Wednesday
February 10, 2016

Posts by DrBob222

Total # Posts: 51,344

chemistry
7.5 g CaCl2*9H2O x (molar mass CaCl2/molar mass CaCl2*9H2O)_
November 16, 2015

Chemistry
Surely you have made a typo (or two). There is no way the pH can be 4.90. The equivalence point for the titration of a weak acid and strong base is approximately 8.3 or so. Adding BASE to that will make it higher, not lower.
November 16, 2015

chemistry
H2O ==> H^+ + OH^- Kw = (H^+)(OH^-) pH = 4.73 = -log(H^+) and I get approx 2E-5 but that's just a close estimate for (H^+). That makes (OH^-) = estimated 5E-10M # mols OH^- = M x L = ? and each mols has 6.02E23 ions.
November 16, 2015

Chemistry
It depends upon exactly what you mean by saturated. If it is just saturated and there is no solid in the solution, nothing will happen. If, however, there is a relatively small amount of KNO3 solid, the solid will dissolve as the solution is heated and the solution will be ...
November 16, 2015

chem
to do what? make 0.148 M NaI in 500 mL? How many mols do you need? That's M x L = mols. Then mols = grams/molar mass. You have mols and molar mass, solve for grams.
November 16, 2015

chemistry
You need to find the arrow key(s) and use it(them). --> or ==> Keq = (NH3)^2/(N2)(H2)^3 It's always (product)/(reactants) and each coefficient becomes an exponent.
November 16, 2015

Chemistry
We can't draw diagrams on this forum. You can look on Google for that.
November 16, 2015

Chemistry
I would look at a, c(slight with anything almost), and d.
November 16, 2015

Analytical Chemistry
I gave you detailed instructions for this problem yesterday (late yesterday).
November 16, 2015

Chemistry
Which constant and for what?
November 16, 2015

Science: Chemistry
dHrxn = (n*dHf products) - (n*dHf reactants) = ?
November 15, 2015

Science: Chemistry
mols pentane = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols pentane to mols CO2. Then g CO2 = mols CO2 x molar mass CO2 and this is the mass at 100% yield. Mass CO2 at 58.0% yield is mass at 100% yield x 0.580 = ?
November 15, 2015

chem
You gave the electron configuration for Al, not Al^3+. You should remove the last three electrons for the Al^3+ ion. Same thing for P^3-. You should add 3e to what you have.
November 15, 2015

Chem
Al + N2 ==> Al3N2 (not balanced) Al is zero on the left and +3 on the right. N is zero on the left and -3 on the left. Oxidation is the loss of electrons; reduction is the gain of electrons.
November 15, 2015

chemistry Dr BOB
The oxidation half equation is Fe^2+ ==> Fe^3+ + e The reduction half equation is MnO4^- + 8H^+ + 5e ==> Mn^2+ + 4H2O
November 15, 2015

Analytical Chemistry
You have 0.0398 g CuSO4.5H2O. Convert that to g Cu as follows: 0.0398 x (atomic mass Cu/molar mass CuSO4.5H2O) = ? That gives you g Cu/100 mL (technically, that should be 100 mL OF SOLUTION. Then convert 0.0398 g Cu to mg Cu which is in 100 mL of solution then multiply by 10 ...
November 15, 2015

Chemistry 102
What are you using for Kformation for Ni(CN)4?
November 15, 2015

Chemistry
You balance the equations. NaCl(aq) ==> H2(g) + Cl2(g) + NaOH(aq) NaCl(l) ==> Na(l) + Cl2(g) (Note: For NaCl to be liquid, the temperature must be hot enough that Na will be melted also. The same applies to K beldow.) KBr(l) ==> K(l) + Br2(g)
November 15, 2015

Chemistry
The easiest way to do this is to reverse equation 1 and add in equation 2 for PbO2 + 4H^+ + SO4^2- + Pb + SO4^2- --> PbSO4 + PbSO4 or PbO2 + 2H2SO4 --> 2PbSO4 + 2H2O Ecell = 2.041 Then Ecell = Eocell - (0.05916/n)*log(1/(H2SO4). Plug in the numbers and solve for Ecell.
November 15, 2015

Chemistry
I don't see anything wrong with what you have.
November 15, 2015

Chemistry
H2A + 2NaOH ==> Na2A + 2H2O mols NaOH = M x L = ? Using the coefficients in the balanced equation, convert mols NaOH to mols H2A (that is 1/2 mols NaOH) Then mols = grams/molar mass. You know grams and mols, solve for molar mass.
November 15, 2015

Chemistry
25.5(0.861) + 29.2(1-0.861) = ?
November 15, 2015

Chemistry
Technically, both C2H4 and NBr3 have polar covalent bonds but most organic chemists don't consider the C-H bond to be polar.
November 15, 2015

chemistry
2HNO3(aq) Na2CO3(aq)=>2NaNO3(aq) H20(l) CO2(g) mols HNO3 = M x L = ? Using the coefficients in the balanced equation, convert mols HNO3 to mols Na2CO3 (That will be 1/2 mols HNO3) Then grams Na2CO3 = mols Na2CO3 x molar mass Na2CO3. This will be the grams in the 25 cc of ...
November 15, 2015

Chemistry
The easy way to do this is Step 1. 2Fe2O3 + 3C ==> 3CO2 + 4Fe Step 2. Then don't worry about the tonnes. Step 3. mols Fe2O3 = 10,000/molar mass Fe2O3. Step 4. Using the coefficients in the balanced equation, convert mols Fe2O3 to mols Fe. Step 5. Then grams Fe = mols Fe...
November 15, 2015

chemisty
How many mols do you need? That's M x L = ? Then mols = g/molar mass. You know mols and molar mass, solve for grams needed.
November 15, 2015

Chemistry
mols = grams/molar mass. You know grams and mols, solve for molar mass.
November 15, 2015

Chem
a. P*molar mass = density*RT Substitute and solve for molar mass. b. Use the equation in a to solve for density c. XO2 = molar mass = ? 2*atomic mass O = 32 Subtract to find atomic mass X.
November 15, 2015

Chem
I made a stab at answering this once. You need to tell us what you did for us to know the system you're using.
November 15, 2015

Chemistry
See your other post.
November 15, 2015

chemistry
wavelength = h/mv You know wavelength (convert o m), you know h, you know v (0.01*3E8) so solve for m for mass of one atom. Convert to a mol of atoms.
November 14, 2015

Chem
The question asks how you did it and I don't know that. What does decorated mean? Ag HCl to ppt AgCl without the others. Add NaOH to ppt Al(OH)3 without the others. Adding NaOH will convert the NH4Cl to NH3 and that can be expelled. K^+ will be left.
November 14, 2015

Chemistry
I believe this is a screwed up question from the get go.
November 14, 2015

Chem
I guess slats is salts. But I don't know what the addition of his is.
November 14, 2015

Chemistry
The answer is c. a won't work. Why? Ni^2+ is -0.25 with H2 is 0 so Ecell is negative and that isn't spontaneous. But c will. Why? Ag^+ is 0.8 Ni to Ni^+ is +0.25 Add and Ecell is + so rxn is spontaneous. You can go through the others to convince yourself that all are ...
November 14, 2015

Chemistry
1/wavelength = R(1/(n1)^2 - 1/(n2)^2 The first term is 3^2 and the second is 4^2. R you can find in your book or on the web.
November 14, 2015

chemistry
We can't draw diagrams on this forum.
November 14, 2015

Chemistry
.......2HBr + 2K ==> 2KBr + H2 mols K = grams/molar mass Using the coefficients in the balanced equation, convert mols K to mols HBr. Now convert mols HBr to volume using M HBr = mols HBr/L HBr. You know M and mols, solve for L.
November 14, 2015

chemistry
I can't tell the difference between the question and what I assume is your answer.The skeleton equation is simply 5Fe^2+ + MnO4^- ==> 5Fe^3+ + Mn^2+ and you can add the states. Most of the rest of what you wrote is not right but the final equation you came up with is ...
November 14, 2015

chemistry
Use PV = nRT with n = g N2/molar mass N2. Remember T must be in kelvin.
November 14, 2015

Chemistry
a cd b However, I prefer to say the water molecules are attracted to the Na ions (of the crystal) and Cl ions (of the crystal).
November 14, 2015

Chemistry
The correct answer is b.
November 14, 2015

chemistry
........NH3 + H2O ==>NH4^+ + OH^- I........5............0.......0 C.......-x............x.......x E.......5-x...........x.......x Substitute the E line into Kb expression and solve for x = OH^-, then convert to pH.
November 14, 2015

Chemistry
q = [mass H2O x specific heat H2O x (Ttinal-Tinitial)] + Ccal x (Tfinal-Tinitial) and that gives you q for 2.1. Change to q for 1 g.
November 13, 2015

Chemistry
See your other post. Apparently you ignore the Ccal.
November 13, 2015

Chemistry
1000 kg coal = 1,000,000 g coal and if that contains 0.050% FeS2, then 1,000,000 x 0.0005 = ? g FeS2 to start. Go through the stoichiometry to find how much SO2 is produced, then do the stoichiometry to find NaOH required.
November 13, 2015

Chemistry (Check)
You did it right; I used 11/760 and left it in the calculator.
November 13, 2015

Chemistry (Check)
You have too many s.f. in that answer for A. Also, I don't get that exactly; the problem, I suspect, is that you rounded with intermediate numbers and I didn't. B is ok.
November 13, 2015

Chemistry
right
November 13, 2015

NOTE: Chemistry
I want to point out that you aren't allowed 4 significant figures.
November 13, 2015

Chemistry
Nope. Right digits but wrong decimal. By the way, the problem below with an answer of 0.530 is ok but the site wouldn't let me post an ok.
November 13, 2015

Chemistry (Check)
good. Come back anytime.
November 13, 2015

Chemistry (Check)
The difference: If I use 900/760 and round that number to 1.18 (which is correct), I get 12.22 which rounds to 12.2. However, if I set my calculator to read 6 places (which I do routinely for all of my work) then go through without taking anything out of the calculator; ie., ...
November 13, 2015

Chemistry (Check)
My calculator reads 12.267 so I would round that to 12.3 g.
November 13, 2015

Chemistry (Check)
500 mL x (742/795) = 467 mL
November 13, 2015

Chemistry
OK
November 13, 2015

Chemistry (Check)
ok
November 13, 2015

Chemistry (Check)
OK. You should always include units.
November 13, 2015

Chemistry (Check)
I obtained 0.129 cc. If your answer is in L that is ok.
November 13, 2015

Chemistry (Check)
no. Right digits, wrong decimal.
November 13, 2015

Chemistry (Check)
good
November 13, 2015

oops--Chemistry (Check)
Also 1.00/760 is not 1.32 but 1.32E-3. Thus 1E-6/760 = 1.32E-9 I think.
November 13, 2015

Chemistry (Check)
985mLN / 1000 = .985 L 0.0 degrees C + 273 = 273 K 1.00x10^-6 mmHg / 760 mmHg = 1.32 atm YOU forgot the 10^-6 1.32 atm x .985 L = n ( .08206 Latm / molK)x273K n = .0580 moles x 6.022x10^23 = 3.50 x 10^23 molecules. For digits I obtained 3.48; the difference is that you rounded...
November 13, 2015

Chemistry (Check)
I don't like that answer either. Post your work and let me find the error. By the way, the 12 atm to 25 atm problem below is OK but the site will not let me post an OK.
November 13, 2015

Chemistry (Check)
The digits are close but the 10^? is missing.
November 13, 2015

Chemistry
mass # = #protons + #neutrons
November 13, 2015

Chemistry-Dr.Bob
This is a limiting reagent (LR) problem. You know that because an amount is given for both reactants. 3KOH + Fe(NO3)3 ==> Fe(OH)3 + 3KNO3 mols KOH = M x L = ? mols Fe(NO3)3 = M x L = ? Using the coefficients in the balanced equation, convert mols KOH to mols Fe(OH)3. Do the...
November 13, 2015

Chemistry
EDTA forms 1:1 complexes with metals; therefore, 6.25E-5 mols from the previous problem will be that amount with EDTA. M = mols/L 0.00420 = 6.25E-5/L. Solve for L and convert to mL if desired.
November 13, 2015

chemistry
Write the hydrolysis equation. Call aniline BNH2, then ........BNH2 + H2O ==> BNH3^+ + OH^- I........1M.............0.......0 C........-x.............x.......x E........1-x............x.......x Kb = (x)(x)/(1-x) Solve for x = OH and convert to pH.
November 13, 2015

Chemistry
See Damon's response below.;
November 13, 2015

Chemistry
Calculate the oxidation state of each atom in the equation and note that each has the same oxidation state on the left that it has on the right.
November 13, 2015

Chemistry
See your other post.
November 13, 2015

Chemistry
dHrxn = (n*dHf products) - (n*dHf reactants)
November 13, 2015

chemistry
OK, so I'll start over. Below I have erased all I wrote but kept what you wrote. My response is in bold. A chunk of iron weighs 4.32 g. a) How many iron atoms are there in this sample? 55.85 g Fe = 1.00 mol Fe = 6.022 x 1023 atoms Fe What you have written is exactly right...
November 12, 2015

chemistry
A chunk of iron weighs 4.32 g. a) How many iron atoms are there in this sample? 55.85 g Fe = 1.00 mol Fe = 6.022 x 1023 atoms Fe mols Fe = grams Fe/55.85 Then mols Fe x 6.022E23 = ? no. atoms. b) How many moles of iron are there in this sample? See above. 2. . You have a ...
November 12, 2015

Chemistry
You have a typo in #1, that should be 3C(s). Reverse #1, add to 3x #2, and to 4x #3.
November 12, 2015

Chemistry
Basically it's the size of the atom. Here is a table. http://www.science.uwaterloo.ca/~cchieh/cact/c120/bondel.html
November 12, 2015

chemistry
Great!
November 12, 2015

chemistry
No, No, No. The 2 in front of the Ca is a coefficient, not the charge. It is a zero oxidation state because it is a free element. All free elements (those not in a compound) are zero. O2 is zero for the same reason. So Ca goes from zero on the left to 2+ on the right; ...
November 12, 2015

chemistry
Oxidation is the loss of electrons. Ca is zero on the left and +2 on the right. O is zero on the left and 2 on the right. Which element (Ca or O) lost electrons?
November 12, 2015

chemistry
You misunderstood on 1. mols = M x L = 0.600 x 0.450 = 0.270. Then you omitted the second step which I wrote in my first response which is grams = mols x molar mass = ? That will be grams = 0.270 x molar mass CaCl2 = ?
November 12, 2015

chemistry
1. You forgot to change 600 mL to L. The answer is 0.270 mols. 2. is yes 3. I don't get your answer. M x L = 1.75 x 3.65 = ? ? x molar mass = ? x 111 = approx 710 grams.
November 12, 2015

chemistry
1. mols CaCl2 = M x L = ? Then grams = mols x molar mass 2. The base is what's left after the H is gone. 3. How many mols do you need? That's mols = M x L How many grams is that many mols? That's grams = mols x molar mass = ?
November 12, 2015

Chemistry
Look up delta H formation and plug into dHrxn = (n*dHf products) - (n*dHf reactants). If the sign is - it is exothermic; endothermis is + sign.
November 12, 2015

Chemistry
xxx
November 12, 2015

Chemistry
mols Ag2O = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols Ag2O to mols Ag.
November 12, 2015

Chemistry
Calculate dH for each reaction of interest (or all of them) as dHrxn = (n*dHf products) - (n*dHf reactants) then compare to answer the question. Yes it is a state function because the sum is equal to the individual parts and to be a state function it doesn't matter how we ...
November 12, 2015

Chemistry (Check)
Off hand I wouldn't think so. q = mass H2O x specific heat H2O x delta T = ?,I think the question is stated improperly. This is the dH for the reaction as shown. What the problem wants, I think, is dH for the reaction/mol. That is Then q/mol CH4 = dH for the reaction. I ...
November 12, 2015

Chemistry
46.9 psi = 3.19 atmospheres. Then use PV = nRT and solve for n
November 12, 2015

Chemistry
-2511.14 kJ/2 mols x 2 mols = ? -2511.14 kJ/2 mols x 1 mol = ?
November 12, 2015

Chemistry Lab Work Help!
I don't get what you did? Burets usually are used to measure the volume taken FROM the buret and the final reading is greater than the initial volume. You seem to be adding to the buret. Explain what you did. If you want the volume that was ADDED you subtract 49.97-30.49. ...
November 12, 2015

Chemistry
Combustion reactions produce heat. This is a combustion reaction. It can be measured with a calorimeter.
November 12, 2015

Chemistry
A is probably right but I don't there there is enough information there to know that. You must go to a periodic table to check it out. I don't think B is right. The average of all of the isotopes is 40.078 but Ca-40 is not that mass. C is ok. D is not right. D would be...
November 12, 2015

chemistry
empirical mass is 25.846 103.38/25.846 = 3.999 which rounds to 4 So molecular formula is (BCH3)4 or B4C4H12
November 12, 2015

Chemistry
1 mol contains 6.02E23 so 4.53E-15 must contain ......?
November 12, 2015

Chemistry - Energy: Phase Changes
Why didn't you tell us where you THINK you should start? Let y = mass ice cube To melt ice cube at zero C it is y*heat fusion. Add that to in as this, Then (y*heat fusion) + [y*specific heat H2O x (Tfinal-Tinitial)] + [(mass H2O in cup x specific heat H2O x (Tfina-Tinitial...
November 12, 2015

Chemistry - Energy: Phase Changes
Yes, 2.23 mols ice are melted? How many grms is that? grams = mols x molar mass = approx 40 g. How much ice did you have? That's 1,000 g. How much ice is left. Approx 1000-40 = ?
November 12, 2015

Chemistry
Yes on both answers.
November 12, 2015

Chemistry
q = mass benzene x heat vaporization = ? heat vaporization must be available in tables.
November 12, 2015

Chemistry
So the neutral atom will be [Kr]4d^10 5s^2 5p^2 and that adds to 36 + 10 + 2 + 2 = ? as the atomic number and look that up on the periodic chart.
November 12, 2015

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