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December 22, 2014

Posts by Hannah


Total # Posts: 2,923

ChemHelp
Chem Help! Limiting and excess reagent? Identify the limiting and excess reagent for each of the following scenarios involving the formation of silicone dioxide, SiO2. Please explain!!! Thank you! Si + O2 --> SiO2 a. 2 atoms of silicone and 2 molecules of oxygen gas b. 28.1...
February 23, 2012

Physical Science
Balance this equation: I2+HNO3 = HIO3+NO2+H2O
February 22, 2012

Chemistry(Urgent, please help,thank you)
oh ok I understand thank you so much for all of your help!!!
February 21, 2012

Chemistry(Urgent, please help,thank you)
After performing a freezing point depression experiment I had to find the molecular weight of glycol. Now I have to answer the question what value did I assume "i" to equal and why did I make this assumption. My teacher told us the value of i to use for this was 1. I...
February 21, 2012

Chemistry
I need to calculate the molecular mass of ehtylene glycol based on the freezing point depression. The teacher said that for glycol i=1 and to use the equation m=delta T / Kf X i Kf = -1.86C/m so I did -2.5C / -1.86 X 1 = 1.344 I know that 1.344 can't be the weight for ...
February 21, 2012

Chemistry
1) For a freezing point depression experiment we had to create an ice bath and add salt to the ice. I have to answer the question, why was salting the ice necessary in order to complete the experiment and how does this apply to the principles/concepts behind this experiment? ...
February 21, 2012

Physics
Suppose your power company charges $1.00 per kWh as its power rate. (a) What is the power in kW for an air conditioner that pulls 5 A on your standard 115 V household circuit? (b) How much does it cost you to run your air conditioner for 12 hours?
February 21, 2012

Physics
what is the voltage acros a 60.0 resistor with a current of 3 1/3 a?
February 21, 2012

Chemistry(Please help)
so for molality I got 1.344 then I did 1.344 = mols/0.10kg = 0.1344 Im not sure if I did this step right Then I did mm= g/mol 6.200 was the mass of the solute so mm=6.200 / 0.1344 = 46.13. I guess I made a mistake somewhere in my calculations because I thought that the mm of ...
February 20, 2012

Chemistry(Please help)
Disregard question I understand now. I have to solve for mols.
February 20, 2012

Chemistry(Please help)
the only info that I have is the mass of solute(g) and mass of solvent(kg) for glycol so im confused on what to use for mols?
February 20, 2012

Chemistry(Please help)
I need to calculate the molecular mass of ehtylene glycol based on the freezing point depression. The teacher said that for glycol i=1 and to use the equation m=delta T / Kf X i Kf = -1.86C/m so I did -2.5C / -1.86 X 1 = 1.344 I know that 1.344 can't be the weight for ...
February 20, 2012

Chemistry(Please help,thank you)
Nevermind, I made a mistake im sorry. Disregard the question.
February 20, 2012

Chemistry(Please help,thank you)
Ok and for sucrose I did -4.5C = -1.86C/m X 0.1004 mol X i -4.5 = -0.1867i i =24 Can i be a big number like this?
February 20, 2012

Chemistry(Please help,thank you)
Is it ok that "i" is negative?
February 20, 2012

Chemistry(Please help,thank you)
I have to find the calculation of Van't Hoff factor "i" for NaCl and sucrose. The directions say to use the equation delta Tf = kf X m X i and to use Kf for water = -1.86C/m So I have the molality of NaCl and sucrose as well as delta Tf so for NaCl I plugged the ...
February 20, 2012

Chemistry
For 0.06697mol / 0.1kg = 0.6697 mol/kg does my answer have the correct amount of sig figs? Same for 0.1004mol / 0.1kg = 1.004mol/kg ?
February 20, 2012

Chemistry
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 ...
February 20, 2012

Chemistry(Thank you for helping)
1) Given this data in a study on how the rate of a reaction was affected by the concentration of the reactants Initial Rate, RUN # (A), M (B), M (C), M mol L-1 s-1 1 0.200 0.100 0.600 5.00 2 0.200 0.400 0.400 80.0 3 0.600 0.100 0.200 15.0 4 0.200 0.100 0.200 5.00 5 0.200 0.200...
February 20, 2012

Chemistry
I am trying to find th e# of moles of NaCl but I am not sure of the units. For my answer I get 0.0669. Should I leave it like this or do 6.69e-2?
February 20, 2012

Chemistry
Would it be k[XO]^2[O2] because second order is squared?
February 20, 2012

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]...
February 20, 2012

Chemistry
For both NaCl and sucrose we had to mix it with 100ml of water so for the mass of solvent (kg) I would do 100mL X 1.00g/mL = 100g and then to get kg I would divide by 1000 so 0.1kg. This would be the answer for sucrose as well. Is this correct?
February 20, 2012

Chemistry
so do I use the weight that I got for NaCl and multiply by 1.00g/mol? Or the solvent in this case is water and we used 100mL
February 20, 2012

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.
February 20, 2012

Chemistry
Ok and the units I use would be degrees celsius correct?
February 20, 2012

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?
February 20, 2012

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 ...
February 20, 2012

Chemistry
for my answer I get 0.0669. Should I leave it like this or do 6.69e-2?
February 20, 2012

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.
February 20, 2012

Chemistry
Is this correct?
February 20, 2012

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...
February 20, 2012

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...
February 20, 2012

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 ...
February 20, 2012

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.
February 20, 2012

Chemistry(Please check)
Oh ok I did realize that. Now I got 0.0775M
February 19, 2012

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?
February 19, 2012

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...
February 19, 2012

Chemistry(Please help)
Disregard question.
February 19, 2012

Chemistry(Please help)
I subtracted again and got 9.83. So do I set it up like this 453.74= Xether * 463.57
February 19, 2012

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...
February 19, 2012

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 ...
February 19, 2012

Chemistry
ok thank you!!!
February 19, 2012

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 ...
February 19, 2012

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?
February 19, 2012

Chemistry
thank you!
February 19, 2012

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...
February 19, 2012

Chemistry(Please check)
Ok, thank you for your help!!
February 19, 2012

Chemistry(Please check)
so then answers 2 and 3 are not correct?
February 19, 2012

Chemistry(Please check)
So wouldn't a catalyst just speed up the rate too and not the rate constant?
February 19, 2012

Chemistry(Please check)
Oh ok I understand, thank you.
February 19, 2012

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?
February 19, 2012

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...
February 19, 2012

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...
February 19, 2012

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.
February 19, 2012

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 ...
February 19, 2012

Chemistry(Please check)
oh I understand you have to add them. Thank you.
February 19, 2012

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.
February 19, 2012

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?
February 19, 2012

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?
February 19, 2012

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?
February 19, 2012

Chemistry(Please help)
So I would do 0.0346/180.1 for aspirin and 2.04/119.40 for CHCH3?
February 19, 2012

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 ...
February 19, 2012

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 ...
February 19, 2012

Chemistry(Please help, thank you!)
Disregard this question. I actually got the answer.
February 19, 2012

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
February 19, 2012

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?
February 18, 2012

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.
February 18, 2012

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.
February 18, 2012

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.
February 18, 2012

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 ...
February 18, 2012

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 ...
February 15, 2012

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 ...
February 14, 2012

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?
February 14, 2012

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 ...
February 14, 2012

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...
February 13, 2012

Chemistry(Please help, thank you)
So in that case I would just divide my answer of4842756.8 by 1000 = 4842.76 kJ/mol correct?
February 13, 2012

Chemistry(Please help, thank you)
The units for the specific heat of water that they gave me were J/ g x K
February 13, 2012

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?
February 13, 2012

Chemistry(Please help, thank you)
ok thank you very much!!!
February 13, 2012

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?
February 13, 2012

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?
February 13, 2012

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 ...
February 13, 2012

Chemistry
Or should I use the # of moles that I calculated for Mg which was 6.25e-3.
February 13, 2012

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?
February 13, 2012

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 ...
February 13, 2012

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 ...
February 13, 2012

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?
February 13, 2012

Chemistry
They give the specific heat capacity for water, is that what I use?
February 13, 2012

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 ...
February 13, 2012

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 ...
February 13, 2012

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 ...
February 13, 2012

Chemistry
Its suppose to be deltaT f. So would the minimum data required be Tf, Kf, and mass of solute?
February 13, 2012

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 ...
February 13, 2012

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
February 13, 2012

Chemistry
so delta T would be 1.86 but Im not sure what Kf would be?
February 12, 2012

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 ...
February 12, 2012

Chemistry
Ok thank you
February 12, 2012

Chemistry
27.8/80=0.3475 but I dont understand what to do next.
February 12, 2012

Chemistry
the answer choices that were given are: a)769g b)36.2g c)972g d)34.8g e)157g
February 12, 2012

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