Friday
April 18, 2014

Posts by lena


Total # Posts: 989

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

chem
Thanks :D

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 rel...

pH calculations
Thank you :D

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,...

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...

Chem
Thanks :D

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 gase...

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...

Chem
The question asked why the irritation occur specifically in the area of lower acidity.

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

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?

Chem
Ohhh. Should have thought about that. Thanks a lot Dr Bob :D

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

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

Chem
are we doing the ratio between the number of mols? ;S

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

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) St...

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

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

Chem
but would I keep one significant digit cause on the 0.1?

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...

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?

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?

Chem
Does the R just represent a chain?

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 ?

Chem
Thanks :)

Chem
Thanks :)

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?

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?

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 what...

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?

CHEM
Thanks :)

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 undissoci...

chem
Thanks a lot Dr Bob :)

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 :)

chem
I redid it and I got 11.25 :) Thanks :)

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 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?

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 dont know how to figure out percent dissociation) For the HCN I ...

Chem
We weren't given the molarity of Ca(OH)2, thats why I dont 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 c...

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 clea...

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 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...

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) <--> PCl...

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 w...

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

Chem
Thank you :)

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?

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 molec...

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 gre...

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!

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