Thursday
October 30, 2014

Posts by DrBob222


Total # Posts: 44,869

Chem---DrBob222
One example of #1 is amino acids. They are colorless so you don't see the spots until sprayed with a solution of ninhydrin. Tht turns them a visible color. A second example is any compound that fluoresces in uv light. Shining the light makes them visible. A third example ...
September 23, 2014

chemistry
You certainly did; however, I showed you how to work the problem. All you need to do now is to convert miles to cm and feet to cm, calculate the volume of the "cylinder" (pi*r^2*depth) in cc, convert that to mL and plug in mL in the formula I gave you. Here is the ...
September 23, 2014

Science
http://lgfl.skoool.co.uk/content/keystage3/Physics/pc/learningsteps/DTGLC/launch.html
September 23, 2014

chemistry
What is the total mL of the lake? 215 ng/mL x ?mL = ? ng Hg which is ? x 10^-12 kg
September 23, 2014

chemistry
I agree with Sarah. And note that a kg/dm^3 is a kg/L = g/mL
September 23, 2014

Chemistry 15
See if this helps, https://www.google.com/search?q=open+ended+manometer&client=firefox-a&hs=9SJ&rls=org.mozilla:en-US:official&channel=sb&tbm=isch&imgil=w34sEIDaVOM6VM%253A%253BLgFOgH86wkfc_M%253Bhttp%25253A%25252F%25252Fwps.prenhall.com%25252Fwps%25252Fmedia%25252Fobjects%...
September 23, 2014

Organic Chem Help
There is more than one factor. First you hope that the impurities are more soluble than the major product so some of the impurity is lost in the dissolution step. Second, even if the solubility difference is not that great you lose some of the impurity at the same time ...
September 23, 2014

Chemistry
mass in grams = mL milk mass in grams = mL coffee heat lost by coffee + heat gained by milk = 0 [mass coffee x specific heat coffee x (Tfinal-Tinitial)] + [mass milk x specific heat milk x (Tfinal-Tinitial)] = 0 Substitute the numbers and solve for mass milk in grams which = ...
September 23, 2014

Chemistry, HELP!!
a. density = mass vapor in grams/volume in mL b. I would use the modified ideal gas formula of PM = dRT where P is pressure in atm, M is molar mass, d is density in g/L (note, not g/mL), R is 0.08205 and T is 298K.
September 23, 2014

Chemistry, empirical formula
Both are solved the same way. I'll do the first one. Take a 100 g sample which gives you 47.7 g Cr 52.3 g F Convert to mols. mol = g/atomic mass mols Cr = 47.7/52 = about 0.92 mols F = 52.3/19 = about 2.75 Now find the ratio of one element to the other with the smallest ...
September 23, 2014

chemistry
heat capacity of the calorimeter is 1.40 J/g*C x 5 g = 7.00 J/C heat lost by metal + heat gained by calorimeter + heat gained by water = 0 [mass metal x specific heat metal x (Tfinal-Tinitial)] + [7.00 x (Tfinal-Tinitial)] + [mass liquid x specific heat liquid x (Tfinal-...
September 23, 2014

chemistry
Isn't c given in the problem for the calorimeter as 1.40 J/g*C?
September 23, 2014

science Help
I agree with c.
September 23, 2014

science Help
I agree with c.
September 23, 2014

Science! Help
I don't agree with A.
September 23, 2014

Science! Help
I agree
September 23, 2014

To Dfca---Science
I answered this for you below and gave you enough examples for you to pick and choose. Look for that response. If you can't find it post here and I'll find it for you.
September 23, 2014

chemistry
Pb(NO3)2 + Na2SO4 ==> PbSO4(s) + 2NaNO3
September 23, 2014

Chemistry
1.673E-24 g/atom x # atoms = 5.6g Solve for # atoms.
September 23, 2014

chemistry
mass NaCl = 25.0g-mass NH4Cl - mass SiO2. % NaCl = (mass NaCl/mass sample)*100 = ?
September 23, 2014

Chemistry
See your post above.
September 23, 2014

Science
I don't agree with D. d = m/v. Making the boat wider increased the volume.
September 23, 2014

Science
density = mass/volume. d usually is expressed as g/cc or kg/L. Substitute and solve for d.
September 23, 2014

chem
mols NaOH = M x L = estimated 0.0018 Therefore, mols KHP = estimated 0.0018 g KHP = mols KHP x molar mass KHP = ? % KHP = (mass KHP.mass sampe)*100 = ?
September 23, 2014

chem
mols NaOH used = M x L = estimated 0.0028 but you need a more accurate answer. Convert mols NaOH to mols acetic acid and that is 1:1; therefore, mols acetic acid (vinegar) = estimated 0.0028. g acetic acid = mols x molar mass = approx 0.0028 x about 60 = about 0.17g. So you ...
September 23, 2014

science
mols HNO3 = grams/molar mass Then m = mols/kg solvent.
September 23, 2014

Chemistry
q = mass H2O x specific heat H2O x (Tfinal-Tinitial) q = 100g x 4.184 J/g*C x (80C-60C) q = ?
September 23, 2014

Analytical Chemistry (Titrations)
There are several units for concentration. One is molarity, but there is also molality, normality, % by mass, % by volume, % by weight/volume and others. Usually titrations are done and the concn is reported in molarity which is mols/L solution.
September 23, 2014

Analytical Chemistry (Titrations)
2HCl + Na2CO3 ==> 2NaCl + H2O + CO2 mols Na2CO3 = grams/molar mass = estimated 0.0029 mols HCl = mols Na2CO3 x (2 mol HCl/1 mol Na2CO3) = approx 0.0029 x 2/1 = approx 0.0058 mols HCl M HCl = mols HCl/L HCl. You know mols HCl and L HCl (0.03509 from the problem), solve for M...
September 23, 2014

Science
Explain why double pane windows are more efficient than single pane windows at keeping heat outside and cool inside or the reverse. Explain how refrigeration works (and how air conditioning works). Heat pumps. Explain how smog forms. Explain how gasoline powered engines work, ...
September 23, 2014

Science--Help.
If you will repost and mark your answers with *** I shall be happy to check them. #1 is carbon.
September 23, 2014

science
mols of what inside the bubble? PV = nRT P = 1 atm V = (4/3)*pi*r^2 n = ? R = 0.08205 T = 25 + 273 = ?
September 23, 2014

Chemistry
There are 6.022E23 C atoms in a mole of C and there is just 1 C atom in Na2CO3 molecule. You have 1.773E17 C atoms which must mean 1.773E17 Na2CO3 molecules so that is 1.77E17/6.022E23 = estimated 3E-7 mols. Convert that to grams; g = mols x molar mass = ?
September 22, 2014

Chemistry
What's the size of the protons? You can look up the diameter and the area of a sphere (if you assume they are spheres) is (4/3)*pi*4^3. Do you want the Hg in cubic inches or cubic centimeters. If cc, then 8.5 in x (2.54 cm/in) = ? cm Area of Hg is pi*r^2 thickness is 0.25 ...
September 22, 2014

Chemistry
10 lbs x (453.6 g/lb) = ? g sugar How many mols sugar is that. ?g sugar/molar mass sugar = mols sugar. In ONE (1) mols sugar there are 6.022E23 molecules. There are 6 atoms C in ONE (1) molecule sugar.
September 22, 2014

Chemistry
mass = 3.4 mg = 0.0034 grams. volume Au = mass/density. You will need to look up the density of Au. Then volume = length x width x thickness. You are given the thickness, you've calculated the volume, left is length and width but since that is a square, you solve for that...
September 22, 2014

Science
tsk! tsk! an answer moocher
September 22, 2014

chemistry
225 g Fe = how many mols? That's 225/atomic mass Fe = estimated 4.0 So you want about 4.0 mols Cu atoms and that will be estimated 4.0 x atomic mass Cu = ?
September 22, 2014

Analytical Chem
Thanks. You scare me away when I see that much work ahead. Here is a table I have in my quant text. I don't know if you're allowed to use that or not but I'll follow up with the Debye-Huckel equation (which you probably have in your text, too). 4-4.5 Angstrom for ...
September 22, 2014

Analytical Chem
This is a huge undertaking. Can you tell us what your problem is. Surely you know how to do parts of this.
September 22, 2014

Chemistry
IF AT EQUILIBRIUM THE [NO2] = 0.400 M [O2] = 0.875 M AND THE KEQ OF THE EQUILIBRIUM IS .65 I wouldn't do that. You don't add in anything. Just plug the numbers into the Keq expression and solve for (NO). 2 NO (G) + O2 (G) > 2 NO2 (G) Keq = (NO2)^2/(NO)^2(O2) 0.65...
September 22, 2014

Chemistry
Can you explain in detail what you don't understand. I'm have difficult knowing what your trouble is if you've done all that research and reading. For example, the expression for Keq is straight forward.
September 22, 2014

chemistry
This is a straight forward stoichiometry problem. 2NaHCO3 ==> Na2CO3 + CO2 + H2O mols NaHCO3 = grams/molar mass = approx (estimated) 0.03 Convert to mols Na2CO3. The ratio in the equation is 2:1; therefore, mols Na2CO3 formed is estimated 0.015 grams Na2CO3 formed is g = ...
September 22, 2014

Chemistry
volume of metal = pi*r^2*h pi you know. r = 3.8/2 = ? cm h = 5.4 cm v = ? cc. What ever the volume of the cylinder it will displace that much of the water so final volume of water in graduated cylinder = 56.3 + volume metal.(all of this assumes the cylinder of metal is SOLID ...
September 22, 2014

pha
Let x = grams 2% and 120-x = grams 21% --------------- 2x + (120-x)*21 = 120*7 Solve for x and 120-x
September 22, 2014

Chemistry
You need help with 5. mols Cu you have from 4 (0.38/63.5) = ? Cu(NO3)2 + 2NaOH ==> 2NaNO3 + Cu(OH)2 You know mols Cu and that's the same as mols Cu(NO3)2. mols NaOH = twice that Theh L NaOH = mols NaOH/M NaOH and solve for L
September 22, 2014

Science(Energy)
C is the opposite of what you want. The solar panel takes EM energy and makes electricity just as the statement says. I think B is what you're looking for. You are taking the EM energy from the sun, it goes through the glass of the car and is absorbed. The interior of the ...
September 22, 2014

CHEMESTRY
http://en.wikipedia.org/wiki/Atom
September 22, 2014

chemistry
36.5% is a saturated solution of the gas in water. No more of the gas will dissolve in the water at room temperature.
September 22, 2014

CHEMISTRY
4 C3H5(NO3)3(s) --> 12 CO2(g) + 10 H2O(g) + 6 N2(g) + O2(g) Look up the density of nitroglycerin and calculate the volume of 1 mole. Then count the volume produced by the products. That will be 29 mols O2. Use PV = nRT to convert 29 mols at 450K to volume in L. Then delta V...
September 22, 2014

Chemistry
FIRST, one NEVER washes away spilled HCl with NaOH. Pellets of NaOH will cause more skin burns than 10% HCl every will. To neutralize acid spills use sodium hydrogen carbonate (baking soda) NaHCO3. Na2CO3 can be used also. But to the problem. NaOH + HCl --> NaCl + H2O 10% ...
September 22, 2014

Chem
I agree with the 9.2% w/v as well as the number of mols NaCl. I assume this is a beginning chemistry course and I also assume that the author of the problem just "made a mental error" in writing the problem and PROBABLY meant to ask how many ions were dissolved which...
September 22, 2014

Chem
I think that will give you the number of "molecules" of NaCl. I would think twice that would be the number of atoms dissolved if we call the ions in solution atoms. Technically there were no "atoms" dissolved, only ions.
September 22, 2014

CHEMISTRY
I'm still not sure of the question so I'll restate it as I think you are asking. Why is the phase change from vapor to liquid exothermic? My response and I'll use water as an example: H2O(liquid) + heat ==> H2O(gas) which clearly is an endothermic reaction. BUT ...
September 22, 2014

CHEMISTRY
What does "when the phase is down" mean?
September 22, 2014

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

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