Tuesday
September 2, 2014

Posts by David


Total # Posts: 1,638

o-chem
explain how the rate of crystal growth can affect the purity of a recrystallized compound
October 7, 2008

o-chem
well im confused because you said one needs to be great and the other has to be poor. so if you combine both do you get a great solvent or a horrible one?
September 29, 2008

o-chem
thanks. i understand why e won't work, but im a little confused on choice a. they both dissolve a wide range of solutes so would it be a great solvent?
September 29, 2008

o-chem
Explain whether or not each of the following pairs of solvents might be useful as a solvent pair for recrystallization. (a) ethanol-methanol (b) hexane-cyclohexane (c) acetone-ethanol (d) water-ethanol (e) water-cyclohexane
September 29, 2008

O- chemistry
During a recrystalliztion experiment, a student allows the hot solution to cool to room temperature, then chills the solution in an ice bath. Is the student using correct recrystallization technique? Why does the student not simply chill the hot solution in an ice bath initially?
September 29, 2008

AP US History
1775 to 1800
September 24, 2008

Re
i need to find eveidence of 3 things that jesus did and 3 things jesus didn`t do. thanks!
September 22, 2008

grammar
What part of speech is the word "Below" used in the following sentence. Below the main level, we have a large playroom.
September 16, 2008

education
Just to take the very first term you've listed, are you suggesting that income is a characteristic of a multicultural school? What would that mean - that a multicultural school has income? And if so, is that what you're trying to say? I don't think it is, is it? Or...
September 13, 2008

Calculus
8/h -> infinity as h -> 0, so I don't see how the above expression can tend to anything other than minus infinity.
September 12, 2008

Math
Can I throw in a note of clarification? Melissa'a answers are actually correct: what's INcorrect is the algebra that apparently gave rise to them. As Bob pointed out, the "16 divided by 6" is actually a measure of inches per car, not cars per inch. Also, the ...
September 10, 2008

algebra ll
im having trouble with this problem 6( n - 4 ) = 3n
August 26, 2008

Math
No, I'm sure the problem is written like this: [(3a^3-27a)/(2a^2+13a-7)]/[9a^2/4a^2-1)] And to divide you multiply by the reciprocal. So i still don't get the problem I also know to factor, but I'm stil confused.
August 7, 2008

Math
No, I'm sure the problem is written like this: [(3a^3-27a)/(2a^2+13a-7)]/[9a^2/4a^2-1)] And to divide you multiply by the reciprocal. So i still don't get the problem I also know to factor, but I'm stil confused.
August 7, 2008

Math
I'm totally stuck on this problem!! Simplify: (2a^2+13a-7/3a^3-27a)(4a^2-1/9a^2)
August 7, 2008

Algebra II/Trig
No, Problem! Thank you so much for the answer!
August 7, 2008

Algebra II/Trig
Simplify: (n/4)/(n/m) As my answer I got: 4m Is this response correct? If not, please let me know what I did wrong.
August 7, 2008

Math check
No, you distributed the 4 to the y only. You also need to distribute the 4 to the 8. This would then make the answer 4y+32
August 7, 2008

Math
Simplify: 24w^7t^4/6w^9t^2 And How Exactly do u do this? I got 4w^16t^6
August 5, 2008

Algebra II/Trigonometry
Thank you so much drwls! I can not believe I did not figure that out!
July 27, 2008

Algebra II/Trigonometry
Simplify this problem: (1/2m^4n^5)^2
July 27, 2008

English
No. I think you should work the subject back in, in place of "it" and remove the "s" tacked on to the end of accomplishment
July 27, 2008

math
Can someone show me all the combinations possible with these things A B X Y LB RB LT RT L R U D
July 26, 2008

math
img59.imageshack.us/img59/4912/dsc00716qy7.jpg
July 4, 2008

Physics
A passenger on a train traveling 90km/h on a straight, level track notes that it takes another train (180 m long and moving with constant velocity) 4.0s to pass by. What is the velocity of that passing train relative to the ground? **please include explanation** thnx!!
July 1, 2008

Chemistry
Nope, Kristen is right. It can also be written as 4-methylpent-2-yne but it's the same thing.
June 5, 2008

MAT 116 Algebra 1A
V = 1/5 ð t^2 s
May 26, 2008

Physics **PLEASE HELP**
plz ignore the 1st part just plz help with this: what's the relation between resistance and voltage?
May 22, 2008

Physics **PLEASE HELP**
During a short circuit, why does the voltage go down? I know that the resistance is almost zero...but what's the relation between resistance and voltage?
May 22, 2008

Geometry
They are similar. because ALL triangles have and will always have 180 degrees. BOTH of the right triangles have an 90 degrees angle, which leaves 90 degrees left in both triangles than they have an another angle which is less than 90 (x degree) just by knowing this, you can ...
May 2, 2008

Chemistry
For the following electrochemical cell: Fe(s) | Fe2+(aq) || MnO4–(aq), Mn2+(aq) | Pt(s) Which letter corresponds to the correct balanced chemical equation in an acidic solution? A. 2Mn2+(aq) + 8H2O(l) + 5Fe2+(aq)-> 5Fe(s) + 16H+(aq) + 2MnO4–(aq) B. Fe(s)+8H+(aq)+...
April 21, 2008

Chemistry
For the following balanced equation: 2Ag+(aq) + Cu(s)<->Cu2+ (aq) + 2 Ag(s) Which letter corresponds to the correct cell notation at standard state conditions? A. Cu(s) | Cu2+(aq) || Ag+(aq) | Ag(s) B. Ag+(aq) | Cu2+(aq) || Cu(s) | Ag(s) C. 2Ag+(aq) | Cu2+(aq) || 2Ag(s...
April 21, 2008

chemistry
The first step of the synthesis is described by the reaction below. When 1.200 g of Fe(NH4)2(SO4)2 6H2O is mixed with 13 mL of 1.0 M H2C2O4 , the theoretical yield of FeC2O42H2O is grams. Fe(NH4)2(SO4)26H2O(s) + H2C2O4(aq)-> FeC2O42H2O(s) + (NH4)2SO4(aq) + H2SO4(aq) + 4 ...
April 20, 2008

math
Astro Knots
April 17, 2008

chem
H2 + H2O ->??
April 15, 2008

chemistry
Because solution pH is a measurement of either [H3O+] or [-OH] concentration, the acidic or basic nature of the acids and bases used in this experiment can be ascertained by inspecting just the density (electrostatic) potentials from the products (which contain either H3O+ or...
April 14, 2008

Chemistry
What does the density potential (also known as the electrostatic potential) measure? What do the colors on the images indicate?
April 14, 2008

chemistry
calculate the equilibrium constant for the reactionas written at 940K. NH4Cl->NH3+HCl delta H= NH4Cl -1779, NH3 -46, HCl -92 delta s= NH4Cl - 682,NH3 192,HCl 187 i dont know how to solve for the equilibrium constant without the concentration of the values???
April 14, 2008

chemistry
The standard solution of FeSCN2+ (prepared by combining 9.00 mL of 0.200 M Fe(NO3)3 w/1.00 mL of 0.0020 M KSCN) has an absorbance of 0.520. If a trial's absorbance is measured to be 0.275 and its initial concentration of SCN– was 0.00060 M, the equilibrium ...
April 14, 2008

chemistry
thanks
April 10, 2008

chemistry
The correct interpretation of the equation below is:? Fe3+(aq) + SCN¨C(aq)¡ú FeSCN2+(aq) A. The reaction is incomplete because the product is still charged. B. A heterogeneous equilibrium exists because of the charged ions. C. The equilibrium constant is Kc...
April 10, 2008

chemistry
the concentration of OH ions in a household ammonia cleaning solution is0.0035M. Calculate the concentration of H ions. would it be pH=-log (.0035)??? or Kc=1/.0035???
April 10, 2008

chemistry
If a solution is diluted, say by adding 100ml of solvent, does the number of moles of solute change? Does the concentration increase, decrease, or stay the same? i think it depends on what the solvent is, for example if its water then the concentration would decrease?? please ...
April 10, 2008

Algebra 2
A package with square ends has a combined length and girth (girth is the perimeter of a cross section) of 120 in. The surface area of the entire package is 3600 sq. in. Determine the dimensions of thr package. s in.*s in.*l in. one solution is: 11.08in*11.08in*75.68in. find ...
April 8, 2008

chemistry
how would i do something like this? Calculate the concentration of borate ion for each titration. Use the borate ion concentration to determine Ksp at each temperature.
April 8, 2008

chemistry
thanks soo much
April 8, 2008

chemistry
1)Does the solubility of borax in water increase or decrease as temperature increases? 2)Is the solvation of borax in water an exothermic or endothermic process? please help ive tried asking my ta but i cant understand him. he explains it through this weird process.
April 8, 2008

chemistry
Which of the following is NOT true of colligative properties? Colligative properties are... A. dependent on the mass of solute present. B. responsible for lowering the vapor pressure of a solution versus the vapor pressure of the pure solvent. C. independent of the chemical ...
April 7, 2008

chemistry
thanks sooo much
April 7, 2008

chemistry
When 18 g of ethylene glycol C2H6O2 is dissolved in 150 g of pure water, the freezing point of the solution is _C . (The freezing point depression constant for water is 1.86C kg) what i tried was 18/62 to find the moles. then i got .29/.150 to solve for the molality. then i ...
April 7, 2008

chemistry
thanks. sorry i go to ucla.hahaha
April 7, 2008

chemistry
Solid borax dissolves in water according to the equation: Na2B4O7 10H2O(s) 2Na+ (aq) + B4O5(OH)42–(aq) + 8H2O(l) The sign of Ssys will be A. positive B. negative because there are A. more B. less moles of products generated. i've tried solving this problem and i think...
April 7, 2008

math riddle ALGEBRA WITH PIZZAZZ
They are made for two wrists.
April 6, 2008

Accounting Multiple choice
ACON lTD ACQUIRES THE ASSETS AND ASSUMES THE LIABILITIES OF BIRD LTD WHICH HAVE OPEN MARKET VALUES OF A Assets $120,000 Liabilities $15,000 Acorn is to issue a debenture of $50,000 and 10,000 $1 Ordinary shares for the balance of consideration. What will be the credit to the ...
April 3, 2008

math
This cube has five cubes along each edge. The faces are covered, but the cube is hollow inside. Can it be divided into two pieces of equal volume? Explain. I am not sure what this question is asking? Does this look right? l x w x h= 5x5x5=125 125/2=62.5 Both sides have 62.5, ...
April 2, 2008

chemistry
d is the correct answer
April 2, 2008

gr 7 math
This cube has five cubes along each edge. The faces are covered, but the cube is hollow inside. Can it be divided into two pieces of equal volume? Explain. I am not sure what this question is asking?
April 2, 2008

Calculus - Integrals
I made this question, just wanted to make sure it didn't drown under the tide... I've set a problem up, something like this. s^4: A+D=0 s^3: -2A+B-3D+E=0 s^2: 2A-B+C+3D-3E=0 s^1: -2A+B-D+3E=4 s^0: A+C-E=4 Count Iblis -It's easier to substitute for s the values that...
March 25, 2008

Calculus - Partial Integrals
I'm confused. As soon as I get the so called 'Basic Equation,' I just don't know what to do after....
March 25, 2008

Calculus - Partial Integrals
The paragraph after the thing with s as a variable is copy and pasted from Count Iblis.
March 25, 2008

Calculus - Partial Integrals
I made this question, just wanted to make sure it didn't drown under the tide... I've set a problem up, something like this. s^4: A+D=0 s^3: -2A+B-3D+E=0 s^2: 2A-B+C+3D-3E=0 s^1: -2A+B-D+3E=4 s^0: A+C-E=4 It's easier to substitute for s the values that make the ...
March 25, 2008

Calculus - Partial Fractions
Would anybody mind showing it out? I tried what Count Iblis said, but it didn't really work out well...
March 24, 2008

Calculus - Partial Fractions
I'm sorry. I forgot to say that I don't know how to solve for A, B, C, D, and E... Help there would be appreciated.
March 24, 2008

Calculus - Partial Fractions
I've set a problem up, something like this. s^4: A+D=0 s^3: -2A+B-3D+E=0 s^2: 2A-B+C+3D-3E=0 s^1: -2A+B-D+3E=4 s^0: A+C-E=4
March 24, 2008

Calculus - Integrals
That's my problem. When I tried solving for A, B, C, D, and E in that first problem, it didn't really work out right...
March 24, 2008

Calculus - Integrals
1) A/x + B/(1+x) 2) A/x + B/x^2 + C/(1+x) I think I'm right....
March 24, 2008

Calculus - Integrals
I'm not quite sure about your explanation on Partial Fractions... And Liouville's Therom. We haven't done that in class... so...
March 24, 2008

Calculus - Integrals
I have 3 questions, and I cannot find method that actually solves them. 1) Integral [(4s+4)/([s^2+1]*([S-1]^3))] 2) Integral [ 2*sqrt[(1+cosx)/2]] 3) Integral [ 20*(sec(x))^4 Thanks in advance.
March 24, 2008

Calculus - Integrals
Could you expand on #1 a bit more? I tried Partial Fractions, but I couldn't get a definite answer...
March 23, 2008

Calculus - Integrals
I have 3 questions, and I cannot find method that actually solves them. 1) Integral [(4s+4)/([s^2+1]*([S-1]^3))] 2) Integral [ 2*sqrt[(1+cosx)/2]] 3) Integral [ 20*(sec(x))^4 Thanks in advance.
March 23, 2008

critical thinking
premise--terrorists attacks of September 11, 2001, produced a response among American officialsm the media and public conclusion--matched only by the attack on Pearl Harbor
March 20, 2008

APA FORMATTING
I think it's C. Am I right? When using APA, which of the following describes the method in which a work without page numbers should be presented in in-text citations? A. No mention of the page number is required in APA B. If no page number is present, it is not a credible ...
March 19, 2008

English
I think it's a, but document formatting messes me up a little :) Any help would be great, and much appericated When citing a source within the body of your essay, what must be included after the quotation marks at the end of the sentence (when the author’s name has ...
March 19, 2008

Geography AS level
why are waterfalls tempary features
March 18, 2008

Oceanography
What are the steps and timing of the whales, dolphins, porpoises evolution.
March 13, 2008

Oceanography
How did the extinction of the Mesozoic marine megafauna allow evolution of cetaceans?
March 13, 2008

Business Ethics
In the case study of Geletx, what should Jed do? Is this a violation of FAPA?
March 12, 2008

Social studies
all I need to know is is it hudusim or Buddism?
March 8, 2008

Social studies
of Hindusim and Buddhism which has a definite indentifiable start?
March 8, 2008

Social studies
What is the climatic issue that significantly influences the Indian subcontinent?
March 8, 2008

social studies
What architectural wonder was completed in 1648?
February 28, 2008

engineering physics 2
A 19 m long piece of wire of density 8.34 g/m3 has a diameter of 12.593 mm. The resistiv- ity of the wire is 1.7e-8(ohm)(m) at 20 degrees celsius. The temperature coefficient for the wire is 0.0038(degrees celsius)^-1. Calculate the resistance of the wire at 20degrees Celsius...
February 28, 2008

chemistry
2Al+3Cl2=2AlCl3 calculate the amount(number) of excess reagen units remaining when 4.03x10^23 Al atoms and 6.42x10^23 Cl2 molecules react? please help!!!!! thanks
February 23, 2008

french
does any one know the french meaning of la nouvelle .
February 23, 2008

year 7 french
i need to translate countries written in french into english . does anyone know if there are any good sites that will help me. thanks
February 23, 2008

math
I tried to answer this but i don't know if i am even close. I included my work .Thanks. The island's travelling sales monkey is selling gold watches that washed up on the beach. The islanders use green stones, pink clamshells and ox horns for money.Sixty-two green ...
February 13, 2008

grade 7math
The island's travelling sales monkey is selling gold watches that washed up on the beach. The islanders use green stones, pink clamshells and ox horns for money.Sixty-two green stones have the same value as 17 ox horns and 258 pink clamshells have the same value as 89 ...
February 13, 2008

Economics
In running a regression model with three variables, two of the three come back as statistically significant at the 95% level of confidence. The one that doesn't is the intercept - so is my model still valid?
February 9, 2008

math
Thanks so much.I worked on this while i was waiting and ended up doing it backwards from you but got the same answer. 150+6=156 156/13=12 364+26=390 390/13=30 60+5=65 65/13=5 60 is the common multipler, so i got 60 days. Is this still right?
February 6, 2008

math
I really don't know where to start or what stratedgy to use.
February 6, 2008

math
Days on Planet Red are 13 hours long. The animals on Planet Red have regular eating and sleeping habits. The silver snake sleeps for 150 hours, eats for 6 hours, then goes back to sleep. The green walking fish sleeps for 364 hours, eats for 26 hours and then goes back to sleep...
February 6, 2008

Physics
Can I use P1/P2=(T1/T2)y/y-1 to find the temperature when we pressure liquid refrigerant, for example liquid propane?
February 6, 2008

Physics 11
The brakes on a car permit it to decelerate at the rate of -8.0m/s^2. How much distance is required to stop this car when it is travelling 60.0km/hr? The answer given is 173.6m I solved it this way 60km/h = 16.667m/s A=V/T 16.667m/s / -.80m/s^2 = 20.834 seconds D=RT 16.667m/s ...
February 6, 2008

History
Yea i thinks its D also... all the other answers are not as good, so im goin with that Palmer. Page 462 is what ive found Right under the purple section...
February 2, 2008

Chemistry
A 15.0g sample of liquid ethanol, C2H5OH, absorbs 5.13x10^3 J of heat at its normal boiling point, 78.0C. The molar enthalpy of vaporization of ethanol is 39.3kJ/mol. (a) What volume of ethanol vapor is produced? The voume is measured at 78.0C and 1.00atm pressure. (b) What ...
January 27, 2008

social health
I want a picture of social health
January 23, 2008

science
how does a magnet attract a paperclip ?
January 7, 2008

Chemistry
If I have 1.27 cm^3, how do I convert into picometers?
January 2, 2008

Chemistry
Metallic sodium adopts a body-centered cubic structure at 25 degrees C and 1 atm. The density of sodium under these conditions is 0.97 g/cm^3. What is the unit cell length?
January 2, 2008

math
haylee is geting a job for moing lanws her dad lowns her 190 dollars to by a lawn mower. when she startes she is in depth 190 dollars. in week two she is in depth 70 dollars. how did she get to be depth 70 dollars
December 16, 2007

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