Posts by DrBob222

Total # Posts: 56,664

  1. science

    Bob Pursley worked this for you earlier today.
  2. Chemistry

    a. See your previus post. b. Most salts; i.e.,KAl(SO4)2, (NH4)2SO4 are ionic. Technically NH4OH doesn't exist. It is a solution of NH3 gas and H2O(aq) NH3 + HOH ==> NH4^+ + OH^-
  3. Chemistry

    I suggest you look at the number of OH on the left and make that equal to the number on the right. Go from there to finish.
  4. chemistry

    Check over your post. I'm wondering if that was 2 drops Mg ion you added before titration with EDTA.
  5. science

    CH3OH (g) ==>CO2(g) + H2(g) Do you have the balanced equation? 1. Balance the equation. 2. Write the expression for Kp 3. Substitute the numbers from the problem. 4. Solve for Kp. Post your work if you get stuck.
  6. Chemistry

    So how many electrons were lost or gained in going from +3 to +5 oxidations states.
  7. Chemistry

    As is +3 on the left for EACH atom and +5 on the right.
  8. Chemistry

    My instructions were to post your work, not your answers with no work.
  9. Chemistry

    First you need to know k in the formula ln(No/N) = kt. No = 300 g N = what you solve for. This is what's left k = 0.693/half life t = time = 22 days Then you want 300-N to give you what has decayed. Post your work if you get stuck.
  10. chemistry

    Valence is related to the number of electrons in the outside shell (sometimes the outide two shells). For 1A, IIA, IIIA elemenets the valence is the same as the numbrer of electrons in the outside shell.; i.e., 1, 2, or 3+. For elements in the V, VI, or VII columns, it is the ...
  11. chemistry

    mols Na2C2O4 = grams/molar mass = ? M = mols/L solution. L soln is 0.250 L.
  12. Chemistry

    The ppt could be wet or even impure.
  13. Chemistry

    You did this in your procedure unless you did a dry lab so you should know what steps you took to obtain the correct crystals.
  14. Chemistry

    1.It would be nice to know what the first part was. 2. It would be nice to know the molarity of the NaOH. The problem can't be worked without it.
  15. chemistry

    Lactic acid is a monoprotic acid which I will designate as HL. HL + KOH ==> KL + H2O Then mols KOH used = M x L = ? mols HL = mols KOH since the equation is 1:1 in HL:KOH grams HL = mols HL x molar mas HL = ? Then % w/v = (grams HL/25 mL)*100 = ?
  16. Chem

    The theoretical yield is 100%. I assume you want to calculate the mass of the CaSO4.H2O remaining. CaSO4,2H2O ==> CaSO4.H2O + H2O mm stands for molar mss 1.5 g x (mm CaSO4.H2O/mm CaSO4.2H2O) = ? g CaSO4.H2O
  17. Chemistry

    Right, OR 9.0000E2
  18. Chemistry

    pH = pKa + log (base)/(acid) So if pH = pKa then log (base)/(acid) must = 0 and (base/(acid) = 1 so (base) = (acid) so is that 50%?
  19. Chemistry

    Ecell = Eox + Ered = ? But you have an error or a typo. Li = Li+ + e is not -3.05
  20. Chemistry

    Calculate Qp and compare with Kp.
  21. chem

    I don't know what Ero stands for. These are reductions that you've written. To make a spontaneous reaction you want Ecell to be + so you want to reverse the most negative reaction and add the other to it. See if you can do that. Remember you ant to have the electrons ...
  22. Chemistry

    Rose, Amy, please use the same screen name.
  23. Chem

    Why confused. The problem tells you to take the Cl2 reactin as written and use the other other one reversed (because you want to add OH^- to it) and add them together. Keep the electrons equal by multiplying the 2e x 2 and the 4e by 1
  24. chemistry

    Mg(OH)2 + 2HCl ==> MgCl2 + 2H2O HCl + NaOH ==> NaCl + H2O millimols HCl initially added to sample = mL x M = 50*0.1 = 5 millimols HCl in excess (titrated with NaOH) = 36.30*0.1 = 3.63 millimols HCl used = 5-3.63 = 1.37 Convert 1.37 mmols HCl used to Mg(OH)2 = 1.37 x (1 ...
  25. Chemistry

    That's what I would choose.
  26. Chemistry

    A and D can't be right because of the "molar hydrocarbon chain" statement. Between B and C you make the choice on whether H2O is a polar or a non-polar molecule.
  27. Chem

    I couldn't get that image.
  28. Chemistry

    I don't agree. If you are solving this problem by comparing the Ksp values, that's the wrong way to do it. You must actually calculate the solubility BECAUSE a and b are sqrt Ksp while c and d are (Ksp/4)^1/3. Without going through any of the calculations I suspect b ...
  29. Chemistry

    B is wrong. A is right. Typically you want to pick pKa withing +/- 1 of the desired pH.
  30. Chemistry

    Kb = Kw/Ka = ? Larger Kb means stronger base. I put in this extra step so as not to confuse Ka and Kb. The weakest acid should be the strongest base.
  31. chemistry

    millimols Ca = mL EDTA x M EDTA = ? grams Ca = mols Ca x atomic mas Ca = ? % w/w = (grams Ca/mass sample)*100 = ?
  32. Chemistry

    Frankly, I'm not sure how to answer this. If all conditions means temperature changes, also, we know K changes (so K may not be >1 anymore) with temperature and when K changes products/reactants may change. But with K not > 1 anymore that changes the question. I'...
  33. Chemistry

    dG = dH - TdS but I'm confused about the problem. The dGo, by definition, is dG at 25C and not 35. You can calculate dG at 35 but then it isn't dGo.
  34. Chemistry

    If you mean it goes to the left that is right.
  35. Chemistry

    B is not right. You have worked the problem as if it said N2O4 was 0.5M and NO2 was 0.15, the WHAT ARE THE CONCENTRATIONS AT EQUILIBRIUM. That is the problem. They want to know if the system is at equilibrium when those concentrations are present and not what will they be at ...
  36. Chemistry

    I agree with c. There could be some instantaneous dipole-induced dipole too but that isn't a choice.
  37. Chemistry

  38. Chemistry

    The problem gives KI as 0.4M and not 2*0.4 and that term is squared and not to the first power.. Two errors.
  39. Calculating delta H

    Perhaps we should straighten what you are trying to calculate. I have assume it is dHrxn and that is products - reactants. Are you calculating dH reaction or bond energies.
  40. Calculating delta H

    dHo rxn = (n*dHo products) - (n*dHo reactants) It appears to me that you have left off the - sign. It isn't 99.9 but -99.9. Show your work if you're still stuck.
  41. electron configuration

    What is your problem in doing this? What do you not understand?
  42. Chemistry

    Frankly, I don't like any of th statements but D may be the best of the four. I don't like D because of the word "extra". It does not have any EXTRA electrons.
  43. Chemistry

    fuel? What fuel?

    Surely you aren't serious. 1. Weigh the sample. 2. Heat the sample at whatever temperature to drive off the water until constant weight is obtained. 3. Weigh the dehydrated sample. 4. The difference is weight is the weight of the H2O released.
  45. Chemistry

    I say 1 is right. I just checked the procedure and not the math.
  46. Chemistry

    1 is right. 2 is wrong. In 2 you divided grams HX by molar mass NaOH to find mols
  47. Chemistry

    Bob Pursley answered your question yesterday. The mole fraction of gases is the percent; i.e., oxygen is about 21% oxygen so the mole fraction is 0.21. pO2 = XO2 x Ptotal
  48. Chemistry

    Convert 6.80 mm Hg to atmospheres. 6.80/760 = ? = pi (not 3.14 but pi in this case is osmotic pressure). pi = MRT pi from above. You know R and T (remember T must be in kelvin). Solve for M = molarity = mols/L You know M and L, solve for mols. Then mols = grams/molar mass. You...
  49. Chemistry

    1. Here is the part of the equation you need to work the problem. You can fill in all the rest of it. MnO4^- + 5Fe^2+ ==> 5Fe^3+ + Mn^2+ 2. mols KMnO4 = M x L = ? mols Fe = 5 x mols KMnO4 grams Fe = mols Fe x atomic mass Fe = ? %Fe in sample = (grams Fe/grams sample)*100...
  50. chemistry

    Do you have a set of words? If so you should have listed them. My shot in the dark is oxidized, reducing agents.
  51. chemistry

    q = 1125 = mass Fe x specific heat Fe x (Tfinal-Tinitial) Substitute and solve for Tinitial. Post your work if you get stuck.
  52. chemistry

    First place, this reaction will not occur. But if it did, then 2Li^+ + Zn ==> 2Li + Zn^2+ Is 3 a guess or did you figure out it was 3? I am interested in how you solved the problem.
  53. chemistry

    Let me rewrite the equation. A(s) + BC2(aq) ==>AC2(aq) + B2(g) + heat Remember that solids do not, as long as a little of it is present, change concentration as more is added. I'm not sure that the correct answer is listed. It appears to me that the author of the ...
  54. Chemistry

    delta T = i*Kb*molality You know delta T is 100.68 - 100.00 = ? i = 1 You know Kb. Solve for m = molality Then m = mols/kg solvent. You know kg solvent = 0.3000 Knowing m and kg solvent you solve for mols. Then mols = g/molar mass You know mols and grams, solve for molar mass.
  55. Science

    g H2O = volume x density. Substitute and solve for grams H2O. Then % w/w = [(grams glucose)/(grams glucose + grams H2O)]*100 =
  56. chemistry

    First let me suggest you find the caps key on your keyboard and use it. There is a big difference between Co, CO, and co. kmno4 doen't mean much to me. I'll balance the redox part; you can finish. 5Fe^2+ + KMnO4 ==> 5Fe^3+ + Mn^2+ mols KMnO4 = M x L = ? mols Fe = ...
  57. chemistry

    We try to help on this web site but this looks more like a paper you want us to write. Perhaps we can help if you ask specific questions that will help you write the paper.
  58. Chemistry

    mols KClO3 = grams/molar mass = ? For every 2 mols KClO3 you get 3 mol O2. 1 mol O2 @ STP occupies 22.4 L so ? mols will give ...... 1 mol O2 @ SATP occup;ies 24.5 L so ? mols will give ..... Post your work if you get stuck..
  59. chemistry 2

    delta T =i*K*molality So look at this sensibly. m is the same for all, K is the same for all, so delta T changes only with i, the van't Hoff factor and that is the number of particles per mole of the material. CaCl2 has ? when dissolved in water. NaCl has ?when dissolved ...
  60. chem

    That isn't right. Write the equation and balance it. Convert g H2C2O4 to mols. mol = g/molar mass = ? Convert mols H2C2O4 to mols NaOH. M NaOH = mols NaOH/L NaOH = ? Post your work if you get stuck.
  61. Chemistry

    Your post is not well organized. I assume those temperatures at the top are Tinitial and Tfinal for H2O and not the meal. [mass metal x specific heat metal x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0 #2. dS0 = (n*dSo products) - (n*dSo ...
  62. Science

    The more dense, the more easily it sinks to the ground.
  63. Chemistry

  64. Chemistry

    What's the problem? As you say there are rules. All you need to do is to supply the rules. The first one is OK. There is at least one more that is OK.
  65. Chemistry

    What units do you want for concentration? I assume you meant moles and not miles. Molarity = mols/L = ?
  66. Chemistry

    C'mon. It's moles and not miles. How many moles do you want ? mols = M x L = ? You know M and you know L, solve for mols. I don't see the right answer listed.
  67. chemistry

    cleansing agent for what? How do you define better?
  68. general chemistry II

    You don't give the thickness of the sample for the final absorbance so I will assume it is the same (say 1 cm) as when the standards were made. So A = ec*1 0.234 = 75 c c = 0.234/75 = estimated 0.003 M but that was the final solution. The original M must be approx 0.003 x...
  69. Chemistry

    The IUPAC name for HNO3 is nitric acid and not that weirdo name you wrote.
  70. Chemistry

    compound X is CH3CH2CH2CH2CH2COOH Y is CH3CH2CH2CH2CH2CHO = C6H12O Y is the aldehyde and X is the acid. Aldehydes are oxidized witrh dichromate to carboxylic acids. In general RCHO ==> RCO2H
  71. chemistry

    pKa for NH3 = about 9.74 but should do that conversion yourself and use something other than my estimate. Also, I assume you mean 0.1M in NH3. pH = pKa + log (NH3/NH4Cl) 8.0 = 9.74(or whatever) + log 0.1/(NH4Cl) Solve for (NH4Cl) and convert to grams for a liter of solutiion.
  72. Chemistry

    I would have worked the problem almost the same except I would have used101.325 since you used 3.17 which gives a slightly different answer of 98.15. That will change the moles slightly, too. However, I think I know how the book obtained 96.8 kPa. Standard pressure is often ...
  73. Chemistry

    a. Don't you have a table in the book (or look it up on the web) to find the vapor pressure. b. Ptotal = pH2 + pH2O. Ptotal is 1 atm and you know pH2O, solve for pH2. c. Use PV = nRT. P from above, V is given, you know R and T is 25C (converted to K). Post your work if you...
  74. Chemistry

    If that is the correct interpretation, then 1/3 x 120 = ? and 2/3 x 120 = ?
  75. Chemistry

    You didn't change anything. You retyped the same question and you didn't answer my question.
  76. Chemistry

    So what do you mean ? Is Ne 1/3 the mass 1/3 the pressure, 1/3 the mols?
  77. chem

    You don't provide much information. Normally, I want to wash with cold water in order to minimize the solubility of the ppt in the wash water but that isn't one of the choices. I suspect 3 is the correct answer which means you haven't told me all of the story. What...
  78. science

    [mass metal x specific heat metal x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0 Plug in all the numbers given and solve for specific heat metal. Post your work if you get stuck.
  79. Chemistry

    What's you have suggested sounds OK to me. That will give you the molar mass. The second part (with 0.500 g X) lets you calculate the empirical formula. 1, Convert the CO2 to grams C. 2. Convert the H2O to grams H. 3 Grams O = 0.500 g - g C - g H = ? Now convert g C, H, O ...
  80. Chemistry

    KOH + HNO3 ==> KNO3 + H2O so you know it's 1 mol KOH to 1 mol HNO3. mols HNO3 = M x L = ? mols KOH = mols HNO3 mols KOH = grams/molar mass. You know mols and molar mass, solve for grams. HCl + NaOH ==> NaCl + H2O again 1:1 mols NaOH = M x L = ? mols HCl = mols NaOH M...
  81. Chemistry Stiochiometry

    You should proof your questions before posting. As posted your problem doesn't make sense.
  82. Chemistry Stiochiometry

    You can do it all in one line but I think it's easier to do it in two in order not to be confused. To convert 50 mL of 2.8 M H2SO4 to mols (sorry I forgot that ) you do 0.05 x 2.8 = ?mols H2SO4.
  83. Chemistry Stiochiometry

    This is a limiting reagent (LR) problem. You know that afbecasue amounts are given for BOTH reactants. Here are the steps. Print this out; it will work all of your LR problems. 1. Write and balance the equation. You've done that. 2. Convert grams to mols mols = grams/molar...
  84. Chemistry

    mass = volume x density You know mass and you know density, substitute and solve for volume in mL.
  85. Chem HELP!

    After you find grams H2O lost, then mols H2O = grams h2O/molar mass H2O. The question may actually be asking for mole H2O per 1 mol CoCl2. If so that's just one more step. Find the ratio of mols H2O lost per mol CoCl2 and that will be 6 ols H2O/1 mol CoCl2. But alrady know...
  86. Chem HELP!

    13,1 g = weight xble + CoCl2.6H2O + NaBr -11,36 f = weight xble ------------------ 1,74 = weight sample but note that the 4 is not significant and I would record the weight of the sample as 1.7 g.All others were weighed to 4 places; I wonder why this one was weighed only to ...
  87. Chemistry

    1. Write and balance the equation. 2Mg + O2 ==> 2MgO 2. Convert what you have to mols. a. mols Mg = grams/atomic mass = ? b. mols O2 = grams/molar mass = ? 3. Using the coefficients in the balanced equation, convert mols Mg and mols O2 to mols of MgO a. You likely will find...
  88. Organic Chemistry

    Here is a good set of diagrams.
  89. biochem

    I think the pH of 2.14 is correct but this is really a complex question. As for the concentrations, H2PO4^- = 5 mmols/1010 mL = ? HPO4^2- = 0 H3PO4 is 5 mmols/1010 mL but the problem doesn't ask for that. I approached the problem this way. The HH equation with the pH of 7....
  90. Chemistry

    Jane, your question(s) is(are) confusing. For example, the mole ratio of HCl to CCL4 (IN WHAT) makes no sense to me. Please post one question at a time and CLEARLY indicate what you don't understand about it. The last part of your post seems to be a note or two to yourself.
  91. Chemistry

    BaSO4 ==> Ba^2+ + SO4^2- (eqn 1) and SO4^2- + H^+ ==> HSO4^- (eqn 2)eqn 2 Let S = solubility so (Ba^2+) = S and (SO4^2-) +(HSO4^-) = S You want to find S. You know k2 for HSO4^- which is 0.0102 = (H^+)(SO4^2-)/(HSO4^-). You know(H^+) and k2 from the problem so you ...
  92. Chem

    Doesn't this all depend upon how much acid and how much bicarbonate are there and their concentrations? For example, a small amount of acetic acid and a lot of NaHCO3 leaves just NaHCO3 in excess. Conversely if you have a small amount of NaHCO3 you have acetic acid in excess.
  93. Chemistry

    ln (K2/K1) = (dHo/R) x (1/T1 - 1/T2) is the van't Hoff equation. Use 8.314 for R.
  94. chemistry

    0.40% m/v means 0.4 g NaCl/100 mL. So (0.40 g/100 mL) x ?mL = 2 g. Solve for ?mL.
  95. Science

    q1 = heat to change T of ice @ -10 C to ice @ zero. q1 = mass ice x specific heat ice x (T1-T2) = ? T2 is 0 and T1 is -10 q2 = heat to change solid water (ice) to liquid water (liquid) q2 = mass ice x heat fusion = ? q3 = heat needed to change liquid water @ 0 to liquid at +10...
  96. kilauea

    I see in the news reports that when the lava hits the ocean there is a spray of HYDROCHLORIC ACID. I don't see any way HCl can be formed. Acid, yes. H2SO3 yes. But not HCl. Any comments? Thanks.
  97. Chemistry

    Probably the only thing that will happen at 150 C is that the water associated with BaCl2.2H2O will be driven off and you will be left with BaCl2 and KCl.
  98. Chemistry

    1,9 g/mL x 1000 mL = mass 1 L solution mass 1 L soln x 0.99 = mass H2SO4 in the 1 L. grams H2SO4/molar mass H2SO4 = mols H2SO4. Then mols H2SO4/L solution = Molarity
  99. Chemistry

    4Al+3O2---->2Al2O3 mols Al = grams Al/atomic mass Al. Using the coefficients in the balanced equation, convert mols Al to mols Al2O3. You can see that 2 mol Al2O3 are formed for every 4 mols Al initially. Then convert mols Al2O3 to grams. g = mols x molar mass = ? Post your...
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