# Posts by DrBob222

Total # Posts: 55,109

Chemistry
a. 2NH3 + 3CuO ==> N2 + 3Cu + 3H2O First this is a limiting reagent (LR) problem. You know that because amounts are given for BOTH reactants. b. mols NH3 = grams/molar mass = ? mols CuO = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols NH3...

chemistry
You didn't copy all of the H-H equation but you meant pH = pKa + log (b/a) For an acid, HA, it is HA ==> H^+ + A^- Ka = (H^+)(A^-)/(HA) Solve for (H^+). (H^+) = Ka*(HA)/(A^-) but that is (H^+) = Ka*(acid)/(base) or (H^+) = Ka*(a/b) Multiply by -1 -(H^+) = -Ka*(a/b) then...

chemistry
Use the H-H equation I just derived for you. Next, decide how much want to prepare. Make it easy to prepare 1 L. 3.79 = pKa + log (b/a) Solve for b/a. Assume you want to a to be 1M, the solve for b = ?*a. That gives b. Knowing you want a to be 1M and you want 1 L, calculate ...

Chemistry 30
This will do it. http://www.chemteam.info/Redox/Redox-Rules.html

chemistry
% w/w = [(mass solute)/(total mass soln)]*100 = ? mass soln is mass solute + mass solvent. If the total is 100 g and mass solute is 9.25 g, what is mass solvent.

Chemistry
I don't see a question here.

Chemistry
1 calorie = 4.184 J

Chemistry
K = (SO3)^2/(SO2)^2(O2) You are given the concentrations of each (I assume that m stands for M). Just substitute and you get K. What happens to the equilibrium constant if SO2 is added or O2 removed? Nothing happens. The CONCENTRATIONS will change but the K will not.

Chemistry
Sorry but we aren't taking the exam.

Chemistry 1
I was stumped, also, but after thinking long and hard I believe the answer is C. Choices a, b, and d are cases in which the solute is completely soluble in the solvent. Methanol and hexane are not miscible so there is an equilibrium set up between the two for the solubility of...

Chemistry 1
2Mg + O2 ==> 2MgO 3Mg + N2 ==> Mg3N2 mols Mg3N2 = grams/molar mass = approx 0.0016 but you need a more accurate answer than that estimate. Convert mols Mg3N2 to mols Mg used. That's 0.0016 x (3 mols Mg/1 mol Mg3N2) = approx 0.0045. Convert that to g Mg = mols Mg x ...

Chemistry
2KClO3 ==> 2KCl + 3O2 mols KClO3 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols KClO3 to mols O2 produced. Now convert mols O2 to grams O2. g O2 = mols O2 x molar mass O2 = ? This is the theoretical yield (TY). The actual yield (AY) is ...

chemistry
Please re-read your post and define "therapy". Perhaps you meant enthalpy or some other word. Perhaps you want heat of neutralization. That's the most likely, I think. Enthalpy of neutralization is the same thing.

Chemistry
You want to what? Changing 0.150 M NaOH to 0.390 M isn't exactly a dilution.

CHEMISTRY
Confused? That makes two of us. And I don't go with Fluffy's explanation either. It all depends upon the color of the solution you are measuring. Also, "lighter colored" doesn't mean anything either. That's a relative term. I understand the difference...

Chemistry
See your post above. It makes it a lot easier to answer your questions if you use the same screen name. Sammy and Marlene are not the same in my book.

Chemistry (Molarity) Help
What's the total volume? That's 0.50 + 2.50 + 2.00 mL = 5.00 mL. How many mols FeSCN^2+ do you have? That's mols = M x L = 1.25E-4 x 0.0005 = ? (You're assuming here that the formation constant for FeSCN^2+ is so large that the reaction goes so far to the right...

Chemistry
A = ebc As e (molar absorptivity) increases so does A. As b (path length) decreases, so does A.

Don't know why. 1.25E-4M x 100 mL = 0.0025M*mL Solve for mL of the 0.0025 M solution, add that to a 100 mL volumetric flask, dilute to the mark, mix thoroughly, stopper, voila!

chemistry
CaCO3 ==> CaO + CO2 mols CaCO3 = grams/molar mass = ? You see 1 mol CaCO3 produces 1 mol CO2 Then use PV = nRT, solve for V in L.

chemistry

Chemistry
V1/T1 = V2/T2. For A, it is 600/400 = 800/T2. Solve for T2 Do the same for the 800 to 1200(that's B). Compare T2 values.

chemistry
An electron in an excited atom is at a higher orbit in the H atom. When it falls to a lower orbit, the energy is emitted as a specific energy and that has a specific wavelength.

Chemistry
The 0.01 M HCl has been diluted to 0.01 x (1 mL/1001 mL) = 9.99E-6 M ....H2O ==> H^+ + OH^- I.........9.99E-6..0 C...........x......x E.......9.99E-6+x..x Kw = (H^)(OH^-) 1E-14 = (9.99E-6+x)(x) Solve the quadratic, add x to 9.99E-6 to find total H^+, then convert to pH.

Chemistry
[mass cool H2O x specific heat H2O x (Tfinal-Tinitial)] + [mass warm H2O x specific heat H2O x (Tfinal-Tinitial)] = 0 mass cool H2O = x look up specific heat H2O Tf cool H2O = 40 Ti cool H2O = 10 mass warm H2O = 300 g Tfinal warm water = 40 Tinitial warm water = 80 Solve for x

Chemistry
First calculate M. 1000 mL x 1.0 g/mL x 0.36 x (1/molar mass HCl) = ? M. Then convert M to pH using pH = -log(H^+).

Chemistry
mols NH4NO3 = grams/molar mass = ? This is approx 180 but that's just an estimate. You need a more accurate answer. Then mols N2 formed = 180 x (2 mols N2/2 mols NH4NO3) = approx 180. mols O2 formed = 180 x (1 mol O2/2 mols NH4NO3) = approx 180/2 = approx 90 mols H2O (gas...

Chemistry
I assume you want the molarity of the Na^+. Also, I assume the temerature of the water is such that the density is 1.00 g/mL. How many mols H2O do we have? That's 256 molecule x (1 mol/6.02E23) = ? How many grams is that? That's ?mols H2O x (18 g/mol) = ? How many mL ...

chemistry
Here are the definitions. Loss of electrons is oxidation. Gain of electrons is reduction. The material oxidized is the reducing agent. The material reduced is the oxidizing agent. 2Fe3+ + Sn ==> 2Fe2+ + Sn2+ You can see that 2Fe^3+ goes from 6+ to 4+ so that is a gain of ...

chemistry
I ASSUME the temperature of the liquid ether is at its boiling point of 34.6 C because you didn't list that; however, in problems of this type, especially since you gave the specific heat of the liquid, that the initial T is less than 34.6 C. q needed to convert liquid ...

Chemistry
dT = Kb*molality You know Kb and dT, solve for m. m = mols sugar/kg solvent You know m and you don't know kg H2O. Can't go further. If you hae that info, then substitute and solve for mols sugar.

Chemistry
dE = hc/wavelength

Chemistry
1. There are 6.02E23 molecules in 1 mol. 2. grams PbO = mols PbO x molar mass PbO

Chemistry
Use PV = nRT and solve for n in the flask initially. Then mols N2 added = 2 grams/molar mass N2. Add to find total n (no of mols), and substitute into a new PV = nRT along with the new conditions and solve for the new pressure. Don't forget that T must be in kelvin.

Biochemistry
Use Henderson-Hasselbalch equation and solve for (base)/(acid) ratio. That is equation 1. Use pKa2. Then set up (base) + (acid) = 0.2 for equation 2. Solve those simultaneously for (acid) and (base) Convert (acid) to grams NaH2PO4 Convert (base) to grams Na2HPO4. Remember this...

The short answer is that I beg to differ with you but I thank you for your comments; however, if you will read the question again, along with my response, you will see I stated it will not react AND I stated WHY there is no reaction. I see we agree on that. But those four ...

Chemistry
no reaction. Rxn occur for only a few reasons. 1. A ppt is formed. none here. 2. A gas is formed. none here. 3. A weak electrolyte is formed. none here. 4. redox rxn. none here.

Chemistry
Something tells me you haven't posted all of the problem. You can't get NaOH with an NH3 solution.

chemistry
You made a typo. You meant HNO3 and you omitted H2O as one of the products. Cu + HNO3-Cu(NO3)2 + NO + H2O Cu on left has oxidation number 0; on right is +2. N on left is +5 and on right is +2 (in NO) and for the moment ignore the NO3 ion in Cu(NO3)2. So multiply the Cu change ...

Chemistry
Adam, I can't begin to decipher your post. No caps, no arrow, no differentiation between reactants and products, no question.

Chemisty
Use the coefficients. 18 L CO2 x (7 mols O2/4 mols CO2) = 18 x 7/4 = ? The answer is NOT 22.909.

Analytical chemistry
mols B6 = grams B6/molar mass B6 =? Then M B6 = mols B6/L soln = mols B6/0.1L = ? Do same for caffeine. Note: I assume you want concn in molarity; however, not that you could do it in g/L, M, m, N, etc.

Chemistry
M HI = mols/L = 4.00/2.00 = 2.00 .......2HI ==> H2 + I2 I ......2.......0....0 C.......-2x.....x....x E.....2-2x......x....x Substitute the E line into Keq expression. You know x = (H2) = 0.4,calculate concns and Keq from that.

chemistry
Technically you can't do this without knowing the reaction. But USUALLY, when the reaction isn't know, one assume that one takes the molarity and multiplies by the total positive or negative charge. mols Na2CO3 = grams/molar mass. M = mols/L N = M x 2.

chemistry
hydrated

Chemistry
Six problems in here. What do you know about any of these?

chemistry
Actually, this can't be answered because you didn't identify the numbers; however, I have assumed the first number is n, the second is l and the third and fourth are ms. If that isn't correct ignore the following. i no. Can't have two ms of 1/2 ii no, Can't...

AP Chem
This is a limiting reagent (LR) problem and you know that because amounts are given for BOTH reactants. CaCl2 + 2AgNO3 ==> Ca(NO3)2 + 2AgCl mols CaCl2 = M x L = ? = approx 0.001 but you need to confirm. mol AgNO3 = M x L = approx 0.001 x 1 = 0.001. You see the mols AgCl are...

Chemistry
I would use specific heat water as 1 cal/g*C and not do the Joule to calories conversion. q = cal = mass H2O x specific heat H2O x (Tfinal-Tinitial). If you want to use 4.182 J/g*C, the do that and convert to cal by 1 cal = 4.182 J.

Chemistry
15 mg/mL x # mL = 12 mg Solve for # mL.

chemistry
mass = volume x density You have the mass and density, substitute and solve for volume.

Chemistry
I think you just made a a couple of typos. You left no space between Sn+2Ag and you omitted the 2Ag on the right. Sn + 2Ag ==> An^2+ + 2Ag

chemistry
If you intended KClO2 (and not KClO3), here is he scoop. K is +1. It's ALWAYS +1 because it's in group I of the periodic table. Cl is +3 on the left (remember all compounds are 0 so K + Cl + 2O = 0; therefore, 1 + ? + 2*-2 = 0. That makes Cl +3) and O is -2 for EACH ...

Chemistry
I think it's important that you define what you mean by 80:20 mixture. Is that 80:20 by mass, by moles, or by volume?

chemistry
a. What are you talking about. What subject, what experiment, what source? b. What sources have ALREADY been mentioned?

Chemistry 20
The 1.82 is 100%. That is theoretical yield (TY). The 1.94 is actual yield (AY) % yield = (AY/TY)*100 = ? You can take the difference.

Chemistry 20
Technically, none since H2CO3 decomposes as fast as it is formed. H2CO3 ==> H2O + CO2. However, ignoring that, then 2HNO3 + Na2CO3 ==> 2NaNO3 + H2CO3 The equation tells you that 2 mols HNO3 will produce 1 mol H2CO3. So 1.2E-3 mols will produce ......?

Chemistry 20
This is done the same way as the HNO3 problem.

chemisty
Cu + 2AgNO3 ==> Cu(NO3)2 + 2Ag mols Cu = grams/atomic mass = ? mols Ag = 2x mols Cu

Chem1020
Use PV = nRT. You know V(in L), n,R and T(in kelvin). Solve for P in atm and convert to mm. 1 atm = 760 mm Hg.

Chem1020
PV = nRT. You know P(must be in atm), V(must be in L), R and T(must be in kelvin). Solve for n = mols. Then n = grams/molar mass. You know n and grams, solve for molar mass.

Chemistry
dE = 2.18E-18(1/x^2 - 1/10^2)

Chemistry
50 g x (atomic mass Cu/molar mass CuO) = ? g Cu.

Chemistry
You need Keq and the reaction for that K.

chemistry
dT = 15 x (6/2) = /

Qualitative analysis
copper carbonate

Qualitative analysis
All form a hydroxide insoluble in water. Pb^2+ is the only one to form Pb(OH)2 which dissolves in an excess of NaOH by forming a complex ion of [Pb(OH)4]^2-

oops--Qualitative analysis (Chem)
Fe)OH)2 is green and gelatinous with white streaks and changes to a red/brn.

Qualitative analysis (Chem)
Al(OH)3 is not colored. Cu(OH)2, Fe(OH)2 and Fe(OH)3 are colored. Fe(OH)2 is the only one that is colored and changes color on standing because it is being oxidized to Fe(OH)3 by air. So Fe(OH) is greenish and it changes to a red/brown.

Chemistry
React with what to form what? I assume that is to decompose to H2 and O2 but I don't know that. Write the equation. 2H2O ==> 2H2 + O2 546.234 mols H2 x (2 mol H2O/2 mol H2) = 546.234 x (2/2) = 546.234 x 1/1 = 546.234 mol H2O. It's done with the coefficients. 2H2O

Chemistry
CH4 1 mol CH4/4 mol H or 4 mol H/1 mol CH4

Chemistry
I don't know what the C stands for but you seem to have ignored it in the calculation. I didn't go through the calculations with a calculator but the methods seems OK EXCEPT that you haven't added in the heat from steam at 100 to steam at 110

chemistry
melting ice at zero is mass ice*heat fusion = ? Cooling 540 g water from 25 to zero is mass H2O * specific heat ice x (Tfinal-Tinitial). Put those together to obtain (mass ice*heat fusion) + (mass H2O x specific heat water x (Tfinal-Tinitial) = 0 Solve for mass ice.

Chemistry
I said you were right yesterday.

chemistry
What are the conditions? T, P? I will assume STP but technically this problem can't be worked without that informatiion. 1.7 dm-3 H2 produced. Convert to mols. That's 1.7 x (1 mol/22.4 dm-3) = ? Convert to mols Zn. mols Zn = mols H2 (look at the coefficients in the ...

chemistry
g C = 1.500 g CO2 x (atomic mass C/molar mass CO2) = ? g H = 0.401 g H2O x (2*atomic mass H/molar mass H2O) = ? g O = 1.00-g C - g H = ? Convert grams to mols. mols C = g C/12 = ? mols H = g H/1 = ? mols O = g O/16 = ? Find the ratio of the elements to each other with the ...

Chemistry
What's Ksp for CaCO3? What's (H3O^+)?

Chemistry
thio (sulfur) compounds pyridines (N compounds)

Chemistry
mass = volume x density. You know mass and density, substitute and solve for grams.

@CaSO4...chemistry
You are removing products. Le Chatelier's Principle says that if a system in equilibrium is disturbed, then the system will shift so as to undo what we did to it. Therefore, it we remove the products, more CaSO4 will decompose to form the products we removed. You can take ...

chemistry
Please don't post another question as an answer to another question. A. See below for ethanol problem. B. Convert 2 kg glucose to L ethanol formed using the same procedure used in the previous problem. This will give you the theoretical yield (TY)( that's the yield as...

chemistry
C6H12O6(aq) ? 2 C2H5OH(l) + 2 CO2(g) mols glucose = grams/molar mass = ? mols ethanol = 2x that (look at the coefficients in the balanced equation). g ethanol = mols ethanol x molar mass ethanol. Convert to mL. volume in mL = grams/density.

Organic chemistry (QA)
This is hardly organic chemistry. Some reasons for pptn rxns. 1. A ppt is formed. 2. A gas is formed. 3. A weak electrolyte is formed. You asked only about pptn so look at the equations and see if a ppt will form. Basically this requires that you know the solubility rules for ...

Chem
First, you can NOT write an equation because you don't know the formula of gold chloride not the formula of gold nitrate.. The Cl in gold chloride was converted to AgCl. So how much Cl must have been there with the gold? That's 464 mg x (atomic mass Cl/molar mass AgCl...

Chemistry
I agree with you.Book must be wrong.

Chemistry
A. mols Al = grams/atomic mass = ? This is n in part B. B. Use PV = nRT. You know n, R, V and T. Remember V is in L, T in kelvin, R=0.08205. Solve for P in atm. C. Ptotal = pH2 + pH2O. Ptotal and pH2O are given. Solve for pH2.

chemisty
I assume you want an equation. 2Na + I2 ==> 2NaI

chemistry
1/(2E5)^3 = 1/(2E15) = 1.25E-16

Chemistry
I would assume 20 g Ne and 20 g He (but any number will do as long as it is the same for both). mols Ne = grams/atomic mass = ? mols He = grams/atomic mass = ? Total mols = ? XNe = mols Ne/total mols pNe = XNe*Ptotal = ?

Chemistry
Whatever number you choose, I guess, since you didn't post any conditions.

Chemistry
I worked this for you yesterday. http://www.jiskha.com/display.cgi?id=1479258354

Chemistry

chemistry
q = mass H2O x dHvap.

Chemistry
How can we help you with this without doing all of the work?

Chemistry
mols Al(OH)3 = grams Al(OH)3/molar mass Al(OH)3 = ? To do part b just rearrange the equation above to grams = mols x molar mass and substitute the data for Mg(OH)2. Remember to convert grams to mg at the end.

Chemistry
You're right. They are that.

Chemistry
Your abswer if 7 g makes no sense since specific heat is measured in J/g*C (or KJ)or cal/g*C. I'm not sure the problem can be worked without knowing the calorimeter constant.

Chemistry
CaCO3 ==> CaO + CO2 Use PV = nRT and solve for n for CO2 Convert mols CO2 to mols CaCO3, then to grams CaCO3 Finally, multiply g CaCO3 by 2 since it is only 50% pure.

chemistry
Just add the electrons, protons will be the same, look up the atomic number.18+2+10+4 looks like 34 = Se to me.

@A--Chemistry
Probably you should show your work. I don't buy those numbers. And yes, limiting reagent is a factor.

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