have the quantities. 20 g of 20% means you have 20*0.2 - 4 g CaCO3 to start.
October 15, 2014

Chemistry
heat lost by Cu + heat gained by water = 0 (mass Cu x specific heat Cu x (Tfinal-Tinitial) + (mass H2O x specific heat H2O x (Tfinal-Tinitial) = 0 Substitute the numbers and solve for Tf.
October 15, 2014

Chem
1 mol CaCO3 will produce 1 mol CO2
October 15, 2014

Chem
I'm not sure I understand the question. Is that a mixture of CaCO3 and Ca(HCO3)2. Or are you asking for the rxn you wrote? The rxn you wrote can be corrected as follows: 2CaCO3 + 2HCl ==> Ca(HCO3)2 + CaCl2 or if you decomose the CO3^2- all way it will be CaCO3 + 2HCl...
October 15, 2014

Chmistry
Look up the atomic weights and add them; e.g., you probably meant K2SO4.12H2O. The following is just from memory; you should look them up for more accurate numbers. (2*39.1) + 32 +(4*16) + (12*18) = ?
October 15, 2014

Analytical CHM
My personal opinion is that the second derivative method is best. The bisection method, in my opinion, loses some of its preciseness because the flat parts of the graph are not parallel to each other which leads to not being exactly where the end point is. The first derivative...
October 15, 2014

chemistry
By mass, by volume, by what. I'll assume by mass. [(x)/(g soln)]*100 = 1.15 Solve for x = grams solute. That's about 5 g but you need a more accurate number than that. Dissolve approx 5 g in approx 445 g H2O. Remember to confirm the numbers with better accuracy.
October 15, 2014

chemistry
grams = M x L x molar mass
October 15, 2014

6th grade math
If the diver were 30 feet below sea level and she went down another 12 feet then she must be 42 feet below sea level. That makes it -42 feet.
October 15, 2014

Chemistry
You can't assign V1, V2, T1, and T2 or is it some other problem?
October 14, 2014

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

Chem---DrBob222
If that is 2-bromo-2-methylpropane here it is. https://www.google.com/search?q=2-bromo-2-methylpropane&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=sb
October 14, 2014

chemistry
q = mass x heat vaporization
October 14, 2014

Chemistry
You'll never get the correct answer without the correct conversion factor. Note carefully that you have no decimal. It should be 1 km = 0.6214 miles 1000 m = 1 km 60 seconds = 1 minute 60 minutes = 1 hour. 2.998E8 m/s x (1 km/1000m) x (0.6214 miles/km) x (60 sec/min) x (60...
October 14, 2014

Math (Ms.Sue)
Look at Ms.Sue's answer and my diagram.
October 14, 2014

Math (Ms.Sue)
home | | 2.67 mi | | | park..now back home |_1.5_\
October 14, 2014

Science
KE = 1/2 mv^2 m will be in kg.
October 14, 2014

chemistry
KNO3(s) + H2O ==> KNO3(aq) The temperature DECREASED so the solution process is endothermic. Heat is absorbed. q = mass H2O x specific heat H2O x (Tfinal-Tinitial) + Ccal*(Tfinal-Tinitial) q = [200g H2O x 4.184 J/g*C x (22.63-23.57)] + [8.33(22.63-23.57)] q = -?. That's...
October 14, 2014

chemistry
This could easily be a page of writing. You fill in the spaces. Mg + 2HCl ==> MgCl2 + H2(g) 3MgCl2 + 2Na3PO4 ==> Mg3(PO4)2 + 6NaCl
October 14, 2014

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

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

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