# Posts by lena

Total # Posts: 1,049

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...

Chem
I understand now. Thank you :)

Chem
I don't 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?

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...

chem
Yes I figured out that problem. :) Thanks a lot!

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

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 don't know how to figure out percent dissociation) For the ...

Chem
We weren't given the molarity of Ca(OH)2, that's why I don't understand how to do the question.

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

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 ...

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

Chem
Thank You :D

Chem
sorry about the re-post it was an accident

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

chemisty
Thanks :)

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 ...

chemisty
What would happen if you reacted potassium dicarbonate with HCL and NaOH?

Chem
Thank You :)

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

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 :)

Chem
Thank You :)

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?

Chem
I don't 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 ...

Chemistry
Thank you :)

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

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

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?

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) <--> ...

Chemistry
Ohh. I understand now. Thank you so much :)

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?

Chemistry
is the 1000 k, 1000 kelvin? :S

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.

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 ...

sci
are radiocarbon dating and carbon-14 dating the same thing?

Chem
Thank you :)

Chem
I don't 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?

Chem
should I have 6 around every F? :S

Chem
Would the I have a lone pair?

Chem
oops, you`re right. Thanks :)

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

Chem
where is the lone pair? isn't iodine completely bonded to the fluorines?

Chem
IF5 would be not equal to 0 right?

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>?

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 ...

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 ...

Chem
Ohh. Yes I do see that. Thanks :)

Chem
Ohhhh OK. Thank you :)

Chem
Why isnt the carbon negetive ?

Chem
For something that has 3 different elements how would I know which is positive and which is negetive? For exmaple HCN.

Chem
How do I know which part of a compund is negectivly charged and which side is positivly charged? In BH3 how would I know if the B is positivly charged or negetively charged? and for hydrogen?

Chem
Thank you :)

Chem
Ok. Thank you :)

Chem
Is a C-H bond polar or non-polar? Is a C-Cl bond polar or non-polar? I have different sources giving me different ranges. One says that anything with an electronegetivity of 0.5 or less is non-polar and I have anothre source saying anything 0.3 and less is non-polar. Which one...

chem
Thank you :)

chem
what does the delta mean?

chem
U have to show the partial charges and bond dipoles on my ;lewis structure of CH3Cl For the partial charges would I just have a negetive sign as the superscript of Cl and a positive sign and the superscript of C ? What exactly must I do to show bond dipoles? I didn't know ...

Chem
When you said "While a physical appearance of an element makes it easier to explain to beginning students the how and why of chemical reactions," do you mean there are rules set in place and exceptions but they aren't explained; as students we just accept them as...

Chem
What are some pros and cons for energy level diagrams and electron configuration diagrams? I was very long for elements like uranium and such but im not sure if those are the types of answers im supposed to be giving. Are there any flaws in the two methods (obvious con)?

Chem
Thank you :)

Chem
Is this a possible quantum number: 3,2,2,-1/2 This is my thikning: n=3 so therefore l = 0-2 so therefore ml could = 2 However, many of my classmates said it was impossible.

Chem
Thank you :)

Chem
What 4 quantum numbers describes one of the outermost electrons in a strontium atom in ground state? 5,0,0,1/2 Is my answer correct?

Chem
I finally understand it. Thank you so much!

Chem
When I said below I meant on the actually forum; the previous question I posted.

Chem
Thank you :) Could you also please answer the question below? I still don't understand it.

Chem
when I said configuration I meant electron configuration

Chem
Theres this one question in my homework that says that there is an unusual but actual condensed configuration and they said to write it. Which element are they referring to? :S

Chem
Thank you so much :)

Chem
So we are following the Aufbau Principle?

Chem
"But the half filled rule, and the one you apparently used to fill the s half way and the p orbitals half way, ARE FOR THE SAME ORBITAL" So the 2S and 2P are both in the second orbital so therefore there is no electron promotion?

Chem
My teacher was saying that its better for the shells to be half full rather than one being completely full and the other being not half full. He was referring to Hund's law. What do you think about this?

Chem
I was asked to fraw the energy level diagram for carbon. Carbon has 6 electrons so would the 2s and 2p orbitals both be half full? 1s = 2 electrons 2s= 1 electron 2p = 3 electrons

Chem
Ohhh.. OK. I understand. Thank you soo much for all your help today :)

Chem
A -> 3C The molar mass of A is 10.0g/mol If 2.0 grams of A reacts, how many moles of C will be produced? A -------------------> 3C m.mass= 10.0g/mol mass = 2.0 g moles = 2.0 g/10.0 g/mol =0.2 mol moles of c = 3 x 0.2 = 0.6 mol Did I do this correctly?

Chem
Thanks :)

Chem
Are the followinf true: atomic radii decreases from left to right, across a row atomic radii increases from top to bottom of a column

Chem
Thank you so much :)

Chem
mass = 4.550 g molar mass = 142.05 g/mol n= 0.032030975 mol c= 0.032030975/0.125 = 0.256 mol/L would I have 3 or 4 sig. digs? cause when I converted 125.0mL into 0.125 L I lost a sig dig;or should it be 0.1250 L?

Chem
As a part of a study to see whther just the chloride ion on NaCl accelerates the rusting of iron, a student decided to see whtjer iron rusted in a solution on Na2SO4. The solution was made by dissolving 4.550 g of Na2SO4 in water using 125.0 mL volumetric flask to adjust the ...

Chem
I did make a mistake on my calculator. Thanks a lot :)

Chem
volume = 322 mL temperature = 150 celcius pressure = 175 kPa mass = 0.448 Calculate the molar mass of the gas. First I converted volume to 0.332 L. Second I converted 150 celcius into 423 kelvin. PV = nRt (175)(0.322) = n(8.314)(423) n= 0.016022988 molar mass = 0.448/0....

Chem
Thanks :D

Chem
Thanks a lot DrBob :)

Chem
A tank car containing concentrated HCL (molarity 12.1) derails and spills exactly 1500 L of acid. Solid potassium hydroxide is required ot neutralize the spill. (a) Write a balanced chemical equation. HCl + KOH -> kCl + H2O (b) What is the molar ratio between acid and base...

Chem
I think I understand it now. They also said at STP. I didn't notice that at first. Thanks :)

Chem
One of my questions asks me to find the volume of neon gas. I thought neon didn't attach with other atoms because it had a full valence shell, how would it form into a gas? What would the formula be? N2, N3 ?

Chem
Thank you :) If I would have had something like 2.4 would I round it to 2 because of significant digits?

Chem
How many moles of hydrogen and oxygen are in 2 moles of water? water: h2o # of molecules = (6.022 x 10^23)(2)= 1.2044 x 10^23 # of hydrogen atoms = (1.2044 x 10^23)(2)= 2.4088 x 10^24 # of oxygen atoms = 1.2044 x 10^24 Did I do this correctly? What do I do about significant ...

Chem
Ohh.. thank you :)

Chem
Hg(CN) I don't know how to name this. I know that Hg is mercury and C is carbon and N is nitrogen.

Chem
Thank you :)

Chem
superscript:226 element:Z subscript:29 Whats does the subscript and superscript represent?

Chem
Thanks :)

Chem
Does electron affintity increase from left to right on the periodic table? And are there any trends for the groups?

Science/Careers
OK. Thank you soo much.

Science/Careers
I wanted to know how universities look at summer school courses. My guidance counseller told me that it dosen't matter whether the course you take is in (normal)school or summer school but others are saying that some universities don't accept it. Im taking a core grade...

Careers/Science
Thank you :)

Careers/Science
How long in the undergraduate program to get into PharmD? And are there any school that's allow you to go right into PharmD from highschool?

Careers/Science
After the PharmD program are you officially a pharmacist or is there more education you have to go through?

Math
We're learning something about transformations on the exponents of a function. For exmaple 2^x becomes 2^4(x-2)+2. Would this mean that the 2^x graph stretched vertically by a factor of 4, moved two units to the right and 2 units downwards?

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