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ISC chemistry students often know their organic reactions well and still drop marks in the lab examination, on rules they never read: how a titre value is chosen, how many decimal places a molarity needs, which tests must not be performed. This post sets out how CISCE structures ISC 2027 chemistry, what the specimen theory paper looks like, how the practical paper is set, and one titration calculation worked the way the syllabus asks.
How are ISC 2027 chemistry marks divided?
The CISCE ISC 2027 Chemistry syllabus gives Class XII two papers:
Paper I, Theory: 3 hours, 70 marks.
Paper II, Practical: 3 hours, 15 marks.
Project Work: 10 marks.
Practical File: 5 marks.
The theory marks are grouped into three areas:
Physical chemistry, 25 marks: solutions, electrochemistry, chemical kinetics.
Inorganic chemistry, 14 marks: d- and f-block elements, coordination compounds.
Organic chemistry, 31 marks: haloalkanes and haloarenes; alcohols, phenols and ethers; aldehydes, ketones and carboxylic acids; nitrogen compounds; biomolecules.
Check: 25 + 14 + 31 = 70. CISCE revises syllabuses by examination year, so confirm the document for your year.
What does the ISC 2027 specimen theory paper look like?
The ISC 2027 Chemistry specimen paper gives three hours plus 15 minutes of reading time:
Section A: 14 one-mark items (fill in the blanks, multiple choice and a short passage).
Section B: ten questions of 2 marks.
Section C: seven questions of 3 marks.
Section D: three questions of 5 marks.
That is 14 + 20 + 21 + 15 = 70. Internal choices appear in two questions each in Sections B, C and D. The instructions ask for balanced equations wherever possible and "all essential workings" in numerical problems.
How is the practical paper set?
The syllabus fixes the pattern. Question 1 is volumetric analysis. Question 2 is one or a combination of: rate of reaction, identifying organic functional groups, tests for carbohydrates and proteins, pH, and a simple voltaic cell. Question 3 is qualitative analysis of a single salt with one anion and one cation.
Some rules cost marks every year:
The titre value is the concordant reading: two consecutive values that are exactly the same. "Average will not be accepted as titre value."
Molarity "must be calculated upto 4 decimal places at least."
The observation table is completed in ink, with no overwriting.
The chromyl chloride, carbylamine and acrolein tests are not to be performed.
For wet tests of anions, use the sodium carbonate extract, except for carbonate.
The project and the file are assessed by a Visiting Examiner appointed locally and approved by CISCE. The file is judged on the practical record you kept during the year.
Worked example: potassium manganate(VII) against Mohr's salt
Sample numbers. A solution of ammonium iron(II) sulphate (Mohr's salt, molar mass 392 g/mol) contains 9.80 g per litre. You pipette 20.0 mL of it and titrate against potassium manganate(VII). Your burette readings give titres of 9.70, 9.60 and 9.60 mL. Find the molarity and strength of the KMnO4 solution.
Molarity of Mohr's salt: 9.80 ÷ 392 = 0.0250 M.
Equation: MnO4⁻ + 5Fe²⁺ + 8H⁺ → Mn²⁺ + 5Fe³⁺ + 4H2O. One mole of manganate(VII) reacts with five moles of iron(II).
Titre value: the concordant reading, 9.60 mL.
Molarity of KMnO4: M = (0.0250 × 20.0) ÷ (5 × 9.60) = 0.500 ÷ 48.0 = 0.0104 M, to 4 decimal places.
Strength: 0.0104 × 158 (molar mass of KMnO4) = 1.64 g per litre.
Common mistakes: using a 1 : 1 ratio instead of 1 : 5; averaging titres; rounding molarity to 0.01; and recording readings in pencil. For more practice, see our posts on the KMnO4 and oxalic acid titration and salt analysis.
A practice routine for the term
Weekly, theory: one Section C and one Section D question from organic chemistry, which carries the most marks.
Weekly, practical: one titration calculation from old readings, with molarity to four decimal places.
Fortnightly: one full salt analysis written in the formal procedure, groups in order.
Ongoing: record each practical in your file the week you do it.
Our post on ISC physics paper structure covers the same 70 + 30 split in physics. If a mechanism or an idea like the van't Hoff factor is not clear from the textbook, the Fermi Concept Library covers every concept in chemistry with its own lesson.
Before your next practical, write the five rules above on the inside cover of your practical file.
