Wednesday
February 10, 2016

Posts by DrBob222

Total # Posts: 51,344

Chemistry
You seem to be on the right track. Convert mols of products to pressure for each. To find the O2 pressure at the end of the reaction, you know moles O2 initially, convert mols CH4 used to mols O2 used, then mols O2 initially - mols O2 used = mols O2 left unreacted. Then change...
October 13, 2015

chemistry
I'll get you started. mols SCN^- initially = M x L = ? mols Fe^3+ initially = M x L = ? (SCN^-) initially = 0.002 x 4/10 = 8E-4M (Fe^3+) initially = 0.002 x 5/10 = 0.001M .........Fe^3+ + SCN^- ==> FeNCS^2+ I.......8E-4.....1E-3........0 C........-x.......-x.........x E...
October 13, 2015

Chemistry
I don't understand your last post. Using 3.5E-4 for Ka, that 7.58 you calculated is correct. I calculated it with and without the quadratic formula and got the same answer.
October 12, 2015

Chemistry
I can't check your answer because you don't give the Ka value you used for HF. Books differ with tables for Ka and Kb. I obtained 7.42 for pH If you will post your work I will check it.
October 12, 2015

Chemistry
mols HBr = M x L = ? mols KBr = mols HBr x (1 mol KBr/1 mol HBr) = ?
October 12, 2015

Chemistry
Yes and that's what Mr. Pursley told you. You must calculate the mols AgCl.
October 12, 2015

Chemistry
Use the CaCO3 equation you have and add this one for the titration. NaOH + HCl ==> NaCl + H2O mols HCl initially = M x L = 0.01 excess HCl = mols NaOH = 0.002 mols HCl used for the tablet = 0.008 0.008 mols HCl x (1 mol CaCO3/2 mols HCl) = 0.004 mols CaCO3 g CaCO3 = mols ...
October 12, 2015

Chemistry
I would take 49.5 as the freezing point or you could use 49.5, 49.6 and 49.5, take the average as 49.53 which rounds to 49.5. For #2, what is the solid? Is that Naphthalene (by the way, note the spelling) or is that the mixture of PDB and naphthalene.
October 12, 2015

Chemistry
See the other post.
October 12, 2015

Chemistry
2C2H2 + 5O2 ==> 4CO2 + 2H2O Use PV = nRT and solve for mols oxygen. Use the coefficients in the balanced equation to convert mols O2 from your first calculation above to mols C2H2. Then use PV = nRT to convert mols C2H2 to pressure. Post your work if you get stuck.
October 12, 2015

Chemistry
I don't know what quantum level 1, 2, 3 are. Are you talking about N = 1, 2, 3? or some other notation. Any what do you not understand that keeps you from counting them?
October 12, 2015

chemistry
Read the intro statement at the top of the page then click on some of the links below that for more information. https://www.google.com/search?q=are+pi+bonds+symmetrical&ie=utf-8&oe=utf-8
October 12, 2015

chemistry
I don't know what that means. The acetylene molecule is a linear molecule which makes it symmetrical in two dimensions but not in three. I suggest you Google sigma bonds and pi bonds and look at the pictures. If we knew what kind of symmetry the question was talking about ...
October 12, 2015

chemistry
You need to watch your typing. 2KClO3 ==> 2KCl + 3O2 mols KClO3 = grams/molar mass = ? Using the coefficients in the balanced equation convert mols KClO3 to mols O2 What do you mean by "How much"? If you want grams, that is grams = mols O2 x molar mass O2. If you ...
October 12, 2015

chem
The Na2S reacts with AgNO3 but not with NaNO3. Na2S + 2AgNO3 ==> Ag2S + 2NaNO3 mols Ag2S = 0.46/molar mass Ag2S = ? Using the coefficients in the balanced equation, convert mols Ag2S to mols AgNO3. Since the mixture has a mass of 1.27 g, 1.27- mass AgNO3 from above = mass ...
October 12, 2015

Chemistry
Let x = volume in mL of 0.149 M HCl to be added and mmols = millimols. mmols 0.285M + mmols 0.149M = mmols 0.205M (0.285*100) + (0.149x) = 0.205*(100+x) Solve for x. You should prove that by adding mmols 0.285M to mmols 0.149M and see if total mmols/total volume in mL = 0.205M
October 12, 2015

Chemistry
It would have been nice if you had just posted the problem. As it is I'm working in the dark. The Csys is the total and it's made up of the two components listed. Ccal is the heat capacity of the calorimeter. Csol is the heat capacity of the solution.
October 12, 2015

Chemistry
I believe you may have omitted the power of 10 for part A. For part b I get 1.68 but not the 10^-8
October 11, 2015

Chemistry
charge = 2*1.602E-19 C mass: convert amu to kg Calculate C/kg
October 11, 2015

chemistry
w = wavelength 1/w = 1.0973E7(1/1 - 1/x^2) Convert 93.73 nm to m and solve for x. That will tell you to which orbit the electron has been moved. Then, 1/w = 1.0973(1/y^2 - 1/x^2). Solve for y.
October 11, 2015

chemistry - HELP!
..........A + B ==> AB I.....0.1580..4.721E-5....0 C........-x....-x.........x E....0.1580-x..4.721E-5-x..x Substitute the E line into the Kc expression and solve for x, then evaluate A and B.
October 11, 2015

Chemistry
You don't need to memorize a new formula for this. Remember what you do for %yield. It is %yield = (actual amount/theoretical yield)*100 92.3 = actual amount/theoretical yield theoretical = actual/%yield
October 11, 2015

Chemistry
After you finish the calculation to find the g cyclohexanol needed with 86.2% yield, that is if the cyclohexanolis 100% pure. Since it is only 92.3% pure, the amount for 100%/0.923 = amount needed for 92.3% purity.
October 11, 2015

Chemistry
2MnO4^- + 5C2O4^2- ==> 10CO2 + 2Mn^2+ (Note: that doesn't balance all of the equation but the H2SO4, K^+, etc are just spectator ions.) mols C2O4^2- = M x L = 0.111 x 0.02115=? Using the coefficients in the balanced equation, convert mols C2O4^2- to mols MnO4^-. That ...
October 11, 2015

Chemistry
2NaOH + H2SO4 ==> 2H2O + Na2SO4 mols NaOH = M x L = ? Use the coefficients in the balanced equation to convert mols NaOH to mols H2SO4. (You can see mols H2SO4 = 1/2 mols NaOH) Then M H2SO4 = mols H2SO4/L H2SO4. You know M and mols, solve for L and convert to mL.
October 11, 2015

Chemistry
Add the reverse of eqn 1 to 2x the reverse of equation 2 to eqn 3, then take 1/2 of the sum. Post your work if you gets stuck.
October 11, 2015

Chemistry
mols glucose = grams/molar mass = ? m = mols glucose/kg solvent delta T = Kb*m Add delta T to 94 to find the new boiling point.
October 11, 2015

Chemistry
I think you have made a typo. There is no way to get 0.571 (I assume that is torr) from the problem you posted. I think you have made a typo in the 750 g sucrose; I believe that must be 75.0 g sucrose I will assume my assumption is right. mols sucrose = 75.0/342 = ? mols H2O...
October 11, 2015

Chemsitry
Let x = M H2SO4 and y = M NaOH (Note that it takes 2 mols NaOH to react with 1 mol H2SO4.) In words; eqn 1: mols H2SO4 + mols HCl = mols NaOH eqn 2: mols H2SO4 + mols HCl = mols NaOH Change word equation to numbers. 10x*2 + 30y = 2.5*20 is eqn 1. 30x*2 + 10y = 2.5*28 is eqn 2...
October 11, 2015

Chemistry
mols H2SO4 = M x L = 0.05 mols H2SO4 back titration = M x L = 0.02 mols NaOH 2NaOH + H2SO4 ==> Na2SO4 + 2H2O 0.02 mols NaOH = 1/2 * 0.02 = 0.01 mols H2SO4 in excess. How much H2SO4 was used by the MgO? That's 0.05 mols H2SO4 initially - 0.01 = 0.04 mols. g MgO = mols ...
October 11, 2015

chem
You know it is reactive by one of the following: 1. A gas is formed 2. A solid (insoluble in solvent) is formed. 3. A weak electrolyte is formed. These are aqueous solutions so 1 is out. All of these are strong electrolytes so 3 is out. For 2 you need to know the solubility ...
October 11, 2015

Chemistry
Most if not all of the "other" material is water and the assumption is that only the vinegar reacts with the Na2CO3. Na2CO3 + 2HOOCCH3 ==> H2O + CO2 + 2NaOOCCH3 What you have so far looks good. The above gives you the balanced equation. That little bump may be all...
October 10, 2015

Chem
If 20 drops to the mL then each drop is 1 mL/20 drops = 0.05 mL/drop. Then 10 drops x 0.05 mL/drop = ? mL and 20 drops x 0.05 mL/drop = ? mL
October 10, 2015

Chemistry
Looks ok to me.
October 10, 2015

AP Chem
On D. With k1 = about 10^-8 and k2 = about 10^-12, that is about 10,000 less for K2 so whatever (H^+) is from k1, the contribution from k2 is 10,000 less than that. So with 5.6E-5 for k1, trying to add a 10,000th of that is fruitless. I think part of your confusion stems from ...
October 10, 2015

AP Chem
A. 4.97 and 9.02 are right but I obtained 1.066E-5 and not 1.060E-5. B. ok for KHCO3 but I think your reasoning why is weak. The moon is made of green cheese, too, because of its components. The problem doesn't ask for a reason but the answer is because of the hydrolysis ...
October 10, 2015

Chemistry
or cancel 1 Cu(s) for 2Cu^+ ==> Cu^2+ + Cu which is the disproportionation reaction for Cu^+. 1 goes down to Cu(s) and the other goes up to Cu^2+.
October 10, 2015

Chemistry
Is your equation balanced? You know it isn't because the charges don't balance.
October 10, 2015

High School
I would name this 3,5-dimethyl-3-heptene
October 10, 2015

Prove also need help
Yes, 13/11 = 2 XIII ----- = II = 2 XI That works the same way as 12/2 = 7 XII. Now draw a line half way down do you leave a VII on top and VII is 7.
October 10, 2015

Chemistry
You need to understand that this is a limiting reagent problem. The reason you can't use EITHER Zn or CuSO4 is because one of them will be used up before the other is; i.e., one reagent will be used and the other one will be in excess. mols CuSO4 = 0.1 mols Zn = 3.22/65.4...
October 10, 2015

Chemistry
I don't think so. The question probably is to determine delta H in kJ/mol for the reaction.
October 10, 2015

Chemistry
A very interesting post but I don't see a question.
October 10, 2015

chemistry
Pb(ClO3)2 + 2NaI ==> PbI2 + 2NaClO3 mols NaI = M x L = ? mols PbI2 = 1/2 mols NaI (use the coefficients in the balanced equation to see this) g PbI2 = mols PbI2 x molar mass PbI2.
October 10, 2015

Chemistry
The problem with your problem is that it doesn't list a temperature so I had to assume a T of 70 F. The density of water changes with T. The density of H2O at 70 F is 62.31. Here is where I obtained the density of 62.31. http://www.engineeringtoolbox.com/water-specific-...
October 10, 2015

Chemistry
1E-13 cm = ? pm (? pm/52.9) = ? as a fraction.
October 10, 2015

Chemistry
185 yd^3 x (3 ft/yd) x (3 ft/yd) x *3 ft/yd) = ? cubic feet. Density H2O is 62.3 lbs/ft^3 @ 70 F. mass = volume x density mass in lbs = volume in ft^3 x density (lbs/ft^3)
October 10, 2015

chemistry
Interesting but I don't see a question.
October 9, 2015

chemistry
In the HH equation didn't you say it was salt/acid. KNO2 is the salt; HNO2 is the acid.
October 9, 2015

Chemistry
Convert 3.6 m to cm and 1.3 m to cm. volume = (pi*dia/4) density = 1.00 g/cc mass = volume x density = grams Convert to kg.
October 9, 2015

chemistry
[(2*atomic mass N)/molar mass (NH4)2CO3]*100 = ?
October 9, 2015

Chem
How many mols KOH in 5.61 g KOH? about 0.1 mol? Then you have 5.85 kJ/0.1 mol = ?
October 9, 2015

AP Chemistry
I didn't go through the math but I plugged the new values for products and reactants into the Kc expression and obtained 7.03 so I would have confidence that these were right.
October 9, 2015

chemistry
9.58E7 = c/m 9.58E7*mass = charge Substitute and solve for mass
October 9, 2015

incomplete==chem 11
no beginning volume. Use P1V1 = P2V2
October 8, 2015

AP Chemistry
Show your work and we can check it.
October 8, 2015

Chemistry RUSH, Please
1. You need an equation for this since CH4 and Cl2 react to give several products. 2. mols CH3OH = grams/molar mass = ? Then M = mols CH3OH/L solution
October 8, 2015

chemistry
1. Write and balanced the equation. 2. Convert 22.4 g benzene to mols. mols = grams/molar mass = ? 3. Using the coefficients in the balanced equation, convert mols benzene to mols nitrobenzene. This is the theoretical (TY) for the reaction. 4. The actual yield (AY) is 31.6 5...
October 8, 2015

chemistry
It could be but what they use is cheaper.
October 8, 2015

chemistry
How many mols of the stock solution do you want? That's M x L = 0.500 x 0.100 K2CrO4 = ? For the 0.0025 M solution use the dilution formula. mL1 x M1 = mL2 x M2 10 mL x 0.0025 = mL2 x 0.100M Solve for mL2, pipet that volume and make to 10 mL. Assuming the volumes add, the ...
October 8, 2015

general chemistry
2NaOH + H2SO4 ==> Na2SO4 + 2H2O mols NaOH = M x L = ? mols H2SO4 = 1/2 mols NaOH (look at the coefficients in the balanced equation). M H2SO4 = mols H2SO4/L H2SO4
October 8, 2015

Chemistry
mols NaOH you need = M x L = 2.00 x 0.300 = ? Then grams = mols NaOH x M NaOH = ?
October 7, 2015

Chemistry
I don't think you need to add anything. In fact I would delete everything after the second comma (causing a full reaction)
October 7, 2015

Organic Chemisty
Kd = (org layer)/(water layer) Don't you have a volume of water. Is the 2-10 mL and 1-20 mL the organic solvent?
October 7, 2015

Chemistry
And you have what? Show your work and explain what you don't understand.
October 7, 2015

Chemistry
F2 is a halogen, too. Halogens replace the ions below it; e.g., F2 + 2Cl^- ==> Cl2 + 2F^- F2 + 2Br^- ==> Br2 + 2F^- etc Cl2 + 2Br^- ==> 2Cl^- + Br2 Cl2 + 2I^- ==> 2Cl^- + I2 Br2 + 2I^- --> 2Br^- + I2
October 7, 2015

Chemistry
See your post above.
October 7, 2015

chemistry
M = (1/2)*N = 1/2 * 0.1 = 0.05 mL1 x M1 = mL2 x M2 mL2 x 2.5 = 300*0.05
October 7, 2015

Chem11
1.81E23 Cl atoms/6.02E23 = ? mols Cl atoms You can make 1/3 of that number of FeCl3 moles.
October 7, 2015

chemistry
mols = grams/atomic mass
October 7, 2015

chem 215
mass solution = 158.5-145.0 = ? g. density = mass/volume = ?
October 7, 2015

chemistry
What is the volume of the silver metal? That's volume = mass/density = ? Then that volume will displace the water in the graduated cylinder the same amount so 17.0 + volume Ag = new volume in mL.
October 7, 2015

chem
And I read this last night and couldn't figure out exactly what was going on. I just don't know the procedure you did.
October 7, 2015

Chemistry
Technically you don't know because the solution volumes are not additive; i.e., 10 mL + 90 mL is not 100 mL. However, the author of the problem meant this to be a 10 to 100 dilution which is a dilution of 10x so the 40 mg/L must be 10 x stronger or 400 mg/L. b. 400 mL/L x ...
October 6, 2015

CHEMISTRY
I agree with part of the first sentence but not the second. The water is boiled off too so it is separated about as much as you could want. For the first sentence, don't you want the water to be boiled off and that is the reason you get the remaining anhydrous salt. In ...
October 6, 2015

CHEM
2.44 g = mass BaCl2 + xH2O -0.36 g = mass H2O ---------- 2.08 g = mass BaCl2 mols BaCl2 = 2.08/208 = 0.01 mols H2O = 0.36/18 = 0.02 BaCl2.2H2O
October 6, 2015

CHEMISTRY
It isn't clear as to when the sample is contaminated; i.e., before the original sample is weighed or after it is weighed. a. If the sample is weighed, then contaminated, the %H2O in the hydrated salt will be unaffected. For example, say we take a sample, weigh it at 15 g, ...
October 6, 2015

Chemistry
2C2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(g) In all gas systems volume may be used as mols and that cuts out a step or two. 14 L ethane x (4 mols CO2/2 mol C2H6) = about 28 L CO2 possibly formed 14 L O2 x (4 mols CO2/7 mols O2) = 8 L CO2 possibly formed. Therefore, 8 L CO2 will...
October 6, 2015

Chemistry
Close but I don't think so. mols AlCl3 = M x L = 0.3M x 0.1L = ? Then mols Cl^- is 3x that. . I don't think you need to convert to grams; the problem asks for mols.
October 6, 2015

ChemistryPRELABS
My first line shows you how to find mols S2O3^2- and the second line shows how to convert to mols IO3^-.
October 6, 2015

ChemistryPRELABS
mols S2O3^2- = M x L = ? mols IO3^- = 1/6 * mols S2O3^- grams KIO3= mols KIO3 x molar mass KIO3 Post your work if you get stuck.
October 6, 2015

Chemistry
1.045 g AgCl x (atomic mass Cl/molar mass AgCl) = approx 0.26 g Cl^- but you need to do it more accurately. Then [0.26/(mass sample)]*100 = 63.9% Solve for mass sample.
October 6, 2015

Chemistry
Let X = cc CH4 and Y = cc C2H2 --------------------- equation 1 is X + Y = 30 cc Combustion equations. CH4 + 2O2 ==> CO2 + 2H2O 2C2H2 + 5O2 ==> 4CO2 + 2H2O equation 2 is made up of [cc O2 needed to burn CH4 + cc O2 needed to burn C2H2 = 70] so equation 2 is X(2mols O2/1 ...
October 6, 2015

Himma International College Minna
Could be because it IS chemistry. See the post above.
October 6, 2015

Chemistry
1.045 g AgCl x (atomic mass Cl/molar mass AgCl) = about 0.26 but you need a closer answer than that. Then [(0.26)/(mass sample)]*100 = 63.9% Solve for mass sample.
October 6, 2015

Chem
2H2 + O2 ==> 2H2O mols H2 gas initially = 1.20/4 = 0.3 and since the ratio of H2O produced to mols H2 initially is 2/2 we must have produced 0.3 mols H2O. q = heat capacity x (Tfinal-Tinitial) = ? kJ = dH rxn. So dH rxn in kJ is for 0.3 mol H2O produced so dH rxn/0.3 gives ...
October 5, 2015

Chemistry
mols Cl^- = M x L = approx 0.011 mols. 0.011 mol Cl^- x (1 mol FeCl3/3 mols Cl^-) = approx 0.004 Then grams = mols FeCl3 x molar mass FeCl3 = ?
October 5, 2015

chemistery
2Ce4+ + 2e ==> 2Ce3+ 1.61 v. Zn --> Zn2+ + 2e 0.76v ----------------------- 2Ce^4+ + 2e + Zn ==> Zn2+ +2e + 2Ce3+ Eocell = 1.61 + 0.76 = ? v. Then nFEo = RTlnK Substitute and solve for K.
October 5, 2015

chemistry
Follow the problem steps at your other post (John).
October 5, 2015

Chemistry
Sarah, why don't you show your work and let us find where you went wrong (instead of us working everything including what you did right and letting you check to see where we went right).
October 5, 2015

chemistry
Your data allows three places in the answer and you have only two.
October 5, 2015

Chemistry
H2SO4 + 2NaOH ==> Na2SO4 + 2H2O mols NaOH = M x L = ? (Note: the M and N of NaOH are the same.) Using the coefficients in the balanced equation, convert mols NaOH to mols H2SO4. That will be mols H2SO4 = 1/2 mols NaOH. Then M H2SO4 = mols H2SO4/L H2SO4 = ? To convert to N, ...
October 5, 2015

Chemistry
Surely you are confused a little or I just don't know what's going on. Usually something like KI is added to the KIO3 and that produces I2, then the I2 is titrated with Na2S2O3. To my knowledge, thiosulfate used as a titrant is used only for I2.
October 5, 2015

chemistry
emission.
October 5, 2015

chemistry
Yes, you have 1 and 2 correct Electrons are unstable and move from an higher energy state to a lower energy state. I will put this as 3 although I don't like the statement. Electrons are NOT unstable; it's the excited state that is unstable and that allows the ...
October 5, 2015

Chemistry
Looking at 23.319, the 233 and 1 are known but the last number is uncertain. The average is 23.3198 which rounds to 23.320 but the 0 is in the uncertain column so it is reported as 23.32.
October 5, 2015

Chem
q1 = heat absorbed to move ice from -21 to zero C. q1 = mass ice x specific heat ice x (Tfinal-Tinital) q2 = heat needed to melt the ice; i.e., change solid ice @ zero C to liquid water @ zero C. q2 = mass ice x heat fusion ice q3 = heat needed to change T of water at zero C ...
October 5, 2015

chemistry
Most fireworks add some chemical to make the color red, green, blue, etc. What happens is that the energy from the blast vaporizes the chemical, the atoms of the chemical absorb energy and move the atom(s) from the ground state to the excited state. The excited state is not ...
October 5, 2015

organic chemistry
Is there a question here?
October 5, 2015

Chemistry
The two half equations are Fe^2+ ==> Fe^3+ + e MnO4^- + 8H^+ + 5e ==> 4H2O + Mn^2+ Multiply equation 1 by 5 and equation 2 by 1 and add them. Cancel the electrons and you are left with the net ionic equation. Use the coefficients in the balanced equation to convert 1.2E-...
October 4, 2015

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