Incorrect statement for the use of indicators in acid-base titration is :
Incorrect statement for the use of indicators in acid-base titration is :
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- Methyl orange may be used for a weak acid vs weak base titration.
Phenolphthalein may be used for a strong acid vs strong base titration.
- Methyl orange is a suitable indicator for a strong acid vs weak base titration.
- Phenolphthalein is a suitable indicator for a weak acid vs strong base titration.
The Correct Option is A
Approach Solution - 1
| Indicator | pH range |
| Methyl orange | 3.2 - 4.5 |
| Phenolpthalein | 8.3 - 10.5 |
Methyl orange may be used for a strong acid vs strong base and strong acid vs weak base titration. Phenolpthalein may be used for a strong acid vs strong base and weak acid vs strong base titration
So , the correct option is (A) : Methyl orange may be used for a weak acid vs weak base titration.
Approach Solution -2
The suitable indicators for different types of acid-base titrations are:
- Methyl orange is generally used for titrations involving strong acid vs weak base because it changes color in the acidic pH range (red at pH < 3.4 and yellow at pH > 4.4).
- Phenolphthalein is suitable for titrations involving weak acids vs strong bases as it changes color in the basic pH range (colorless below pH 4.8 and pink above pH 6.4).
- The statement that methyl orange may be used for weak acid vs weak base titration is incorrect because it is not suitable for that combination. For weak acid vs weak base titrations, neutral red or bromothymol blue would be more appropriate.
Thus, the incorrect statement is option (1).
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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. |
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