What is the pKa of phenolphthalein?
Table of Contents
- 1 What is the pKa of phenolphthalein?
- 2 Why is phenolphthalein not a suitable indicator to determine the pH of a substance?
- 3 What is phenolphthalein class 7th?
- 4 Why does phenolphthalein give pink in basic medium?
- 5 Why is pH at the equivalence point larger than 7 when you titrate a weak acid with a strong base?
- 6 What Colour does phenolphthalein give at pH less than 7?
- 7 What colour does phenolphthalein give at pH less than 7?
What is the pKa of phenolphthalein?
9.3
Phenolphthalein has a pKa of 9.3. When conducting a titration of an acid analyte with a base titrant using phenolphthalein as the indicator, the pH will be low at the beginning, so the phenolphthalein will be mostly in the un-ionized or “protonated” “acid” form (we’ll refer to as HIn).
Why is phenolphthalein not a suitable indicator to determine the pH of a substance?
Hence the main reason is that phenolphthalein is a weaker acid than the acid that is to be titrated. The endpoint pH (equivalent point) of a reaction between a weak acid and a strong base is given by pH = 1/2 pKw + 1/2pKa + 1/2 log [acid]. Phenolphthalein changes color in the pH range of 8.3 to 10.
Why phenolphthalein is not a suitable indicator for titrating a weak base against a strong acid?
Answer: Why is phenolphthalein not a suitable indicator for titrating weak base against strong acid? – Quora. Because the equivalence point of a weak base-strong acid system is likely going to be outside of the color indicator range of phenolphthalein.
What is phenolphthalein class 7th?
(c) Phenolphthalein: Phenolphthalein is an indicator solution which turns colourless in the presence of acids. Therefore, in the presence of sulphuric acid, phenolphthalein turns colourless.
Why does phenolphthalein give pink in basic medium?
Phenolphthalein solution turns pink in the presence of a base. This is because the hydroxide ions react with the acidic group present and lead to the formation of ions. These ions impart color to the solution. This is how phenolphthalein solution acts as an acid-base indicator in titrations.
Why is phenolphthalein not much appropriate to identify whether the given solution is acid-base or salt?
Both in acid medium and neutral medium, Phenlopthalin makes the solution colorless and only in Basic medium, It shows pink color. So, I think it’s not appropriate.
Why is pH at the equivalence point larger than 7 when you titrate a weak acid with a strong base?
At the equivalence point, all of the weak acid is neutralized and converted to its conjugate base (the number of moles of H+ = added number of moles of OH–). However, the pH at the equivalence point does not equal 7. This is due to the production of conjugate base during the titration.
What Colour does phenolphthalein give at pH less than 7?
A substance below pH 7 is considered acidic; above pH 7 is considered basic. Phenolphthalein is naturally colorless but turns pink in alkaline solutions.
Why phenolphthalein Cannot show any Colour even at pH 7?
Phenolphthalein is a weak acid and is colorless in solution although its ion is pink. Adding hydroxide ions (OH-, as found in bases) will change the phenolphthalein into its ion and turn the solution pink.