Wednesday
April 16, 2014

Posts by hannah


Total # Posts: 2,796

Chemistry
Now I have to calculate the mass of solvent(kg) for both NaCl and Sucrose and I have to assume that the density of water is 1.00g/mol. I am not sure how to figure this out. I think you already answered this for me once but I cant find my original post with the answer. Im sorry.

Chemistry
Ok and the units I use would be degrees celsius correct?

Chemistry
ok so my freezing point for NaCl was -2.0 so I can do -2.0-(0.5)= -2.5 degrees celsius. My freezing point for DI water was positive 0.5. So delta T would be -2.5?

Chemistry
I had to perform an experiment for the freezing point depression in which we had to determine the frezzing points of water as a pure solvent, sodium chloride, sucrose, and ethylene glycol. We had to work with a partner so I completed the experiment for water, NaCl, and the gl...

Chemistry
for my answer I get 0.0669. Should I leave it like this or do 6.69e-2?

Chemistry
I am trying to find th e# of moles of NaCl but I am not sure of the units. 3.914g NaCl / mm=58.44 so is it 3.914g/mol divided by 58.44g/mol = 0.0669moles. I am not sure how many significant figues to use.

Chemistry
Is this correct?

Chemistry
For the reaction, 2 XO + O2 = 2 X02, some data obtained from measurement of the initial rate of reaction at varying concentrations are given below. run # [XO] [O2] rate, mol L-ls-l 1 0.010 0.010 2.5 2 0.010 0.020 5.0 3 0.030 0.020 45.0 The rate law is therefore a. rate = k[XO...

Chemistry(Please check)
8. The half-life of a reaction was found to be inversely dependent on the concentration of the starting material. Thus, we can say that a. the reaction is zero order b.the reaction is first order c.the reaction is second order d. the reaction starts out first order and changes...

Chemistry(Please check)
The decomposition of an aldehyde solution in carbon tetrachloride is a first order reaction with a rate constant of 1.20 x 10-3 min-l. If we start with [aldehyde] = 0.0500 molar, what will the concentration be 150 minutes later? 1.20e-3(150) = 0.18 0.18(0.0500)=0.009M The conc...

Chemistry
1)For the reaction, A = B + C, the rate law is k(A). If it takes 80.0 seconds for 70.0% of a 10.0 gram sample of A to be transformed into products, what is the value of the rate constant? I was going to do 80/10 = 8 and then 8 times .70 but im not sure this is correct.

Chemistry(Please check)
Oh ok I did realize that. Now I got 0.0775M

Chemistry(Please check)
The initial concentration of a reactant in a first order reaction is 0.620 molar. What will be its concentration after 3 half-lives? I did 0.620 -> 0.31 ->0.155 0.155M will be the concentration. Is this correct?

Chemistry(Please help)
The common laboratory solvent diethyl ether (ether) is often used to purify substances dissolved in it. The vapor pressure of diethyl ether , CH3CH2OCH2CH3, is 463.57 mm Hg at 25oC. In a laboratory experiment, students synthesized a new compound and found that when 27.18 grams...

Chemistry(Please help)
Disregard question.

Chemistry(Please help)
I subtracted again and got 9.83. So do I set it up like this 453.74= Xether * 463.57

Chemistry(Please help)
The vapor pressure of diethyl ether is 463.57 mm Hg at 25 degrees celsius. How many grams of aspirin C9H8O4, a non volatile nonelectrolyte (mw=180.1g/mol), must be added to 216.7g of ether to reduce the vapor pressure to 453.74 mm Hg. Ether=74.12g/mol so I did 463.57 - 453.74 ...

Chemistry
The vapor pressure of chloroform is 173.11 mm Hg at 25 degrees celsius. A nonvolatile, nonelectrolyte that dissolves in chloroform is aspirin. Calculate the vapor pressure of the solution at 25 degrees celsius when 6.243g of aspirin (180.1g/mol) are dissolved in 244.5g of chlo...

Chemistry
ok thank you!!!

Chemistry
I had to perform an experiment for the freezing point depression in which we had to determine the freezing points of water as a pure solvent, sodium chloride, sucrose, and ethylene glycol. We had to work with a partner so I completed the experiment for water, NaCl, and the gly...

Chemistry
Bauxite ore contains aluminum oxide Al2O3(s) which is decomposed using electricity to produce aluminum metal and oxygen gas. What mass of aluminum metal can be procuced from 155g of aluminum oxide?

Chemistry
thank you!

Chemistry
1. Nitric oxide reacts with bromine gas at elevated temperatures according to the equation, 2 NO(g) + Br2(g) = 2 NOBr(g) The experimental rate law is rate = k[NO][Br2]. In a certain reaction mixture the rate of formation of NOBr(g) was found to be 4.50 x 10-4 mol L-l s-l. What...

Chemistry(Please check)
Ok, thank you for your help!!

Chemistry(Please check)
so then answers 2 and 3 are not correct?

Chemistry(Please check)
So wouldn't a catalyst just speed up the rate too and not the rate constant?

Chemistry(Please check)
Oh ok I understand, thank you.

Chemistry(Please check)
I just thought that if the concentration was doubled there would be more molecular collisions which would increase the rate law. So only the first two are correct then?

Chemistry(Please check)
1) The reaction A + B + C = products has a rate law rate = k times A times C squared. Which of the following will result in an increase in the rate constant for the reaction? #1 - increasing the temperature #2 - adding a catalyst #3 - doubling the concentration of reactant C I...

Chemistry(Please check)
The units of a rate constant for zero, first, and second order reactions are given in the textbook. If the time units are minutes, what would you expect the units to be for a third order reaction? 1) 1/min^3 2) mol^2/L^2-min 3) L/mol-min^2 4) L^2/mol^2-min 5) L^2/mol^2-min^2 I...

Chemistry
so I did 463.57 - 453.74 = 7.600 Then I found moles of ether to be 4.0313. I do not understand the next step to find Xether.

Chemistry
The vapor pressure of diethyl ether is 463.57 mm Hg at 25 degrees celsius. How many grams of aspirin C9H8O4, a non volatile nonelectrolyte (mw=180.1g/mol), must be added to 216.7g of ether to reduce the vapor pressure to 453.74 mm Hg. Ether=74.12g/mol This question is similar ...

Chemistry(Please check)
oh I understand you have to add them. Thank you.

Chemistry(Please check)
Sorry I had to post the question using the word times but for some reason this site would not let me post the original equation using the brackets.

Chemistry(Please check)
A reaction has a rate law, rate = k times A times B squared. What is the overall order of the reaction. I think that the order is 0. Is this correct?

Chemistry(Please help)
Yes im sorry I am sort of confused. So is the total number of moles what they gave me in the problem, 6.243?

Chemistry(Please help)
Yes it just says calculate the vp of the solution when aspirin is dissolved in the CHCl3. So then I do not have to calculate the moles/total moles?

Chemistry(Please help)
So I would do 0.0346/180.1 for aspirin and 2.04/119.40 for CHCH3?

Chemistry(Please help)
The vapor pressure of chloroform is 173.11 mm Hg at 25 degrees celsius. A nonvolatile, nonelectrolyte that dissolves in chloroform is aspirin. Calculate the vapor pressure of the solution at 25 degrees celsius when 6.243g of aspirin (180.1g/mol) are dissolved in 244.5g of chl...

Chemistry
The vapor pressure of chloroform is 173.11 mm Hg at 25 degrees celsius. A nonvolatile, nonelectrolyte that dissolves in chloroform is aspirin. Calculate the vapor pressure of the solution at 25 degrees celsius when 6.243g of aspirin (180.1g/mol) are dissolved in 244.5g of chlo...

Chemistry(Please help, thank you!)
Disregard this question. I actually got the answer.

Chemistry(Please help, thank you!)
How would I find the molality of NaCl with the following information? initial temperature= 98degrees celsius final temp=100 degrees celsius. Kbp(water)=0.512

Chemistry
We had to measure out 5.800g of NaCl and record the exact weight. First I weighed the measuring boat and then I poured in the NaCl so to get the exact weight I subtracted the mass of the measuring boat with NaCl from the mass of just the boat. Is this correct?

Chemistry
The next calculation is to actually find the mass of solvent(kg) for both NaCl and sucrose and my lab books says to assume that the density of water is 1.00g/mL.

Chemistry
In my lab book it just says delta Tf = the change in the freezing point (Tsolution - Tpure solvent = negative number) So for the delta T of NaCl I do 0.50 which was the freezing point - the solvent? I do not know how to find the fp of the solvent.

Chemistry
The very frist thing that was asked for the calculations was the freezing point in degrees celsius for NaCl and Sucrose and I put -2.0C for NaCl and for sucrose my partner got -4.0C.

Chemistry
I had to perform an experiment for the freezing point depression in which we had to determine the frezzing points of water as a pure solvent, sodium chloride, sucrose, and ethylene glycol. We had to work with a partner so I completed the experiment for water, NaCl, and the gly...

Chemistry
A solution was made by dissolving 62.07grams of a compound in 500g of water. The compound was not ionic. The freezing point of the solution was measured and found to be -1.86degrees celsius. The molar mass of this compound can be calculated to be? I know I already posted this ...

Chemistry
For the first equation I did 0 + 2(-167.159) -> 0 + 0 0 - 334.318 = deltaH1 = -334.318 Second equation I did -601.24 + (-334.318) -> -285.83 -285.83 -(-935.558) = deltaH2 = 649.728 Then deltaH3 = -241.8 On my lab report it says to find the deltaH formation of MgO and it ...

Chemistry
The only problem is that when I looked up the thermodynamic values I could not find MgCl2(aq) so would this just be 0?

Chemistry
Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g) delta H1? MgO(s) + 2HCl(aq) ->MgCl2(aq) + H2O(l) delta H2? To make these equations add up to the formation reaction of MgO, you will need to include the following: H2(g) + 1/2O2(l) delta H =-241.8 kJ Using Hess's Law and manipula...

Chemistry(Please help, thank you)
I now need to find the enthalpies for Mg and MgO and then use the equations Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g) MgO(s) + 2HCl(aq) ->MgCl2(aq) + H2O(l) H2(g) + 1/2O2(l) delta H =-241.8 kJ I do not understand how you find the values for the first two equations when there...

Chemistry(Please help, thank you)
So in that case I would just divide my answer of4842756.8 by 1000 = 4842.76 kJ/mol correct?

Chemistry(Please help, thank you)
The units for the specific heat of water that they gave me were J/ g x K

Chemistry(Please help, thank you)
My qrxn value was 30267.23J and # of moles was 6.25e-3mol so that = 4842756.8 but are the units J/mol and do you think I should convert to kj?

Chemistry(Please help, thank you)
ok thank you very much!!!

Chemistry(Please help, thank you)
For the equation: deltaHrxn = qrxn / mol substance to calculate deltaH per mole what does the mol substance mean? Does this mean that you use the mm of the substance or if you already calculated the # of moles of a substance do you use that?

Chemistry
For the equation: deltaHrxn = qrxn / mol substance to calculate deltaH per mole what does the mol substance mean? Does this mean that you use the mm of the substance or if you already calculated the # of moles of a substance do you use that?

Chemistry
I had to perform an experiment using a coffee-cup calorimeter to determine the enthalpies of two seperate reactions. For part 1 we worked with magnesium metal, and magnesium oxide. Data was collected and now I need to find the q, heat transferred for both magnesium and magnes...

Chemistry
Or should I use the # of moles that I calculated for Mg which was 6.25e-3.

Chemistry
Then it says that to find deltaH rxn the equation is qrxn/mol substance. So I use the 30267.23 / 0.152 to get my answer correct?

Chemistry
It also says to assume that none of the heat produced in the reaction is lost by the calorimeter to the rest of the surroundings. It says that the energy as heat lost by reaction will equal that gained by the solution which is represented by qreaction =-qsolution. So for Mg I ...

Chemistry
Im sorry it so confusing and there is alot of data. This whole experiment was split into two parts. I had to work in a group with two other people to do part 2 and for part 1 we had to get the data from another group so I just have some of their data. For part I guess the whol...

Chemistry
So for Magnesium I did q=(4.184 J/g X K)(24.371g)(296.83K) = 30267.23 J Is this correct so far?

Chemistry
They give the specific heat capacity for water, is that what I use?

Chemistry
0.150g of Mg was used and 0.250g MgO was used.For the first reaction we had to mix 25ml of HCl with the Mg and record the temp with a Labpro interface device. The second reaction we had to use the same thing except with MgO. So for the mass of rxn mixture for Mg the value is 2...

Chemistry
I had to perform an experiment using a coffee-cup calorimeter to determine the enthalpies of two seperate reactions. For part 1 we worked with magnesium metal, and magnesium oxide. Data was collected and now I need to find the q, heat transferred for both magnesium and magnesi...

Chemistry
The vapor pressure of chloroform is 173.11 mm Hg at 25 degrees celsius. A nonvolatile, nonelectrolyte that dissolves in chloroform is aspirin. Calculate the vapor pressure of the solution at 25 degrees celsius when 6.243g of aspirin (180.1g/mol) are dissolved in 244.5g of chlo...

Chemistry
Its suppose to be deltaT f. So would the minimum data required be Tf, Kf, and mass of solute?

Chemistry
1) The molecular mass of a substance was determined by the freezing point depression technique. The minimum data required for the determination are a. ƒ´Tf and Kf only. b. ƒ´Tf , Kf and mass of solute. c. ƒ´Tf , Kf , mass of solute and mass of ...

Chemistry
How would I find the molality of NaCl with the following information? initial temperature= 98degrees celsius final temp=100 degrees celsius. Kbp(water)=0.512

Chemistry
so delta T would be 1.86 but Im not sure what Kf would be?

Chemistry
A solution was made by dissolving 62.07 grams of a compound in 500g of water. The compound was not ionic. The freezing point of the solution was measured and found to be -1.86 degrees celsius. Using the Kf value in your textbook, the molar mass of this conpound can be calculat...

Chemistry
Ok thank you

Chemistry
27.8/80=0.3475 but I dont understand what to do next.

Chemistry
the answer choices that were given are: a)769g b)36.2g c)972g d)34.8g e)157g

Chemistry
How many grams of water are needed to dissolve 27.8g of NH4NO3 (80.0 g/mol) in order to prepare a 0.452 m (molal) solution? 27.8g / 80g/mol X 0.452 = 0.157 Is this correct?

Chemistry
would it be delta T = -5.07C/m * 0.210m?

Chemistry
1) Benzene freezes at 5.45 degrees celsius. The Kf for benzene is -5.07C/m. What would be the freezing point of a 0.210m solution of octane in benzene? I am not sure how to start this. I know the equation for freezing point is Kfp * m solute.

Chemistry
so 0.30m BaCl2 has the largest delta T at 0.90 so it has the lowest freezing point. Would you agree?

Chemistry
Ok thank you!

Chemistry
so NH4NO3 is 2 and MgS04 is 4?

Chemistry
If all ionic substances completely ionized, the aqueous solution with the lowest freezing point would be 1)0.25m NH4NO3 2)0.30m BaCl2 3) 0.35m LiBr 4) 0.50m Sucrose 5) 0.40m MgSO4 I know that i have to multiply m and i to find the largest delta T. I am just not sure if the val...

Chemistry
Which of the following contributes to the bubbling from a cold can of soda when left standing at room temperature. Choose all that apply. 1) the initial rush of CO2 out of the can drags other CO2 molecules out of the solution. 2) the decrease in CO2 partial pressure lowers the...

Chemistry
Thank you for all your help!!

Chemistry
Which aqueous solution below is expected to have the lowest freezing point? Assume 100% dissociation for ionic species. 1)0.25m MgBr2 2)0.30m Na2SO4 3) 0.50m KCl 4) 1.0m sucrose 5) 0.40m Cr(NO3)3 I think that the answer is 0.30NaSO4 but I am not positive. Is this correct? Chem...

Chemistry(Please check)
1) The molecular mass of a substance was determined by the freezing point depression technique. The minimum data required for the determination are: a) delta T and Kf only b) delta T, Kf, and mass of solute c) delta T, Kf, mass of solute, and mass of solvent d) delta T, Kf, m...

Physics
A 520 Hz tuning fork produces a standing wave in a column of air in a closed tube. If the speed of sound is 340 m/s, what is the length of the air column?

physics
a) What is the frequency of a photon of UV radiation ( = 2.00 x 10^-7 m)? (b) Calculate the energy of a photon of UV radiation. (C) What is the frequency of a photon of infrared radiation ( = 1.083 x 10^-6 m)? (d) Calculate the energy of a photon of infrared radiation. (e) How...

Physics
In black-and-white photography, a photon energy of about 4.00 x 10-19 J is needed to bring about the changes in the silver compounds used in the film. (a) What is the frequency of the light needed to bring about these changes? (b) Explain why a red light used in a darkroom do...

Chemistry
when 7.50 grams of iodine (I2) is added to 48.7grams of carbon tetrachloride (CCl4), the iodine dissolves and a solution is formed. The weight percent of the iodine in the solution is? 7.50g I2/ 7.50 + 48.7 X 100 = 13.3 Did I do this correctly?

Chemistry(Please check)
Ok now I got 0.0931, so this is the mole fraction for NaCl?

Chemistry(Please check)
Ok so 100/58.44= 1.71

Chemistry(Please check)
1) If exactly 100.0 grams of NaCl (mm=58.44g/mol) are dissolved in 300 grams of water (mm=18.02g/mol), the mole fraction of NaCl is? a) 1.71 b) 0.0932 c) 0.250 d) 0.103 e) 4.75 I did 100g / 100g + 300g = 100/40 = 0.250. Did I do this correctly?

Chemistry(Please check)
1) The molecular mass of a substance was determined by the freezing point depression technique. The minimum data required for the determination are: a) delta T and Kf only b) delta T, Kf, and mass of solute c) delta T, Kf, mass of solute, and mass of solvent d) delta T, Kf, ma...

Chemistry(Please check)
Thank you!

Chemistry(Please check)
1)For electrolyte solutions, the _____ the concentration of the electrolyte and the ____ the ion charges, then the ____ the ion-pairing. a) lower, smaller, greater b) higher, smaller, smaller c) higher, greater, greater d) lower, greater, smaller e) lower, greater, greater I c...

chemistry(Please check)
ok thank you

chemistry(Please check)
1) In comparing the phase diagram for water with that of a solution of sugar in water, all of the following decrease except a) the vapor pressure b) the boiling point c) the freezing point d) the triple point I chose the boiling point as the answer. Is this correct? Thank you.

Chemistry
Ok so then I just have to find the mass of each solution so KCl = 74.55 X 2 MgBr2 = 184.11 X 3 Na2SO4 = 94.05 X 3 Cr(SO4)3 = 340.21 X 4 So Cr(SO4)3 would have the largest delta T, so the lowest freezing point. Is this correct?

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