GATE — Life Sciences (XL), Section U Food Technology · India · IITs and IISc on rotation (2026: IIT Guwahati)
Original practice questions written to the published syllabus · not past papersThe chemistry a food scientist uses every day: bonding, acids and bases, buffers, organic functional groups and reaction mechanisms, chemical kinetics and thermodynamics, and the physical chemistry of solutions, surfaces and colloids. Students who take GATE XL (Life Sciences) sit a compulsory chemistry section alongside the Food Technology section.
In the exams: GATE XL-P (compulsory chemistry section for XL candidates who choose XL-U Food Technology); background for ICAR AIEEA-PG Code 18 Unit I
How our questions for GATE spread across the units of Chemistry for Food Science (General, Organic & Physical). Difficulty: 20 easy, 34 medium, 8 hard.
| Chemical kinetics: rate laws, reaction order and the Arrhenius equation | 7 | |
| Acids, bases, pH, buffers and the Henderson-Hasselbalch equation | 6 | |
| Chemical equilibrium and solubility | 6 | |
| Stereochemistry and optical activity | 6 | |
| Surface chemistry, adsorption and an introduction to colloids | 6 | |
| Atomic structure, periodicity and chemical bonding | 5 | |
| Colligative properties: freezing-point depression, boiling-point elevation and osmotic pressure | 5 | |
| Organic reaction mechanisms relevant to food: oxidation, hydrolysis, esterification and condensation | 5 | |
| Chemical thermodynamics: enthalpy, entropy and free energy | 4 | |
| Organic functional groups and nomenclature | 4 | |
| Electrochemistry and redox potential | 4 | |
| Stoichiometry, concentration units and solution preparation | 2 | |
| Coordination chemistry and metal ions in foods | 2 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
A buffer contains 0.2 M sodium acetate and 0.1 M acetic acid (pKa 4.76). What is its pH?
A. 5.06
Henderson-Hasselbalch: pH = pKa + log([A⁻]/[HA]) = 4.76 + log 2 = 4.76 + 0.30 = 5.06. 4.46 inverts the ratio; 4.76 assumes equal amounts; 5.76 adds a whole unit as if the ratio were 10.
Further reading: Atkins' Physical Chemistry; Fennema's Food Chemistry
Sorbic acid has a pKa of about 4.8. In which product is a given dose most effective as an antimicrobial?
A. A fruit filling at pH 3.5
The undissociated acid crosses microbial membranes; at pH 3.5, more than 95% of sorbic acid is undissociated, against under 10% at pH 5.8 and less above that. The higher-pH products need more preservative for the same effect.
Further reading: Atkins' Physical Chemistry; Fennema's Food Chemistry
A weak acid preservative has pKa 5.2. What fraction of it is in the ionised (A⁻) form at pH 3.2?
C. 1%
log([A⁻]/[HA]) = pH − pKa = −2, so [A⁻]/[HA] = 0.01 and the ionised fraction = 0.01/1.01 = 1% (99% is undissociated). 50% would be at pH = pKa; 99% is the undissociated fraction, not the ionised one; 10% is close to the ionised fraction one pH unit below pKa (about 9%).
Further reading: Atkins' Physical Chemistry; Fennema's Food Chemistry
The Ksp of silver chloride is 1.8 × 10⁻¹⁰ at 25 °C. What is its molar solubility in pure water?
D. 1.3 × 10⁻⁵ M
AgCl ⇌ Ag⁺ + Cl⁻, so Ksp = s² and s = √(1.8 × 10⁻¹⁰) = 1.34 × 10⁻⁵ M. 1.8 × 10⁻¹⁰ is Ksp itself; 9.0 × 10⁻¹¹ halves Ksp; 3.6 × 10⁻⁵ M is an arithmetic slip.
Further reading: Atkins' Physical Chemistry; Fennema's Food Chemistry
A salt of the type AB₂ has molar solubility s. What is its Ksp?
C. 4s³
AB₂ ⇌ A²⁺ + 2B⁻: [A²⁺] = s and [B⁻] = 2s, so Ksp = s(2s)² = 4s³. s² applies to an AB salt; 2s³ forgets to square the 2; s³ ignores the stoichiometry.
Further reading: Atkins' Physical Chemistry; Fennema's Food Chemistry
The rate constant of a reaction has units of s⁻¹. What is its order?
A. First order
Rate (mol L⁻¹ s⁻¹) = k[A]ⁿ, so k has units (mol L⁻¹)^(1−n) s⁻¹. s⁻¹ alone means n = 1. Zero order gives mol L⁻¹ s⁻¹; second order L mol⁻¹ s⁻¹.
Further reading: Atkins' Physical Chemistry; Fennema's Food Chemistry
What is the osmotic pressure of a 0.1 M sucrose solution at 25 °C? (R = 0.08206 L·atm/(mol·K))
B. 2.45 atm
π = iCRT = 1 × 0.1 × 0.08206 × 298.15 = 2.45 atm. 0.21 atm uses 25 °C instead of 298 K; 4.89 atm uses i = 2; 0.10 atm leaves out RT.
Further reading: Atkins' Physical Chemistry; Fennema's Food Chemistry
In the propagation step of lipid autoxidation, what does a peroxyl radical (LOO•) do?
C. Abstracts a hydrogen from another lipid, forming a hydroperoxide and a new radical
LOO• + LH → LOOH + L•, so the chain continues. Radical combination is termination; initiation needs a radical or a sensitiser; release of free fatty acids is hydrolysis, not oxidation.
Further reading: Clayden, Greeves and Warren, Organic Chemistry; Fennema's Food Chemistry
What is the first step of the Maillard reaction?
B. Condensation of a reducing-sugar carbonyl with an amino group to form a glycosylamine
The carbonyl of a reducing sugar condenses with a free amino group (losing water) to form a Schiff base and glycosylamine, which rearranges to an Amadori or Heyns product. Caramelisation needs no amino group; lipid oxidation and proteolysis are different reactions.
Further reading: Clayden, Greeves and Warren, Organic Chemistry; Fennema's Food Chemistry
R-(−)-Carvone smells of spearmint and S-(+)-carvone of caraway. What does this show?
C. Odour receptors are chiral and distinguish enantiomers
Enantiomers have identical physical properties in an achiral environment, but chiral receptors bind them differently. They have the same formula, the nose does not detect rotation, and they are mirror-image enantiomers, not cis-trans isomers.
Further reading: Clayden, Greeves and Warren, Organic Chemistry; Fennema's Food Chemistry
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