CheMentor AI Grader Dr. Noimur Rahman

CBSE & ISC Board SeriesChemistry · Organic & Physical Chemistry Mid-Term Exam

Answer BookletRoll #24
100%
Answer sheet page 1
Q1(4/4)
Q2(3/3)
✓ 4/4 Perfect Product
✓ 3/3 Correct Molarity
ROLL #24

Aarav Sharma

Chemistry (Class 11/12 · CBSE/NEET) · Multi-Page Booklet (Pages: 2)

9.5/10
95% Score
A+
Key Strengths
  • Accurate chemical equation & major product IUPAC nomenclature
  • Precise molarity substitution with units (0.4 M)
Action Areas
  • Did not explicitly state atomic size comparison between N and P in Q3
1 item flagged for review: Verify partial credit wording before final approval.
Q1 Full Marks
4/4 Marks
Student Handwriting (OCR Transcription)

Markovnikov rule: Negative part of reagent attaches to carbon with lesser hydrogen atoms. CH3-CH=CH2 + HBr -> CH3-CH(Br)-CH3 (2-Bromopropane)

Step-Wise Rubric Breakdown
1Negative part adds to carbon with fewer H atoms
2/2
2Correct reactants written: CH₃-CH=CH₂ + HBr
1/1
3Major product 2-Bromopropane formed
1/1
Quick Notes:

"Flawless statement and clear chemical reaction with major product named."

Q2 Full Marks
3/3 Marks
Student Handwriting (OCR Transcription)

M = (w_B * 1000) / (M_B * V_mL). M = (4.0 * 1000) / (40 * 250) = 0.4 M

Step-Wise Rubric Breakdown
1Molarity formula stated
1/1
2Correct values substituted (4g, 40 g/mol, 250 mL)
1/1
3Calculated value 0.4 M with unit
1/1
Quick Notes:

"Correct molarity formula, calculation, and final unit (0.4 M)."

Q3 Action Needed
2.5/3 Marks
Student Handwriting (OCR Transcription)

NH3 has higher b.p. than PH3 because of H-bonding. Nitrogen is very electronegative so forms intermolecular hydrogen bonds. PH3 has no H-bonds.

Step-Wise Rubric Breakdown
1Intermolecular Hydrogen bonding in NH₃ identified
1/1
2Reason: High electronegativity and small size of N
0.5/1
3Contrast with PH₃: Lack of H-bonding
1/1
Quick Notes:

Borderline answer: omitted atomic size comparison between Nitrogen and Phosphorus.

AI Suggestion: Award 2.5/3 or give grace mark 3/3 if taught informally.

"Well reasoned. Mention smaller atomic radius of N along with electronegativity for full marks."