Tuesday
October 21, 2014

Posts by lena


Total # Posts: 1,001

English
Thank you :)
September 23, 2009

English
Is it wrong to start your intro with the name of the media text. For example: "The Secret Life of Walter Mitty," byt James Thurber is a ....
September 23, 2009

physics
how does a magnify glass create a virtual image?
September 21, 2009

Chem
Why are electrons paired in orbits?
September 21, 2009

Math
(9x)^1/2 (8x)^1/3 would the 1/2 be distributed to the 9 and the x or is 9x one term and the 1/2 is given to the whole term? thanks :)
September 16, 2009

english
We must not squander our power, helplessly and ignorantly, squirting half the house in order to water a single rose-bush (1).” I was thinking that this quote means to focus on one thing at a time. Is there anything else I am missing from it. It's from Virginia Woolf; ...
September 11, 2009

English
Thanks a bunch :D
September 11, 2009

English
If you hang back and reserve and criticise at first, you are preventing yourself from getting the fullest possible value from what you read. But if you open your mind as widely as possible, then signs and hints of almost imperceptible fineness, from the twist and turn of the ...
September 11, 2009

Math:Polynomial Functions
Thank you :D
September 8, 2009

Math:Polynomial Functions
and for something like y=cosx that dosent work cause cos is not a real number?
September 8, 2009

Math:Polynomial Functions
must the value of n always be nonnegetive?
September 8, 2009

Math:Polynomial Functions
why would something like y=x^-3 not be a polynomial function?
September 8, 2009

Math:Polynomial Functions
h(x) = -7x I was thinking that this was not a polynomial function because -7x is just one term making it a monomial but the answer key says it is a polynomial function. Could someone explain why that is so? Thanks :D
September 8, 2009

Chem
thanks :)
July 29, 2009

Chem
My teacher adds the 2 half reactions. What is that called?
July 29, 2009

Chem
if I add them together they become the redox reaction?
July 29, 2009

Chem
How do you write redox reactions. I was given this equation below: 2Mg + O2 --> 2MgO I have to write the redox reaction
July 29, 2009

chem
Thanks :D
July 27, 2009

chem
un-ionized aspirn molecules can readily penetrate the stomach lining into a region of less adicity. This is where the stomach irritation associated with aspirn occurs. Use Le Chatelier's principle to explain why irritation occurs in this area. Could someone explain the ...
July 27, 2009

pH calculations
Thank you :D
July 27, 2009

pH calculations
A backyard pool as a pH of 7.4. At this level, the concentrations of hypochlorus acid and hypochlorite are approximetly equal. HClO(aq) <--> H^+ (aq) + ClO^- (aq) (a) Predict the effect of increasing pH has on the concentration of HClO(aq) in the pool. For this question...
July 27, 2009

Chem
The question is telling me that NaOH (24.00 grams) is diluted in water (750 mL). Find the pH and pOH. This is what I did so far: NaOH ---> Na+ + OH- NaOH: mass = 24.00 grams v= 750 ml = 0.750 L M= 40.00 grams/mol n= 0.6000 mol c= 0.800 mol/L Since NaOH dissociates 100%, the...
July 27, 2009

Chem
Thanks :D
July 27, 2009

Chem
Co2(g) ---> CO2(l) + heat This equation was given to me and asked why high pressure was needed to keep carbon dioxide in the liquid state. With the information given; I don't exactly know how to answer the question. How do you increase the pressure of a liquid. For ...
July 27, 2009

Chem
Dr Bob, I think I read the questions wrong. It said that un-ionized aspirn molecules can readily penetrate the stomach lining into a regio of less adicity. This is where the stomach irritation associated with aspirn occurs. Use le Chateliers principle to explain why irritation...
July 26, 2009

Chem
The question asked why the irritation occur specifically in the area of lower acidity.
July 26, 2009

Chem
Le Chatelier's principle involves equillibriums. I don't understand the equillibrium involved in thsi situation?
July 26, 2009

Chem
I have another question related to this one. The un-ionized aspirn penetrates the area of the stomach were there is less acidity thus causing irritation. How would Le Chatelier's principle explain why the irritation occurs?
July 26, 2009

Chem
Ohhh. Should have thought about that. Thanks a lot Dr Bob :D
July 26, 2009

Chem
What does the comparison tell us? :S Does it tell us that there is more acid than aspirn?
July 26, 2009

Chem
did you do this to find out A-: 3.2 x 10^-4 = (10^-1.5)^2/HA
July 26, 2009

Chem
are we doing the ratio between the number of mols? ;S
July 26, 2009

Chem
Isn't the ratio of Hasp to asp 1 from the balanced chemical equation?
July 26, 2009

Chem
stomach wall has a protective lining of mucous that prevent the acid from penetrating the underlying tissues. using asprin too often can damage the stomach wall. Aspirn is a weak carboxlyliic acid with a Ka of 3.2 x 10^-4. HC8H7O2CO2(aq) <--> H^+(aq) + C8H7O2CO2^-(aq) ...
July 26, 2009

Chem
didn't I give K to one place :S 4 x 10^-10 I dont understand how it is 2 decimal places. 0.1 only has one signifcant digit
July 26, 2009

Chem
didn't I give K to one place :S 4 x 10^-10 I dont understand how it is 2 decimal places. 0.1 only has one signifca
July 26, 2009

Chem
but would I keep one significant digit cause on the 0.1?
July 26, 2009

Chem
This is what I did: pH = 8.81 pH + pOH = 14 pOH = 5.19 [OH-] = 10^-5.19 = 6.64 x 10^-6 __ArNH2 + HOH ==> ArNH4^+ + OH^- I 0.1_____________O___________O C -6.46 x 10^-6 +6.46 x 10^-6 +6.46 x 10^-6 E 0.1-6.46 x 10^-6 +6.46 x 10^-6 +6.46 x 10^-6 Kb = {6.46 x 10^-6)^2 / 0.1 = 4...
July 26, 2009

Chem
wait I want to correct myself. I think I would subtract 8.81 from 14 to get the POH and then figure out the concentration of OH. Is this correct?
July 26, 2009

Chem
Thanks :) I did the ice table but I don't know what to do from there. They haven't given me the Kb value so how do I find x? Or do I find the concentration of H+ from ph= -log[h+] and then divide it by 1 x 10^-14 to find the concentration on OH in the ice table?
July 26, 2009

Chem
Does the R just represent a chain?
July 26, 2009

Chem
I need to find the Kb of Analine. I've been told the ph is 8.81 and that the concentration of the solution is 0.1 mol/L. What would be the equation I'm working with :S ?
July 26, 2009

Chem
Thanks :)
July 26, 2009

Chem
That dosent seem to work out :S Everyone says that the best treatment is putting a 100% oxygen mask on the person. Why do that?
July 26, 2009

Chem
When you have carbon monoxide poisoning and you put on a 100% oxygen mask, will the CO react with the O to make CO2 which the body will exhale?
July 26, 2009

Chem
This is what I think. When we breath in oxygenm we breath out carbon dioxide. The carbon dioxide reacts with the lithium oxide and continues to produce h2o and li2co3. if they keep releasing carbondioxide, they'll keep producing li2co3 and h20. I don't exactly see ...
July 25, 2009

Chem
An air purifiction system involving litium hydroxide, LiOH, was used. LiOH absorbs carbon dioxide. 2LiOH(s) + CO2(g) <---> Li2CO3(s) + H2O(l) Use Le Chatelier's principle to explain why the amount of time astronauts can spend in a space-craft is limited?
July 25, 2009

CHEM
Thanks :)
July 24, 2009

CHEM
A concentrated weak acid is best described as which of the following? (a) a solution with a high pH (b) a solution where the concentration of undissociated acid particles is high and relative quantity of hydronium ions is low (c) a solution where the concentration of ...
July 24, 2009

chem
Thanks a lot Dr Bob :)
July 24, 2009

chem
NH4Br has been dissolved into 1 L of water at 25 degrees celcius. the solution has a pH of 5.16. calculate number of grams of NH4Br. I dont even know how to write the equation for this. Could someone please write the water + NH4 equation for me. Thanks :)
July 24, 2009

chem
I redid it and I got 11.25 :) Thanks :)
July 24, 2009

chem
Calculate the pH of 0.20 M NaCN solution. NaCN ---> Na+ + CN- CN- + H20+ ---> HCN+ + OH- Initial conc. of CN- = 0.20 mol/L change = -x equillibrium = 0.20-x HCN equill. = +x OH equill. = 1x10^-7+x Ka= 6.2 x 10^-10 Kb = KW/Ka = 1x10^-14/6n2 x 10^-10 = 1.6 x 10^-5 1.6 x 10...
July 24, 2009

Chem
I understand now. Thank you :)
July 23, 2009

Chem
I dont understand how to figure out the equation. I thought it would be this: CH3NH2 + HOH ==> CH3NH+ + H30 :S How do I know what the products will be?
July 23, 2009

Chem
Methylaime, CH3NH2. If a 0.100 mol/L solution of methyamine has a pH of 11.80, calculate the ionization constant for the weak base. What is an ionization constant. Is it just K? This is what I did so far: 11.80 = -log (concentration of h3o+) 10^-11.80 = (concentration of h3o...
July 23, 2009

chem
Yes I figured out that problem. :) Thanks a lot!
July 23, 2009

chem
Do we always have to do an ICE table for weak acids and bases?
July 23, 2009

chem
Calculate the [h3o+] and [oh-], pH and the percent dissociation for both 0.25 mol/L HCl and 0.25 mol/L HCN. 0.25 mol/L HCL [H+] = 0.25 mol/L [OH-] = 1 x 10^-14 / 0.25 = 4 x 10^-14 pH = 0.60 % dissociation = ? ( I dont know how to figure out percent dissociation) For the HCN I ...
July 23, 2009

Chem
We weren't given the molarity of Ca(OH)2, thats why I dont understand how to do the question.
July 22, 2009

Chem
but M is in grams/mol.d When I said M I meant molar mass not molarity.
July 22, 2009

Chem
I did an experiment were I added some water and KHP into a beaker and phenophalene [sp?]. It was a titration lab. We slowly added calciuum hydroxide into the beaker and waited till the solution turned into a faint pink. The question is asking me to find the number of mols of ...
July 22, 2009

Chem
If I were to use dichromate and add HCL and Ba(NO3)2 and NaOH , what should form? Im thinking the Ba(NO3)2 would still form a precipitate but im not too sure about everything else
July 22, 2009

Chem
Thank You :D
July 22, 2009

Chem
sorry about the re-post it was an accident
July 22, 2009

Chem
If I were to use dichromate and add HCL and Ba(NO3)2 and NaOH , what should form? Im thinking the Ba(NO3)2 would still form a precipitate but im not too sure about everything else
July 22, 2009

chemisty
Thanks :)
July 22, 2009

chemisty
oops sorry :S I meant Cromate. Potassium Dichromate. In a lab that I did I mixed 0.1 M K2CrO4 with 2 drops of NaOH and I added Ba(NO)2 until I noticed a color change. When I did this, the K2CrO4 which was initally yellow formed a white precipitate and on the top there was ...
July 22, 2009

chemisty
What would happen if you reacted potassium dicarbonate with HCL and NaOH?
July 22, 2009

Chem
Thank You :)
July 21, 2009

Chem
So is K2CrO4 the equillibrium concentration of CrO4-2 is high whereas in K2CrO7 the CrO4-2 equillibrium concentration is low?
July 21, 2009

Chem
One of my questions asks, when can you conclude about the relative equillibrium concentrations of CrO4^2- in each of the colutions 0.1 M K2Cr2O7 and 0.1 M K2CrO4? Im really confused by this question. Could someone clarify it for me? Thanks :)
July 21, 2009

Chem
Thank You :)
July 19, 2009

Chem
Ohh wow, what an awesome tip! Thank you so much. This was so confusing until now :D So for something like (losing heat) 2A + B <-> 2C delta H postive it would be 2A + B <-> 2C -heat the reaction would move right?
July 19, 2009

Chem
I dont understand the effect of temperature on a reaction. For exmaple: CO + 3H2 <-> CH4 + H2O deltaH= -230 KJ If there were an increase in temperature then the CH4 and H2O would have a harding time becoming the CO and H2 so therefore the reaction would move to the right...
July 19, 2009

Chemistry
Thank you :)
July 19, 2009

Chemistry
so for the Kc value it would change correct? I did this: Kc = [PCl3][Cl2]/[PCl5] = [0.30][0.12]/[0.72] = 0.05
July 19, 2009

Chemistry
OHHHH. OK! But the equllibriums for the rest is correct, right?
July 19, 2009

Chemistry
Divide what :S I actually guessed how to do this. Im not too sure what I did. How would I get the 0.72 for the equllibrium of PCl5?
July 19, 2009

Chemistry
Initially, 1.68 mol of PCl5(g) and 0.36 mol of PCl3(g) are in mixed in a 2.00 l container. It is later found that 1.44 mol of PCl5 are present when the system has reached equillibrium. Calculate the value of the equllibrium. This is what I did: Equation: PCl5(g) <--> ...
July 19, 2009

Chemistry
Ohh. I understand now. Thank you so much :)
July 19, 2009

Chemistry
I want to turn the 19.6 into 280 and in order to do that I must make the numerator larger and the numerator is the SO3 so therefore the reaction will move to the left?
July 19, 2009

Chemistry
is the 1000 k, 1000 kelvin? :S
July 19, 2009

Chemistry
that is the second part of the question; figuring out whether the reaction will move to the left or right. Im not too sure how to figure that out.
July 19, 2009

Chemistry
0.500 mol of SO2, 0.100 mol of O2 and 0.700 mol of SO3 re intorduced simutaneously into a 1.00 L vessel at 1000 K. For the equillibirum, 2SO2 (g) + O2(g) <---> 2SO3(g), the value of Kc at 1000K is 280. Show mathemtically that the mixture is NOT at equillibrium. This is ...
July 19, 2009

sci
are radiocarbon dating and carbon-14 dating the same thing?
July 19, 2009

Chem
Thank you :)
July 9, 2009

Chem
I dont understand how Rutherford's gold foil experiment proved that the positive charge of the atom had a very small volume in comparison to the whole atom. Could someone explain this to me please?
July 9, 2009

Chem
should I have 6 around every F? :S
July 8, 2009

Chem
Would the I have a lone pair?
July 8, 2009

Chem
oops, you`re right. Thanks :)
July 8, 2009

Chem
the molecular geometry would be a trigonal bipyramidal though, correct?
July 8, 2009

Chem
where is the lone pair? isn't iodine completely bonded to the fluorines?
July 8, 2009

Chem
IF5 would be not equal to 0 right?
July 8, 2009

Chem
Where would I use N/A ? If the molecule is polar then the sum would be not = 0 and if it isnt polr then the sum would be 0. Correct>?
July 8, 2009

Chem
Basically it gives me a formula like Ch3Cl and it says to draw the lewis structure and the VSEPR name. The it asks for the number of bonded atoms and number of lone pairs the molecule geometry, whether or not there are polar bonds, the sum of bond dipoles and whether the ...
July 8, 2009

Chem
There is this one question that akss for the sum of bond dipoles. I don't understand that at all. What is the question asking? I thought I was figuring out if the difference between the dipoles and if I got a 0 then the molecule would be non-polar and if I got anything ...
July 8, 2009

Chem
Ohh. Yes I do see that. Thanks :)
July 8, 2009

Chem
Ohhhh OK. Thank you :)
July 8, 2009

Chem
Why isnt the carbon negetive ?
July 8, 2009

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