The following acid-base indicators are available to follow the titration. Which of them would be most appropriate for signaling the endpoint of the titration? EXPLAIN
------- COLOR CHANGE ------
INDICATOR <-> Acid form <-> Base Form <-> pH Transition Interval
Bromphenol blue <-> yellow <-> blue <-> 3.0-5.0
Bromthymol blue <->yellow <-> blue <-> 6.0-7.6
Thymol blue <-> yellow <-> blue <-> 8.0-9.6
PLEASE ANSWER IT!!!!!!!!!!!!!!!
thank u and next time i will show some work
What are you titrating? It makes a difference. Look up or calculate the approximate pH for the equivalence point; pick the indicator from that.
it says the titration of 0.145g of a weak acid with 0.100M NaOH as the titrant
A weak acid titrated with a strong base has an equivalence point of about 8.7 or so; therefore, you want to use an indicator that changes color as close to 8.7 as possible. (The average of 8.0 and 9.6 is 8.8) There is only one indicator in your list that comes close. Given a choice, I would choose phenolphthalein which has a range of about 8 to 10 for a mid point of ab out 9.
THANX. but did u guess 8.7 or did u calculate it? if so could u show howw???
To determine which acid-base indicator would be most appropriate for signaling the endpoint of the titration, we need to consider the pH at which the endpoint occurs. The endpoint of a titration is the point at which the acid and base have reacted completely, indicating the completion of the reaction. This is typically signaled by a significant change in color of the indicator.
Looking at the available indicators and their pH transition intervals:
1. Bromphenol blue: It transitions from yellow to blue within the pH range of 3.0-5.0.
2. Bromthymol blue: It transitions from yellow to blue within the pH range of 6.0-7.6.
3. Thymol blue: It transitions from yellow to blue within the pH range of 8.0-9.6.
To choose the most appropriate indicator, we need to consider the pH range at which the titration is expected to reach its endpoint.
If the expected pH at the endpoint falls within the pH transition interval of any of the indicators, then that indicator would be suitable.
If the pH at the endpoint is below 5.0, then bromphenol blue would be the most appropriate indicator as it transitions in the desired range. If the pH at the endpoint is between 6.0 and 7.6, then bromthymol blue would be the best choice. Thymol blue would be suitable if the pH at the endpoint is between 8.0 and 9.6.
Without more information about the specific titration being performed, it is not possible to determine which indicator would be most appropriate for signaling the endpoint. The choice of indicator depends on the expected pH at the endpoint, which varies depending on the specific acid and base being titrated.
I did not guess. You said a weak acid and NaOH so I picked acetic acid (which I will call HAc) with NaOH. I used 0.1M HAc and titrated with 0.1M NaOH. At the equivalence point we will have 0.05M NaAc which is hydrolyzed in the water solution.
...........Ac^= + HOH ==> HAc + OH^-
initial....0.05M...........x.....x
change.....-x..............x......x
equil....0.05-x..........x.......x
Kb for the Ac^- = (Kw/Ka for HAc) = (x)(x)/(0.05)
Ka is 1.8E-5, Kw is 1E-14 and I obtained 5.27E-6 = x = (OH^-). I converted that to pOH and stuck it into pH + pOH = pKw = 14 and pH = 8.72.
By the way, we're glad to help but I've answered quite a few questions for you gratis; it's time you start showing some of your work. After all, this is a home work HELP site and not some place for you to dump all of your home work. The idea here is for you to learn how to do these yourself.