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February 1, 2015

Posts by DrBob222


Total # Posts: 46,677

Science Help!
I don't agree with your answer. What is different about the reactants and products in C? I don't see any difference (except for a typo on C4H1 and I'm sure you meant to type in C4H10.)
November 14, 2014

chem
In one neat and tidy equation it is 1.125 g/cc x 1000 cc x (20/100) x (1 mol/40g) = ? Molar In pieces. mass of 1000 cc is 1.125 g/cc x 1000 cc = ? mass of NaOH in that 1000 cc solution is ?mass x 0.20 = ? mols NaOH in that mass NaOH is ?grams/molar mass All of that gives you ...
November 14, 2014

science Help 911!!
B and D are not right which leaves you with the only other two that must be right. It is true that Na and Cl2 WILL REACT TOGETHER to form an ionic bond but they do that by forming a Na^+ ion and a Cl^- ion. The question is what is "part" of an ionic bond; not wht ...
November 14, 2014

Science Help!
Absolutely. An endothermic reaction uses heat from the surroundings to make it go. An exothermic reaction gives off heat. Exploding fireworks, paper burning, and cellular respiration (such as humans breathing) all are examples of exothermic reactions in which heat is released ...
November 14, 2014

Science Help!
That's right. Do you think fireworks exploding is ABSORBING heat from the surroundings? Do you think paper burnins is absorbing heat from the surroundings?
November 14, 2014

Science Help!
What is an endothermic reaction?
November 14, 2014

Science Help!
I don't think C is the right answer. I don't think humans engage in photosynthesis. Plants do that. Now let me ask a question. I see you have posted more than a few science questions. Are we doing all of your homework for you in science?
November 14, 2014

Science
OK. It's obvious that if you don't know what Thomson's model is you can't very well describe the differences and similarities. You could have read about that model in your text or you could have done a Google on it. But I can do that for you here. Thomson ...
November 14, 2014

Science
Can you tell me... what is Bohr's model? What is JJ Thomson's model?
November 14, 2014

Science Help!
D is correct.
November 14, 2014

Science Help!
D is correct.
November 14, 2014

Science Help!
A is not the right answer. Look up the difference between a physical change and a chemical change.
November 14, 2014

Science Help!
I would go with b also.
November 14, 2014

science Help 911!!
I would go with A also but I don't know why B couldn't be correct too. In fact I've always more or less equated atomic theory with the atomic model.
November 14, 2014

science Help 911!!
Yes, it form a covalent bond but papers that say chemical bond should be counted right also because a covalent bond is a chemical bond.
November 14, 2014

Chemistry
HCl + NaOH ==> NaCl + H2O mols HCl = M x L = ? Look at the coefficients in the balanced equation. mols HCl = mols NaOH. Then g NaOH = mols NaOH x molar mass NaOH = ? This is the theoretical yield. %yield = (mass NaOH/mass sample)*100 = ?
November 14, 2014

Chemistry
mols H2 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols H2 to mols H2SO4. Then M H2SO4 = mols H2SO4/L H2SO4. You know mols and M, solve for L.
November 14, 2014

Organic Chem
This is a limiting reagent (LR) problem. You know that because amounts are given for BOTH reactants. Using the coefficients in the balancaed equation, convert 12 mols KO2 to mols O2. Do the same to convert mols CO2 to mols O2. It is likely the two values will not be the same ...
November 14, 2014

chemistry
We can't draw these on this forum and I can find an OF^- on Google. Follow this AND the added instructions. Hope it makes sense. :O:F:. Add .. top of O, top of F, bottom of O, bottom of F and add -1 charge to the ion and you'll have it.
November 14, 2014

chemistry
Did you make up this problem or have it handed to you? However it was done you should recognize that H2S is a gas and isn't about to stand around in a titration vessel and wait to be titrated. Anyway, in the spirit of the problem here is how it is solved. H2S + Sr(OH)2 ==&...
November 14, 2014

chemistry
The problem says 22.11 and not 21.11 (and I made the same typo in my response) and atomic mass Zn is 65.38 and not 65.28.
November 13, 2014

chemistry
Did you make a typo? From your work I assume Ti is 15 and not 1 as you posted. Your q calculation is almost correct. It should be 100 mL x 4.18 x (21.11-Ti) = q in Joules. Note it's the water you're heating and although the Zn absorbs a little heat you're ignoring ...
November 13, 2014

sixth grade math
1 yes 2 no 3 yes
November 13, 2014

Chem
wavelength in m = h/mv mass is 9.1E-31 kg. Solve for wavelength and convert to nm.
November 13, 2014

Chemistry
OK. Let's look at the two 1s electrons. Remember those configurations give you n and l. So for 1s2 n must be 1 and s electrons have ell = 0 and the two electrons of 1s2 can have +1/2 and other one -1/2 Therefore, one electron has n = 1, l = 0 mL = 0 (see the rules;; i.e., ...
November 13, 2014

Chemistry
16S = 1s2 2s2 2p6 3s2 3p4 What is it about this that you don't understand? Here are the rules. n can be any whole number starting with 1. l can be any whole number less than n-1. ml can be -ell to +ell including 0. ms can be either +1/2 or -1/2.
November 13, 2014

chemistry
54.3 g/formula unit mass = ?
November 13, 2014

CHEM
0.254 what? mm, atm, kPa? and you want the total pressure where? in the flask? I don't know what you mean by total pressure.
November 13, 2014

O-Chem
We can't draw diagrams on this forum. Sorry about that. I suggest you try Google. Many of the sites show the mechanism.
November 13, 2014

chemistry
Two ways. If you have the grams NaCl, mols = grams/molar mass = ? If you have a solution (M) of NaCl, mols = M x L = ? Of if the solution is in molality(m), mols = m x kg solvent = ?
November 13, 2014

Chemistry
1. 2H2O2 ==> 2H2O + O2 mols H2O2 = grams/molar mass = 10/34 = 0.294/ Using the coefficients in the balanced equation, convert mols H2O2 to mols O2. That's 0.294 mols H2O2 x (1 mol O2/2 mols H2O2) = 0.294 mols H2O2 x 1/2 = 0.147 mols O2. Now convert mols O2 to grams. g ...
November 13, 2014

Chemistry
You must scroll down and find the original post. Here is a link. http://www.jiskha.com/display.cgi?id=1415924736
November 13, 2014

Chemistry
Bob Pursley answered your first post. It's below.
November 13, 2014

Chemistry
I've tried to help at your other post.
November 13, 2014

chemistry
3CaSO4 + 2K3PO4 ==> Ca3(PO4)2 + 3K2SO4
November 13, 2014

chemistry
Convert g H2 to volume using 1 mol H2 occupies 22.4 L at STP (alternatively you can use the PV = nRT and solve for volume). Convert g He to volume He the same way. Then plug into your v/v formula and solve for percent each.
November 13, 2014

Chemistry 11
I'm not sure I understand what you did. Here is what I would do. % anything = (g/total mass)*100 = ? Atomic mass Zn = 65.4 from your post. molar mass Zn(ClO3)2 from your post = 232.3 molar mass H2O = 18 The 21.5% Zn is (note you used 21%) percent Zn in the hydrate so %Zn...
November 13, 2014

chemistry
work in joules = kg x 9.81 x height in m = ?
November 13, 2014

chemistry
Yes but if your prof is picky about the number of significant figures you will get marked down. You're allowed 2 places (because of the 8.1 so you should round that number fo 0.26 AND place a unit on it of L.
November 13, 2014

chemistry
The usual formula for %v/v is (volume gas/total volume)*100 = %. (x L CO2/3.16L)*100 = 8.1% Solve for x L CO2.
November 13, 2014

Average problem word solving epicness
He needs a total of 5*65 = 325 points. He has(55+60+65+65) = 245 He needs 325-245 = 80 If you want to set this up in equation form it will be (55+60+65+65+x)/5 = = 65 and solve for x
November 13, 2014

chemistry
Use PV = nRT and solve for n = number of mols. Then n = grams/molar mass. You know molar mass and n, solve for grams.
November 13, 2014

science
Perhaps I may interject a little insight into this rudeness thing. 1. This is a homework help site, not a homework do site; i.e., our objective on this site is to help students understand a concept so they may work through a problem. That is to say that we USUALLY do NOT ...
November 13, 2014

Urgent- Science
Do you not get the disconnection between "indivisible" by Dalton and "pieces" by the neutron and electrons. Read about the plum pudding by Thomson. Do you understand what Rutherford showed with his alpha particle bombardment experiment?
November 13, 2014

Urgent- Science
Dalton thought atoms to be indivisible. JJ Thomson discovered electrons as a part of atoms and used the plum pudding model for the pieces of an atom. Rutherford was responsible for showing that the mass of an atom was concentrated in a very small center and the rest of the ...
November 13, 2014

Chemistry
Yes, 2-2x is right but you didn't finish. 2x is 2*0.947 = 1.89 Then 2-1.89 = 0.11 = (HI)
November 13, 2014

Chemistry
Yes, that's exactly what you do. 19x = 18 19x/19 = 18/19 x = 18/19 = 0.947 But I wouldn't round to 0.95. You're allowed 3 s.f. You have 4.00 mols, 2.00 L, 81.0 for K and all of those have 3 s.f. You're multiplying and/or dividing so that allows 3 s.f. I would ...
November 13, 2014

Chemistry
You're ok so far. You've done the hard part. What's left? move the x to one side and numbers to the other and solve for x 18 = 19x x = ?
November 13, 2014

newsome
1. How many mols do you need? That's mols = M x L = ? Then mols = grams/molar mass. You know molar mass and mols from above, solve for grams. 2. You have mols/L and you know grams/L from 1. % w/v = grams/100 mL. Just change grams/L to grams/100 mL.
November 13, 2014

Chemistry (Equilibrium)
Close but no cigar. You didn't square the (0.5-0.171) which makes the 0.329 squared also. I have 0.0675
November 13, 2014

Chemistry (Equilibrium)
You went wrong on the C step and E step. (HBr) = mols/L = 0.5/1 L = 0.5M which you hvave correctly. ..............2HBr <==> H2 + Br2 I..............0.5.......0....0 C..............-2x.......x....x E............0.5-2x......x....x The problem states that (Br2) is 0.0855 (...
November 13, 2014

chemistry
I don't get it. rastor? I assume molar mass is 46. You don't list grams water. Is that density of 1.86? 1.86 WHAT units? That isn't the density of ethanol. What about just reposting the question.
November 13, 2014

Equilibrium
Yes and no. 3.9 is the correct answer and I would not round up to 4 since you are allowed two s.f. in the answer. But you choose 4.0 as the answer since that's the closest of the choices.
November 13, 2014

Equilibrium
Looks like the second set up is correct but you punched in the wrong numbers on your calculator. I get about 4 or close to that.
November 13, 2014

Chemistry
It makes it easier if you don't change screen names. Use the HH equation as in in the formic acid/sodium formate buffer There is one difference. In the formic/formate buffer you have the components separated. In this one you must combine the acid and base, calculate how ...
November 13, 2014

Chemistry
Use the Henderson-Hasselbalch equation. Convert Ka to pKa. 10.0 mL x 1.0 M sodium format is 10 millimols base. 20.0 mL x 1.00 M formic acid is 20 mmols of the acid. Plug and chug.
November 13, 2014

sixth grade math
12/15 is a fraction already. Both 12 and 15 are divisible by 3 to make it 4/5. As a decimal divide 4 by 5 to obtain 0.80 and multiply that by 100 to obtain 80%.
November 12, 2014

Chemistry (Equilibrium)
I have removed the (g) designation in order to get all of this on one line. ..........H20 + CO <==> H2 + CO2 I.........5.0...4.0.....0.....0 C.........-x.....-x.....x.....x. E.......................2......... If 2.0 mols H2 are present at equilbrium then x must be 2.0 ...
November 12, 2014

chemistry
mols solute = M x L = ? Calculate each and the highest wins.
November 12, 2014

chemistry
It was 0.1 in the V1 (whatever volume that is) and you diluted it to 250 sothe new concn is It's 0.1 x (V1/250) = ? I don't know why you wrote it was placed in a V2.0 volumetric flask. If it were brought to 250.0 mL I would assume it was placed in a 250 mL flask.
November 12, 2014

chemistry
You just do the reverse of the previous problem. How many mols do you need? That's M x L = ? Then mols = grams/molar mass. You have mols and molar mass, calculate grams.
November 12, 2014

chemistry
mols CaCl2 = grams/molar mass M CaCl2 solution = mols CaCl2/L solution.
November 12, 2014

Chemistry 11
I'm glad you asked that question. All of the work you have done is exactly right BUT you haven't worked the problem. You worked a similar problem but not the one stated. % Na FROM THE DATA IN THE PROBLEM is (g Na/total g)*100 = (13.45/24.34)*100 = 55.26% Then % Cl = ...
November 12, 2014

Chemistry
That's right. You start with 2.0 (intial), take away -2x (the change) and end up with 2-2x (equilibrium).
November 12, 2014

Chemistry
To do the equilibrium sign you simply use the < the > and == like this <==>. Most of use just use a straight arrow, either --> or ==> and let it go. (HI) = mols/L = 4.0/2.00 = 2.00M Set up an ICE chart as below: ........2HI ==> H2 + I2 I.......2.0M.....0...
November 12, 2014

Chemistry
Cl2(g) + 2NaBr(aq) ==> Br2(l) + 2NaCl The second part of the question. You "bubble in" (I guess it means mark in) E which is Br2 and D which is NaCl.
November 12, 2014

chemistry
Three equations work almost all of these. In general here they are. Fit them to your problem. WITHIN a phase (all liquid, all steam, all ice) use q = mass of the phase x specific heat of the phase x (Tfinal-Tinital) At a phase change (example melting point) use q = mass of the...
November 12, 2014

chemistry
mass = volume x density. You will need to look up the density. You can look it up on Google. I'm not sure I remember it right but I think it is 0.789 g/mL.
November 12, 2014

Chemistry
Volume = mass/density volume Fe = 52.3/7.87 = ? New volume water is the sum of initial volume + volume Fe. Note that two objects can't occupy the same volume at the same time; therefore, the Fe must displace the water by the iron's volume.
November 12, 2014

chemistry
You can do a ratio/proportion like this: (g/atoms) = (g/atoms) (28.09g/6.02E23atoms) = (x g/1.06E25 atom) and solve for x. OR you can remember that 1 mol of atoms contains 6.02E23 atoms so how many mols do you have? That's 1.06E25/6.02E23 = ? 1 mol has a mass of 28.09 g so...
November 12, 2014

Chemistry
See your post above.
November 12, 2014

chemistry
2NaOH + H2SO4 ==>Na2SO4 + 2H2O 1. The NaOH is the titrant; H2SO4 is the analyte. 2. mols NaOH = M x L mols H2SO4 = 1/2 mols NaOH (Look at the coefficients in the balanced equation.) 3. M H2SO4 = mols H2SO4/L H2SO4 4. g H2SO4 = mols H2SO4 x molar mass H2SO4 5. mass S = mass ...
November 12, 2014

chemistry
2K + 2H2O ==> 2KOH + H2
November 12, 2014

chemistry
See your post above.
November 12, 2014

Chemistry
Zn(OH)42-
November 11, 2014

Chemistry
Ag is 2 Cd is 4 (en) is 2 + 2Br = 4.
November 11, 2014

AP Chem
OK. We'll take your number of 0.116M for the solubility of KBr in a saturated solution. I don't know what value you used for Ksp but I used one from the web and ended up with 0.0118M so the answers are pretty close. You probably used a value for Ksp close to what I ...
November 11, 2014

Chemistry
Use PV = nRT T will have units of kelvin
November 11, 2014

chemistry
ln(k2/k1) = A*Ea*(1/T1 - /T2)/RT Substitute and solve for k2. Remember to convert kJ to J.
November 11, 2014

chemistry
This is a limiting reagent (LR) problem and you know that because amounts are given for BOTH reactants. Pb(NO3)2 + 2KIO3 ==> Pb(IO3)2 + 2KNO3 mols Pb(NO3)2 = M x L = ? mols KIO3 = M x L = ? Using the coefficients in the balanced equation, convert mols Pb(NO3)2 to mols Pb(...
November 11, 2014

Chem
Yes. n, l, and mL are the same BECAUSE one of the electrons is ms = +1/2 and the other one is ms = -1/2.
November 11, 2014

Ochem
How would you like for us to help you with this assignment?
November 11, 2014

Chemistry
See your original post.
November 11, 2014

Chemistry
Since can't draw diagrams on this forum here is the best I can do. Below are the electrons changes; you can draw the lines/arrows and whatever else you need to do but this is the heart of the problem. C2H5OH. Both carbons are -4 total. CH3COOH. Both carbons are zero each(...
November 11, 2014

chemistry
The pressure inside the container will be 100 mm Hg when equilibrium is reached. Use PV = nRT and solve for n, then n = grams/molar mass to solve for grams. Compare grams in the vapor with grams of the liquid to know if all will have evaporated.
November 11, 2014

chemistry
You didn't give the specific heat of the metal but see this post and response. http://www.jiskha.com/display.cgi?id=1415735118
November 11, 2014

chem
This is a limiting reagent (LR) problem and you know that because amounts are given for BOTH reactants. mols Ba(NO3)2 = M x L = ? mols Na2SO4 = M x L = ? Using the coefficients in the balanced equation, convert mols Ba(NO3)2 to mols BaSO4. Do the same for mols Na2SO4 to mols ...
November 11, 2014

Chem 130
Look at the limiting reagent problem you posted just above. This is worked the same way. Your equation looks ok.
November 11, 2014

Chemistry
Frankly I don't know how to answer this question. I don't know if it is a trick question or not. Here is my problem. The equivalence point is the theoretical point at which the acid just neutralizes the base. The end point (different from the equivalence point) is the ...
November 11, 2014

Chemistry
Tell me your problem here. Do you know how to write the Keq expression? It tells you in the problem what Keq is.
November 11, 2014

Chemistry
Are those the equilibrium concentrations? I assume they are. Writ the Keq expression, substitute those numbers and solve for Keq. Post your work if you get stuck.
November 11, 2014

Chemistry
Note the correct spelling of celsius. You have half of it but not the other half. The metal is heated to 95 C then placed in the water. Then heat lost by the metal + heat gained by the water = 0 heat lost by metal is q = mass metal x specific heat metal x (Tfinal-Tinitial) ...
November 11, 2014

Science-Chemistry
I suggest you look in your text or notes and if that is not an option look for the tables on Google.
November 11, 2014

Chem 2 help
http://en.wikipedia.org/wiki/Half-life See the above for q 1 and 2. For q 3, depending upon the age, the method may be used. Here is another link that describes the other "dating" methods starting with paragraph 3 then see the table just below that with a list of the...
November 11, 2014

science
Do you know the proportions (average I guess) of each in the human body.
November 10, 2014

science
q = 1673 J = mass H2O x specific heat H2O x delta T. You will need to look up the specific heat of liquid water. Delta T is 2.0 C and mass will come out i grams if specific heat is substituted in joules/g*C.
November 10, 2014

incomplete--chemistry
You didn't post a question AND you didn't post the total amount of solution for each nor the amount of each solution.
November 10, 2014

science
q = mass graphite x specific heat graphite x (Tfinal-Tinitial) q = 350 J mass graphite is 33.0 g You will need to look up the specific heat graphite. delta T is Tfinal-Tinitial and you are to solve for delta T.
November 10, 2014

science
q = mass H2O x specific heat H2O x (Tfinal-Tinitial)
November 10, 2014

History (1 word)
Jane, I apologize but the devil made me do it. I think the word you're looking for is "nullify". Here are a couple of links to read. http://en.wikipedia.org/wiki/Nullification_%28U.S._Constitution%29 http://www.cato.org/publications/commentary/yes-states-can-...
November 10, 2014

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