Tuesday
April 21, 2015

Posts by DrBob222


Total # Posts: 48,430

chemistry
q = -15.3 kJ/mol x (18.8/molar mass KC2H3O2) = approx - 3.03 kJ or 3030 J. Then -3030 = mass H2O x specific heat H2O x Tfinal-Tinitial) Substitute the numbers and solve for Tfinal
March 3, 2015

Chemistry Dr. Bob222
You know I know how to calculate the TY and AY and %Y now, but I'm confused on the finding limiting reactant? umm Let me see if I can figure it out and you let me know if I'm on the right track... 2.02g NaHCO3 mols = 2.02/84 = 0.0240 mols the ratio is 3/1 for ...
March 3, 2015

Chemistry Dr. Bob
. Show that the equivalence amount of citric acid for 2.00 g of sodium bicarbonate is 1.52 g. *** 1 mol citric acid reacts with 3 mols sodium bicarbonate, molar mass NaHCO3=84g/mol 2 moles in 2 g? = 2/84? = 0.0238 mols 2g NaHCO3? then to find the citric acid? is it.. 0.0238/3...
March 3, 2015

chemistry
Like charges repel; unlike charges attract.
March 3, 2015

chemistry
Wouldn't you expect it to get stronger (as long as the electron is in the same shell).
March 3, 2015

Chemistry Ap
We can't draw diagrams on this forum but it is easy to see if I could draw a graph. Basically this is what you do. XH2O = Pomethanol-Ptotal/(Pomethanol-PoH2O) That gives you (89.0-35.5)/(89.0 - 17.5) = 0.748 for H2O I can never remember the formula; I draw it out with a ...
March 3, 2015

chemistry
I agree Good work.
March 3, 2015

chemistry
I see. I do all of the typing so you can check your values. How about us turning that around. You do the typing (show me what you have or tell me what you don't understand) and let me check your results. You have the right equation, the right products, and it's ...
March 3, 2015

chemistry
This looks simple enough. What do you not understand? Acid + base = salt + H2O
March 3, 2015

Chemistry
12. Negative charge must equal positive charge since all elements are neutral.
March 3, 2015

AP CHEM LAB
mols HCl = M x L = ? mols NaOH = mols HCl (since there is 1 mol HCl reacting with 1 mol NaOH) Then M NaOH = mols NaOH/L NaOH. You know mols and M, solve for L NaOH.
March 3, 2015

Chemistry
Atomic masses are average masses of the different isotopes of that element that occur naturally. For example, the mass of Cl-35 and the mass of Cl-37 are averaged (about 76% for 35 and 24% for 37) and the weighted average is about 35.5 for naturally occurring Cl2.
March 3, 2015

Chemistry Dr. Bob
You did the 1 g NaHCO3 vs 0.76 g citric acid (as you posted earlier) correctly. For #2 you use YOUR numbers. mols in 1g NaHCO3 = 1.02/84 = about 0.012 Convert to mols CO2. That's approx 0.012 x 1 mol CO2/1 mol NaHCO3 = about 0.012 mols CO2. Convert to grams CO2. 0.012 mol ...
March 3, 2015

chemistry
1 for Cu in the ground state. 5 are in the valence shell of As.
March 3, 2015

Chemistry
The first ionization energy (first IP) generally increases as one moves from the left to the right on the periodic table (in the same period). That's because the nuclear charge in increasing but the added electrons are going into the same shell so the attractive force is ...
March 3, 2015

chemistry
Those intermolecular forces add up to extra holding power; therefore, it is harder to break the bonds from a liquid to a vapor state. That means more energy must be transferred to the liquid and that means a higher boiling point.
March 3, 2015

chemistry
NH4I(s) + H2O(l) ==> NH4^+(aq) + I^-(aq)
March 3, 2015

Chemistry
You would expect the boiling point to be higher for H2O than for H2S because of hydrogen bonding in H2O. The problem didn't ask about boiling point, you say? Yes it did. It asks for volatility, that is vapor pressure, and that leads to boiling point.
March 3, 2015

Chemistry Dr. Bob
I answered below at the first post and I don't agree with your calculations. You never had 1g CO2 did you?
March 3, 2015

Chemistry
There are shorter ways to do this but they are harder to explain. I do them the long way this way. mols N2 = grams/molar mass = ? mols Mg = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols N2 to mols Mg3N2. Do the same for mols Mg to mols ...
March 3, 2015

Chemistry
I told you how to do it. You could try following my instructions. Here is how you do the sodium propionate. You want 1 L of 0.1M CH3CH2COONa mols needed = M x L = 0.1 M x 1 L = 0.1 mol Then mol = grams/molar mass 0.1 mol = grams/96 grams = 96 x 0.1 = 9.6 grams. Place 9.6 g the...
March 3, 2015

Chemistry
I don't buy any of this. The numbers, even if they are right, (and they may be), are not realistic. Who would want to make 0.01 mL of such a solution? That's about two drops. :-)
March 3, 2015

Chemistry
The way I read the question is that there are two questions; i.e., 1. How to prepare 0.1M solution of propionic acid and 2. How to prepare 0.1M solution of the salt. 1. Since no volume is given you just assume some volume you want to prepare. 1L is the easiest to assume ...
March 3, 2015

Chem Dr. Bob Plz
mols in 1g NaHCO3 = 1/84 = ? mols CO2 produced = same or 1/84 grams CO2 = mols x molar mass = theoretical yield. You're right that mols CO2 = 1g/molar mass CO2 IF YOU HAD 1 g CO2 but you didn't. You said you had 1 g NaHCO3; furthermore, you calculated the mass CO2 as 0...
March 3, 2015

Chemistry
Use PV = nRT Remember T must be in kelin. V is in L.P in atm.
March 3, 2015

Chemistry
Yes it has 5 valence electrons. But aren't those bonding electrons? The question is for non-bonding electrons.
March 3, 2015

Science 8th Grade
I don't agree with your answer. Why not use some numbers and see what happens. For example, E = 100, I = 50; R = ?. Then E = 100 and I = 50; R = ?. The general rule is E = IR so R = E/I. If I is constant than R = E*(1/k); therefore, if E goes up then R goes up. If E goes ...
March 3, 2015

Chemistry
I have the same answer and that will be ok. If your prof is picky about significant figures s/he may have issue depending upon the numbers you used to make that calculation.
March 3, 2015

Chemistry
Is that your answer? The molar mass N2O was not the question.
March 3, 2015

Chemistry
[(2*atomic mass N/molar mass O2)]*100 = ?
March 3, 2015

pharmacy tech
You need to know what kind of percent it is; i.e., % by mass(w/w), % w/v or % v/v. If % w/v for example, that is mass [(solute/mL solution)]*100 = % If it is a 5% w/v solution that is 5 g solute in 100 mL solution and you want to know grams in 50 mL, that is (x/50)*100 = 5 (x/...
March 3, 2015

Chemistry (organic)
Do you have a K. I usually use them as g/g and if your prof does the same, then Ko/a = K(16.9/9.5) = 1.78 Then K = (concn organic phase/concn aqueous phase). Let x = g in organic phase, then 5-x = g in aqueous phase. For org phase you have x/100 For aqueous phase you have (5-x...
March 3, 2015

chemistry
C'mon. Use that caps key when needed. PbO + CO ==> Pb + CO2 Use PV = nRT and solve for n = number of mols for CO at room T. T will be 298 K if you use 25C as room T. V will be 2400 and P will be 1 atm. Then convert mols CO to mols PbO using the coefficients in the ...
March 3, 2015

chemistry
What temperature? what pressure? Is that at STP? What Pb; i.e., PbO or PbO2. IF at STP, then mols CO = 2400 cm3/22.4 dm3 = ? But I can't even write an equation with know the kind of lead oxide.
March 3, 2015

chemistry help fast
1. Convert 16 tonnes of Fe2O3 to grams. 2. Convert g Fe2O3 to mols. mols = grams/molar mass 3. Using the coefficients in the balanced equationk convert mols Fe2o3 o mols CO. 4. Convert mols CO to grams. grams CO = mols CO x molar mass CO
March 3, 2015

Chemistry
I worked this for you last night and added an addendum to it this morning. I assume you've not looked for it. If you have some questions about it or the solution to it, repost it along with whatever solution and/or questions you have.
March 3, 2015

chemistry help
That is CO2, not Co2. CO is carbon monoxide. Co2 is diatomic cobalt. CO2 + C ==> 2CO mols CO2 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols CO2 to mols CO Now convert mols CO to grams CO. g CO = mols CO x molar mass CO
March 3, 2015

Chemistry Help
If H3O^+ > 10-7M, acid If H3O^+ = 10^-7M, neutral If H3O^+ < 10^-7M, basic
March 3, 2015

more on #1--Chemistry Help
(H3O^+)(OH^-) = Kw = 1E-14. You know Kw and H3O^+, solve for OH^-
March 3, 2015

Chemistry Help
You would do well to post separate posts. Sometimes we don't have time to answer 4-5 questions at a time. Calculate the concentration of OH− and the pH value of an aqueous solution in which [H3O+] is 0.014M at 25°C. Is this solution acidic, basic or neutral? pH...
March 3, 2015

Chemistry Help
If they dissociate they are electrolytes. Na2CO3 yes. O2 no
March 3, 2015

Chemistry help!! Fast
I really don't know but if we go with the "like dissolves like" slogan, I would think it false since the larger molecules have a higher molar mass and they should dissolve better is solvents with high molar mass.
March 3, 2015

Chemistry
yes if you make that (182/4780)*100 = ? What you want is (182*100/4780) = ?
March 3, 2015

Chemistry Basics- Please Help!
I agree with what you have.
March 3, 2015

CHEMISTRY
You have two/three problems in one here. First I would determine the base and acid concentrations in the initial buffer. To do that use pH = pKa + log (base)/(acid) and solve for base/acid ratio. Then you know acid + base = 0.2 Solve those two equation simultaneously to ...
March 3, 2015

Chemistry
density = mass/volume. Plug and Chug.
March 3, 2015

chenistry
You're still trying to make grams go to grams. You CAN'T do that. You MUST change grams to mols, convert mols of what you have to mols of what you want, then change back to grams.
March 3, 2015

Chemistry Help
yes
March 3, 2015

Chemistry Help
You have mols H2SO4 = M x L = 0.178 x 0.2 = ? Since there are 2 H atoms per 1 molecule H2SO4, then there will be twice as many H atoms as there are mols H2SO4.
March 3, 2015

Chemistry Dr. Bob
You don't convert anything to grams. Use mols to convert from what you have to what you want. Then convert to grams. Reactions go by mols, not grams.
March 3, 2015

Chemistry
At the beginning you have pure NH3 solution. ......NH3 + H2O ==> NH4^+ + OH- I.....0.1............0.......0 C......-x............x.......x E.....0.1-x...........x......x Plug the E line into the Kb expression and solve for x = OH, then convert to pH. For part b. You started...
March 3, 2015

Chemistry
You stuck in numbers with the Na2O question without showing the units and you reversed the factor. The units are not there and that's why you can't find the error. First I would not have rounded the 0.84 but kept 0.838. Why throw a perfectly good digit away. You have ...
March 2, 2015

college chemistry
I found a conversion factor to convert 0.737 g/mL to pounds/gallon. 0.737 g/cc = 6.15 pounds/gallon. So 23 gallons x 6.15 pounds/gallon = ?
March 2, 2015

Chemistry
20 uci/kg x 50 kg = ?uci and convert to mci.
March 2, 2015

Chemistry
Yes, it matters what is being neutralized AND chemicals reactions don't occur between grams but between mols so you can't make the statement you made (at least and be right).
March 2, 2015

Science
You don't give us much to go on. NaOH + H2CO3 will make Na2CO3 + H2O
March 2, 2015

Science // Chemistry
Start by asking yourself how many mols you need? Moles KOH you want = 1.00 L x (1.3 mols/L) = ? mols and that is 1.3 moles KOH. Then 1.3 moles KOH x (56.1 grams KOH/mol KOH) = grams KOH you need for 1 L of 1.3M KOH.
March 2, 2015

Chem-mystery
You meant Ca(OH)2. This is new to me but I believe this is an acid/base reaction between HN3 and Ca(OH)2. I think the equation is 2HN3 + Ca(OH)2 ==> Ca(N3)2 + 2H2O mols HN3 = M x L = 0.2 x 0.05 = 0.01 mols Ca(OH)2 = M x L = 0.2 x 0.05 = 0.01 We start with this probably ...
March 2, 2015

Chem-mystery
You don't need M Ca(OH)2??? I don't think you can work the problem without it. .
March 2, 2015

Science
It depends upon how many significant figures you are reporting. You are allowed 4 and I get 24.32 x 100.09 = 2434.189 so you can legitimately report 2434 g with 4 places. There is nothing wrong with reporting it as 2.434E3 grams.
March 2, 2015

Science
You aren't missing anything. You are right on. Thanks for showing your work. When you do that it takes just a glance to know if things are ok.
March 2, 2015

Chemistry
I worked this below.
March 2, 2015

Chemistry
I re-thought that problem (all night long) and there is nothing wrong with the first part; i.e., (H^+) must be 0.0018 to make it work and you must add 2.83 mL of the 0.2 M acid to get that. When I tried to check it to see if all that worked the best I could do was 0.99% and ...
March 2, 2015

oops--Chemistry
I made a typo part way down the page. Instead of retyping the whole things, since it is so long, here is the line in bold. I show it as multiplied and it should be divided. If you want (Ac^-)/(HAc) to be 0.01, then (H^+) must be what?
March 2, 2015

Chemistry
I would do this. ........HAc ==> H^+ + Ac^- I.......0.1......0.....0 C........-x......x.....x E.....0.1-x......x......x Plug the E line into the Ka expression and solve for x = (H^+). I obtained 1.34E-3M for (H^+) .........HAc ==> H^+ + Ac^- What you want to do now is to...
March 2, 2015

Chemistry
When you ask a question like this you should tell us what you used for Ka. Our tables may not give us the same value as your table(s). Therefore, we don't know if you've done it right or not. I used 6.2E-10 for Ka for HCN and using that value Kb for CN^- is 1.6E-5.
March 2, 2015

Chemistry
.........Ba(OH)2 ==> Ba^2+ + 2OH^- I.......3.5E-4........0.......0 C......-3.5E-4.....3.5E-4..2*3.5E-4 E........0.........3.5E-4...7.0E-4 So the (OH^-) from Ba(OH)2 = 7.0E-4. We want to know how much CN^- it will take to produce OH^- = 7.0E-4 M. .........CN^- + HOH ==> ...
March 2, 2015

CHEM
This is a limiting reagent (LR) problem and you know that because amounts are given for all of the reactants instead of just one. NH3 + CO2 + H2O ==> NH4HCO3 I do these the long way. 1. How much product can we get from 50.0 g NH3 if all of the others are in excess? mols NH3...
March 2, 2015

Chemistry
mass = volume x density density is given volume = 4 cm*4 cm*4 cm = ? cm^3.
March 2, 2015

Chemistry
You need to copy that format I gave you earlier. All of these stoichiometry problems are worked the same way. 2C4H10 + 13O2-->10H2O + 8CO2 Step 1. Write and balance the equation. You have that. Step 2. Convert what you have (in this case butane) into mols. mols = grams/...
March 2, 2015

Chemistry
You need to copy that format I gave you earlier. All of these stoichiometry problems are worked the same way. 2C4H10 + 13O2-->10H2O + 8CO2 Step 1. Write and balance the equation. You have that. Step 2. Convert what you have (in this case butane) into mols. mols = grams/...
March 2, 2015

Science
Be careful with the units. If you use the water as 100 g I would change the metal from kg to grams.
March 2, 2015

Science
heat lost by mtal + heat gained by H2O = 0 [mass metal x specific heat metal x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0 Substitute the numbers and solve for specific heat metal which is the only unknown in the equation.
March 2, 2015

Science
heat lost by Cu + heat gained by Al + heat gained by water = 0 [mass Cu x specific heat Cu x (Tfinal-Tinitial)] + [mass Al x specific heat Al x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0 I would convert all to grams and use specific heat in J/g*C
March 2, 2015

Science
See your other H2O/Cu/Al problem just above.
March 2, 2015

Chemistry
Models give us a visual idea of how to imaging the atoms/molecules/bonding, etc. The real understanding of atoms and how reactions take place is in advanced math, wave mechanics, etc. Many of us simply don't have the math background, especially in high school and lower ...
March 2, 2015

chemistry
This is no different than those problems we've been doing. You can convert any mole in an equation to any mole of something else in the same equation just by using the coefficients in the balanced equation CO2(g)+4H2(g)→CH4(g)+2H2O(g) Step 1. You have the balanced ...
March 2, 2015

Science for ms. Sue
There is no way this statement is true. It get's stronger as you get closer and if you get close enough the high voltage will jump a short distance through the air to you.
March 2, 2015

chemistry
A lot of work here. I don't want to just give you the answers but I'll be happy to help you through them. Exactly what do you not understand?
March 2, 2015

chemistry
g = mols x molar mass
March 2, 2015

chemistry
same as # mols NaOH mols NaOH = M x L
March 1, 2015

Chemistry
4. 2Na + Cl2 ==> 2NaCl is one way. 6 & 7. I don't know the cost of making it; it is almost dirt cheap to buy. I can buy a box of salt for less than a dollar. In most cases I don't think it's made. Much of it is mined as NaCl in salt mines in Louisiana (among ...
March 1, 2015

Chemistry
Yes, and I would convert 2.00 g azomethane to mols first.
March 1, 2015

Chem
A = ebc where e is the molar absorptivity = slope of the line. 0.455 = 3163.9*c Calculate c.
March 1, 2015

Chemistry Need Help
Thanks for letting us know.
March 1, 2015

Chemistry
dHrxn = (n*dHf products) - (n*dHf reactants)
March 1, 2015

oops---chemistry
http://en.wikipedia.org/wiki/Standard_state
March 1, 2015

chemistry
I would think this would be covered in your text/notes. Here is a reference but IUPAC rules don't always follow through in chemistry texts/journals. For example, most U.S. based chem text use 1 atm as standard pressure but IUPAC suggest 100 kPa (1 bar).
March 1, 2015

chemisty
......2NO2 (aq) ==== 2NO (aq) + O2(aq) I....0.750............0..........0 C......-2x.............2x.........x E....0.750-2x..........2x.........x So the problem tells you x [which is (O2)] = 1.25M which makes 2x (the concn of NO) just twice that. NO2 then is 0.75-2x
March 1, 2015

chemistry
I don't understand the problem you'r having. Write K exprssion for the reaction, substitute the numbers as shown and punch them into your calculator.
March 1, 2015

chem
It's the product of the right side over the product of the left side and each coefficient becomes an exponent for that substance.
March 1, 2015

chem
I don't see a question. Probably it's to evaluate Z but what in the world is Z. By the way, Does your equation have an extra Fe in it?
March 1, 2015

science
I don't see a question. That's CaCl2
March 1, 2015

Chemistry
I calculated the same number as you; I suspect the problem is that you're reorting too many significnt figures. If you posted the problem EXACTLY as stated, then you're allowed only two places by the 2.1 and I would round the answer to 2.2E3 J. If that 2.1 is really 2....
March 1, 2015

Chemistry
[mass milk x specific heat milk x (Tfinal-Tinitial)] + [mass coffee x specific heat coffee x (Tfinal-Tinitial)] = 0 Substitute and solve for mass milk.
March 1, 2015

chemistry
dHrxn = (n*dHformation products) - (n*dHformation reactants)
March 1, 2015

Chemistry
The pH is determined by the hydrolysis of the salt at the equivalence point. If we call the acid HA (the problem doesn't identify it) nor does it say it is monoprotic or not (but only one pKa suggests monoprotic) so the anion will be A^-. Volume of NaOH to reach the ...
March 1, 2015

Chemistry
You don't have enough information. mols Na3PO4 = M x L but I don't see a L. Same for the Co salt, no M
March 1, 2015

chemistry
mols AgNO3 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols AgNO3 to mols AgCl. Now convert mols AgCl to grams. grams AgCl = mols AgCl x molar mass AgCl.
March 1, 2015

Chemistry combined gas law
I answered this below that it was not correct and what was wrong as well as how to correct it.
March 1, 2015

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