These free B.Pharm notes on acid-base titrations cover chapter 9 of Pharmaceutical Inorganic and Analytical Chemistry (BP106T), a first-semester subject. Read the key points below, then study the complete chapter PDF. You can browse every chapter in the Pharmaceutical Inorganic and Analytical Chemistry category.
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Overview of acid-base titrations
These notes start with volumetric analysis and direct, back and indirect titrations, then describe natural, synthetic, olfactory and universal indicators. They explain Ostwald’s theory and the resonance (quinonoid) theory, the four types of acid-base titration with their curves, preparation and standardisation of titrants, titration of very weak acids and bases, and the assay of ammonium hydroxide.
Key points on acid-base titrations
- At the equivalence point the amount of titrant added is chemically equal to the amount of analyte, and a colour indicator shows this point.
- Ostwald’s theory states that indicators are weak acids or weak bases whose unionised form has a different colour from the ionised form.
- The quinonoid form of an indicator has a longer conjugated system of electrons, absorbs visible light and gives a strong colour.
- Phenolphthalein has a pH range of 8.0 to 9.8 and is the best indicator for titrating a weak acid against a strong base.
- In a weak acid against weak base titration there is no sharp pH jump, so a pH meter or mixed indicator is used.
Relevance to pharmacy practice
Acid-base titrations are among the most common methods used to assay pharmaceutical substances and to standardise solutions such as hydrochloric acid and sodium hydroxide. Choosing the right indicator for each titration type gives accurate results, which is essential for quality control in a pharmacy laboratory.
Every chapter in this subject builds on the one before it, so do not skip topics that look simple. Definitions, principles, procedures and examples are the parts that examiners return to most often, and a clear understanding here will also make later subjects easier to follow in the coming semesters.
Frequently asked questions on acid-base titrations
What is the difference between direct and back titration?
In direct titration the analyte is titrated straight with the titrant. In back titration a known excess of standard titrant is added and the unused excess is titrated with a second standard titrant.
Why is hydrochloric acid not a primary standard?
Hydrochloric acid absorbs moisture, contains impurities and, being a volatile gas, escapes and loses strength with time. It is standardised against anhydrous sodium carbonate using methyl orange or methyl red.
Which indicator is used for strong acid against weak base titration?
Methyl orange is the usual indicator. The steep part of the curve lies in the acidic range, pH 3 to 7, and the pH at the equivalence point is always less than 7.0.
Quick revision checklist
Use this self-test after reading the chapter on acid-base titrations. If you can do all of the following without looking at your notes, you are ready for the exam.
- I can explain: direct, back and indirect titrations
- I can explain: the Ostwald theory of acid-base indicators
- I can explain: the resonance or quinonoid theory
- I can explain: titration curves for the four titration types
- I can explain: standardisation of sodium hydroxide and hydrochloric acid
Study and exam tips
Start by reading the chapter once for the overall idea, then revise acid-base titrations using headings, definitions, principles, reactions and examples. Short-answer questions in the university exam usually ask for definitions, principles, procedures, reactions and uses, so write these in your own words and practise the equations, tables and flow charts that the chapter has.
For wider reading, standard books and open resources such as the NCBI Bookshelf help you confirm terms and see more examples. Revise acid-base titrations again a day later and again a week later, because spaced revision improves long-term memory.
This page is part of the Pharmaceutical Inorganic and Analytical Chemistry series for first-semester B.Pharm students on B.Pharm Guru, where every chapter has a short summary and a full PDF. Bookmark this page and share it with classmates who are preparing for the same exam.
Related notes: 11. PRECIPITATION TITRATIONS AND GRAVIMETRY, 12. COMPLEXOMETRIC TITRATIONS.
Next: 10. NON-AQUEOUS TITRATIONS. Back to the Pharmaceutical Inorganic and Analytical Chemistry category.
