Class 12 Chemistry Practicals: Salt Analysis, Titration and the Viva

Salt analysis, as a procedure rather than a memory test

Students who find salt analysis hard almost always try to remember outcomes instead of following the sequence. The sequence is fixed and short: preliminary examination (colour, smell, solubility), then the systematic anion tests with dilute and concentrated acid, then the cation groups in order. Working out of order produces confident wrong conclusions, because a later group reagent will happily precipitate an ion that should have been removed earlier.

Titration: where accuracy marks actually go

Marks are awarded for concordant readings, not for a value close to the expected answer. Three readings within about 0.1 mL is the standard expectation. The most common causes of loss are entirely mechanical: an air bubble left in the burette tip, the meniscus read from above or below eye level, and the last drop delivered too quickly past the end point. All three are habits, and all three are fixed by doing the titration more than once before the exam day.

Preparing for the viva

Viva questions come from the experiments the student actually performed, and they are usually about the reason rather than the step. Why is dilute acid used before concentrated? Why is the salt solution acidified before adding barium chloride? Why must the conical flask not be rinsed with the solution being titrated? A student who has written up each experiment properly can answer these; one who has copied a file cannot, and it shows within two questions.

A workable plan for the term

• Write up each experiment in the week it is performed, including observations that went wrong and why.
• Repeat every titration at least twice before the exam, aiming for concordant readings rather than a target value.
• Keep a running list of viva questions per experiment — three or four each is enough.
• Two weeks before, run one full mock practical under time, including the write-up.

FAQs

How much do practicals count in Class 12 Chemistry?

Practical work carries a meaningful share of the total for the subject and is assessed internally alongside the board practical. Because the marking is largely procedural, it is the most reliably scoring part of the course for a prepared student.

Why do my titration readings vary?

Most often an air bubble in the burette tip, inconsistent meniscus reading, or over-shooting the end point by delivering the final drops too fast. All three are technique rather than understanding, and all three improve quickly with repetition.

Can practicals be prepared through online tuition?

The theory, the reasoning and viva preparation transfer well online. The physical technique — burette handling, end-point judgement, precipitate observation — needs apparatus, so it is better done at school or at a centre.

What is the single most common viva mistake?

Describing what was done rather than why. The examiner already has the procedure in the file; the question is testing whether the student understood the reason behind a step.