Wednesday
May 25, 2016

Posts by DrBob222

Total # Posts: 52,418

Chemistry
There are 6.02E23 molecules in 18 g H2O (1 mol). 36 grams is 2 mols.
January 13, 2016

chemistry
Balance the equation. Then use the coefficients in the balanced equation to convert mols NaHCO3 to mols CO2. Finally, convert mols CO2 to grams by g = mols x molar mass.
January 12, 2016

chemistry
Josh, did you proof your problem? You can calculate the original (acid) and (base) this way. pH = pKa2 + log base/acid 7.2 = 7.2 + log base/acid 0 = log b/a 1 = b/a is equation 1 equation 2 is a + b = 0.05 Solve those two equations simultaneously and A = B = 0.025M The buffer ...
January 12, 2016

Chemistry
If you start with neutral S and make a sulfide ion (S^2-) out of it, do you add or lose electrons?
January 12, 2016

chemistry
If the copper sulfate is in solution, this is it. Zn(s) + CuSO4(aq) ==> ZnSO4(aq) + Cu(s) The Zn displaces the Cu^2+ ion.
January 12, 2016

chemistry
H2 + Cl2 ==> 2HCl Since these are gases one may use L (volume) as if the volume were mols. 0.5 L HCl x (1 mol H2/2 mols HCl) = 0.5 x 1/2 = ?
January 12, 2016

Chemistry
2KNO3 ==> 2KNO2 + O2
January 12, 2016

chemistry
First there is no such thing as calcium(iii) oxycarbonate. Ditto for calcium(iv) oxide. CaCO3 + 2HCl ==> H2O + CO2 + CaCl2 mols CaCO3 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols CaCO3 to mols CaO. Convert mols CaO to grams CaO by ...
January 12, 2016

Chemistry
Look up the atomic mass of Al and weight exactly that amount of Al on an analytical balance.
January 11, 2016

chemistry
Ivan, Anthony, Juan, we prefer you not change screen names. We can help you better if you keep the same name when you post. %Na = (atomic mass Na/molar mass NaHCO3)&100 = ?
January 11, 2016

chemistry
Technically, I don't think it can be done because I think the problem is misstated. You don't mix solids with 1 L H2O; when making molar solution you use mols and add enough WATER TO MAKE A TOTAL VOLUME OF 1 L. But the think the intent of the problem is to answer as ...
January 11, 2016

Chemistry
a.) How many grams of Hydrogen will be contained in a 100.000 g sample of magnesium hydroxide.? mols MgIOH)2 = grams/molar mass = ? Then mols H ATOMS (not molecules) will be twice that since there are two H atoms per mol Mg(OH)2. Then grams H ATOMS will be g = mols x atomic ...
January 11, 2016

Chem
Would you believe 44.009 grams/mol or the molar mass is 44.009.
January 11, 2016

Chemistry
The percent composition in these problems means to calculate the percent of each element versus the entire compound. It works this way. Suppose you have 10 lbs apples and 5 pounds oranges. What is %apples and %os. %apples = (weight apples/total weight)*100 = (10/15)*100 = 66....
January 11, 2016

Chemistry
Yes. When a reaction gives off heat it is said to be exothermic and the enthalpy of the reaction is negative.
January 11, 2016

Chemistry
The reaction of Mg with oxygen of the air produces heat. It takes more energy to produce white light than red light.
January 11, 2016

@ Damon--math/ chemistry
Already on it. :-)
January 11, 2016

math/ chemistry
Solubility MgF2 = 1.72E-3 g/100 mL. The molar mass is closer to 62.3 than to 62. mols = g/molar mass = 1.72E-3/62.3 = 2.76E-5 mols amd that is in 100 mL; therefore, M = 2.76E-5 mols/0.1L = 2.76E-4. .......MgF2 ==> Mg^2+ + 2F^- I......solid....0........0 C......solid....x...
January 11, 2016

chemistry
It isn't clear what you want? I assume that is you want the specific heat of the metal. Here is your work. = (20g)(c)(x-165)+(125(8.8-5(4.18) Just a change or two. 1. Make that = 0. 2. x is 8.8. If the final T is 8.8, that is not only the final T for the water but also the...
January 11, 2016

Chemistry
The easy way to do this is to solve the Rydberg equation using n1 = 1 and n2 = 7 and a second time for n1 = 6 and n2 = 7. That gives you the range from the shortest wavelength to the longest wavelength, then compare these with the electromagnetic chart to see what range of the...
January 11, 2016

Chemistry
My response above gave only the flame test possibilities. If you mean by "emission spectrum test" the use of a spectroscope or spectrograph instrument, then there are no problems. One can detect and identify as many as about 60 elements with such an instrument and ...
January 10, 2016

Chemistry
Sometimes yes, sometimes no. It all depends upon which elements are to be identified. For example, a mixture of Na and K. The Na yellow flames is so bright that it masks the lavender/purple of the K; however, if you see the Na test, a blue cobalt glass (just a square of glass ...
January 10, 2016

Chemistry
Because some other element may have a line at the same wavelength. So we use TWO lines minimum since an interfering element USUALLY doesn't have a second interfering line. In saying this however, bear in mind that element A may be interfered with at the primary line with ...
January 10, 2016

Chemistry-Dr.Bob
What you say may be right but I believe a better answer is that chemical rxns carried out in an open container do so at constant pressure. The enthalpy, qp is delta H. Energy carried out at constant volume, (in a bomb), qv measured delta E.
January 10, 2016

Chemestry
huh? What about proofing your questions before posting.
January 10, 2016

chemistry
I noticed you used different screen names of Gerry and Bob. It helps us help you better if you stick with the same name.
January 10, 2016

chemistry
Yes, mols = grams/molar mass. By the way, it doesn't matter whether the gas is at STP or any other pressure/temperature combinations, the fact is that 3.59 g is so many moles regardless of the pressure/temperature.
January 10, 2016

Chemistry
Yes, as long as the pressure/temperature of the CH4 is the same as the CO2 being produced.
January 10, 2016

chemistry
units = grams/formula mass mols = grams/molar mass molecules in what? 1 mol of anything contains 6.02E23 of that material.
January 10, 2016

chemistry
mols NO = grams/molar mass 1 mol contains 6.02E23 molecules. So calculate molecules in that many moles.
January 10, 2016

chemistry
See you NO problem.
January 10, 2016

chemistry
See you NO and NH3 problem above.
January 10, 2016

chemistry
How many mols Ar do you have? Since 1 mole contains 6.02E23 atoms, then 6.2E24 atoms of Ar will be 6.2E24/6.02E23 = # moles of Ar atoms. Then since 1 mol Ar weighs 39.9 g, the your # mols will weigh what?
January 10, 2016

stoichiometry
1. You need to find the arrow key(s) and use them. --> is the way to do it. 2. It is better to give a problem with numbers because it makes it easier to explain. In this case mols Fe will be twice the mols Fe2O3. That's what the coefficients in the balanced equation ...
January 10, 2016

Chemistry
No but why can't you do this? You NEVER have to write an equation and ask if it's balanced. You count the atoms and see. I cuont 2C on th left and 2 on the right. I count 4 H on the left and 3 on the right so it isn't balanced. This isn't part of the question ...
January 10, 2016

To Divao ----chemistry
You need to learn where the caps key is and use it. m stands for molality; M stands for molarity. Which do you mean?
January 10, 2016

Chemistry
Your question is about as clear as mud. You should learn how to ask a question. I assume, put into plain English, you have 7E-5 mols CaCl2 and 7E-5 mols Na2SO4, how much BaSO4 is produced. The answer is none. You can't produce BaSO4 unless barium ion is reacted with a ...
January 9, 2016

Chemistry
See my response above to a later post.
January 9, 2016

Chemistry
If the half life was 13 minutes, then 26 minutes is two half lives so you will have just 1/4 (1/2 x 1/2) o 12.5 grams. Here is the way all of these are done. k = 0.693/t1/2 = 0.693/13 = 0.0533 Then ln(No/N) = kt ln(50/N) = 0.0533(26) ln(50/N) = 1.386 50/N = 4 N = 50/4 = 12.5
January 9, 2016

chemistry
The usual case is for the boiling points to be different. I looked up the ortho, meta, and para isomers of toluic acid (methyl benzoic acid). p is 274 C o is 260 C m is 263 C
January 9, 2016

Chemistry
pKa = 3.74 Use the Henderson-Hasselbalch equation. pH = pKa + log base/acid 4.00 = 3.74 + log (HCOONa)/0.1 Solve for (HCOONa).
January 9, 2016

Chemistry
You may work this problem using the Henderson-Hasselbalch equation. Technically that uss concentration of base and acid but you may also use mols and the answer comes out the same. I use mols although concentration is supposed to be substituted. millimols HAc = mL x M = 50 x 0...
January 9, 2016

Chemistry
2C4H10 + 13O2 ==> 8CO2 + 10H2O How much CO2 will you get from 3 mols C4H10. That's 3 x (8/2) = 12. How much CO2 will you get from 12 mols O2? That's 12 x (8/13) - 7.4 The answers are different so you will have some C4H10 left over. All of the O2 will be used.
January 9, 2016

Chemistry
dG = -RTlnK
January 9, 2016

science
I think your question needs clarification. Do you want to know the age of the dog in dog years or do you want to know the age of the dog in human years?
January 8, 2016

Chemistry
Bob P set up the chemistry part. What you are having trouble with is the math. No, you don't put zero for q. You don't need to solve for q. The heat lost by one material + the heat gained by the other material must = to zero and that's the way Bob P set up the ...
January 8, 2016

Chemistry
Jennifer, Bob P set it up for you. All you need to do is to solve for Tf (and look up specific heats).
January 8, 2016

chemistry
Pick a number. Any number you choose will be correct because you didn't specify how much (NH3)3PO4 you have. I assume you means for 1 molecule. There are 3N, 9H, 1P and 4O for a total of 17 per molecule.
January 8, 2016

Chemistry
A limiting reagent problem. 2AgNO3 + Cu ==> Cu(NO3)2 + 2Ag mols Cu = grams/atomic mass = ? mols AgNO3 = grams/molar mass = ? Using the coefficients in the balanced equation: Convert mols Cu to mols Ag Convert mols AgNO3 to mols Ag The smaller number wins; i.e., if AgNO3 is ...
January 8, 2016

Chemistry-Dr.Bob, I need you!!!!
I don't agree with either answer. q from H2O = 200*4.184(5.98) = ? q from calorimeter = 100*5.98 Total q for 0.1 mols is the sum of the two above. Then q/mol = sum/0.1 = ? I get about 55 kJ/mol
January 8, 2016

chemistry
Pb(NO3)2 + 2HCl ==> PbCl2 + 2HNO3 Assuming you meant 0.1M and not 0.1m, millimols Pb(NO3)2 = mL x M = ? millimols HCl = mL x M = ? Determine the limiting reagent and you should see that to be HCl so that means you heave 10 millimols Pb(NO3)2 excess. Convert to mols, then ...
January 8, 2016

Chemistry
What do you mean by "results are attached"? Are those the answers in the key or your answers. Check you typo. H2SO3- should be HSO3^-. ..........NaHSO3 ==> Na^+ + HSO3^- I..........0.05.......0......0 C........-0.05.......0.05....0.05 E..........0.........0.05.......
January 7, 2016

CHM 105
mols CH3COOH = mols NaOH = M x L = ? grams CH3COOH = mols CH3COOH x molar mass CH3COOH % w/w = (mass CH3COOH/mass sample)*100 = ?
January 6, 2016

Chemistry
BeCl2 is a polar compound and is soluble in water. There is no such compound as H-C=C-H. If you mean ethylene (H2-C=C-H2) it is hardly soluble. If you mean acetylene (HCtripleCH) it is slightly soluble but neither are polar.
January 6, 2016

Chemistry
If you have trouble with a problem like this with "reasoning it out", I suggest you assign numbers. Perhaps something like this. Say A = 100 g and is twice B which makes B 50 g. Check that. Specific heat A = 1. B is 2x A so B is 2. Check that. Initial T A = 100; ...
January 6, 2016

Chemistry
You would have done better to post the problem. It's harder to explain in words and not numbers. mols MgCl2 = grams MgCl2/molar mass MgCl2. Then there is 1 mol Mg atoms in 1 mol MgCl2. That is, the number of mols Mg atoms will be the same as the mols MgCl2.
January 6, 2016

Chemistry
CCl4 is the highEST boiling point which means CCl4 should be at the top. CH4 has the lowest b.p. so it should be at the bottom. CH4.....(CHCl3/CH3Cl).....CCl4. So place CHCl3 and CH3Cl in the proper order to make it increasing b.p. from CH4 to CCl4.
January 6, 2016

Chemistry
Try this. The higher boiling point often is the compound with the higher molar mass.
January 6, 2016

Chemistry
There are 6.02E23 atoms in 1 mol. mols Cl2 = 1.2E24/6.02E23 = ? grams = mols x molar mass = ?
January 6, 2016

Chemistry:normal notation plz help
Is that the last electron, the single electron, the outside electron. I assume it's the single electron. Go through each one this way. 19K = 1s2 2s2 2p6 3s2 3p6 4s1 For the 4s1 electron, n = 4 so it can't be K. Also note that s electrons have l = 0; another reason it ...
January 6, 2016

Chemistry
Cu(OH)2 ==> Cu^2+ + 2OH^- i. Adding HCl. The H^+ reacts with the OH^- to produce H2O (H^+ + OH^- => H2O), the OH^- is reduced and that shifts the equilibrium to the right (to increase the OH) which means the solubility is increased. ii. Cu(NO3)2 ==> Cu^2+ + 2NO3^2- ...
January 3, 2016

Chemistry
1. First, balance the Fe/MnO4 equation but correct it first. The part that matters is 5Fe^2+ + MnO4^- ==> 5Fe^3+ + Mn^2+. a. Millimols MnO4 used = M x mL = 12.08 x 0.200 = approx 2.4. Using the coefficients in the balanced equation, convert mmols MnO4 to mmols Fe. That'...
January 3, 2016

chemistry
You need to explain what the direct and indirect methods are.
January 3, 2016

chemistry
Adding a common ion to an insoluble salt decreases the solubility of the salt. Cl from the HCl is the common ion (to Cl in AgCl).
January 3, 2016

chemistry
lead nitrate is soluble. The white ppt formed with NH3 is Pb(OH)2. NH3 + H2O ==> NH4^+ + OH^- Pb^2+ + 2OH^- ==> Pb(OH)2
January 3, 2016

Chemistry
Of course there are but doesn't it all depend upon what you want it to do? For example, it is very good at measuring the masses of groups of atoms but not very good at measuring the boiling point or freezing point of a material.
December 29, 2015

chemistry
How much of the stock solution do you need to prepare? Then mols you need = M x L = ? Then mol = grams/molar mass. You know molar mass of the material and mols, solve for grams.
December 29, 2015

Chemistry
I assume methyl benzene will dissolve sulfur. Dissolve, filter and the iron filings stay in the filter paper. Let the filtrate sit and the solvent evaporates leaving the S behind.
December 29, 2015

chemistry
Your question isn't clear to me. The amount of water necessary to dissolve 10g of the compound is 100 x (10/6.8) = ? but that isn't what is needed to crystallize.
December 29, 2015

chemistry
How much do you need to prepare? mols needed = M x L = ? Then mols = grams/molar mass. You know mols and molar mass, solve for grams.
December 29, 2015

chemistry
mols NaOH = M x L = ? Using the coefficients in the balanced equation convert mols NaOH to mols H2SO4. Then M H2SO4 = mols H2SO4/L H2SO4 = ?
December 27, 2015

Chemistry
"equal volumes of these low" WHAT? If the acids are strong acids we can take 100 mL of each. For pH = 10 we have 100 x 1E-10 = 1E-8 millimols. Add 100 mL pH = 12 and we have 100 x 1E-10 millimols. Add 1E-8 mmols and 1E-10 mmols = 1.01E-8 millimols and that is in 200 ...
December 27, 2015

problem's on gay lussac's equation
This looks like a pure de ol' stoichiometry problem to me. 2C2H2 + 5O2 ==> 4CO2 + 2H2O By using volumes directly as if they were mols, a short cut can be used which cuts out a couple of steps. I suppose we assume that C2H2 and O2 are there is proportional amounts and ...
December 26, 2015

Chemistry
a. Take a 100 g sample which gives you 61.7g Cl and 38.3 F. Convert to mols. 61.7/19 = about 3.25 38.3/25.5 = about 1.1 Determine the empirical formula. The easy way to do this is to divide the smaller number by itself and divide the other number by the same small number. 3.25...
December 26, 2015

chemistry
You mean sulfuric acid (US) or sulphuric acid (UK). And you need to know what the beginning concentration of H2SO4 is. Also you need to know how much stock solution you need. Let's assume you want 1000 mL of the 0.04M solution. The stuff in the pure bottle comes out to be ...
December 24, 2015

Chemistry
I do these the long way. 1. Balance the equation. 2. Convert g NH3 to mols. mols = grams/molar mass = ? 3. Convert g O2 to mols. 4. Using the coefficients in the balanced equation, convert mols NH3 5o mols NO. 5. Do the same and convert mols O2 to mols NO. 6. It is quite ...
December 21, 2015

Chemistry
What's an ff solution? 25% w/v NaCl. How much do you want? Let's say you want 100 mL. Dissolve 15 g NaCl in some water and make to a final volume of 100 mL.
December 21, 2015

chemistry
...........PbSO4 ==> Pb^2+ + SO4^2- I.........solid.......0........0 C.........solid.......x........x E.........solid.......x........x Ksp = 1.6E-6 = (Pb^2+)(SO4^2-) Substitute the E line into the Ksp expression and solve for x = (PbSO4) in mols/L. Convert to grams Pb/L ...
December 21, 2015

Chemistry
https://en.wikipedia.org/wiki/Ionic_strength
December 21, 2015

Chemistry
http://dwb.unl.edu/Teacher/NSF/C06/C06Links/www.uis.edu/7Etrammell/organic/introduction/polarity.htm
December 20, 2015

Chemistry
Take a 100 g sample which gives you 39.9 g C 6.9 g H 53.2 g O Convert to mols. mols C = 39.9/12 = approx 3.3 mols H = 6.9/1 = approx 6.9 mols O = 53.2/16 = 3.3 Now find the ratio of the three to each other with the lowest number being 1. The easy way to do this is to divide ...
December 19, 2015

Chemistry
See your other post. Show your work if you have further questions.
December 19, 2015

Chemistry
(NO2) at equilibrium = 0.250 mols/5 L = 0.05 Kc = (NO2)^2/(N2O4) = 0.133 (NO2)2 = x^2 (N2O4 = 0.05 Solve for x
December 17, 2015

CHEMISTRY
If you're looking for dHrxn it is dHrxn = (n*dHfo products) - (n*dHfo reactants) = ?
December 17, 2015

Chemistry
How many mols do you need? That's mols = M x L = ? Then mols = g/molar mass. you know molar mass and mols, solve for grams.
December 13, 2015

CHEMISTRY
% w/w = (grams solute/g solution)*100 = ?. M = 8.4 mols/L. mols = grams/molar mass so g = mols x molar mass = 8.4 x 62 = approx 521 g in the solution so g solute = approx 521. The solution has a mass of 1.3g x 1000 = approx 1300 grams. Now % = approx 521/1300)*100 = ?
December 13, 2015

Chemistry
HI + KOH ==>KI + H2O mols HI = M x L = ? mols KOH = M x L = ? One of them will be the limiting reagent; i.e., the one with the smaller mols. That will give you the mols of H2O produced. You know q is 1.52 kJ and that is dHrxn. USUALLY you want kJ/mol. Then dHrxn/mols H2O ...
December 11, 2015

Chemistry
What's wrong with using the Arrhenius equation?
December 11, 2015

Chemistry
Wouldn't you think CH3CH2CH3 would be the highest since it has only London forces. CH3OCH3 would have the next (that's acetone) and you know that is volatile. Then ethyl alcohol has H bonding so should be the next one up. I believe I have ranked them in reverse order (...
December 11, 2015

Chemistry
Apparently you don't know where the caps key is. You should find it because 2.61 m and 2.61M don't meant the same thing. I will assume that is 2.61 M and 0.855 M. 2KOH + H2SO4 ==> K2SO4 + 2H2O mols KOH = M x L = ? mols H2SO4 = 1/2 mols KOH. Look at the coefficients ...
December 11, 2015

Chemistry
See your other post.
December 11, 2015

Chemistry
Do you have an equation for the reaction? I assume the reaction is 3CCl4 + 2SbF3 ==> 3CCl2F2 + 2SbCl3 mols CCl4 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols CCl4 to mols CCl2F2. Then g CCl2F2 = mols CCl2F2 x molar mass CCl2F2 = ?
December 11, 2015

Chemistery
N2O5 + H2O ==> 2HNO3 If you want XHNO3 = 0.5 and mols H2O to be 1.0, then mols HNO3 must be 1.0. XHNO2 = 1.0 mol HNO3/2 mol total = 0.5 To obtain 1 mol HNO3 will require only 1/2 mol N2O5.
December 11, 2015

Chemistry 12
You're right. You started out wrong. q = mols H2O x heat condensation mols H2O = grams/molar mass = 3/18 = ? q = (3/18) x 42,000 J = ? J released.
December 10, 2015

Chemistry
4Fe + 3O2> 2Fe2O3 + heat and light
December 10, 2015

Chemistry
yes. There is more motion at a higher T; therefore, delta S is + from going to a higher T.
December 10, 2015

Chemistry
Yes, Fe in Fe2O3 is going from +6 total to +4 total in 2FeSO4. Fe on the left is going to +2 on the right. The easiest way to do this is to write it in half equations; i.e., Fe2O3 ==> 2Fe^2+ and Fe ==> Fe^2+ and add the spectator ions later. S
December 8, 2015

applied chemistry
We can't draw on this forum; however, you can google lewis dot structure CO2 etc and find them on the web.
December 8, 2015

Chemistry
Scroll down in the link below starting with "ionic compounds have high melting points...." http://chemistry.about.com/od/moleculescompounds/a/Ionic-Compound-Properties.htm
December 8, 2015

chem
Yes, adding HCl will do it because the H^+ combines with F to make HF and that is a weak acid. Adding a salt that will ppt with F will work also. BaF2, MgF2, PbF2 are insoluble so adding MgCl2 should work.
December 8, 2015

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