I recently took part in the nsw titration competition and in the first part, we put unknown concentration of NaOH in burette, and 25mL of 0.1292mol/L of HCL in the conical flask. Then we put 3 drops of phenolphthalein indicator into the conical flask, and let the NaOH run into the conical flask until the solution in the flask turned a light pink colour. From this we recorded the volume and found out the concentration of the NaOH solution.
But my question is how come we can you can still use PHENOLPHTHALEIN (meant to be used when equivalence point is between 8.3 - 10 pH), when we are using a STRONG ACID and a STRONG BASE, which means it will have an equivalence point of 7.
As a matter of fact the whole idea of the equivalence point is that they do 100% neutralise one another. The pH of the solution would be 7 since a neutralisation between a strong acid and base gives a solution of pH of 7.
In terms of the question, the reason why we can use methyl orange, bromothymol blue and phenolphthalein as indictors for this particular titration is because the change in pH is so drastic, it doesn't matter which of the three we use. So the colour will drastically turn from colourless to pink as you put more NaOH in. So the transition range of indicators doesn't necessarily have to be where the equivalence point is.
Current Status: Ceasefire with HSC
^ QUOTE (Ekman)
"As a matter of fact the whole idea of the equivalence point is that they do 100% neutralise one another. The pH of the solution would be 7 since a neutralisation between a strong acid and base gives a solution of pH of 7.
In terms of the question, the reason why we can use methyl orange, bromothymol blue and phenolphthalein as indictors for this particular titration is because the change in pH is so drastic, it doesn't matter which of the three we use. So the colour will drastically turn from colourless to pink as you put more NaOH in. So the transition range of indicators doesn't necessarily have to be where the equivalence point is. "
with phenolphthalein it is slightly easier to notice the change.
2014 HSC
2015 Gap Year
2016-2018 UOW Bachelor of Maths/Maths Advanced.
Links:
View English Notes (no download)
Maths Notes - Free Sample
thsconline: https://thsconline.github.io/s/
For 2017 papers, check the thread in the Mathematics forum.
Dan will be back 14/10/17
how urgent is URGENT?
2014 HSC
2015 Gap Year
2016-2018 UOW Bachelor of Maths/Maths Advanced.
Links:
View English Notes (no download)
Maths Notes - Free Sample
thsconline: https://thsconline.github.io/s/
For 2017 papers, check the thread in the Mathematics forum.
Dan will be back 14/10/17
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