Friday
October 24, 2014

Posts by DrBob222


Total # Posts: 44,698

chemistry
Cl2(g) + Al(s) --> Al3+(aq) + Cl- Cl2 + 2e --> 2Cl^- Al ===> Al^3+ + 3e Multiply equation 1 by 3 and equation 21 by 2 and add. Cancel the electrons. Here is MnO4^- from part c done this way in detail MnO4^- ==> Mn^2+ 1. The oxidation state Mn on the left is +7; on...
September 28, 2014

Chem help
:NH3 + Na. Here is the best I can do for Lewis structure of NH3. H .. :N:H + Na. .. H Let's pick on the right most H. It leaves and takes its electron with it as H. The Na. donates its electron to make ionic bond and one molecule of NaNH2 with Na^+ charge and NH2^- with H...
September 28, 2014

CHM
I would suggest you look on a can of soda and read the ingredients. That will list the preservative(s).
September 28, 2014

Chemistry
a. k = 0.693/t1/2 Substitute k into the below ln(No/N) = kt No = 5E10 N = ? k from above t = 1 month but change that to days if you use half life in days. b. Basically you don't want to get bombarded with radioactive rays longer than necessary.
September 28, 2014

chemistry
(V1/T1) = (V2/T2) Remember T must be in kelvin.
September 28, 2014

Chem
For the 20 mL of 1.00 M NaOH you have mols = M x L = 0.020 x 1.00 = 0.020 mols and grams = mols x molar mass. diluted solution (0.25M) you have the same, don't you? You added 20 mL of 1.00 M NaOH to 60 mL H2O so you added 0.02 mols for that dilution. Yes the concentration ...
September 28, 2014

Chem
Looks ok to me for the dilution but mols and grams you didn't do.
September 28, 2014

Chemistry
You want to write half reactions but I think you made a typo with FeBr. Should it have been FeBr2 Fe^2+ 2e --> Fe Mg --> Mg^2+ + 2e ------------------- Then add the equations.
September 28, 2014

Chemistry
mass = volume x density or volume = mass/density Look up the density and substitute; solve for volume. If you call the length of the side s, then V = s^3. Solve for s.
September 28, 2014

Redox equation
I have news for you; there is no redox here. Prove it? Let me rewrite it because you've omitted parentheses. Zn(OH)4^2- ==> ZnO2^2- + 2H2O Zn(OH)4^2. Zn = +2 O = 4*-2 = -8 H = 4*+1 = +4 +2-8+4 = -2 which = charge on the complex ion. ZnO2^2- Zn = +2 O = 2*-2 = -4 +2-4= -...
September 28, 2014

Need help badly, Science
What about 0.87 kW/m^2 x 104 m^2 = ?kW. Change that to J/s = x J/s Hvap in J/g x ?g = x J/s Solve for ?g and that will be grams H2O lost/second. Check that.
September 28, 2014

chemistry
21.90 kJ/g x 0.1182 g = ?q = energy obtained by combusting salicylic acid. Then calculate the heat capacity of the calorimeter. That is q from above = C/degree c x 2.84 and solve for C, the heat capacity of the calorimeter. q = heat capacity x delta T q = Cfrom above x 3.50 ...
September 27, 2014

chemistry
I don't agree with the 22 (22 what?) so I didn't bother with the 54; I assume is wrong also.
September 27, 2014

chemistry
a. Ptotal = pH2 + pH2O. Use PV = nRT and solve for n = number of mols. 2Al + 6H^+ ==> Al^3+ + 3H2 Convert mols H2 to mols Al and to grams.
September 27, 2014

chemistry
KHP + NaOH ==> NaKP + H2O mols KHP = grams/molar mass mols NaOH = mols KHP since 1 mol KHP = 1 mol NaOH. M NaOH = mols NaOH/L NaOH Note: You would do well to start sentences with a capital letter. It makes it easier to read the question.
September 27, 2014

chemistry
It means you did something wrong. Post your work and I'll find the error BUT first, did you change 4052 nm to m?
September 27, 2014

chemistry
R = Rydberg constant = 1.0973E7 m^-1
September 27, 2014

chemistry
1/wavelength = R(1/n^2 - 1/25) Remember to convert wavelength to m In the above n^2 is n1 squared and 1/25 is 1/n2 with n2 squared.
September 27, 2014

chemistry
This answer differs from the other answer you have. I will estimate for the following: mols of each = grams/ATOMIC MASS or 53.31/12 = 4.44 35.51/16 = 2.22 11.18/1 = 11.2 To find the empirical formula you want the ratio of the elements to each other with the smallest number ...
September 27, 2014

chemistry
AlCl3.6H2O ==> AlCl3 + 6H2O mols AlCl3 = 8.5g/molar mass AlCl3 = approx 0.06 but you need a more accurate number. Convert mols AlCl3 mols H2O using the coefficients in the balanced equation. That's about 6 x 0.06 = about 0.36. Then plug that into for n in PV = nRT and ...
September 27, 2014

chemistry
0.781 x molar mass N2 = ? 0.209 x molar mass O2 = ? 0.934 x molar mass Ar = ? (sum/22.4L) = density in g/L
September 27, 2014

chemistry
A or himesh or whatever, Why not work this the same way as steam out of AlCl3.62O
September 27, 2014

chem
its a hexane theres a double bond in position 1-2 with two ch3 methyls attached one methyl on top one on bottom but where are the methyls attached? To carbon 1 or another place? If both are attached to c1 then it is a heptene. So it's (CH3)2C=CHCH2CH2CH2CH3 This would be ...
September 27, 2014

chem
I can't tell from your drawing anything about this. Is it supposed to be a cyclic compound? I hope you received my note about the earlier diiodide compound being trans and not cis.
September 27, 2014

chemistry
Convert 0.0125 mol NiS2 to mols NiO. That is 0.0125 mol NiS2 x (2 mol NiO/2 mol NiS2) = 0.0125 mol NiS2 x 2/2 = 0.0125 mol NiO. Then g = mols NiO x molar mass NiO= ? For part b convert g NiS2 to mols, convert that to mols O2 and that to grams O2. Follow the steps from part a.
September 27, 2014

chem
1/wavelength = R(1/1^2 - 1/n^2) Remember to use wavelength in m. R is 1.0973E7 The 1/1^2 in the above is 1/n1 and n1 is squared. The 1/n^2 in the above is 1/n2 and the n2 is squared. Solve for n. This 121.6 nm line is the first line of the Lyman series and has a value for n of...
September 27, 2014

Chemistry
That's just another stoichiometric problem isn't it? You have mols Fe, use the coefficients in the balanced equation to convert mols Fe to mols Fe2O3 and convert that to grams. OR since you already have mols H2, you can use mols H2 and convert using coefficients to ...
September 27, 2014

Chemistry
2Fe + 3H2O ==> 3H2 + Fe2O3 mols Fe = grams/molar mass = approx 9 but that's an estimate. You need a more accurate number than that. Using the coefficients in the balanced equation, convert mols Fe to mols H2. That's approx 9 mols Fe x (3 mols H2/2 mols Fe) = approx ...
September 27, 2014

Check my answers? Math help.
I don't agree that the answer to #4 is -3.
September 27, 2014

TO M--urgent
I named that compound as cis and it should be trans. The I atoms are on opposite sides and that's trans, not cis.
September 27, 2014

CHEM
Please note on the earlier question and on the note I wrote above to you that the diiodo compound I named is trans and not cis. Trans is named when the groups are on opposite sides; cis is used when they are on the same side. On this and related question why don't you ...
September 27, 2014

chemistry
k = 0.693/t1/2 Substitute k into the below. ln(No/N) = kt No = 4800 N = 600 k from above Solve for t(which will be in seconds) and convert to minutes.
September 27, 2014

Chemistry
It would help if you wrote questions that could be interpreted. You might try looking at the post to see how it is shown. What you have makes no sense; I have hit the enter button to try and separate your one reaction into three separate reactions. I hope I hit the enter key ...
September 27, 2014

oops--oops--CHEM
I have no idea why I named this cis because the I atoms are on opposite side and it should be named trans. I just had cis on my mind when I typed it in and typed in cis--Sorry about that.
September 27, 2014

CHEM
I didn't know what to do with that so I didn't number them. They are cis-1,2-diiodoethene BUT cis IMPLIES they must be on different carbons. If we had 1,1-diiodoethene (we wouldn't name it 2,2-diiodoethene because 1,1 uses smaller numbers) there is no need for cis ...
September 27, 2014

CHEM
This forum doesn't allow spaces. The spaces after the first space is ignored. I would name this cis-diiodoethene
September 27, 2014

chem
Is that ClCH2CH2C(triplebond)CCH3? How about 5-chloro-2-pentyne?
September 27, 2014

CHEMISTRY
Some do both. Gaseous HCl, for example, is a molecular compound (and polar covalent). When added to water HCl + H2O ==> H3O^+ + Cl^- In this case we show the H^+ as being hydrated. Although we hardly ever show it the Cl^- is hydrated, also. Compounds like glucose dissolve ...
September 27, 2014

chemistry
mols base = mols acid M x L base = M x L acid M x (add all the L base) = M x L (add on the L acid) The only unknown is M acid.
September 27, 2014

chemistry
What you have doesn't make sense to me; please clarify it. I think the first part is 230/90Th + 4/2He but I don't know if the ________ are arrows or not. Is that a Po +2 ion? Are those 2 H^+ (as in hydrogen ions). Perhaps you intend 2H^+ to be 2 protons. And what's...
September 27, 2014

chemistry
You won't have trouble with this if you just look at the formula. You have 4.70 mol H2O There are two H atoms in 1 molecule H2O. Therefore, there must be 2*4.70 = 9.40 mols H in 4.70 mols H2O. How many mols O in 4.70 mols H2O? That's 4.70 mols, of course. Said another ...
September 27, 2014

Math--1 question
I think the answer is supposed to be A but if I interpret that correctly it would not be right. I think A is saying 3*(d+5) and that is 3d + 15 which isn't the initial equation. One of the math guru's will set us straight.
September 26, 2014

ordering decimals from least to greatest
Then -1.4555555..... -1.455 -1.45 -1.4
September 26, 2014

ordering decimals from least to greatest
Least to greatest what? From least positive to most positive? And did you intend to have two number the same value? -1.455 is the least positive (most negative) -1.45/-1.45 -1.4 most positive (least negative)
September 26, 2014

Chemistry
Refer to your post below.
September 26, 2014

Organic chemistry
To have a comparison with the Rf value of each.
September 26, 2014

Anthropology
See your post below.
September 26, 2014

biology
Here is some information. I suggest you Google this subject. http://www.aaanet.org/stmts/evolution.htm
September 26, 2014

Chemistry
John, Mandi, whomever-- You should go back and look at your other posts. I answered this below an hour ago. Here is a link. http://www.jiskha.com/display.cgi?id=1411784311
September 26, 2014

Microbiology
What does your book say? What do your notes say?
September 26, 2014

Microbiology
I would think someone here would be happy to read and critique your paper but few of us will write this ten page (or more) report for you.
September 26, 2014

CHEM
weight % = (grams solute/100 g solution)*100 = ? %impure NaCl w/w = (1.522/51.522)*100 =
September 26, 2014

Microbiology
Soaps are made to clean and they do a good job (they wash the germs away) of that but they do not sterilize (they get rid of the germs but they don't kill the germs).
September 26, 2014

Microbiology
1. The time frame it is effective. 2. How long it stays in the environment. 3. It's decomposition products. 4. Toxicity to humans/pets.
September 26, 2014

Chemistry
3CaCl2(aq) + 2K3PO4(aq) ==> Ca3(PO4)2(s) + 6KCl(aq) You add the phases. 3Ca^2+ + 6Cl^- + 6K^+ + 2PO4^3- ==> Ca3(PO4)2(s) + 6K^+ + 6Cl^- You turn that into a net ionic equation by canceling those items that appear on both sides; i.e., the Cl^- and K^+ to leave you with ...
September 26, 2014

CHM 300
You want the pH to be about 9 and Na2CO3 will do that. It aids in preventing decomposition of the thiosulfate.
September 26, 2014

CHM 300
In iodometry, the I2 is released by chemical reaction, then the released I2 is titrated with thiosulfate. I2 is not a good primary standard because it sublimes so easily. That means that the mass will change between the time it is weighed and the time it is used.
September 26, 2014

chemistry
dE = q + w q = +4070 J w = -2442 J dE = ?
September 26, 2014

Math Help.
The suggestion made by Ms. Sue is very good but in addition I suggest you note your answers by EACH question, too. To read an unnumbered question, then scroll down what seems like forever to find your answer is just too confusing. If you placed an asterisk or noted below the ...
September 26, 2014

Science URGENT
1 wave/4s = ?
September 26, 2014

chemistry
I have no idea what this looks like. Use dE = q + w q will be joules of heat. If the arrow goes INTO the object it is +, if OUT OF the object it is -. Same sign convention for work. If the arrow goes INTO the object it is +w; if out of the object it is -w.
September 26, 2014

Science
See your post above.
September 26, 2014

Chemistry
Are these the answers? What's the question?
September 26, 2014

chem
AgNO3 ==> Ag^+ + NO3^-
September 26, 2014

Chemistry of Life
Water molecules move randomly around each other. Without the proper balance of water, chemical reactions in cells could not take place. It enables water molecules to bond to each other.
September 26, 2014

Science
If 757 g is your answer I don't agree. On second thought that looks like another choice for an answer. I don't understand your problem. If D = M/V then mass = volume x density. Just plug and chug.
September 26, 2014

Chemistry
distance = rate x time. d = 55.0 mi/hr x 4.25 hr = ?
September 26, 2014

Chemisty
You work through these things logically. The best advice I have for beginning students is to think "moles". How many mols CF3Cl2 are in 38.0 g. I will estimate all of these numbers; you should do them more accurately. mols = grams/molar mass = 38/121 = approx 0.3 ...
September 26, 2014

Chemistry
mols = grams/atomic mass 11 g Zn sounds high to me but then I'm not an MD. Are you sure that isn't 11 mg?
September 26, 2014

CHEM
ketone CH3COCH3 in which the C and O are CH3 | C=O | CH3
September 26, 2014

oops---CHEMISTRY
I believe the IUPAC name is 2-aminobutane
September 26, 2014

CHEMISTRY
As you can see this forum does not allow spaces. Anything over one space is ignored so drawing structures is almost impossible although with some footwork i can be done as in the next response for you. I thin the easy way to do this kind of question is to write the formula as ...
September 26, 2014

Chemistry
It took 20 minutes to type all of that stuff. :-)
September 26, 2014

Chemistry
18.7% by mass means 18.7 g Ba(NO3)2 in 100 g solution. Use density to calculate the volume. mass = volume x density or volume = mass/density = 100 g/1.09 = approx 91.7 mL. Therefore, you have 18.7 g Ba(NO3)2 in 91.7 mL or 18.7 g Ba(NO3)2 in 9.17 dL. In 87.6 dL you will have 18...
September 26, 2014

chemistry
That's the "ethyl" group.
September 26, 2014

Electrophoresis
I'm not sure you can get there with that route. mols glucose needed = 4 M x 0.400 L = ? Then mols = grams/molar mass. You know mols and molar mass, solve for grams.
September 26, 2014

Chemistry
1. Write and balance the equation. HNO3 + NaOH ==> NaNO3 + H2O 2. mols NaOH = M x L = 2.0 M x 2.500 L = 5.0 3. Using the coefficients in the balanced equation convert mols NaOH to mols HNO3. 5.0 mols NaOH x (1 mol HNO3/1 mol NaOH) = 5.0 x 1/1 = 5.0 mols HNO3 4. M HNO3 = ...
September 26, 2014

Chemistry
If the density of the water is 1.00 g/mL, the mass of the water is 100 g and the total mass is 105 grams. If your prof is picky about the number of significant figures you need to be careful how to report that. 100 has only 1 significant figure and would be written as 1.E2 to ...
September 25, 2014

chemistry
Yes, I get 43.988 g which rounds to 44.0 to 3 s.f.
September 25, 2014

chemistry
It's just another stoichiometry problem. mols CuCl2 = grams/molar mass = approx 0.4 but you need to be more accurate than that. Then 0.4 mol CuCl2 x (1 mol Na2CO3/1 mol CuCl2) = 0.4 x 1/1 = 0.4 mol Na2CO3. To convert that to grams you have g = mols Na2CO3 x molar mass Na3CO3.
September 25, 2014

Chemistry
Yes and no. First, the problem asks about N and not H. You do use H in determining the molar mass NH3 which is 14 for N and 3*1 = 3 for H to make 17 for NH3. Since you know the number of atoms of N, however, it is easy to calculate the number of atoms of H in NH3. It's ...
September 25, 2014

Chemistry
There are 6.02E23 molecules in 1 mol. In 5.00E-3 mols NH3 there are 5.00E-3 x 6.02E23 molecules = approx 3E21. Then there is 1 N atom in 1 molecule of NH3; therefore, there must be about 3E21 atoms N. If your prof is picky about significant figures you need to make the answer ...
September 25, 2014

Chemistry
Thanks for telling me where you're stuck but why didn't you show what you had done so I could check it first. The molecular equation is as follows: BaI2(aq) + Hg(NO3)2(aq) ==> HgI2(s) + Ba(NO3)2(aq) Now change that to a complete ionic equation. The rules are that if...
September 25, 2014

chemistry
heat lost by metal + heat gained by water = 0 [mass metal x specific heat metal x (Tfinal-Tinitial)] + [mass water x specific heat water x (Tfinal-Tinitial)] = 0 Substitute and solve for specific heat metal.
September 25, 2014

chemistry
J = mass x specific heat x (Tfinal-Tinitial) = 0 99 J = mass Pb x 24.92 J/mol Solve for mass Pb in mols. Convert to grams. mol = g/molar mass
September 25, 2014

Chemistry
I think I showed you how to set this up earlier. Please post what you've done so I can figure out where your trouble is.
September 25, 2014

science
metabolism
September 25, 2014

chemistry
First determine the heat capacity of the calorimeter. salicylic acid + O2 ==> CO2 + H2O (not balanced) + 21.90 kJ/gram; therefore q = 21.90 x 0.1182g = ? kJ q = heat capacity x delta T Substitute q and delta T and solve for C (heat capacity) if the calorimeter. E of ...
September 25, 2014

chemistry
q = mass Au x specific heat Au x (Tfinal-Tinitial) 690.8 = 525 x 0.1290 x delta T. Solve for delta T.
September 25, 2014

Chemistry
For part B heat lost by metal + heat gained by water = 0 [mass metal x sp.h. metal x 43.5] + [mass H2O x sp.h water x 3.20] = 0 Solve for sp.h. (specific heat) metal
September 25, 2014

Chemistry
Refer to your post using Kate. Same type problem. I'll be happy to check your work if you post it.
September 25, 2014

Chemistry
In these problems one material loses heat and the other gains heat. In this case, the warm coffee loses heat and the cold milk gains heat. All of that exchange must be zero. heat lost by coffee + heat gained by milk = 0 heat lost by coffee is mass coffee x specific heat coffee...
September 25, 2014

Chemistry
dHrxn = (n*BE reactants) - (n*BE products). BE = bond energy. For example You have broken 4 C-H bonds so that is 4*99 = ? kcal. You have broken 2*119 O bonds = ? kcal you have formed two C-O bonds for CO2 etc.
September 25, 2014

chemistry
radius is 131 pm diameter is 2*131 pm 2*131 pm x (1 mm/10^9) x #atoms = 4.53 mm Solve for # atoms
September 25, 2014

chemistry
I have looked at this problem (many times) and I don't see anything wrong with your answer. I have thought of dividing your final answer by 2 since the problem asks for J/mol REACTANTS and you have two mols reactants but that doesn't get close to the answer either. I ...
September 25, 2014

P5 Science
The test for starch is to add I2. The presence of starch is indicated by the dark-blue color formed upon the addition of the I2. The part that didn't turn blue-black has stopped making carbohydrates (starch) due to injury or natural dying of the leaf or due to seasonal ...
September 25, 2014

BIOCHEMISTRY
What's the problem? This is just a plug and chug problem pH = pKa + log(base)/(acid) pH = 4.80 pKa = ? base = lactate = 0.87M acid = lactic acid = 0.01M
September 25, 2014

chemistry
This is a limiting reagent (LR) problem wrapped up in a Ksp problem wrapped up in a common ion problem. First calculate how much AgCl we can get and identify the LR. 2AgNO3 + CaCl2 ==> 2AgCl + Ca(NO3)2 millimols AgNO3 = mL x M = 100 x 0.2 = 20 mmols CaCl2 = mL x M = 100 x 0...
September 24, 2014

ap chemistry
When amounts are given for BOTH reactants you know the question is a limiting reagent (LR) problem. 3BaCl2 + Fe2(SO4)3 ==> 3BaSO4 + 2FeCl3 millimols BaCl2 = mL x M = 100 x 0.1 = 10 mmols Fe3(SO4)3 = 100 x 0.1 = 10 How much BaSO4 can be formed from the BaCl2 IF we had all of...
September 24, 2014

ap chemistry
You made a typo in Na3PO4. 3Pb(NO3)2 + 2Na3PO4 ==> Pb3(PO4)2 + 6NaNO3 mols Pb(NO3)2 = M x L = ? mols Na3PO4 = mols Pb(NO3)2 x (2 mols Na3PO4/3 mols Pb(NO3)2) = ? Then M Na3PO4 = mols Na3PO4/L Na3PO4. YOu know mols and M, solve for L and convert to mL if you wish.
September 24, 2014

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