Sunday
May 1, 2016

Posts by DrBob222

Total # Posts: 52,201

Chemistry
http://www.jiskha.com/display.cgi?id=1453339010
January 22, 2016

Chemistry
What's the half-life of Rn222? I think that's approx 4 days but you can look that information up in your text/notes. It takes 1 half life to reduce the amount to 1/2 of what you started and another (to make 2 half lives) to reduce another 1/2 or 1/4 (that's 1/2 x 1...
January 22, 2016

Chemistry
Ca + 2H2O ==> Ca(OH)2 + H2 mols Ca(OH)2 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols Ca(OH)2 to mols H2. Then use PV = nRT OR 1 mol at STP is 22.4L to convert to volume. For grams Ca, g = mols x molar mass.
January 22, 2016

Biochemistry
Yes, the lowest specific heat material will undergo the largest temperature change for the same amount of heat applied.
January 22, 2016

Chemistry
I did that above. (CO2) is read as concentration of CO2 in mols/L = M
January 22, 2016

Chemistry
C2H5OH + 3O2 ==> 2CO2 + 3H2O Determine mass ethanol from density. mass = volume x density mass = approx 400 but you need a more accurate answer than that. mols ethanol = grams/molar mass = about 9 mols. Again you need to confirm an accurate answer. For every 1 mol ethanol ...
January 22, 2016

chemistry (moles)
The HNO3 reacts only with BaIOH)2. Ba(OH)2 + 2HNO3 ==> Ba(NO3)2 + 2H2O mols HNO3 required = M x L = approx 0.0019 0.0019 mols HNO3 x (1 mol Ba(OH)2/2 mols HNO3) = approx 0.00095 g Ba(8OH)2 = mols x molar mass - 0.0095 x approx 171 = about 0.16 g in the 20 cc. In the 250 cc ...
January 21, 2016

chemistry
Use the Henderson-Hasselbalch equation. I don't know the value you are using for pk2 so I can't work the problem for you. 6.9 = pK2 + log base/acid Solve for base/acid = ? That's equation 1. Equation 2 is base + acid = 0.2M Solve those two equations simultaneously ...
January 21, 2016

Chemistry
Your question is so broad I'm not sure what kind of answer you're looking for but the solubility of Ca(OH)2 is about 173 mg at 20 C so most of the material will dissolve leaving about 25 mg or so not dissolved.
January 21, 2016

Chemistry 101
Convert miles to meters = approx 1.5E11 meters Then 3E8 m/s x # sec = 1.5E11 Convert to minutes by dividing the answer by 60 sec/min
January 21, 2016

Chemistry
As written this makes no sense. Proof and correct please. Also, are those mols you quote at equilibrium or not.
January 21, 2016

chemisty
You write the equations, identify the gas produced in each case, then think about your knowledge of chemistry about how you would identify the gas. If you need more hints, show what you have done and where you are stuck.
January 21, 2016

Chemistry
2. mols = grams/molar mass = ? 1. mols Na = grams/atomic mass = 4.6/approx 23 = ? Then mols S = grams S/atomic mass S ? mols Na = grams S/atomic mass S and solvle for grams S.
January 21, 2016

Chemistry
So substitute and solve but you need more information than what you've listed. At normal boil T, whatever that is, P is 760 mm. That gives you p1 and t1. You have a T2 listed at 39.2 C, There should be a p2 to go with that.
January 21, 2016

chemistry
You want to end up with pH = 2 or (H^+) = 0.02M HCl + NaOH ==> NaCl + H2O You have 10 mL of 4M NaOH = 40 millimolsl NaOH. You will need 40 mmols HCl to neutralize the NaOH. How many mL of 6M HCl is required for that? mL x M = mmols mL x 6 = 40 and mL needed is 16.67 of the ...
January 21, 2016

Chemisty
C3H8 + 5O2 ==> 3CO2 + 4H2O mols o2 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols O2 to mols propane. Then convert mols propane to grams. g = mols x molar mass = ?
January 21, 2016

chemistry
You still don't have it Sonia. Of course you meant 2.0 M BUT you have no volume of solution. Since M = mols/L, you have M and you want mols but L must be in thee somewhere.
January 21, 2016

chemistry
We can't draw on this forum. I suggest you go to Google to see how it looks and go from there.
January 21, 2016

Chemistry
Try this for 2. It would have helped if you showed you work so we wouldn't need to guess what you did. p1v1 = p2v2. 45.1*5.2 = 1.56*v2 I obtained approx 150 L for v2 but you should get a better answer. Then work = -1.56(V2-V1) which gives an answer in L*atm. That x 101.325...
January 21, 2016

Chemistry
mols HNO3 = M x L = ? mols KOH = M x L = ? Look to see which has more mols then subtract the smaller from the larger. The excess will determine the pH. If acid is in excess then mols excess/total volume in L = (H^+) and convert to pH. If KOH is in excess then excess/total ...
January 20, 2016

Chemistry
I tried to find Keq for N2 + O2 ==> 2NO2 but no luck. You can calculate it. Look up delta Go in the tables for the formation constant of NO2 (from the above equation. Then dGo = -RTlnK. Solve for K at 100 C. Call that Kf. Take 1/Kf for the decomposition of NO2. I found the ...
January 20, 2016

Chemistry
1 gallon = 3.785 L octane. mass octane = volume x density = approx 0.7 x 3785 mL = approx 250 g mols octane = grams/molar mass = approx 23 23 mols C8H18 x (25 mols O2/2 mol octane) = approx 300 mols oxygen needed. Check all of these numbers. Then use PV = nRT to solve for ...
January 20, 2016

Chemistry
3CuSO4 + 2Al ==> Al2(SO4)3 + 3Cu mols Al = grams/atomic mass Using the coefficients in the balanced equation, convert mols Al to mols Al(SO4)3 produced. Then g Al2(SO4)3 = mols x molar mass = ?
January 20, 2016

Chemistry
Note you should have said -78C and not +78 C. At 25C and 1 atm it is a gas.
January 20, 2016

Chemistry
2H2S + 3O2 ==> 2H2O + 2SO2 63.0 L x (3 mols O2/2 mols H2S) = ?
January 20, 2016

Chemistry
I have re-balanced your equation. 2N2O5 (g) -> 4NO2 (g) + 5O2 (g) a)0.1 mol/s x (4 mols NO2/2 mols N2O5) b) same process.
January 20, 2016

Chemistry
This is a very oddly worded question and I'm not sure what the question is. I will restate what I think it is. A concn of PCl5 at equilibrium is 4 mols/L. The reaction yield was 20%. Calculate Keq. Let y = initial concentration and x = change as equilibrium is established...
January 20, 2016

Science
distance = rate x time. d = 10,000 m t = solve for this in seconds r = rate. I found one source that listed the speed of sound in air as approx 340 m/s and another that listed speed of sound in water as approx 1500 m/s. (You can go to google and look these numbers up if you ...
January 20, 2016

Chemistry -Dr. Bob
Yes and no. PdV is 1 atm*1L = 1 L*atm and that is 101.325 J. Now since the volume is changing from 2 L to 1 L that is work done on the system (you had 2L and now just 1 L so the environment had to do work on the system to make that gas decrease in volume) and that means the ...
January 20, 2016

Chemistry 101
Same answer I gave you yesterday.
January 20, 2016

Chemistry-Dr. Bob
I don't understand how you obtained this value for work. P is 1 atm (STP) and delta V is 1L. Right?
January 20, 2016

Chemistry- Dr.Bob
When I convert 12 psi to atmosphere I don't get your value but something closer to 0.8. Making that change makes the other answers change but the procedure looks ok. I check the calculation for the first one and it is ok (except for P). I didn't check the math for the ...
January 20, 2016

Chemistry 105
If that is 23 g (and not 23.0 or 23.00 etc), then the sum of 23 + 0.022 = 23
January 20, 2016

Chemistry
........HNO2 ==> H^+ + NO2^- I.......0.02.....0......0 C......-6e-4....6e-4...6e-4 E........you fill in.
January 20, 2016

Chemistry
What about it?
January 20, 2016

chemistry
Use the Clausius-Clapeyron equation but you will need the heat of vaporization.
January 20, 2016

Chemistry
It's LeChatelier's Principle. If a reagent is added to a system at equilibrium the reaction will shift so as to undo what we've done to it. So if you add water, it will shift so as to use up the water you've added. Since H2O is on the right the rxn will shift ...
January 20, 2016

Chemistry- Dr.Bob!
Start out with PV = nRT, plug in the numbers and solve for n = number of mols of air. Correct for 20% O2 and go from there. Post your work if you get stuck.
January 20, 2016

Chemistry
I agree with Scott.
January 19, 2016

Chemistry
Why don't you show the math so we will know what is confusing you instead of us guessing at the problem. Here is the chemistry. .........N2 + 3H2 ==> 2NH3 I.......0.1...0.1......0.1 C.......-x....-3x......2x E......0.1-x..0.1-3x...2x Kc = 0.04 = (NH3)^2/(N2)(H2)^3
January 19, 2016

Chemistry
4Al + 3O2 ==> 2Al2O3 mols Al = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols Al to mols Al2O3. Finally, convert mols Al2O3 to grams. g = mols x molar mass = ?
January 19, 2016

Chemistry
The English is not too good, all of the information is not included, and you are using too many screen names. Anitta, Angelica, Marley, to name just three.
January 19, 2016

@ Bob Pursley
I think the answer to that is 10 mL.
January 18, 2016

chemistry
mols NaCl = M x L = 0.25 x 0.01 = ? g NaCl in the dish is mols x molar mass = ? and that's the amount in the dish after evaporation of the water.
January 18, 2016

chemistry
You can balance the entire equation if you wish but the only part that matter is the redox part. Here is that part. 5C2O4^2- + 2MnO4^-==>2Mn^2+ + 10CO2 mols KMnO4 = M x L = ? Using the coefficients in the balanced equation, convert mols KMnO4 to molsl Na2C2O4. Then grams ...
January 18, 2016

Chemistry 101
mass crown - 2,650 grams. volume crown = 145 mL density = m/v = 2,650/145 = 18.3 g/mL. It isn't pure Au.
January 18, 2016

Physical sciences
You need to learn to do these yourself. potassium bromide sodium carbonate iron(II) sulfate chromium(III) chloride.
January 18, 2016

chemistry 110
2HNO3 + Sr(OH)2 ==> Sr(NO3)2 + 2H2O mols Sr(OH)2 = M x L = ? Using the coefficients in the balanced equation, convert mols Sr(OH)2 to mols HNO3. Then M HNO3 = mols/L. You know mols and M HNO3, solve for L (and convert to mL if needed).
January 18, 2016

chemistry
I don't think the problem is made up to be a REAL problem. SCxOy is the compound. 8.99 g Sc used. 8.99-3.56 = 5.43 g O used. Total mass ScxOy = 8.99+5.43 = 14.42 %O = (5.43/14.42)*100 = ? but in REAL Sc2O3 the %O is 34.8%.
January 18, 2016

chemistry
You don't have any units for the coefficients so I don't know where you are but the formula to use is (dL/L)= k*dT So plug in dL and L in the proper units and the 25 and solve for dT. Knowing it is 20 at the end calculate the initial T.
January 18, 2016

Chemistry
Large Kb means large OH so pH will be high.
January 17, 2016

chemistry help plz
mols KMnO4 = grams/molar mass M = mols/L. 5Fe^2+ + MnO4^- ==> 5Fe^3+ + Mn^2+ mols KMnO4 used = M x L. You don't show L KMnO4. Without that you can't finish the problem.
January 17, 2016

chem
Zn + 2HCl ==> H2 + ZnCl2 mols HCl used = M x L = ? Using the coefficients in the balanced equation, convert mols HCl to mols Zn. Then mols Zn = grams Zn/atomic mass Zn. You know atomic mass and mols Zn, solve for grams Zn.
January 17, 2016

chemistry help
mols Na2S2O3.5H2O = grams/molar mass = ? Then M = mols/L.
January 17, 2016

chemistry
mols KMnO4 = grams KMnO4/molar mass KMnO4. M KMnO4 = mols/L Here is the redox part of the reaction and I've balanced that part. You can finish it but the redox part is all that matters. 5Fe^2+ + MnO4^- --> 5Fe^3+ + Mn^2+ mols KMnO4 used = M x L = ? Using the ...
January 17, 2016

chemistry
What do you mean by "characterize"? It is a double salt, it has both ionic and covalent bonds, etc.
January 17, 2016

help fast i need help with a bunsh
Yes, 5/15 = 1/3
January 15, 2016

Chemistry
Would you believe LiCN Li-CN is ionic. C---N is covalent.
January 15, 2016

Chemistry
This is a Limiting Reagent (LR) problem. You know that because amounts are given for BOTH reactants. 1. Write and balance the equation. 2. Convert HBr to mols. mols = grams/molar mass = ? 3. Convert NaOH to mols. mols = grams/molar mass = ? 4. Using the coefficients in the ...
January 15, 2016

Chemistry 101
I would convert feet to cm and mm to cm, then volume = L x W x H = ? density = g/volume in cc.
January 15, 2016

Chemistry
test post?
January 15, 2016

chemistry
Here is a curve for binding energy. Those at the top of the curve have the largest B.E. https://www.google.com/search?q=binding+energy+curve&tbm=isch&imgil=3jjg_qtRsd4lSM%253A%253B8zoG9NlsrjSDlM%253Bhttp%25253A%25252F%25252Fhyperphysics.phy-astr.gsu.edu%25252Fhbase%...
January 15, 2016

Chemistry
mols HNO3 = M x L = ? mols LiOH = M x L = ? mols LiOH - mols HNO3 = mols LiOH in excess. Then (OH^-) = mols excess OH/total volume in L.
January 15, 2016

chemistry
This is about 3 chapters of work. How much do you know how to do on your own? Explain what you do and don't understand.
January 14, 2016

Chemistry
Take a 100 g sample which gives you 69.9 g Fe 30.1 g O mols Fe = grams/atomic mass = ? mols O = grams/atomic mass = ? Now determine the ratio of one element to the other with the smallest being no less than 1.00. The easy way to do that is to divide both numbers by the ...
January 14, 2016

Chemistry
The answer by John suggests that it is the result of each atom having such a small mass (they do) but I assume your question is why are the masses not whole numbers. That's because the value in the periodic table are the averages of all of the different isotopes of the ...
January 14, 2016

Chemistry
CH4 + 2O2 ==> CO2 + H2O dHrxn = (n*dHformation products) - (dHformation reactants) = ? = q for 1 mol CH4. volume of house = 3000cm*3000cm*300cn = ? cc. mols air = ?cc/22,400 = ? How many Joules (or kJ) do you need to heat the house. That's q needed = mols air x specific...
January 14, 2016

chemistry
Use the Henderson-Hasselbalch equation.
January 14, 2016

Chemistry
See my response @ Jan 13 @ 5:25 P.M.
January 13, 2016

Science help....
What air and where in the balloon.
January 13, 2016

Chemistry
Most books now show Fe3O4 as FeO*Fe2O3 (a mixture of Fe(II) and Fe(III) but that shouldn't change any of the calculations. I would have reported 8.54 kg also.
January 13, 2016

Chemistry
It should. 11.8 kg x (3*55.847/231.539) = ? Did you use 0.7236 for the factor (72.36%)?
January 13, 2016

CHEMISTRY
mols C = grams/atomic mass = ? mols H = grams/atomic mass = ? Now find the ratio of the two elements to each other with the smaller number being no less than 1.00. The easy way to do is to divide BOTH numbers by the same small number,then multiply both numbers by any number to...
January 13, 2016

Chem - pH curve
Here is a link with MANY titration curves. Scroll down to the Na2CO3 plus HCl curve and that will be the one you want. http://www.chemguide.co.uk/physical/acidbaseeqia/phcurves.html
January 13, 2016

Chemistry
Ba(NO3)2 + Na2SO4 ==> BaSO4 + 2NaNO3 a. Gravimetric analysis depends upon almost none of the solid dissolving; adding and excess of Na2SO4 is adding a common ion (sulfate ion) which decreases the solubility of the BaSO4. b. mols BaSO4 = grams/molar mass BaSO4 = ? mols Ba(...
January 13, 2016

chemistry
Notice that as you proceed from low to high atomic numbers, the number of neutrons in the nucleus increases faster than the number of protons. Therefore, the high atomic number elements have too many neutrons so the probability is higher to get rid of neutron by converting ...
January 13, 2016

Chemistry Chemical Reactions pls help <3
This is a limiting reagent (LR) problem. mols AgNO3 = grams/molar mass = ? mols CaCl2 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols AgNO3 to mols AgCl. Do the same to convert mols CaCl2 to mols AgCl. It is likely the two values for mols ...
January 13, 2016

Chemistry
CH4 + 2O2 ==> CO2 + 2H2O mols CH4 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols CH4 to mols O2. Then g O2 = mols O2 x molar mass O2 = ?
January 13, 2016

Chemistry
I never heard of a mutualism bond.
January 13, 2016

stoichiometry
For every 100 mol NH3 used 100 mols NO formed at 100% yield. At 70% yield it will form only 70 mols NO. Then 100 molos NH3 initially - 70 mols used = 30 moles left over to be recycled.
January 13, 2016

Chemistry
I think all look ok except I would think Hg is a metallic bond since Hg is a metal. The others look ok. In my book almost nothing is PURE ionic or PURE covalent.
January 13, 2016

chemistry
You must be kidding? 1. Secure tank. 2. Fill tank with water. 3. Unscrew the lid on the jar of Na2CO3. 4. Remove some Na2CO3 5. Sprinkle in tank etc etc. I'm sure you didn't want this but that's what the question asks.
January 13, 2016

Science
50 g sample of ice. -30 C initial T 0 C final T q = mass ice x specific heat solid ice x (Tfinal-Tinitial) = ? To melt the ice at zero to water at zero. q = mass ice x heat fusion ice = ?
January 13, 2016

Chemistry
There are 6.02E23 molecules in 18 g H2O (1 mol). 36 grams is 2 mols.
January 13, 2016

chemistry
Balance the equation. Then use the coefficients in the balanced equation to convert mols NaHCO3 to mols CO2. Finally, convert mols CO2 to grams by g = mols x molar mass.
January 12, 2016

chemistry
Josh, did you proof your problem? You can calculate the original (acid) and (base) this way. pH = pKa2 + log base/acid 7.2 = 7.2 + log base/acid 0 = log b/a 1 = b/a is equation 1 equation 2 is a + b = 0.05 Solve those two equations simultaneously and A = B = 0.025M The buffer ...
January 12, 2016

Chemistry
If you start with neutral S and make a sulfide ion (S^2-) out of it, do you add or lose electrons?
January 12, 2016

chemistry
If the copper sulfate is in solution, this is it. Zn(s) + CuSO4(aq) ==> ZnSO4(aq) + Cu(s) The Zn displaces the Cu^2+ ion.
January 12, 2016

chemistry
H2 + Cl2 ==> 2HCl Since these are gases one may use L (volume) as if the volume were mols. 0.5 L HCl x (1 mol H2/2 mols HCl) = 0.5 x 1/2 = ?
January 12, 2016

Chemistry
2KNO3 ==> 2KNO2 + O2
January 12, 2016

chemistry
First there is no such thing as calcium(iii) oxycarbonate. Ditto for calcium(iv) oxide. CaCO3 + 2HCl ==> H2O + CO2 + CaCl2 mols CaCO3 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols CaCO3 to mols CaO. Convert mols CaO to grams CaO by ...
January 12, 2016

Chemistry
Look up the atomic mass of Al and weight exactly that amount of Al on an analytical balance.
January 11, 2016

chemistry
Ivan, Anthony, Juan, we prefer you not change screen names. We can help you better if you keep the same name when you post. %Na = (atomic mass Na/molar mass NaHCO3)&100 = ?
January 11, 2016

chemistry
Technically, I don't think it can be done because I think the problem is misstated. You don't mix solids with 1 L H2O; when making molar solution you use mols and add enough WATER TO MAKE A TOTAL VOLUME OF 1 L. But the think the intent of the problem is to answer as ...
January 11, 2016

Chemistry
a.) How many grams of Hydrogen will be contained in a 100.000 g sample of magnesium hydroxide.? mols MgIOH)2 = grams/molar mass = ? Then mols H ATOMS (not molecules) will be twice that since there are two H atoms per mol Mg(OH)2. Then grams H ATOMS will be g = mols x atomic ...
January 11, 2016

Chem
Would you believe 44.009 grams/mol or the molar mass is 44.009.
January 11, 2016

Chemistry
The percent composition in these problems means to calculate the percent of each element versus the entire compound. It works this way. Suppose you have 10 lbs apples and 5 pounds oranges. What is %apples and %os. %apples = (weight apples/total weight)*100 = (10/15)*100 = 66....
January 11, 2016

Chemistry
Yes. When a reaction gives off heat it is said to be exothermic and the enthalpy of the reaction is negative.
January 11, 2016

Chemistry
The reaction of Mg with oxygen of the air produces heat. It takes more energy to produce white light than red light.
January 11, 2016

@ Damon--math/ chemistry
Already on it. :-)
January 11, 2016

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