Principles Related to Practical Chemistry — NEET Chemistry MCQs with answers

Principles Related to Practical Chemistry is a Class 11 Chemistry chapter in the NEET (UG) syllabus. NEET720 has 246 reviewed practice questions on it, each with a quick answer and a step-by-step explanation. The 8 questions below are free and fixed, so you can bookmark this page; the full chapter, plus mistake tracking and spaced revision, is in the app.

Topics covered

Titrimetric analysis · Qualitative salt analysis · Detection of organic functional groups · Experimental physical chemistry · Qualitative salt analysis · Titrimetric analysis · Iodometric titration · Chromatography · Iodometric back-titration · Calorimetry · Titration curves · Conductometric titration · Reaction kinetics experiment · Organic qualitative tests · Back-titration · Redox titration + solution preparation · Chromatography + functional group polarity · Lassaigne's test + interference chemistry · Calorimetry + thermochemistry (Hess's law) · Qualitative salt analysis + solubility equilibrium · Iodoform test + back-titration stoichiometry · Flame test · Volumetric glassware · Lassaigne's test · Titration · Acid-base indicators · Chemical kinetics practical · Salt analysis · Thermochemistry practical · Organic qualitative analysis · Physical constants · Volumetric analysis · Colorimetric methods · Reagent storage

8 free Principles Related to Practical Chemistry practice questions with answers

Choose an answer in your head before opening it. Each explanation says why the correct option is right and, where relevant, why the tempting wrong option is wrong.

1. Question 1 · medium · Experimental physical chemistry

   In the thiosulphate-HCl 'disappearing cross' kinetics experiment, why must the same person view the cross mark from the same position and under the same lighting conditions for every trial?

   • A.Because different observers would cause the chemical reaction itself to proceed at a different rate
   • B.Because the judgment of 'when the cross just disappears' is inherently subjective, and inconsistent viewing conditions or observers introduce a variable, non-chemical source of error into the measured time
   • C.Because the reaction only produces enough sulphur turbidity to be visible to one specific trained person
   • D.Because switching observers would change the stoichiometry of the sulphur precipitation reaction
   Show answer and explanation

   Answer: B. Because the judgment of 'when the cross just disappears' is inherently subjective, and inconsistent viewing conditions or observers introduce a variable, non-chemical source of error into the measured time

   Since 'the cross has disappeared' is a subjective visual judgment (not an instrument reading), keeping the observer, viewing angle, and lighting constant across trials minimizes procedural (non-chemical) variability in the recorded times, improving the reliability of the rate comparison.

   The thiosulphate-HCl kinetics experiment relies on a human observer judging the precise moment the sulphur turbidity has become dense enough to obscure a cross mark placed beneath the reaction flask — this is inherently a subjective, qualitative endpoint rather than a precise instrumental reading. Different observers may have different thresholds for 'just disappeared,' and different lighting or viewing angles can shift this perceived endpoint, introducing a systematic or random error unrelated to the actual chemistry. By keeping the same observer, position, and lighting constant across all trials, this source of procedural error is minimized, making the comparison of times (and hence rates) across different concentrations more valid and reproducible. The observer's identity has no bearing on the actual chemical reaction rate, stoichiometry, or visibility physics of the sulphur produced (options B, C, D all incorrectly attribute a chemical or physical effect to the human observer).

   Common mistake: Attributing the need for observer consistency to an actual chemical effect rather than a measurement/judgment consistency issue

2. Question 2 · easy · Titrimetric analysis

   Which indicator is most suitable for the titration of a strong acid against a strong base?

   • A.Only methyl orange, because strong acid-strong base titrations must always be stopped at acidic pH
   • B.Phenolphthalein or methyl orange, since the pH jump at the equivalence point spans both their transition ranges
   • C.Only starch-iodine, since it gives the sharpest colour change for any titration
   • D.No indicator can be used; a pH meter is compulsory for strong acid-strong base titrations
   Show answer and explanation

   Answer: B. Phenolphthalein or methyl orange, since the pH jump at the equivalence point spans both their transition ranges

   In a strong acid-strong base titration the equivalence point pH is 7 and the pH changes very sharply (roughly 4 to 10) with a single drop near the endpoint, so both phenolphthalein (8.3-10) and methyl orange (3.1-4.4) lie within the steep vertical portion of the curve.

   For strong acid vs strong base, the titration curve shows an almost vertical rise of several pH units around the equivalence point (pH = 7). Any indicator whose transition range falls within this steep region gives a sharp, accurate endpoint. Phenolphthalein (colourless to pink, pH 8.3-10.0) and methyl orange (red to yellow, pH 3.1-4.4) both work well here, unlike in weak acid/weak base titrations where only one type of indicator suits the shifted equivalence pH.

   Common mistake: Assuming only phenolphthalein works for all acid-base titrations regardless of acid/base strength

3. Question 3 · easy · Titrimetric analysis

   What is meant by the 'equivalence point' of a titration, as distinguished from the 'endpoint'?

   • A.They are entirely different terms for unrelated concepts; equivalence point applies only to redox titrations and endpoint only to acid-base titrations
   • B.Equivalence point is always reached after the endpoint because the indicator changes colour prematurely
   • C.Equivalence point is where reactants have combined in exactly stoichiometric proportions; endpoint is where the indicator visually signals this, and the two may differ slightly
   • D.There is no difference; the two terms are exact synonyms with no distinction ever needed
   Show answer and explanation

   Answer: C. Equivalence point is where reactants have combined in exactly stoichiometric proportions; endpoint is where the indicator visually signals this, and the two may differ slightly

   The equivalence point is the theoretical point where moles of titrant equal moles of analyte per stoichiometry; the endpoint is the experimentally observed point (indicator colour change) that approximates it, with the small difference called the titration error.

   The equivalence point is defined purely stoichiometrically, from the balanced reaction, and cannot be observed directly. The endpoint is the practical signal (colour change of an indicator, or an instrument reading) used to stop the titration. A well-chosen indicator has a transition range close to the equivalence point pH so that endpoint and equivalence point nearly coincide, minimising titration error, but they are conceptually distinct.

   Common mistake: Using 'equivalence point' and 'endpoint' interchangeably without recognising the titration error concept

4. Question 4 · medium · Titrimetric analysis

   Before starting a titration, the burette is rinsed with the titrant solution while the conical flask is rinsed only with distilled water. What is the reason for this difference?

   • A.Any water left in the burette would dilute the titrant and change its effective concentration, but water left in the flask does not change the fixed number of moles of analyte delivered by the pipette
   • B.The conical flask must never contact water at all, so it is rinsed with acetone instead of water before use
   • C.Rinsing the burette with titrant prevents the glass from reacting chemically with the titrant solution
   • D.Both burette and flask must be rinsed with the titrant for consistency; using only water in the flask is a common but harmless shortcut
   Show answer and explanation

   Answer: A. Any water left in the burette would dilute the titrant and change its effective concentration, but water left in the flask does not change the fixed number of moles of analyte delivered by the pipette

   Residual water in the burette would dilute the titrant, changing its concentration during delivery, so the burette is rinsed with the titrant itself; residual water in the flask does not matter because the moles of analyte transferred by the pipette are fixed regardless of dilution.

   The number of moles of analyte in the conical flask is fixed once measured out by a pipette; adding water afterward only dilutes it without changing the total moles present, so the titration endpoint volume is unaffected. However, if the burette contains residual water, any titrant added on top of it becomes diluted, so the true concentration delivered no longer matches the standardised value, introducing a genuine error in the volume-based calculation. Hence burettes (and pipettes) are always rinsed with the solution they will deliver, while flasks used purely to hold a fixed quantity of analyte need only be rinsed with distilled water.

   Common mistake: Believing both burette and conical flask must be rinsed identically, or that flask rinsing with titrant is harmless

5. Question 5 · medium · Titrimetric analysis

   While preparing a standard oxalic acid solution in a 250 mL volumetric flask, a student adds distilled water slightly past the calibration mark and then attempts to correct the volume by withdrawing some liquid with a dropper. What is wrong with this correction?

   • A.Nothing is wrong; withdrawing the excess liquid restores the exact intended volume and concentration
   • B.The withdrawn liquid carries away some dissolved oxalic acid too, so the remaining solution has fewer moles than intended even though the volume is now correct, giving a wrong (lower) concentration
   • C.The correction is fine only if plain water (not the solution) is withdrawn, which is not physically possible once mixed
   • D.Volumetric flasks do not have a fixed calibration mark, so overshooting the level is not actually an error
   Show answer and explanation

   Answer: B. The withdrawn liquid carries away some dissolved oxalic acid too, so the remaining solution has fewer moles than intended even though the volume is now correct, giving a wrong (lower) concentration

   Once water is added past the mark and mixed, the solution is homogeneous, so withdrawing some of it removes both water and dissolved oxalic acid in proportion, permanently reducing the total moles of oxalic acid present; the concentration cannot be corrected this way, and the solution must be discarded and freshly prepared.

   A volumetric flask is calibrated to contain (TC) one specific, precise volume at its etched mark. If water is added beyond the mark, the solute is now dissolved throughout a larger-than-intended volume, giving a slightly lower concentration; if the excess is well mixed and then withdrawn, the removed portion contains solute in the same proportion as the rest of the solution, so it carries away part of the dissolved oxalic acid. The remaining solution, even after being brought back to exactly 250 mL by careful measurement, now contains fewer moles of oxalic acid than intended, so its concentration is permanently lower than the desired standard value. The only correct fix is to discard the solution and prepare it afresh with proper technique (adding water dropwise near the mark, checking at eye level for the meniscus).

   Common mistake: Believing that withdrawing excess liquid after overshooting the mark restores the intended concentration

6. Question 6 · medium · Titrimetric analysis

   Consider the following statements about titration glassware calibration: (I) A pipette marked 'TD' (to deliver) gives the stated volume when the liquid is allowed to drain naturally, without blowing out the last drop. (II) A burette is calibrated 'to deliver' (TD). (III) A volumetric flask is calibrated 'to contain' (TC) the stated volume up to its mark. (IV) The last drop remaining in a standard TD pipette should always be blown out to obtain the accurate stated volume. Which statements are correct?

   • A.I, II, III and IV
   • B.I, II and III only
   • C.II and III only
   • D.I and IV only
   Show answer and explanation

   Answer: B. I, II and III only

   Statements I, II and III correctly describe standard glassware calibration conventions; statement IV is false and directly contradicts statement I, since a standard TD pipette's stated volume already accounts for the small residual drop remaining in the tip, which must not be blown out.

   (I) True: a 'to deliver' (TD) pipette is calibrated so that its marked volume is correctly delivered when the liquid drains naturally by gravity, leaving a small residual drop in the tip by design. (II) True: burettes are TD instruments, delivering the volume read off the graduated scale. (III) True: volumetric flasks are TC (to contain) instruments, holding the exact stated volume up to the calibration mark when filled correctly, and are not meant to deliver that exact volume on pouring out (some liquid clings to the walls). (IV) False: blowing out the residual drop in a standard TD pipette would deliver more liquid than the calibrated volume, introducing a positive volume error; only 'blow-out' pipettes (marked accordingly) are designed to have their last drop expelled.

   Common mistake: Believing the last drop in any pipette should be blown out to get the full stated volume

7. Question 7 · hard · Titrimetric analysis

   Consider the following statements about sources of error in a titration: (I) A parallax error while reading the burette meniscus (viewing from above or below eye level) can make the recorded titre volume inaccurate even if the actual endpoint was reached correctly. (II) Using an indicator whose transition range lies well outside the steep portion of the titration's pH-jump always introduces a genuine endpoint error, regardless of how carefully the volume is read. (III) Taking only a single titre reading (instead of concordant readings within about 0.1 mL of each other) can hide a large random error in the result. (IV) Air bubbles trapped in the burette tip, if present at the start but gone by the endpoint, cause no error in the recorded titre volume. Which statements are correct?

   • A.I, II and III only
   • B.II, III and IV only
   • C.I, II, III and IV
   • D.I and III only
   Show answer and explanation

   Answer: A. I, II and III only

   Statements I, II and III correctly identify genuine sources of titration error; statement IV is false because an air bubble present at the start but expelled during the titration means the burette reading overstates the true volume of titrant actually delivered, causing a real error.

   (I) True: reading the meniscus from above or below eye level introduces a parallax error, making the recorded volume differ from the true volume delivered, independent of whether the chemical endpoint itself was correctly judged. (II) True: if the indicator's colour-change range does not overlap the steep pH-jump region of the titration curve, the visually observed endpoint will not coincide with the true equivalence point, creating a systematic error no matter how precisely the volume is read. (III) True: a single reading gives no way to check for random error or a mistaken judgment of the endpoint; concordant (matching, within about 0.1 mL) readings are needed to have confidence in the result. (IV) False: if an air bubble occupies part of the burette's internal volume initially and later escapes during delivery, the volume drop recorded on the burette scale includes the bubble's volume as if it were titrant delivered, so the true amount of titrant actually delivered into the flask is less than the recorded volume — this does cause an error.

   Common mistake: Assuming an air bubble that disappears by the endpoint causes no error, when it in fact inflates the recorded titre

8. Question 8 · medium · Titrimetric analysis

   In a titration, a student repeats the titration until at least two titre readings agree closely (typically within about 0.1 mL of each other); these are called 'concordant readings.' Why are concordant readings taken instead of relying on just one titration?

   • A.Concordant readings are required only because the indicator itself becomes less sensitive after the first use and needs a second titration to recalibrate it
   • B.A single titration reading is always chemically incorrect and must legally be repeated according to a fixed laboratory rule with no scientific basis
   • C.A single reading cannot distinguish between a genuinely accurate result and one affected by a random slip (misjudged endpoint, misread scale); repeating and matching readings builds confidence that random error has been minimised
   • D.Concordant readings are taken to average out a real, unavoidable systematic error that always makes the first titration reading exactly 0.2 mL too high
   Show answer and explanation

   Answer: C. A single reading cannot distinguish between a genuinely accurate result and one affected by a random slip (misjudged endpoint, misread scale); repeating and matching readings builds confidence that random error has been minimised

   A single titre volume could be affected by an undetected random mistake (overshooting the endpoint, misreading the burette); taking repeated readings and checking that they agree closely (concordant) gives confidence that the measured volume reflects the true, reproducible endpoint rather than a one-off error.

   Random errors (such as slightly overshooting the endpoint by adding one extra drop, or a momentary misreading of the burette scale) can occur unpredictably in any single titration and cannot be identified from that one reading alone. By repeating the titration and comparing successive readings, a student can identify and discard any reading that is clearly inconsistent with the others (an outlier), and average the readings that agree closely (concordant, typically within about 0.1 mL) to obtain a reliable, reproducible titre volume for further calculation. This practice specifically targets random error, not a fixed systematic error and not indicator degradation.

   Common mistake: Treating concordant readings as an arbitrary rule or confusing them with correcting a fixed systematic error

Questions about Principles Related to Practical Chemistry for NEET

More Chemistry chapters

← Chemical ThermodynamicsAll Chemistry chaptersHydrogen →

Questions are original NEET720 compositions reviewed for correctness, syllabus fit and option quality. Counts update as the bank grows (246 active practice questions in this chapter today).