Wednesday
April 23, 2014

Posts by DrBob222


Total # Posts: 41,890

chemistry
The problem doesn't say that the 1.00 g sample is pure; I'll assume it is. mols Pt = 0.5780/195 = about 0.00296 but you need to do ALL of these calculations more carefully. g Cl = 1.00-0.5760 = 0.422g and convert to mols = approx 0.012 So the empirical formula is PtCl4...

Chemistry
You're having trouble with the basics. I can point out some of the problems taken one at a time. With the decomposition you appear not to understand how to write atoms and molecules. The correct symbolism is: Example: the decomposition reaction of hydrogen sulfide Is it 2H...

Chemistry
No, 20 km is a distance, not a pressure. The problem says the balloon is relesed at sea level on earth's surface. Pressure at sea level is 101.325 kPa or 1 atm or 14.7 lb/sq ft. Since you are using kPa for the second P you should use first P in the same units.

Chemistry
Assuming the T is constant (which it will not be) use p1v1 = p2v2

Chemistry
25% v/v means 25.0 g isopropyl alcohol in 100 mL solution. mols C3H8O = grams/molar mass Convert 100 mL of the solution to grams using density, then M = mols/L soln.

chemistry
2S2O3^2- + I2 ==> 2I^- + S4O6^2- 1. mols I2 = M x L = ? 2. Convert mols I2 to mols S2O3^2-. That is ?mols I2 x (2 mol S2O3^2-/1 mol I2) = ? 3. Then M S2O3^2- = mols S2O3^2-/L S2O3^2-

Chemistry
27.8g KCl/molar mass KCl = approx 0.37 0.37/0.7 = approx 0.53M AgNO3 + KCl ==> AgCl + KNO3 mols KCl used = M x L = 0.0221 x 0.53 = ? mols AgNO3 = the same (since the ratio in the balanced equation is 1:1). Then M AgNO3 = mols AgNO3/L AgNO3.

Science to: DrBob222
1. Most ionic compounds have a crystal structure. You must break the chemical bond and tear away the crystal structure. Basically it takes less energy to break the covalent bonds than an ionic bond. 2. Dissolve the compound in water and test the conductivity. Strong electrolyt...

cHEMISTRY
Yes, KClO3 is potassium chlorate. The best thing I can tell you to memorize the polyatomic ions. For example, ClO3^- is chlorate SO4^2- is sulfate NO3^- is nitrate etc. Here is a table. Time and usage will makes this easier. https://www.google.com/search?q=polyatomic+ion+chart...

College Chemistry - Science
I really don't understand the problem. What are you to judge by? Of course you can deprotonate half of it if you add enough NaOH. If you add enough NaOH I should think you could deprotonate all of the HPO4^2-. But I don't know how you would tell when you were there sin...

chem
I showed you how to do it. You substitute the numbers and go through the calculation. And I have no idea which numbers go with the elements/compounds

Chemistry
density x gravity x height = pressure g/cc.......9.8.......m.......kPa #1. 1.0 x 9.8 x h = (762/760)*101.325 2. You substitute.

chem
dHrxn = (n*dHfproducts) - (n*dHfreactants)

College Chemistry - Science
pH 11.95 means pOH = 2.05 pOH = -log(OH^-) (OH^-) = 0.00891 0.00891 x 30 mL = about 0.27 (Note: Calculations give this as 0.267 but I've rounded to 0.27 because you're allowed only two significant figures.) mmols acid = 45 x 0.002 = 0.09 CH3COOH + NaOH ==> CH3COONa ...

chemistry
H2SO4 + 2NaOH ==> Na2SO4 + 2H2O mols NaOH = M x L = ? mols H2SO4 = 2x mols NaOH (look at the coefficients n the balanced equation.)_ M H2SO4 = mols H2SO4/L H2SO4

chemistry
I answered this earlier.

Chem
I answered this earlier.

chem
It's difficult to answer without knowing the details of the experiment.

chemistry
1. acid + base = salt + water 2HCl + Mg(OH)2 ==> 2H2O + MgCl2 You add the phases. 2. Pb(NO3)2 + Na2S ==> PbS(s) + 2NaNO3(aq) You add the other phases. 3. Pb^2+(aq) + S^2-(aq) ==> PbS(s)

Chemistry
How many mols do you want? That's M x L = ?mols. Then mol = grams/molar mass. I think the point of this question is how to physically describe how it is prepared. Weigh that many grams NaCl, add to a 500 mL volumetric flask, add some water, swirl until all of the NaCl is d...

Chemistry
[Al2(SO4)3] = 0.200M x (15.00/50.00) = ? Then [SO4^2-] = 3x that.

Chem
I would write "no reaction".

Chemistry
Read the problem. "Divers know that the pressure exerted by the water increases about 100 kPa with every 10.2 m of depth. This means that at 10.2 m below the surface, the pressure is 201 kPa;" So the pressure 10.2m below is 100 + whatever it is at the surface (which ...

Chemistry
So the new pressure is 101 + (100*40.32/10.2) = ?. Then p1v1 = p2v2

chemistry
mols H2O = grams/molar mass = ? Then 1 mol contains 6.02E23 so ? mols will contain .....

Chemistry
When you use the spectrophotometer you insert the cuvette containing the blank and use the adjustment knob to make the needle read 100 %T. That is for no Cr solution in the beam. That adjustment takes care of any reflections from the liquid, from the walls of the cuvette, and ...

Chemistry: Check my answers please!
I don't agree with #1 but I do the others. I think the results will be low if I've interpreted the question correctly and this is not a standard additions method. I can't draw it on this board but here is what you do. On a sheet of graph paper, mark the Y axis as A...

Chemistry
Use any one of the points of experimental data. Plug in [O2], [NO2] and the rate, solve for k.

chemistry
1 mol has 6.02E23 so 0.4 mol will have .....

no equilibrium---Chemistry

chemistry
1.Zn metal in MnSO4 Zn metalin AgNO3 Mn metal in Zn(NO3)2 Mn metal in AgNO3 Ag metal in Zn(NO3)2 Ag metal in MnSO4. 2. Is the note about complex ion formation your observation or is that a part of the question. The most likely products are Cu(OH)2 and Mg(OH)2. Mg(OH)2 is not l...

chemistry
I did that for you below but I corrected the typos. 2Cr^3+(aq) + 3CO3^2-(aq) ==> Cr2(CO3)3(s)

math
OK. So it's 15 + 12*9 + 5 = 15 + 108 + 5 which is 128 as you had.

math
If it's $12/class then 10 classes would cost 10*12 = $120 and that + a $5.00 processing fee would make $125 wouldn't it?

oops--my typo--Chemistry
2Cr^3+(aq) + 3CO3^2-(aq) ==> Cr2(CO3)3(s)

Chemistry
I will assume you had those typos and the equation is 2CrI3(aq)+3Na2CO3(aq) ---> Cr2(CO3)3(s) + 6NaI(aq) 2Cr^3+(aq) + 6I^-(aq) + 6Na^+(aq) + 3CO3^2-(aq) ==> Cr2(CO3)3(s) + 6Na^+(aq) + 6I^-(aq) 6I^- cancel 6Na^+ cancel which leaves the net ionic equation as 2Cr^3+(aq) + 3...

Chemistry
I think you have some typos. Is that CrI3(aq)? Is that Na2CO3?

Chemistry
I think my last post shows how I arrive at th final answer. The rules are 1. write the molecular equation. 2. Break the molecules into ions. a. strong electrolytes become all ions. b. solids (precipitates and there are none in this equation) are written as (s) for solids) and ...

Chemistry
CH3COONa(aq) + HNO3(aq) ==> NaNO3(aq) + CH3COOH(aq) If we convert all of that to an ionic equation we have CH3COO^-(aq) + Na^+ + H3O^+ + NO3^-(aq) ==> Na^+(aq) + NO3^-(aq) + C3COOH(aq) Na^+(aq) cancels. NO3^-(aq) cancels. We are left with CH3COO^-(aq) + + H3O^+(aq) ==>...

Chemistry
There is no other "answer" unless you want to include H2O as the other answer. I don't think that's necessary. Since you're using H^+ for H3O^+ that leaves a H2O for the right (but I think all of that is taken care of by the (aq) phases.

Chemistry
CH3COO^- + H^+ ==> CH3COOH

Chemistry
See your other post.

chemistry
Do you really read what you've posted. More importantly do you read the responses? Bob Pursley has answered. Damon has answered. I have answered. In addition I pointed out some errors and you keep repeating those. What's the problem?

Chem
A lot of verbiage, most which is unimportant. .....PtClx ==> Pt + xCl2 I....1.00.....0.....0 E....-1.00..0.5780..(1.00-0.5780) .......0....0.5780...0.422g So if I used twice as much PtClx I would expect twice as much Cl2 or 0.844 g.

chemistry
Isn't this just dE = q + w. They give you q. s is -p*dV

chemistry
dE = q + w q is -2.05 kJ/mol C10H22 w you must obtain from volume on the left - volume on the right, then w = -p*delta V.

chemistry
C2H6O + 3O2 ==> 2CO2 + 3H2O dHrxn = (n*dHfproducts) - (n*dHfreactants) Substitute and solve for dHfC2H6O

chemistry
Two equations and two unknowns. Let X = g CH4 and Y = g C2H6 ------------------ eqn 1 is X + Y = 6.79g eqn 2 is heat generated by CH4 + heat generated by C2H6 = 369 kJ. heat from CH4 is 890.3 kJ/mol x (X/16) heat from C2H6 is 1569.7 kJ/mol x (Y/2*30) so all of that together is...

chemistry
Two errors to point out. You say magnesium chlorate but use potassium chlorate. Second, L is liters, not litters (as in a litter of puppies). Convert grams KClO3 to mols. mols = grams/molar mass Using the coefficients in the balanced equation, convert mols KClO3 to mols O2. Th...

chemistry
millimols HF = mL x M = approx 44.55 mmols NaF = approx 63.25 0.01 mols = 10 mmols NaOH added ..........HF + OH^- ==> F^- + H2O I........44.55..0.......63.25...... add............10............ C........-10...-10......10 E.......34.55...0......73.25 Plug the E line into the...

chemistry
mols Zn(SO3)2 = grams/molar mass m = mols solute/kg solvent.

Chemistry
From the question I assume you did an experiment of some kind and made some observations. What were those observations?

chemistry
4. delta E = q + w q = +901 w = +453

chemistry
2. work is p*delta V. The gas is doing th work so it is -.

chemistry
Most of us don't have the time to work 10 or more time consuming questions. I'll do the first one; if you post them separately someone may get to them. 1. heat lost by Ti + heat gained by H2O = 0 [mass Ti x specific heat Ti x (Tfinal-Tinitial)] + [mass H2O x specific h...

chemistry
q = mass H2O x specific heat H2O x (Tfinal-Tinitial)

Chemistry
initial concn = 0.067/0.250 = approx 0.27 but that's just an estimate. ...........A ==> B I.......0.027...0 C.........-x....x E......0.027-x..x Substitute the E line into Kc expression and solve for x.

chemistry
In what way? Technically, there is no such compound.

Chemistry
CaCO3 + 2HCl ==> CaCl2 + H2O + CO2 mols CaCO2 = grams/molar mass Using the coefficients in the balanced equation, convert mols CaCO3 to mols CaCl2. Now convert mols CaCl2 to g. g = mols x molar mass.

chemistry
pH = pKa + log(base)/(acid) pH = 10.25 + log (0.05/0.1)=? 10.4 = 10.25 + log b/a b/a = ? = approx = 1.4 so b = 1.4a or CO3^2- = approx 1.4*HCO3^-

Analytical Chemistry
Aren't these defined in your text/notes?

Chemistry
I'm confused with the phases unless this reaction is occurring at an elevated temperature. At any rate mols TiCl4 = grams/molar mass Using the coefficients in the balanced equation, convert mols TiCl4 to mols Ti. Now convert mols Ti to grams Ti by g Ti = mols Ti x atomic m...

Chemistry
2NH3 + CO2 ==> (NH2)2CO + H2O 1a. mols NH3 = grams/molar mass 1b. mols CO2 = grams/molar mass 2a. Using the coefficients in the balanced equation, convert mols NH3 to mols of urea. 2b. Do the same to convert mols CO2 to mols urea. 2c. It is likely that these two values will...

Chemistry
I can tell you this will never do it because the spontaneous reaction is the reverse of what you have. However, here is how you work the theoretical (and it's ony theoretical) problem. 1. Write and balance the equation. Pb3(PO4)2 +6NaNO3 ==> 2Na3PO4 + 3Pb(NO3)2 2. Conve...

Chemistry (Thermodynamics)
C2H2 + (5/2)O2 ==> 2CO2 + H2O

Chemistry
It could make a difference depending upon how the question is stated. If you add the SAME AMOUNT of heat(in calories or joules) to a 70 mL sample vs a 100 mL sample, then the 70 mL will have a higher temperature.

Chemistry
This four step process will do volumetric or mass stoichiometry problems all day long. 1. Write and balance the equation. Mg + 2HCl ==> MgCl2 + H2 2. Convert what you have (in this case grams Mg) to mols. mols = grams/molar mass. That's approx 0.2 but you should do it m...

Chemistry
1. density of air @ 20C = ? mass air = volume x density 2. density ice = ? mass ice = volume ice x density ice. Substitute and solve for volume. If density ice is given in g/cc, remember to convert kg to grams. The answer will be in cc, convert to L. 3. volume bar = length x w...

Chemistry
dHrxn = (n*dHreactants) - (n*dHproducts) dE = dH + work work is pdV but I don't see any pressure. dV you can get from 3 mols on the left going to 1 mol on the right.

Chemistry
At STP conditions the density of air is very close to 1.29 g/cc. That's 29/22.4 = ? with 29 being very close to the molar mass air at STP

Chemistry
You will find Zn^2+ + 2e ==> Zn in the standard reduction tables. You want the reverse of this so simply change the sign. Then look up Bi^3+ + 3e ==> Bi Zn number (with changed sign) + Bi number = Eocell. Then dG = -nEF n in this case is 6, E is from above, F is 96,485 c...

Chemistry
No. Each Cr changes from +3 to +2 which is a change of 1e per mol and you have 3 mols so that's 3 electrons. Or you can do it from Bi. Bi changes from 0 on the left to 3+ on the right or a change of 3 e per mol. b. 2e. Mg on the left to Mg^2+ on the right is 2e/mol.

Chem
Oxidation is the loss of electrons. Which of the half reactions has lost electrons. Write each one. Mg(s) ==> Mg^2+(aq) + 2e Zn^2+(aq) + 2e ==> Zn(s)

Chemistry
mols FeCl2 = grams/molar mass Using the coefficients in the balanced equation, convert mols FeCl2 to mols Fe(OH)2. Now convert mols Fe(OH)2 to grams. g = mols x molar mass = ?

empty post---chem

chemistry
Use PV = nRT

chemistry
If the solution is 0.52M and it is 0.52% ionized, then the ions are 0.52% of 2.5M; therefore, (H^+) = (A^-) = 0.0052*2.5 = about 0.013M ......HA ==> H^+ + A^- So plug thes numbers into the Ka expression and solve for Ka. (H^+) = 0.013M (A^-) = 0.013M (HA) = 2.5-0.013 = ?

Single vs double replacement reactions
I don't know how to start. Where do you want to go with this?

Decomposition reaction
1 reactant? multiple products?

Chemistry
p1v1 = p2v2

Chemistry
mols HCl initially = 0.025 x 0.1 = 0.0025 To end up with pH = 3 (0.001M H^+) we want H^+ to be 1E-3. If we work in millimols and let x = mL of 0.1M NaOH, we have then [(25.00 x 0.1M)-(0.1x)/(25+x)] = 1E-3M Solve for x and I obtained approx 24.5 mL of 0.1M NaOH that must be add...

Temperature and Particle Motion
To the touch. To breathe? To the touch hot air is hot because heat flows from the warmer object to our sensory nerves and the brain perceives that as hot. For cold, heat flows(COLD doesn't flow) FROM our sensory nerves to the object and our brain perceives that as cold.

Chemistry help!
2 errors on B 1. should be p1/t1 = p2/t2 2. T must be in kelvin and you used C 3. Ans is about 652. (725/310) = (p2/279) C.wrong formula. v1/t1 = v2/t2 (3.44/310) = v2/210) Ans is approx 2.3 L d.formula is (p1v1/t1) = (p2v2/t2) (725*3.44/310) = p2*16.9/298). Ans is approx 142....

Chemisrry
Your problem here is that you have have calculated n wrong and I pointed that out to you in an earlier response. You must be hitting th wrong keys on your calculator. You should be getting approx 0.02. The problem asks for grams and you quit too early. n = grams/molar mass app...

Chemistry
You're STILL using 0.0821 for R and I distinctly remember saying when you use P in kPa R must be 8.314. To make things a little easier you could have changed to 0.946 L also. P actually is 56.66 but rounding to 56.7 should be ok. n = PV/RT n = 56.7*0.946/(8.314*308) n = ab...

Chemistry
The percentages just tell you how much Na2CO3 and NaHCO3 you start with. 1 x 0.62 =0.62g Na2CO3. 1 x 0.38 = 0.38g NaHCO3. I will estimate from here but you confirm and use better accuracy. It makes the fractions come out better. mols Na2CO3 = 0.62/106 = 0.00585 mols NaHCO3 = 0...

Chemistry
Your numbers don't look all that bad except you are using the wrong R. The value of 0.08206 is used with p in atm. When you use kPa R is 8.314. I would have used 0.946 for 1 qt to L (the easy way to do the conversion is to go to Google, type in "1.00 quart to" wi...

Chemistry
Why don't you show your work and let us find the error? You can play hide and seek with these problems all day long.

Chemistry
Knowing the formulas won't do much good if you don't know how to use them. It is important to use the right units. Looking at the last problem for which you posted your work, see if my correction helps you in the others. If post specific questions, show your work, and ...

Chemistry
Show your work. Probably you aren't following my instructions OR I goofed somewhere.

Chemistry
So do the steps.

Chemistry
Use it. Are you looking for a hand out? We try to help, we try not to do.

Chemistry
use it

Chemistry
630 mL = 0.630 L; right. 20 C is 20+273 = 293K; right. 0.75atm x 0.630L = n*0.08206*293 n = 0.0196 mols. I suspect you just punched in the wrong numbers or hit the wrong button somewhere on your calculator. Also you quit when you had n. Then n = grams/molar mass 0.0196 = g/32 ...

Chemistry
Show your work and let us find the error. A common error is not using kelvin for temperature. Also remember volume must be in L

Chemistry
n = grams/molar mass Then PV = nRT R in 0.08206 L.atm/mol.K gives P in atm atm x 760 = p in torr 1 atm = 14.7 psi

Chemistry
Use mols each gas in PV = nRT and solve for p. Then Ptotal = pN2 + pO2 + pHe

Chemistry
(P1/T1) = (P2/T2)

Chemistry
P1V1 = P2V2

Chemistry
Use PV = nRT and solve for n = number of mols gas. Then n = grams/molar mass and solve for grams.

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