Why Choose Phenolphthalein Over Bromothymol Blue for Equivalence Point at pH 7?

AI Thread Summary
Phenolphthalein is preferred over bromothymol blue for determining the equivalence point at pH 7 due to its clearer color change, which occurs between pH 8.3 and 10.0, allowing for more precise endpoint identification. In contrast, bromothymol blue changes color at a pH range of 6.0 to 7.6, making it difficult to determine the exact endpoint as the solution may appear mixed. The discussion highlights that the choice of indicator should align with the pH range of the equivalence point for accurate titration results. Additionally, there is some confusion regarding which solution should be in the burette, with consensus leaning towards the acid being placed there. Ultimately, selecting the right indicator is crucial for achieving consistent and reliable titration outcomes.
Chocolaty
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Why is it better to use phenolphthalein than bromothymol blue to determine the equivalence point which is equal to 7?

bromothymol blue: 6.0 - 7.6 yellow @ blue
phenolphthalein: 8.3 - 10.0 colorless @ pink

 
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My guess would be that since 7 falls inside the range for the blue you would have to stop the titration while the color is still mixed. With phenolphthalein you stop when it completely changes color which makes it easier to obtain consistent results rather then trying to interpret the mix of colors.
 
zwtipp05 said:
My guess would be that since 7 falls inside the range for the blue you would have to stop the titration while the color is still mixed. With phenolphthalein you stop when it completely changes color which makes it easier to obtain consistent results rather then trying to interpret the mix of colors.
Actually, that is not quite right. The best indicator to use for a titration is one which the equivalence point (pH) falls into the range - preferably the middle - of the indicator. In this case, the bromothymol blue would be ideal, because it would change colour when the pH equals about 7. The phenolphthalein won't even start to change colours.
 
Assuming this is a strong acid vs strong base titration, what solution is in the burette?

From what Zwtipp05 posted, I think he means that the acid is in the burette and the base is in the conical flask along with the indicator.

And according to christinono, the base is in the burette and the acid is in the conical flask along with the indicator.
 
As siddharth said, let's assume it is a strong acid/base titration.

Either way (acid or base in burette), only one of the indicators is the best to use but can Chocolaty tell me which and his reasons why?

However, even though two ways have been suggesed, only one is correct. The acid should go in the burette.

The Bob (2004 ©)
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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