Friday
October 24, 2014

Posts by DrBob222


Total # Posts: 44,698

Physical Science
0.83 WHAT? Is that supposed to be mass human = 100 kg. Is that 85 C or 85 F q = mass x specific heat x (Tfinal-Tinitial) You know q is 1000 kcal. I would change that to calories. You know mass is 100 kg. I would change that to grams. I have no idea what unit 0.83 is but you ...
October 20, 2014

Physical Science
Q = mass Al x specific heat Al x delta T
October 20, 2014

science
Can't you tell from Ms. Sue's first response. She didn't know your choices but practically laid the answer in your lap.
October 20, 2014

Physical Science
Let's use an example. The specific heat of most metals is about 0.3 J/g*C which means it takes 0.3 J to heat a metal 1 degree C. That means it takes very little heat to make the metal hot. If I stick a match to a piece of metal and stick the metal to your arm, it will burn...
October 20, 2014

Chem
See your previous post.
October 20, 2014

Chemistry
#1. k = 0.693/t1/2 Substitute k in the below equation. ln(No/N) = kt No = 5.80g N = ? K = from above t = 552 days Solve for N For #2, you want 1,000,000/2^n = 1,000 Solve for n. The easy way to do that is to solve for 2^n and then n.
October 20, 2014

chemistry
There are 6.022 atoms in 1 mol atoms and 1 mol atoms Al weigh 26.98 grams.
October 20, 2014

Chemistry
Why don't use use the Nernst equation to calculate if the Ag^+ | e ==> Ag half cell goes up or down and how that will affect the voltage of the cell?
October 20, 2014

Chemistry
Yes, c and d are obviously wrong.
October 20, 2014

Chemistry
You didn't answer my previous response. How much do you know about this? Where are you stuck?
October 20, 2014

Chemistry
AgNO3 + KCl ==> AgCl + KNO3 mols AgNO3 = M x L = ? mols KCl needed = mols AgNO3 because of the coefficients in the balanced equation. mols KCl = grams KCl/molar mass KCl. You know molar mass and mols KCl, solve for grams.
October 20, 2014

Chemistry
And you know what about this?
October 20, 2014

Chem
Of course I don't know the contents of Table 6.2. For 2 mols NH3 the equation is N2 + 3H2 ==> 2NH3 (for 2 mols) dH = -46.11*2 kJ 1/2 N2 + 3/2 H2 ==> NH3 (for 1 mol) dH = -46.11 kJ You should add (g) to each to show the phase. I don't know how you got 0. My tables...
October 20, 2014

Easy Chemistry
The half cells are Mg ==> Mg^2+ + 2e Zn^2+ + 2e ==> Zn Oxidation is the loss of electrons.
October 20, 2014

Easy Chemistry
A galvanic cell is essentially a battery. D is the only one using a battery. Technically, a battery is one or more cells made together as in a car battery. The "batteries" in a flashlight are actually single cells.
October 20, 2014

Chemistry
196 x 0.6 = ?lb water. ? lb H2O x (453.6 g/lb) = ? grams H2O The density of H2O is 1.00 g/mL; convert ? g H2O to mL H2O by volume in mL = grams/density. Then mL/1000 = ?L
October 20, 2014

CHM 300
A = absorbance. Sometimes this is measured as %T and if that is done then A = log(100/%T) Then A = ebc where e is the molar absorptivity, b is the cell length in cm and c is the concn in mols/L. You should have measured a standard somewhere in the experiment. Plug in c for the...
October 20, 2014

chemistry
You placed electrodes in in an aqueous solution of HCl. H2 gas bubbled out at the - electrode (the anode) and Cl2 gas was discharged at the cathode (+ elecrode) 2HCl==> H2 + Cl2 . You must fill in from what you did; I wasn't there and don't know what you did.
October 20, 2014

chemistry
NaOH + HCl ==> NaCl + H2O q = mass H2O x specific heat H2O x (Tfinal-Tinitial) mols H2O formed is M x L = 0.0125 dH = q/0.0125 J/mol
October 20, 2014

chemistry
dHrxn = (n*dHf products) - (n*dHf reactants) dHf = delta H formation. Look this up in your text/notes.
October 20, 2014

Chemistry
I'm assuming you meant 1.0 M and not 1.0m. You need to learn the difference. mols KHP = mass/molar mass = 5/204 = about 0.025 mols NaOH needed = 0.025 M NaOH = mols NaOH/L NaOH M = 1.0; mols = 0.025 and L = mols/M = 0.025/1 = about 0.025 L or about 25 mL.
October 20, 2014

Chemistry
Is that % w/v? I assume so. (Xg solute/g)*100 = % (Xg solute/500)*100 = 7%
October 20, 2014

Chemistry need help
1 nitrate ion, NO3^- 2. AgNO3 test shows either Cl^-, Br^-, or I^- present. Oxidation with Cl2 water and mixing with hexane shows either Br^- or I^-. The hexane solvent is purple if I^- so the anion must be Br^-.
October 20, 2014

Chemistry need help please!!!!
1 and 2 answered above. 3 is CO3^2-, carbonate.
October 20, 2014

chemistry
You haven't posted the solubility of benzoic acid at 50C and without that I can't check your work; however, on the surface 1 kg seems too high to me.
October 19, 2014

Chemistry
1. Determine the limiting reagent which will be either HCl or Ba(OH)2. It looks like HCl but you should confirm that before going further. q = 118 kJ x (g HCl/2*molar mass HCl) 2. Then q = mass H2O x specific heat H2O x (Tfinal-Tinitial) Substitute and solve for Tf.
October 19, 2014

chemistry
The molecular equation is 3AgNO3 + Al ==> Al(NO3)3 + 3Ag The net ionic equation is 3Ag^+ + Al ==> Al^3+ + 3Ag The half reactions are Ag^+ + e==> Ag Al ==> Al^3+ + 3e Oxidation is the loss of electrons; reduction is the gain of electrons.
October 19, 2014

Chemistry
3Cu + 8HNO3 ==> 3Cu(NO3)2 + 2NO + 4H2O mols Cu = grams/molar mass Using the coefficients in the balanced equation, convert mols Cu to mols NO. Now convert mols NO to L at STP. 1 mol NO gas at STP occupies 22.4 L.
October 19, 2014

Chemistry
Tbis is a limiting reagent (LR) problem. Pb(NO3)2 + 2NaCl ==> PCl2 + 2NaNO3 mols Pb(NO3)2 = M x L = ? mols NaCl = M x L = ? Using the coefficients in the balanced equation, convert mols Pb(NO3)2 to mols PbCl2. Do the same and convert mols NaCl to mols PbCl2. It is likely ...
October 19, 2014

AP Chemistry
C5H12 + 8O2 ==> 5CO2 + 6H2O dHrxn = (n*dHf products) - (n*dHf reactants). Look up the heat formation of the products and reactants, plug into the above and solve for dHrxn.
October 19, 2014

Chemistry
Could it become a vapor? Have bubbles in the liquid cell? Note the correct spelling of celsius.
October 19, 2014

chemistry
increase. Gases are more soluble in cool water than hot water.
October 19, 2014

AP Chemistry
a. n can be 3 for an excited H atom; l can be 2,1,0; ml can be 0. OK for a. b. n can be 4 for an excited H atom; l can be 3,2,1,0; ml can be -1,0,+1. OK for b. c. n can be 2 for an excited H atom. l can be 1,0. mL can be -1,0,+1 but not -2. not OK. c is out.
October 19, 2014

Chemistry
q = heat to water + heat to calorimeter q = [(mass H2O x specific heat H2O x (Tfinal-Tinitial)] + [Ccal*(Tfinal-Tinital)] Then dH in cal/g= q/2g and dH in cal/mol = cal/g x molar mass NaOH
October 19, 2014

Chemistry
3H2 + N2 ==> 2NH3 4.35 mols N2 x ((2 mols NH3/1 mol N2) = 4.35 x 2 = ? g NH3 = mols NH3 x molar mass NH3
October 19, 2014

Chemistry
gram molecule In fact when I was in freshman chemistry I was taught gram molecular weight and not molar mass. Gram molecular weight was defined as the weight of one grams molecule; i.e., 1 mole. In another part of the "history lesson" we were taught that 1 gram ...
October 19, 2014

Chemistry
6.022E23 give or take a little. You can google it and come up with a bunch more places.
October 19, 2014

Chemistry
Have you worked any chemistry problems recently? When you have you will know why the mole concept is so important.
October 19, 2014

chemistry
You are so right.
October 19, 2014

Chemistry
mols 70.0L x (22.4L/mol) = ? mols N2 Convert mols N2 to mols NaN3 using the coefficients in the balanced equation. Now convert mols NaN3 to g. g NaN3 = mols NaN3 x molar mass NaN3
October 19, 2014

chemistry
1/2 = 1 half life 1/4 = 2 half lives 1/8 = 3 half lives 1/16 = 4 half lives. So the fur coat is 4 half lives old. What's the half life of C-14. I think about 5,700 years but you can look that up. So the fur coat is half life x 4 = ?
October 19, 2014

chemistry
pKa = -log(Ka) = 6.6 Ka = about 2.6E-7 but you need to all of these calculations more accurately. .............HA ==> H^+ + A^- I............100....0......0 C...........39.6...39.6...39.6 E..........60.4....39.6...39.6 Ka = (H^+)A^-)/(HA) Substitute the E line into the Ka ...
October 19, 2014

chemistry
mols KMnO4 = M x L = ? Mole HI = 5x that (from the coefficients of 10/2) M HI = mols/L. You know M and mols, solve for L and convert to mL.
October 18, 2014

Chemistry
If you mean the mass Mg3N2 = 0.0910 then mols = grams/molar mass
October 18, 2014

Chemistry
NaNO3 is soluble Cu(C2H3O2)2 is soluble. No reaction.
October 18, 2014

CHEMISTRY!!!!! HELP!!
Do you know the author? the publisher? anything to help mark this as the one among several hundred.
October 18, 2014

chemistry
What are the other choices. There is no decay going on with the H line spectrum. The H line spectrum is simply an electron in a higher energy level moving to a lower energy level. The difference in energy between the higher state and the lower state is emitted.
October 18, 2014

Chemistry Check
I think this forum uses html coding and that allows the first space. Spaces after the first space are ignored. I have used periods as spaces; it doesn't work that well but it works enough to know what is going on. For example. ..............XO2 ==> X + O2 I................
October 18, 2014

chemistry
Convert mass CO2 to mass C6H12O6. 3.30g CO2 x (molar mass C6H12O6/6CO2) = ?g C6H12O6. Mass NaCl = 4.00 - ?g C6H12O6 = g NaCl %NaCl = (g NaCl/4.00)*100 = ?
October 17, 2014

Science
I assume you meant "properties" and not "priorities". Actually, I don't like any of the answers. Having said that, I think A is the answer to the question because it is obvious that B, C, and D make no sense what so ever. It is true that the elements ...
October 17, 2014

Chemistry
Use the dilution formula. mL1 x M1 = mL2 x M2 500 mL x 0.3M = mL2 x 0.1M mL2 = you do it. mL2 is the final volume of the solution. You want to know how much water to add. Assuming volumes are additive, you would need to add the difference between mL2 and 500 mL. An easier way ...
October 17, 2014

chem
You have omitted the phases. Rather than guess what they are I would rather you posted them.
October 17, 2014

chem
6x that. right?
October 17, 2014

To Brooke--your posts below
I have posted responses to your question on propane/butane and the Fe/Al problem below. They are about a page down from this post.
October 17, 2014

Equilibria
........Cu^2+ + 4NH3 ==> Cu(NH3)4^++ I.......0.1M....1.0M.......0M C......-0.1M...-0.4M......+0.1M E........0?.....0.6M.......0.1M What I usually do is to recognize that with a Kf of 2.1E13 the reaction goes far to the right and you have formed essentially all of the ...
October 17, 2014

chemistry
Read your post and correct.
October 17, 2014

chemistry
A little long but not that complicated. Use PV = nRT and solve for n = total number of mols C3H8 + C4H10. You have P and R but not T and V. I would use convenient numbers for those two and you can do that since the SAME numbers will be used in the CO2 part of the problem. ...
October 17, 2014

chemistry
This is much like the C3H8/C4H10 problem but perhaps a little easier to follow. First I would conver the H2 gas in the PV = nRT formula and solve for n = number of mols. I obtained 0.00139 mols H2 gas at the conditions listed. I didn't know how far to carry the decimal; I ...
October 17, 2014

Chemistry
That equation will tell you how to dilute it. But you still must have the amount of the SrCl2 used. Let's say you used 100 mL, then 100mL x 4.7M = 45000 mL x M Solve for M of the 45 L material.
October 17, 2014

Chemistry
Sr WHAT? How much of that Sr whatever was used. mL1 x M1 = mL2 x M2
October 17, 2014

CHEMISTRY
formula units = mass/formula unit mass formula units = 1.90/60.08 =?
October 16, 2014

chemistry
Note: L is liters; the second celsius is not correct. Use (V1/T1) = (V2/T2) Remember to change T to kelvin.
October 16, 2014

chemistry
That makes it easier. Use mL1 x M1 = mL2 x M2 385*0856 = mL2 x 4.93 Solve for mL2. Directions then would be, measure out mL2 volume of 4.93M solution and add enough water to make 385 mL. The final solution will be 0.856 M.
October 16, 2014

chemistry
I assume you know the difference between 0.856 m and 0.856 M. Is this really m or should it be M?
October 16, 2014

chemistry
H2 + Cl2 ==> 2HCl This is a limiting reagent (LR) problem. You know that because amounts are given for BOTH reactants. mols H2 = grams/molar mass = ? mols Cl2 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols H2 to mols HCl. Do the same ...
October 16, 2014

Chemist - Grade 9 - Urgent.
I'm interested in what kind of trouble you are having answering this question. Ba and Sr are in the same column.
October 16, 2014

science help
Of course.
October 16, 2014

science help
Protons have a +1 charge. Electrons have a -1 charge. If the atom is to be neutral the number of protons MUST be the same as the number of electrons.
October 16, 2014

science help
I agree with A.
October 16, 2014

Ions and octet rule
Look on the periodic table for element #31. The number of protons is 31. If it were neutral it would have 31 electrons; since it has a +3 charge it must have 3 fewer electrons.
October 16, 2014

chemistry
3; i.e., 8,5 and 1. You can write that as 8.51E4 to show that.
October 16, 2014

Chemistry
Balance the equation between Fe(II) and Cr2O7^2-. Frankly, I am not familiar with the term "equivalent to xx mL of yy M" something else. I assume that means that xx mL of yyM was used to titrate it to the equivalence point. If that is it, then Convert mols Cr2O7^2- ...
October 16, 2014

Chemistry
2KClO3 ==> 2KCl + 3O2 dH = -78 kJ or you could write KClO3 ==> KCl + 3/2 O2 dH = -39 kJ/mol
October 16, 2014

big oops--chem
I forgot to tell you that you must convert the 4100 J to L*atm. Divide by 101.325.
October 16, 2014

chem
W = pdV. If the gas is expanding it does work on the surroundings; therefore, W = -4100. -4100 = -2*(V2-V1)
October 16, 2014

chemistry
I am too. Ammonium bromide is a solid and without the density the volume can't be calculated. Since you know 6.022E23 molecules is one (1) mol, you know you have 3.85E24/6.022E23 = ? moles. Then g NH4Br = mols x molar mass = ? Finally, density = mass x volume. You know ...
October 16, 2014

Chemistry
Here is a good diagram and this diagram is for an endothermic reaction and the reaction as shown is endothermic. https://www.google.com/search?q=activation+energy+vs+reverse+activation+energy&client=firefox-a&hs=b6F&rls=org.mozilla:en-US:official&channel=sb&tbm=isch&tbo=u&...
October 16, 2014

Chemistry
These problems are worked the same as a stoichiometry problem. That is, 0.5 mol Fe/10s = 0.05 mol/s, then convert to Fe2O3 by 0.05 mols/x x (1 mol Fe2O3)/2 mols Fe) = 0.025 mol Fe2O3/s.
October 16, 2014

Chemistry
Yes, 3 is a heterogeneous reaction. So is 2.
October 16, 2014

Chemistry
I don't see a reaction 3a. I see a reaction 3 and that one heterogeneous. So is 2. I think the reaction rate will increase for BOTH 2 and 3 although I think 3 is less so than 2.
October 16, 2014

chemistry
2Al ==> Al2(SO4)3.K2SO4.24H2O The above isn't fully balanced but I've balanced the only part that matters. mols Al = grams/molar mass = approx 0.0074 Using the coefficients in the equation convert mols Al to mols of alum. That's 0.0074 x (1 mol alum/2 mol Al) = ...
October 16, 2014

Chemistry
O2 + 2H2 ==> 2H2O This is a limiting reagent (LR) problem. You know that when amounts are given for BOTH reactants. mols O2 = grams/molar mass = approx 0.18 but you need a more accurate answer for this and all of the calculations that follow. mols H2 = 12.0/2 = 6 Using the ...
October 16, 2014

Chemistry
Fe(NO3)2 + 2OH^- ==> Fe(OH)2 + 2NO3^- Then Fe(OH)2 + heat ==> FeO + H2O mols Fe(NO3)2 = mols x L = ? mols FeO = mols Fe(NO3)2 (look at the equation; 1 mol Fe(NO3)2 = 1 mol FeO) Then g Fe) = mols FeO x molar mass FeO.
October 16, 2014

Chemistry
Mn(NO3)2 + 2KOH ==> Mn(OH)2 + 2KNO3 mols Mn^2+ = M x L = ? mols Mn(OH)2 = 2x mols Mn^2+.(look at the equation; it is 2 mols KOH for 1 mol Mn(NO3)2. Then M KOH = mols kOH/L KOH. You know mols KOH and M KOH, solve for L KOH and convert to mL.
October 16, 2014

chemistry
heat lost by Al + heat gained by water = 0 (mass Al x specific heat Al x (Tfinal-Tinitial) + (mass H2O x specific heat H2O x (Tfinal-Tinitial) = 0 Substitute and solve for Tf of the Al and H2O.
October 15, 2014

chemistry
S + O2 ==> SO2 q = Ccal x delta T q = 2.03 kcal/c x 1.17 = ? That q is for 1.07. To find per grams it is q/1.07 = ? kcal/g And q/1.07 x molar mass S gives kcal/mol.
October 15, 2014

Analytical Chem
I think the pH comes from the reaction of citric acid with NaOH. That is a buffer. ...........H3C + NaOH ==> NaH2C + H2O I..........0.3...0..........0 add..............0.7........... C.........-0.3..-0.3.........0.3 E...........0.....0.4........0.3 pH = pKa3 + log (base)/(...
October 15, 2014

Chemistry
%H in the BxHy = (g H/mass sample)*100 g H atoms (0.540 x 2/18)= about 0.0600 and %H atoms = (0.06/0.492)*100 = about 12% but you should be more accurate than that on all calculations that follow. Since the only other element is B, then B must be 100%-12% = about 88% Now take ...
October 15, 2014

chemistry
How did you make isoamyl bromide? What procedure did you follow?
October 15, 2014

Chem
delta T = Kb*m So which will give the largest delta T? Since m is the same it must depend on Kb?
October 15, 2014

chemistry
E is the only correct one. However, your statements don't match the answers. Potassium sulfate is K2SO4 and ammonium nitrate is NH4NO3. Another error is ammonium sulfate is (NH4)2SO4.
October 15, 2014

Chemistry
mols CO2 at STP = 3L/22.4 = ? mols O2 molecules = same since there is 1 O2 in 1 CO2. Then 1 mol contains 6.02E23 molecules.
October 15, 2014

Chemistry
I think the secret is how you search google. I have found that to find calculations that I type in "how to calculate Ksp" without the quotation marks and I get several sites showing Ksp work.. That will usually bring up a calculations page (or several of them) and I ...
October 15, 2014

Chemistry
1 mol CH4 has 6.02E23 molecules 1 mol H2O has 6.02E23 molecules so 1 mol CH4 has same number molecules as 1 mol H2O. mols methane = g/molar mass = 32/16 = 2 mol CH4. That has 2*4 = 8 mols H atoms. mols H2O vs CH4; You must multiply mols H in H2O by 2 to get mols H in CH4. So 2...
October 15, 2014

CHEMISTRY
OK. Remember that compounds must add up with oxidation states to zero; ions must add up to the charge on the ion. So Cr on the left is + 6 EACH and on the right is 3+.(O is -2 and there are two of them which makes -4 total so Cr must be +3 to leave a -1 charge on the CrO2^- ...
October 15, 2014

CHEMISTRY
Tell me what you know to do and I can go from there. Do you have a system; there are two or three available and all of them work very well. Let me know the system too so I won't switch systems on you.
October 15, 2014

typo--Chemistry
I hit the - sign instead of the = sign. you have 20*0.2 = 4 g CaCO3 to start.
October 15, 2014

Chemistry
Do you know how to work a stoichiometry problem if you have the quantities. 20 g of 20% means you have 20*0.2 - 4 g CaCO3 to start.
October 15, 2014

Chemistry
heat lost by Cu + heat gained by water = 0 (mass Cu x specific heat Cu x (Tfinal-Tinitial) + (mass H2O x specific heat H2O x (Tfinal-Tinitial) = 0 Substitute the numbers and solve for Tf.
October 15, 2014

Chem
1 mol CaCO3 will produce 1 mol CO2
October 15, 2014

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