Ice-cream

can i have some confirming plz? 1. The vapour pressure of pure water at 25 degrees c is 23.8 mmHg. Determine the vapour pressure of water at 25 degrees C above a solution containing 33.2 g of urea (a nonvolatile, nonelectrolyte, MW = 60g/mol) dissolved in 75 g of water. (i found no. of moles of urea = 0.5533 and no. of moles of water = 4.1667. since P(solution) = x(solvent) x Pure pressure (solvent), P(solution) = 21.01 mmHg.) does anyone agree with my answer?) 2. Calculate the reaction enthalpy in kJ for the formation of anhydrous aluminium chloride 2Al(s) + 3Cl2(g) --> 2AlCl3(s) from the data: 2Al(s) + 6HCl(aq) --> AlCl3(aq) + 3H2(g) delta H = -1049 kJ HCl(g) --> HCl (aq) delta H = -73.5 kJ H2(g) + Cl2(g) --> 2HCl(g) delta H = -185 kJ AlCl3(s) --> AlCl3(aq) delta H = -323 KJ (the answer i got was -1399kJ...does anyone agree?) thanx

hey guys, can u help me with these 3 questions? 1. Naphthalene combustion can be used to calibrate the heat capacity of a bomb calorimeter. The heat of combustion of naphthalene (C10H8) is 40.1kJ/g. When 0.8210g of naphthalene was combusted in a calorimeter containing 1000g water, a temperature rise of 4.21 degrees C was observed. What is the heat capacity of the bomb calorimeter excluding the water? (What i've got so far is that since heat of combustion is 40.1 kJ/g, so 401 x 0.8210 = 329.221kJ must have been released by naphthalene. Next i think i should use q = ms(delta T) except i'm not sure how we're meant to find the heat capacity of the bomb calorimeter "excluding the water"...can anyone help me out?) 2. Given the following information, CaO(s) + H20 (l) --> Ca(OH)2(s) delta H = -64.8kJ/mol How many grams of CaO must react in order to liberate 504kJ of heat? (I got 7.78 mols of CaO which means m = 435.56g. Does any1 agree?) 3. Thyroxine, an important hormone that controls the rate of metabolism in the body, can be isolated from the thyroid gland. If 0.455g of thyroxine is dissolved in 10.0 g of benzene, the freezing point of the solution is 5.144 degrees C. Pure benzene freezes at 5.444 degrees C and has a value for the molal freezing point depression constant Kf of 5.12 degree C kg mol^(-1). What is the molecular weight of thyroxine? (I know to use delta Tf = Kf x mass of solute...but i don't understand how to find the mols of benzene so that i can find its molecular weight.)

lolz i wonder if i know u...

hey can anyone confirm whether i've got the name of this organic compound right? CH3CH(Br)CH(CH3)CH2CH(phenyl)CH2CH3 is it 2-bromo-3-methyl-5-phenylheptane? (or is it 6-bromo-5-methyl-3-phenylheptane?)

hey guys, just wondering whether u could give me a few ideas to help me with my assignment. i'm really interested in stem cells and coz i'm doing studying pharmacy, i've been looking up info. to do with stem cells and how their development is going to affect pharmacists. i find that there doesn't seem to be anything beneficial to pharmacists in tissue engineering and other aspects of stem cells. what do u guys think?

hey guys can u help me/confirm these 2 questions? i've attached them (their just pictures of the questions that i took with a digital camera - coz im not sure how to just put an image in *blush)..hopefully the attachments worked

well i got it from a shop, which the lady selling them said she bought them all in australia...she says she doesn't buy China products coz they may be fakes...but i don't know, coz the shop's not like some big company so i don't know if i can trust them...

hey guys, lately i brought a few anti-ageing creams and on one of the bottles, it says "Bio-Super Anti-ageing Eye Complex With Bio-Placenta, Collegen & Elastin 30gm" now i noticed that collagen is not spelt as "collegen"...does this mean the cream is a fake? i mean, how can they get the word "collagen" wrong? (or is that another way to spell collagen??) the brand is H & B Health and Beauty...i got told this is an australian brand...but i'm now worried it's a fake. wat do u guys think?

well does any1 know about question 1? coz thats the 1 that I have absolutely no idea!

well in australia, this is first year chemistry at university...so i dunno what that corresponds to in UK...

so if AlH4 (-) and H- are both possible reducing agents...then how do u know which 1 it is in this question?

hey guys, can u help me with these few questions? 1. In the molecule below, which carbon atom is in the highest oxidation state? BrCH2CH(OH)CH(OH)C(=O)CH2C(=O)OCH3 (I have NO idea of what to do!!! Can any1 help me?) 2. In the reduction of carbonyl compounds with LiALH4, the effective reducing species is: (a) Li+ (b) Al(3+) © AlH4(-) (d) AlH3 (e) H- (i think the answer is c...any1 agree?) 3. What is the IUPAC name for the following compound? CH3CH2CH2CH(Cl)C(=O)Cl (a) 1-chloropentanoyl chloride (b) 1-chloro-1-butanoyl chloride © 2-chloropentanoyl chloride (d) 1,2-dichloropentanal (i think the answer is c...wat do u guys think?)

does any1 know anything about the wavelength or the colour of the light absorbed by chromate ions? coz i've been to lots of websites and they all give diff. answers. i think the colour of chromate ions is yellow, so that means it absorbs the purple light (complementary colours)...but i'm not sure if that's right. does any1 agree with me?

I've been given this redox equation to balance: CH3CH2OH + Cr2O7(2-) --> CH3COOH + Cr(3+) The 2 half-reactions are: oxidation of ethanol: CH3CH2OH --> CH3COOH reduction of acidic dichromate ion: Cr2O7(3-) --> Cr(3+) What I got was: Ox: CH3CH2OH + H2O --> CH3COOH + 4H+ + 4e Re: 14H+ + 9e + Cr2O7(2-) --> 2Cr(3+) + 7H2O I then added multipled the top equation by 9, the bottom by 4 and then added the 2 equations together to get: 9CH3CH2OH + 4Cr2O7(2-) + 20H+ --> 9CH3COOH + 8Cr(3+) + 19H2O Does any1 agree with my answer? (I just think the numbers seem a bit big...)

Can any1 tell me if CrO4 (2-) is the formula for a chromate ion? Also, does any1 know the wavelength of it or the colour of light it absorbs? (I've looked on the web and there are diff. answers...) Can some1 plz help me?

ahh, i c, what about the answer itself? do you agree with 535? (i used E = hc/wavelength) (i'm not sure if the time was necessary in the calculations but i found i didn't need to use it...what do u guys say?)

but the answer wants the number of photons...no matter how accurate my answer is, wouldn't it still round up to 535 photons anyway? (the problem is my lecturer said if the answer is wanting the "number" of photons, I shouldn't be getting a decimal answer).

with this question, I'm told that i shouldn't be getting any decimal answers becuase the answer is in the number of photons...so can any1 just tell me whether you agree with my answer? A ruby laser produces radiation of wavelength 633nm in pulses of 1.00e-9 s duration. If the laser produces 1.68e-16J of energy per pulse, how many protons are produced in each pulse? i keep getting an answer of 535.46827.... which i think is approx. 535 photons. what do you guys think?

hey guys, i have 2 questions...hopefully u can help me out! 1. this multiple choice MAY have more than 1 answers...but i only got 1 answer so i just want to know whether u guys think there's only 1 answer as well. Which of the following statements is/are incorrect? (a) The exact momentum and position of an electron cannot be determined. (b) Lower energy orbitals are filled with electrons before higher energy orbitals. © When filling orbitals of equal energy, 2 electrons will occupy the same orbital before filling a new orbital. (d) No two electrons in a particular atom can have the same value for all 4 quantum numbers. (i got © as the incorrect statement. are there anymore there do u think?) 2. For which of the following species if more than one lewis (resonance) structure required to correctly describe the molecule? (a) Li2S (b) NH3 © NO2- (d) ClO4- (e) none of these (i got © where O=N-O. what do u guys think?)

thanx guys, i realised wat i did wrong (i used n=0 for ground state lolz)

hey can any1 confirm my answer? A hydrogen atom in its ground state absorbs a proton of wavelength 121.5nm. To which higher energy state will it be excited? (a) n=2 (b) n=3 © n=4 (d) n=5 (the answer i got was n = 1.15 so roughly n= 1, using bohr's equation and E = hc/wavelength. but that doesn't match any of the multiple choice answers on the worksheet. wat do u guys think?)

Does any1 know whether ethanol is an water-immiscible organic solvent?

hey guys, i have a few problems which i'm not too sure about...hopefully u guys can help me out! 1. A hydrogen atom in its ground state absorbs a photon of wavelength 121.5nm. To which higher energy state will it be excited? a) n=2 b) n=3 c) n=4 d) n=5 (i used E = hc/wavelength to find te energy, which then i made it equal to deltaE = -2.18 x 10^-18 [1/(n final squared) - 1/(n initial squared)] where n initial is 0 because it is in ground state. The answer i got was n = 1.15...which doesn't match any of the choices...can any1 give me some help?) 2. Which of the following molecules has a nonlinear structure? a) XeF2 b) BeCl2 c) O3 d) CO2 e) N20 (central atom is N) (i'm confused about N20 becuase i think theres 2 double bonds; 1 between N-N and 1 between N-O...but i don't think that gives the lowest formal charges...any1 got any other suggestions?) 3. A ruby laser produces radiation of wavelength 633nm in pulses of 1.00e-9 s duration. If the laser produces 1.68e-16 J of energy per pulse, how many photons are produced in each pulse? (i used E = hc/wavelength to find the energy of 1 photon. Then i divided the 1.68e-16J by that energy and got 535.468 photons...do u guys think it's right? coz i didn't use the duration time in my calculation so i'm not sure if its right) Thanx

hey guys, i'm learning about hybridisation at the moment but theres just something im confused about. If im given a lewis diagram of a molecule, i can easily tell where the sigma bonds are (coz they're just between the atoms) but how can i tell where the pi bonds are (coz from what i know, they;re meant to be at different orientations or something). there's got to be a way of just easily seeing how many pi bonds there are and where they are isn't there? can anyone help me plz?

I'm trying to understand how the trends in a periodic table work for electron affinity. I've read that the electron affinity generally increases across a period from left to right, and decreases down a group but there are exceptions - which means if I have a question asking me for eg. which one, Ar or Br has a more favourable(more exothermic) electron affinity...I don't know whether its one of those exceptions or not. Can any1 explain how else I can figure out which atom has a more favourable electron affinity...electron configurations maybe, I don't know for sure?? I'm really confused. Thanx.