A compound ‘X’ is a weak acid and it exhibits colour change at pH close to the equivalence point during neutralization of NaOH with CH3COOH. Compound ‘X’ exists in ionized from in basic medium. The compound ‘X’ is
- Methyl orange
- Methyl red
- Phenolphthalein
- Eriochrome Black T
The Correct Option is C
Approach Solution - 1
The question involves determining which compound acts as an indicator that exhibits a color change at the pH close to the equivalence point during the neutralization of NaOH (a strong base) with CH3COOH (a weak acid), and exists in ionized form in basic medium.
- Identification of equivalence point pH:
- During the neutralization of a strong base like NaOH with a weak acid like CH3COOH, the equivalence point will occur at a pH greater than 7 because the acetate ion (CH3COO-) acts as a weak base in water.
- Properties of given indicators:
- Methyl orange: Changes color at pH 3.1 to 4.4.
- Methyl red: Changes color at pH 4.4 to 6.2.
- Phenolphthalein: Changes color at pH 8.2 to 10.0.
- Eriochrome Black T: Commonly used in complexometric titrations, does not change at the right pH range here.
- Analysis and Conclusion:
- Since the equivalence point for the titration of CH3COOH with NaOH is above 7, Phenolphthalein is the suitable indicator.
- Phenolphthalein changes color around the basic pH where it is ionized, transitioning from colorless in acidic form to pink in its basic form. This suits the requirement of color change at the equivalence point and its existence in ionized form in basic medium.
Therefore, the correct answer is Phenolphthalein.
Approach Solution -2
In basic medium,
[H⨁] decreases and therefore more of (Ph⊖) is produced.
So, the correct option is (C): Phenolphthalein.
Top Questions on Acids and Bases
- What is the pH of a 0.1 M NaOH solution?
- MHT CET - 2025
- Chemistry
- Acids and Bases
- What is the pH of a 0.01 M solution of $ \text{HCl} $?
- MHT CET - 2025
- Chemistry
- Acids and Bases
- What is the molar concentration of hydrogen ions in a solution of $ 0.1 \, \text{M} $ $ \text{HCl} $?
- MHT CET - 2025
- Chemistry
- Acids and Bases
- What is the pH of a 0.001 M solution of hydrochloric acid (HCl)?
- MHT CET - 2025
- Chemistry
- Acids and Bases
- What is the pH of a 0.001 M hydrochloric acid (HCl) solution?
- MHT CET - 2025
- Chemistry
- Acids and Bases
Questions Asked in JEE Main exam
- Identify the correct statements: The presence of –NO\(_2\) group in benzene ring A. activates the ring towards electrophilic substitutions. B. deactivates the ring towards electrophilic substitutions. C. activates the ring towards nucleophilic substitutions. D. deactivates the ring towards nucleophilic substitutions. Choose the correct answer from the options given below:
- JEE Main - 2026
- General Chemistry
- Let $\vec{a}=2\hat{i}-\hat{j}-\hat{k}$, $\vec{b}=\hat{i}+3\hat{j}-\hat{k}$ and $\vec{c}=2\hat{i}+\hat{j}+3\hat{k}$. Let $\vec{v}$ be the vector in the plane of $\vec{a}$ and $\vec{b}$, such that the length of its projection on the vector $\vec{c}$ is $\dfrac{1}{\sqrt{14}}$. Then $|\vec{v}|$ is equal to
- JEE Main - 2026
- Vector Algebra
A substance 'X' (1.5 g) dissolved in 150 g of a solvent 'Y' (molar mass = 300 g mol$^{-1}$) led to an elevation of the boiling point by 0.5 K. The relative lowering in the vapour pressure of the solvent 'Y' is $____________ \(\times 10^{-2}\). (nearest integer)
[Given : $K_{b}$ of the solvent = 5.0 K kg mol$^{-1}$]
Assume the solution to be dilute and no association or dissociation of X takes place in solution.- JEE Main - 2026
- Solutions
- The wavelength of photon 'A' is 400 nm. The frequency of photon 'B' is \(10^{16}\,\text{s}^{-1}\). The wave number of photon 'C' is \(10^{5}\,\text{cm}^{-1}\). The correct order of energy of these photons is:
- JEE Main - 2026
- General Chemistry
- Given below are two statements: Statement I: The increasing order of boiling point of hydrogen halides is HCl<HBr<HI<HF. Statement II: The increasing order of melting point of hydrogen halides is HCl<HBr<HF<HI. In the light of the above statements, choose the correct answer from the options given below:
- JEE Main - 2026
- General Chemistry
Concepts Used:
Acids and Bases
Acid is any hydrogen-containing substance that is capable of donating a proton (hydrogen ion) to another substance. Base is an ion or molecule capable of accepting a hydrogen ion from acid.
Physical Properties of Acids and Bases
| Physical Properties | ACIDS | BASES |
| Taste | Sour | Bitter |
| Colour on Litmus paper | Turns blue litmus red | Turns red litmus blue |
| Ions produced on dissociation | H+ | OH- |
| pH | <7 (less than 7) | >7 (more than 7) |
| Strong acids | HCl, HNO3, H2SO4 | NaOH, KOH |
| Weak Acids | CH3COOH, H3PO4, H2CO3 | NH4OH |
Chemical Properties of Acids and Bases
| Type of Reaction | Acid | Bases |
| Reaction with Metals | Acid + Metal → Salt + Hydrogen gas (H2) E.g., Zn(s)+ dil. H2SO4 → ZnSO4 (Zinc Sulphate) + H2 | Base + Metal → Salt + Hydrogen gas (H2) E.g., 2NaOH +Zn → Na2ZnO2 (Sodium zincate) + H2 |
| Reaction with hydrogen carbonates (bicarbonate) and carbonates | Metal carbonate/Metal hydrogen carbonate + Acid → Salt + Carbon dioxide + Water E.g., HCl+NaOH → NaCl+ H2O 2. Na2CO3+ 2 HCl(aq) →2NaCl(aq)+ H2O(l) + CO2(g) 3. Na2CO3+ 2H2SO4(aq) →2Na2SO4(aq)+ H2O(l) + CO2(g) 4. NaHCO3+ HCl → NaCl+ H2O+ CO2 | Base+ Carbonate/ bicarbonate → No reaction |
| Neutralisation Reaction | Base + Acid → Salt + Water E.g., NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l) | Base + Acid → Salt + Water E.g., CaO+ HCl (l) → CaCl2 (aq)+ H2O (l) |
| Reaction with Oxides | Metal oxide + Acid → Salt + Water E.g., CaO+ HCl (l) → CaCl2 (aq)+ H2O (l) | Non- Metallic oxide + Base → Salt + Water E.g., Ca(OH)2+ CO2 → CaCO3+ H2O |
| Dissolution in Water | Acid gives H+ ions in water. E.g., HCl → H+ + Cl- HCl + H2O → H3O+ + Cl– | Base gives OH- ions in water. |
Read more on Acids, Bases and Salts