Saturday
October 25, 2014

Posts by DrBob222


Total # Posts: 44,714

chemistry
e = molar absorptivity A = ebc and I assume b (length cell) is 1 cm), then 0.427 = 12,100*C Solve for C in mols/L (and I'll call that C) in the diluted solution. In the initial 25.25 mL sample, molarity is C x 100
September 22, 2014

Chem
Look up 1/2 (in years) and solve for k. k = 0.693/t1/2 Substitute k into the below equation. ln(No/N) = kt No = 100.0g N = ? k from above t = 450 years
September 21, 2014

Chemistry
2 hours, 4 minutes, 55 sec 4 min + 55 sec = 240 s + 55 sec = 295 s # hr in 295 s is 295s/60*60 = 0.0819 Total time is 2 + 0.0819 = 2.0819 hrs. 385 yards = ? miles 385 yards x (1 mile/1760 yards) = 0.2187 miles So time is 2.0819 hrs. distance is 26.2187 miles. speed in miles/hr...
September 21, 2014

Chemistry
The old molarity formula. density x mL x %/100 = grams. The density of the solution is d = mass/volume = 76.7/75.0 = whatever, then (76.7/75.0) x ? mL x 0.0396 = 730,000 Solve for ?mL and convert to L.
September 21, 2014

Chem
Do you have any particular reactants in mind?
September 21, 2014

CHM
I answered this below.
September 21, 2014

chemistry
It does if the compound is soluble in water. In fact if it is soluble enough you won't get anything back.
September 21, 2014

Chemistry
66.6 yards x (3 feet/yd) x (12 in/foot) x (2.54 cm/in) = length in cm 12 inches wide x (2.54 cm/inch) = width in cm mass = volume x density or volume = mass/density = 830g/look up density solve for volume in cc. Then volume = length x width x thickness You know v, l, w, and ...
September 21, 2014

Chemistry
pi = iMRT pi = 3*0.150*0.08205*310 = ?
September 21, 2014

Chemistry
p = KcC Kc = p/C = 1/2.21E-3 = ? Then revisit p = KcC You want p, you know Kc and convert 4 mg/L to C in mols/L and solve for p
September 21, 2014

chemistry
Please re-read your post and note you can't work the problem without numbers.
September 21, 2014

Chemistry
multiply 1 by 2 and add to the reverse of 2. That will give you 2Cu + O2 ==> 2CuO which is just twice what you want so divide by 2 for the equation and divide the dH by 2. Remember to multiply dH by 2 when multiplying the equation and remember to reverse the sign of dH when...
September 21, 2014

Chemistry Lab MgO
Let me explain and you do the rest. Burning Mg in air leads both to MgO and Mg3N2.You want the MgO; you don't want the Mg3N2. The amount of MgO is reduced; the amount of oxygen in the MgO is reduced.
September 21, 2014

Chemistry
No, I wouldn't do that because there is enough information to actually calculate the delta H reaction. I ran through the calculation and came up with -940 kJ also so I would pick the closest answer which is -1000 kJ
September 21, 2014

Chemistry
dHrxn = (n*dHf products) - (n*dHf reactants)
September 21, 2014

Chemistry
CaO + H2O --> Ca(OH)2 and this reaction is exothermic and it is a basic solution so the universal indicator would show that.
September 21, 2014

chemistry of solutions
2NaI(aq) + Hg2(C2H3O2)2(aq) ==> Hg2I2(s) + 2NaC2H3O2(aq)
September 21, 2014

chemistry
I'm at a slight disadvantage since I haven't seen part A but I think all you need to do is convert grams to moles, then use dGrxn= (n*dGf products) - (n*dGf reactants)
September 21, 2014

chemistry
and the mass is what?
September 21, 2014

chemistry
The half reaction for KMnO4 is MnO4^- + 8H^+ + 5e ==> Mn^2+ + 4H2O I have no idea what (COMM)2 is
September 21, 2014

CHM Lab
mols CaCO3 = grams/molar mass mols EDTA = mols CaCO3 (it's always 1:1) Then M EDTA = mols EDTA/L EDTA Solve for L EDTA and convert to mL if desired.
September 21, 2014

Chemistry (Ionic Equilibria)
We use the terms weak and strong sometimes inappropriately. You're right. Weak acids are those that don't ionize 100%. Strong acids are those that ionize 100% I think in the context of your question that a strong weak acid means a concentration solution of a weak acid...
September 21, 2014

Chem
Close but I don't know where you came up with 11 difference. The specific heat Al is about 0.9 J/g*C. You can put all of it into one equation as follows: [(mass H2O x sph.H2O x (Tf-Ti)] + [(mass Al x sph.Al x (Tf-Ti)] = 0 [50*4.184*(23.00-21.00)] + [28.4*x*(23-39.4)] = 0 ...
September 21, 2014

chemistry
You do it the same way as C atoms in your other post.
September 20, 2014

chemistry
mols C8H10N4O2 = 0.00025/molar mass = ? There are 6.02E23 molecules in 1 mol of that material. There are 8 C atoms per molecule of that material.
September 20, 2014

Chemistry
I've looked at this problem and something seems not quite right about it. Would you please look over the numbers and make sure they are ok.
September 20, 2014

Science(Magnets)
I want to know how you get two south poles to touch.
September 20, 2014

Chemistry
All of the numbers run together with no spaces so it's hard to know what you've done. However, equation 1 is a reaction that FORMS I2. To know how much is formed you titrate it with standard S2O3^2-. Yes, mols S2O3^2- = M x L and mols I2 which came from equation 1 will...
September 20, 2014

chemistry
You will need to look up the specific heat of H2O and the specific heat of ethanol. heat lost by H2O + heat gained by ethanol = 0 First, use density to convert volumes to grams of each. mass = volume x density [mass H2O x specific heat H2O x (Tfinal-Tinitial)] + [mass ethanol ...
September 19, 2014

chem
See your last post.
September 19, 2014

chem
k = 0.693/t1/2 Solve for k and substitute in the equation below. ln(No/N) = kt No = 2.00 N = unknown k from above t = 1000 years.
September 19, 2014

chem
1 Bq = 1dps; i.e., 1 decay per second or 1 disintegration per second
September 19, 2014

to M - - -chemistry
Let me show you in steps how to do this. It's too simple to let it get to you. C4H8(g) + O2(g)⟶ CO2(g) + H2O(g) Look at C4H8 so YOU KNOW CO2 must be at least 4 so place a 4 there. C4H8(g) + O2(g)⟶ 4CO2(g) + H2O(g) Look at the H so YOU KNOW H2O on the right ...
September 19, 2014

chem
k = 0.693/t1/2 Then substitute k into the below. ln(No/N) = kt No = 10g N = 1.25 k from above Solve for k in days.
September 19, 2014

chemistry
Most solids dissolve faster in hot water than in cold water because of the increased kinetic energy of the solvent.
September 19, 2014

Chemistry
See your other post below.
September 19, 2014

Chemistry
If I read the problem right the third part titrates the formate ion from part 1. Write the equation for formate + KMnO4 in basic solution. 2. You know how many mols formate from part 1. Convert that to mols MnO4^- in part 3. 3. Convert mols in part 3 for the dilution. 4. Then ...
September 19, 2014

Chemistry
Without calculation my gut feeling is that 148 tables is WAY too many. You must be getting a kick back from the antacid company. How much acid do you have to neutralize? That's pH = -log(H^+) = 1.1 = -log(H^+) and (H^+) = 0.0794 millimols acid in stomach is 140 mL x 0.0794...
September 19, 2014

chemsitry
bdef
September 19, 2014

CHM
Because you intend to standardize it with a known.
September 19, 2014

Analytical CHM Lab
I assume the buret correction comes from calibration of your buret vs the reading on the buret. mols KHP = grams/molar mass KHP = ? mols mols NaOH = mols KHP since the reaction between KHP and NaOH is 1:1. Then M NaOH = mols NaOH/L NaOH and L NaOH is the buret reading volume ...
September 19, 2014

chemistry
You might want to talk a bit about solubility in general, that most salts (not all) are more soluble in hot water than in cold water, that size of the particles and stirring affects the speed with which dissolution takes place, something about which salts are more soluble and ...
September 19, 2014

chemistry
4*H = 4*1.007 amu = 4.028 ? amu 1*He = 1*4.002 amu Mass that's converted into energy is 4.028-4.002 = ? Then convert amu to kg and use E = mc^2 to solve for E in joules. Convert to MeV.
September 19, 2014

chemistry
%by mass = (mass solute/mass solution)*100 = ? mass solution = 1000gH2O + 59g glucose + 2.3g NaCl. % glucose = (59/1061.3)*100 = ? % NaCl = (2.3/1061.3)*100 = ? % H2O = (1000/1061.2)*100 = ? % sucrose = 0% If your prof is picky about the number of significant figures be sure ...
September 19, 2014

chemistry
mass = volume x density mass = ? density = 2.70 g/cc volume = 24.7-19.2 = ?mL = which is same as ?cc.
September 19, 2014

chemistry
mass = volume x density or volume = mass/density mass = 85.1g density = 0.79 g/cc solve for volume b. mass = volume x density density from above volume = 125 mL = 125 cc solve for mass
September 19, 2014

chemistry
1 gallon = 3.785 L; therefore, 40 gallons = about approx 151 L - approx 151,000 mL Use density to convert to grams; mass = volume x density = approx 1.06E5 grams. mols C8H18 = grams/molar mass = approx 900 2C8H18 + 25O2 ==> 16CO2 + 18H2O Convert mols octane to mols CO2; ...
September 18, 2014

chemistry
I will assume you are using concentrated HNO3. With concd HNO3 the reduction product is NO2; with dilute HNO3 the reduced product is NO. Cu + 4HNO3 ==> Cu(NO3)2 + 2H2O + 2NO2 mols Cu = grams/molar mass = approx 0.0063 but you need to do it and the calculations that follow ...
September 18, 2014

Physical Science
I see this problem this way. Perhaps another tutor will look at it too. dE = q+w -103 = q + w If the evaporator coils lose 54 kcal that is -54 from the coils(exothermic at the coils) which makes it + 54 kcal to the heat pump. Then -103 = 54 + w w = ?
September 18, 2014

CHEMISTRY
Put the problem into apples (or oranges) and see if that doesn't help. The mass of an apple is 100 grams. Using the unit factor method, calculate how many apples you have if they weigh 500 grams? (100 g/apple) x # apples = 500 g Solve for # apples = 500/100 = 5 PROOF: 100g...
September 18, 2014

chemistry
http://en.wikipedia.org/wiki/Phthalic_acid
September 18, 2014

chemistry
Mo2O3 has mass 15.27g % Mo in Mo2O3 = (2*95.94/239.88)*100 = about 80% but you should do that more accurately. Out of a 15.27g sample, 15.27 x 80% = about 12.2 g Mo and the rest is oxygen. If you started with 12.2 g Mo there must be 12.2 g in the new oxide which means oxygen ...
September 18, 2014

Chemistry
mols NaOH = M x L = ? mol HCl = mols NaOH (look at the coefficients in the balanced equation) Then M HCl = mols HCl/L HCl.
September 18, 2014

general chemistry I
5 drops H2O x (0.05 mL/drop) = 0.25 mL Then (0.25/1.00)*100 = 25% error. The others are done the same way. The purpose of this problem is to demonstrate that an absolute error (in this case one of 0.25 mL) is a larger percentage of the small pipet than of a larger pipet. For ...
September 18, 2014

Chemistry
1.763E-24 g/e x #e = 5.6g
September 18, 2014

science, chemistry
Not the correct spelling of celsius. Use PV = nRT and solve for n. V = pi*r^2 and convert to L.
September 18, 2014

chemistry
This is a limiting reagent(LR) problem. N2 + 3H2 ==> 2NH3 mols N2 = grams/molar mass = 8/28 = approx 0.29 but you need to do all of these calculations yourself and do them more accurately than my estimates. mols H2 = 10/2 = 5 Convert mols N2 to mols H2. That's 0.29 mols...
September 18, 2014

Chemistry
If it isn't too concentrated, rub it between your fingers. Bases have a "slick" feeling. Too concentrated and it may burn your fingers.
September 18, 2014

Chem---DrBob222
For C=C there are four electrons between each C atom. But don't count the bonds or electrons as a way of calculating the oxidation state. Counting the electrons is a way to calculate the formal charge on the atom but that isn't the same thing as oxidation state.
September 18, 2014

Chem---DrBob222
If you go with what I did the oxidation number for each C is 3 1/3 just as I posted. This whole process is just a matter of book keeping. H can have +1 or -1 and we stay out of trouble if we assign +1 in most cases unless we know the compound is a hydride such as NaH or CaH2. ...
September 18, 2014

Chem
You must know how to do parts of this or have some ideas about how to proceed. Let's hear your thoughts and a rationale for why you have those thoughts.
September 17, 2014

oops- - Chem
Steve made two typo but othrwise the problem is ok. Just follow the steps but not the numbers. That should be 28.3g/(2.5) = ?
September 17, 2014

chemistry
The solubility is 0.029g/10 mL or 0.0029g/1 mL so there will be 73.53 times that in 73.53 mL. right?
September 17, 2014

Chemistry
1. If this is a beginning chemistry question the answer is that KCl doesn't do anything to the pH. In advanced courses you will learn that the activity coefficient has an effect and the pH will decrease slightly. 2. Since KOH ionizes 100% it will produce OH^- and that will...
September 17, 2014

AP Chemistry
You want how many mols? That's M x L = mols. Then mols = grams/molar mass. You know molar mass and mols, solve for grams. Dissolve that many g CuSO4.5H2O in some water and make to exactly 300 mL with distilled water.
September 17, 2014

physical science
80 miles x (1 km/0.6214 mi) = ?
September 17, 2014

Physical Science
No but mostly because volume is not measured in grams but in cc or cm^3. volume = mass/density = 3800 g/10 g/cc = 380 cc
September 17, 2014

chemistry
1a. Actually, I don't think it advisable to prepare a slightly more concd solution of KMnO4. I know why this as been broached and that's probably because KMnO4 is not pure straight out of the bottle and because it is reduced to MnO2 when prepared; however, my ...
September 17, 2014

Chem
This programing recognizes one space and ignores after that. I would assign H as +1 each for a total of +7 for H. I would assign N a +3 for a total of +3 for N That leaves -10 for C (to make zero for the compound which it must be) which makes EACH H -3 1/3.
September 17, 2014

CHEMISTRY
The answer in the data base/text/whatever must be wrong. I get 1.93965 which I would round to 1.94 to 3 s.f.
September 17, 2014

CHEM
If CP is cyclopentadienyl you should know that we can't draw structures on this forum. If it's a compound between carbon and phosphorus I know little about it but it appears that can't be the right formula.
September 17, 2014

Physical Science
q = mass spoon x specific heat spoon x (Tfinal-Tinitial)
September 17, 2014

chemistry
I worked a similar problem (just different numbers) yesterday. Look at the chemistry posts to find it. I must leave now and can't do this but I'll be back this afternoon.
September 17, 2014

chemistry
3g CaCl2/0.5 L = 6/L = 0.6g/dL dilute 10 mL to 1000 mL; new concn is 0.6g/dL x (10/1000) = 6E-3g/dL mols = 6E-3/111 = approx 5.41E-5 mols in 6E-3g CaCl2. Then 5.41E-5 mol/dL = 5.41E-4 mol/L - 5.41M. I've estimated here and there; you should go through the math yourself ...
September 17, 2014

REACTION KINECTICS
At 600. Take 100 mols as an arbitrary number. .......CH3CH3CH3 ==> CH3CH=CH2 + H2 I.......100............0..........0 C........-x............x..........x E......100-x...........x..........x Ka = 0.104 = (x)(x)/(100-x) Solve for x for mols = x, then (x/100) = fraction ...
September 17, 2014

Physical Science
Calculate the new pressure with P1V1 = P2V2 The pressure had to decrease if the volume increased. See Boyle's Law
September 16, 2014

chem
Is that 3.00 cmcm a typo and you meant to write 3.00 cm on an edge. mass = volume x density volume = (3.00)^3 = 27 cc density = 8.90 g/cc Substitute and solve for mass in grams.
September 16, 2014

chemistry
CaCO3 + 2HCl ==> CaCl2 + H2O + CO2 You list no data; therefore, no calculations are possible showing loss CO2 or anything else. Please be advised, also, that we can't draw/sketch graphs on this forum.
September 16, 2014

Scientific Method
I would design and implement an experiment before collecting data.
September 16, 2014

Chem-Extraction Lab
Caffeine is too soluble in dichloromethane. You could do a mixed melting point with pure caffeine and the product you think is caffeine.
September 16, 2014

Bio Chem
pH = pKa + log (base)/(acid) pH = 4.87 pKa = 4.87 Therefore, 4.87 = 4.87 + log (base)/(acid) and (base)/(acid) = 1 which means (base) = (acid) If you lower the (H3O^+), that raises the pH so let's substitute a higher number for pH, say 5.87 and see what happens. 5.87 = 4....
September 16, 2014

Organic chem Extraction of caffeine from tea
You may be thinking of suspension or emulsion.
September 16, 2014

Chemistry
The molar mass (molecular weight/molecular mass) is Pb = 207.2 I = 126.9 PbI2 is (207.2 + 2*126.9) = ?
September 16, 2014

chemistry
1 meter = 6.21E-4 miles. 0.11 m/s x (6.21E-4 mi/meter) = ? mi/second 0.11 m/s x (6.21E-4 mi/m) x ? seconds = 5 hrs x (60 min/hr) x (60 s/min)
September 16, 2014

Science! Help!
I agree
September 16, 2014

science
You didn't give the density of water but I suppose we can assume it is 1.0 g/mL. I would NEVER taste it even though some one told me it was alcohol or water. :-). I would carefully smell it. OK so you want to utilize the densities. Place an ice cube in the liquid. If the ...
September 16, 2014

Science
Less mass makes it easy to get off the ground with an airplane. Which plane will weigh less, one made of Al or one made of Cu?
September 16, 2014

Science
I would expect the less dense Cu metal to float on the more dense liquid Hg, at least until the Cu was dissolved. (Many metals (including Cu) will form an amalgam with Hg.)
September 16, 2014

Chemistry
You made a typo in the equation; it should be Pb(NO3)2 + 2NaI ==> PbI2 + 2NaNO3 (should be NO3 and not NO2 with NaNO3. Also, note that you don't put quantities in the equation line. This is a limiting reagent (LR) problem. You know that because amounts are given for ...
September 16, 2014

Science
I agree
September 16, 2014

Chemistry
Area swimming pool is pi*r^2 and that x h is the area of a cylinder. That gives you cubic feet. Let's call that 1000 cubic feet. 1 gallon = 0.134 cubic feet. 7.58 gallons/min x (0.134 ft^3/gallon) = about 0.8 ft^3/min 0.8 ft^3/min x ?min = 1000 ft^3 Solve for min
September 16, 2014

Chemistry
28 strides x (41 in/stride) x (1 m/39.37 in) x (1 km/1000m) = approx 0.03 km in 10 seconds. 0.03 km/10 sec x ?sec = 5 km Solve for seconds ?sec x (1 min/60 sec) = ?min
September 16, 2014

Chemistry Urgent Help Please!
Extraction Sublimation if it's the right kind of sample.
September 16, 2014

chemistry
(Independent variable) causes a change in (Dependent Variable) and it isn't possible that (Dependent Variable) could cause a change in (Independent Variable). I think your are right.
September 16, 2014

OChem
You can make the problem easier by choosing to dissolve 29.1 g acetanilide in 100 mL solvent at 60 C. Then you cool it to O c and it will dissolve 3.53g. How much do you recover? That's 29.1-3.53 = ? grams recovered. What percent is that? That's (?g/29.1)*100 = ?%
September 16, 2014

chemistry
I assume this is 14.5% by mass (w/w), That means 14.5 g/100 g solution. So 14.5g CaCl2 dissolved in (100-14.5)g H2o = what you want.
September 16, 2014

chemistry
mols CO2 needed = grams/molar mass = approx 7.9 but I've estimated. You need to do it more accurately as well as all of the numbers that follow. Using the coefficients in the balanced equation, convert mols CO2 to mols C3H8. That's 7.9 mols CO2 x (1 mol C3H8/3 mols CO2...
September 16, 2014

chemistry
I don't understand the question.
September 16, 2014

chemistry
Here is how you do a and b. a. HNO3 is a strong acid; i.e., it ionizes 100%. Therefore, HNO3 ==> H^+ + NO3^- amd H^+ = 0.01 Then pH = -log(H^+) = -log(0.01) = -(-2) = 2 b. Ba(OH)2 is a strong base and ionizes 100% as in Ba(OH)2 ==> Ba^2+ + 2OH^- In a above you had only 1...
September 16, 2014

chem
I would convert 2.19E-9 to mols and call that No. Then N = initial mols - 1.07E15, and put that into ln(No/N) = kt. You know No, N, and t. Solve for k.
September 16, 2014

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