A community for students.
Here's the question you clicked on:
 0 viewing
alphabeta
 one year ago
Titration question (attached file). Can someone tell me, in as much detail as possible, how I should approach this exercise?
alphabeta
 one year ago
Titration question (attached file). Can someone tell me, in as much detail as possible, how I should approach this exercise?

This Question is Closed

CherokeeGutierrez
 one year ago
Best ResponseYou've already chosen the best response.0idk if this would help but your bascially copying something on the top graph to the bottom.

welshfella
 one year ago
Best ResponseYou've already chosen the best response.0yes with the difference that you include the pH range of the bromophenol blue indicator

alphabeta
 one year ago
Best ResponseYou've already chosen the best response.0Well, I don't believe that the pH range of the indicator is the only difference? For example, the initial pH of the acid should be different I guess (but how do I know where? Is it a value that I just have to learn by heart, or?). Also the halfequivalence point should be different, since you have a weak acid with strong base in this case compared to the first graph (but again, how do I figure this out?).

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0OK dear: you are in the right way, the propanoic acid is a weak acid with a pKa 4.88, and the potassium hydroxide is a strong base. Then the pHrange of the indicator is 3.04.6. The pH of the acid at 0mL titration can be calculated with the formula \[[H ^{+}]= \sqrt{Ka \times Ca}\] where pKa= log Ka = 4.88 Ka= 10^(pka) Ca= initial concentration of the acid = 0.1M The after that you can calculate all the points until the equivalent point with the Henderson Hasselbach equation for a buffer. At the 50% titration (12.5mL) the pH will be equal to the pKa of the acid. then the pH at the equivalence point is going to be a basic salt (potasssium propanoate) an you have to calculate the [OH] and with the Kb and the concentration of the salt and then calculate the pH

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0do you need more details?

welshfella
 one year ago
Best ResponseYou've already chosen the best response.0yes you are right I misread the question

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0dw:1441917412969:dw

alphabeta
 one year ago
Best ResponseYou've already chosen the best response.0Oh, thank you SO much @Cuanchi  really appreciating your informative answer! I was just wondering if you mind demonstrating for me Henderson Hasselbach equation? For instance to find out what the pH would be when 5 cm^3 of KOH were added? (And I guess the same equation is used for what you described in your last paragraph?)

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Here is a very good complete tutorial. See the example 2 for answer your question. http://chemwiki.ucdavis.edu/Analytical_Chemistry/Quantitative_Analysis/Titration/Titration_Of_A_Weak_Acid_With_A_Strong_Base to solve it you have to do and ICE table . I=initial C= change E= Equilibrium to figure out how many moles of each reactants and products you have at each point of your titration. If you know the number of moles and the volume (that will be changing every time that you add more base) you can calculate the concentrations of the different component of the reaction at any given time. in the Henderson Hasselbach equation used to calculate the [H+] in a buffer system \[[H ^{+}]= pKa+\log \frac{ [base] }{[acid] }\] you dont need to calculate the concentration of the base/acid, because both are in the same volume you can use the moles rate in turn ( the result is the same).

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Find the pH after the addition of 5 mL of 0.1 M KOH. SOLUTION 1. The number of millimoles of propanoic acid to be neutralized is 25mL x 0.1M propanoic acid = 2.5 mmol The number of millimoles of OH that will be added within 5 mL is 5mL x 0.1 Mol OH− =0.5 mmol 2. To calculate the pH with this addition of base we must use an ICE Table propanoic acid + OH > H2O + propanoate IInital 2.5 mmol 0 mmol  0 mmol Add 0 mmol 0.5 mmol  Changes 0.5 mmol 0.5 mmol  0.5 mmol EEquilibruim 2.0 mmol 0 mmol  0.5 mmol 3.This calculation of concentrations can be skipped go to (4) However, this only gives us the millimoles. To get the concentration we must divide by the total volume. The total volume is the 25 mL original solution of propanoic acid plus the 5 mL of KOH that was added. Therefore, the total volume is 25mL+5mL=30mL Concentration of propanoic acid: 2.0 mmol propanoic acid x 30mL=0.12 M Concentration of propanoate  : 0.5 mmol propanoate − x 35mL=0.0175 M Since an acid and its conjugant base are in equilibrium we can attempt to use the Hendersonhasselbalch equation. However, for this to work the reaction must follow certain rules. The ratio of the conjugant base and weak acid must be between 0.10 and 10. Also, both the ratio of the conjugant base and ka value and the ratio of the acid and ka value must exceed 100. In this problem the Hendersonhasselbalch equation can be applied because the ratio of propanoate to propanoic acid is 0.0175/0.12=0.146. This is between 0.10 and 10. The ratio of propanoic acid to ka is 0.12M/1.32x10−5=9090.9 and the ratio of propanoate to ka is 0.0175M/1.32x10−5=1325.75. These both exceed one hundred. 4. Therefore, we continue by using the Hendersonhasselbalch equation. pH=pka+log[A−]/[HA] pH=−log(1.32x10−5)+log(0.5/2.0) pH=4.27

alphabeta
 one year ago
Best ResponseYou've already chosen the best response.0So helpful! Thank you @Cuanchi once again! Should have been able to give more medals than just one for this answer!
Ask your own question
Sign UpFind more explanations on OpenStudy
Your question is ready. Sign up for free to start getting answers.
spraguer
(Moderator)
5
→ View Detailed Profile
is replying to Can someone tell me what button the professor is hitting...
23
 Teamwork 19 Teammate
 Problem Solving 19 Hero
 Engagement 19 Mad Hatter
 You have blocked this person.
 ✔ You're a fan Checking fan status...
Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.