## Search found 10 matches

Tue Feb 23, 2021 8:59 pm
Forum: Chemistry forum
Topic: Help with Photometry problem!!!
Replies: 0
Views: 5131

### Help with Photometry problem!!!

The problem is : We will look at a solution called “sample X” containing water and “substance X" We have a path length of 1cm, an extinction coefficient of 0.06 cm-1M-1 and an absorbance at lambda max of .350. . What is the concentration of substance x in our sample? At what concentration would...
Wed Feb 17, 2021 5:59 am
Forum: Chemistry forum
Topic: Help with pI/pH problem? Any input Appreciated!!!
Replies: 7
Views: 2069

### Re: Help with pI/pH problem? Any input Appreciated!!!

Thanks!!! I am having difficulty understanding why 50% dissociated at pH2.4 and 90% has dissociated at pH3.4. That seems like a substantial increase over a short pH difference.
Wed Feb 17, 2021 5:49 am
Forum: Chemistry forum
Topic: Help with pI/pH problem? Any input Appreciated!!!
Replies: 7
Views: 2069

### Re: Help with pI/pH problem? Any input Appreciated!!!

Thank you for explaining. Are you 100% confident that the way to do the problem is using Henderson Hasselback equation and utilizing a pka=2.4?
3.4=2.4 + logA-/HA gets me a 10 to 1 ratio of dissociated acid (A-) to undissociated acid (HA). Is this the correct answer?
Wed Feb 17, 2021 5:33 am
Forum: Chemistry forum
Topic: Help with pI/pH problem? Any input Appreciated!!!
Replies: 7
Views: 2069

### Re: Help with pI/pH problem? Any input Appreciated!!!

Thanks for your reply. 9.6 plus 2.4 equals 12 and 12 divided by 2 equals 6. Looking up the pI of Leucine, I also saw it was 6 so I am pretty sure that is the right answer. The 2nd part of the question asks about when the pH= 3.4. I do not believe that the pka is 2.4 when the pH is 3.4. Therefore I d...
Tue Feb 16, 2021 5:59 pm
Forum: Chemistry forum
Topic: Help with pI/pH problem? Any input Appreciated!!!
Replies: 7
Views: 2069

### Help with pI/pH problem? Any input Appreciated!!!

Hello. My question is as follows :Calculate the pI of Leucine pKa (carboxyl) = 2.4; pKa (amino) = 9.6; What is the ratio of COO- : COOH at pH 3.4? For pI I get 6 (9.6 + 2.4/2 = 6). I am having great difficulty with the 2nd part of the question. I get 63.8% COO-: 36.2% COOH. I deduced this since 50% ...
Tue Feb 09, 2021 3:39 pm
Forum: Chemistry forum
Replies: 4
Views: 1538

I am having difficulty with the following problem: If you dissolve 360mg glucose (Formula Weight: 180.16g/mole) in 5mL of water: 1.What is the concentration of glucose in mM and µM? I got 360 mg x 1mole/180.16 g = .002 moles .002 moles x .005L = 1 x 10^-5 M x 1 x10^3 mM/1M = 1 x 10^-3 mM glucose 1 x...
Tue Feb 02, 2021 5:17 am
Forum: Chemistry forum
Replies: 7
Views: 2189

Thanks for all your help!!! The worksheet says to put everything in scientific notation. Therefore if I get an answer, for example, as 1.5, would I write 1.5 x 10^0? Any input on this would be greatly appreciated!!!!
Tue Feb 02, 2021 4:38 am
Forum: Chemistry forum
Replies: 7
Views: 2189

Thanks again for your reply!!! Do you believe that the question was perhaps a typo? Would I write "Not Applicable" as the answer?
Tue Feb 02, 2021 4:09 am
Forum: Chemistry forum
Replies: 7
Views: 2189