Rucete ✏ AP Chemistry In a Nutshell
14. Experimental Chemistry — Practice Questions 2
This chapter introduces essential laboratory techniques including measurement accuracy, separation methods, data analysis, and safe handling of chemicals in experimental settings.
(Multiple Choice — Click to Reveal Answer)
1. Which laboratory apparatus is best suited for heating a small amount of solid strongly?
(A) Evaporating dish
(B) Crucible
(C) Beaker
(D) Watch glass
Answer
(B) — Crucibles are designed to withstand high temperatures for heating solids.
2. What is the function of a retort stand in a laboratory setup?
(A) Support glassware
(B) Store chemicals
(C) Measure liquids
(D) Clean test tubes
Answer
(A) — A retort stand holds glassware or apparatus during experiments.
3. Which pair of liquids can be separated by using a separating funnel?
(A) Water and sugar
(B) Oil and water
(C) Alcohol and water
(D) Ink and water
Answer
(B) — A separating funnel separates immiscible liquids like oil and water.
4. What safety gear is essential when working with concentrated acids?
(A) Apron
(B) Safety goggles
(C) Gloves
(D) All of the above
Answer
(D) — All listed protective items are recommended for acid handling.
5. Which observation indicates a chemical change?
(A) Ice melting
(B) Water boiling
(C) Formation of a precipitate
(D) Evaporation of alcohol
Answer
(C) — Precipitate formation is a sign of a chemical reaction.
6. Which of the following is a qualitative analysis technique?
(A) Flame test
(B) Titration
(C) Gravimetric analysis
(D) Colorimetry
Answer
(A) — A flame test provides qualitative information about metal ions.
7. How should you read the volume of liquid in a burette?
(A) From the top
(B) From the bottom of the meniscus
(C) From eye level above the burette
(D) At an angle for better visibility
Answer
(B) — Always read from the bottom of the meniscus at eye level.
8. Which process is used to separate colored dyes in ink?
(A) Filtration
(B) Distillation
(C) Crystallization
(D) Chromatography
Answer
(D) — Chromatography separates components based on solubility and movement on paper.
9. What color does potassium ion produce in a flame test?
(A) Yellow
(B) Green
(C) Lilac
(D) Red
Answer
(C) — Potassium ions give a lilac flame.
10. Which reagent is used to test for sulfate ions?
(A) Silver nitrate
(B) Barium chloride
(C) Ammonia solution
(D) Sodium hydroxide
Answer
(B) — Barium chloride forms a white precipitate with sulfate ions.
11. Why should a balance be tared before weighing a substance?
Answer
To ensure only the mass of the substance is measured, not the container.
12. What is the function of a condenser in a distillation setup?
(A) Evaporate the liquid
(B) Cool and condense vapor
(C) Mix two liquids
(D) Hold the solution
Answer
(B) — The condenser cools the vapor and turns it back into liquid.
13. Which of the following is not typically a source of error in titration?
(A) Misreading burette
(B) Incorrect indicator
(C) Pure reagents
(D) Air bubbles in the nozzle
Answer
(C) — Using pure reagents reduces errors; it is not a source of error.
14. Why is a conical flask used in titration instead of a beaker?
(A) It holds more solution
(B) It allows swirling without spilling
(C) It is easier to clean
(D) It gives accurate readings
Answer
(B) — Its shape allows for safe swirling to mix reactants during titration.
15. Which gas will relight a glowing splint?
(A) Hydrogen
(B) Oxygen
(C) Carbon dioxide
(D) Ammonia
Answer
(B) — Oxygen supports combustion and relights a glowing splint.
16. Which safety practice should be followed when using volatile solvents?
(A) Use near open flames
(B) Work in a fume hood
(C) Store in warm areas
(D) Smell directly to test purity
Answer
(B) — Volatile solvents should always be used in a fume hood to avoid inhaling harmful vapors.
17. Which of the following errors is considered systematic?
(A) Misreading the burette
(B) Spilling during transfer
(C) Random splashes
(D) Rounding inconsistencies
Answer
(A) — A consistent misreading of the burette introduces a systematic error.
18. What is the purpose of using filter paper in a funnel during filtration?
(A) Increase reaction rate
(B) Remove dissolved ions
(C) Separate solid from liquid
(D) Concentrate the solution
Answer
(C) — Filter paper retains solid particles while allowing the liquid to pass through.
19. Why is it important to clamp the burette vertically during titration?
(A) Prevents solution mixing
(B) Ensures accurate volume reading
(C) Saves space
(D) Prevents heat loss
Answer
(B) — A vertical burette ensures precise and consistent volume readings.
20. Which change is most likely to occur if a salt is heated strongly?
(A) Change in odor
(B) Flame color change
(C) Decomposition
(D) Change in pH
Answer
(C) — Many salts decompose when heated, especially carbonates and nitrates.
21. What is the advantage of using a digital thermometer over a mercury thermometer?
(A) Measures pressure
(B) Measures volume
(C) Faster and safer temperature reading
(D) More difficult to calibrate
Answer
(C) — Digital thermometers are quicker and safer, with no mercury hazards.
22. Which method is best to separate a mixture of sand and salt?
(A) Chromatography
(B) Filtration and evaporation
(C) Sublimation
(D) Distillation
Answer
(B) — Sand is removed by filtration, and salt is obtained by evaporating the filtrate.
23. Why should glassware be rinsed with distilled water before use?
(A) To remove labels
(B) To prevent breakage
(C) To remove impurities
(D) To speed up reactions
Answer
(C) — Rinsing removes residual chemicals or dust that may interfere with results.
24. Which result indicates the presence of carbonate ions when dilute acid is added?
(A) Color change to red
(B) Formation of green precipitate
(C) Effervescence due to CO₂ release
(D) Strong smell of ammonia
Answer
(C) — Carbonates react with acids to produce carbon dioxide gas, visible as bubbling.
25. In a titration, why is a white tile used under the conical flask?
(A) Reflects light for safety
(B) Prevents solution heating
(C) Makes color change easier to observe
(D) Keeps the flask cool
Answer
(C) — The white background helps detect subtle color changes more clearly.
26. Which of the following would cause a titration result to be consistently too high?
(A) Not rinsing the burette with the titrant
(B) Adding extra indicator
(C) Air bubbles in the pipette
(D) Reading burette from above meniscus
Answer
(A) — Not rinsing with titrant leaves water that dilutes the solution, so more is needed for endpoint, making results high.
27. Why is it necessary to use a desiccator when weighing certain chemical samples?
(A) To prevent reactions with air
(B) To absorb light
(C) To increase temperature
(D) To provide a sterile environment
Answer
(A) — Many samples are hygroscopic or react with air; a desiccator keeps them dry and stable.
28. A student titrates an acid with a base and consistently overshoots the endpoint. Which error does this introduce?
(A) Random error — results scattered
(B) Systematic error — calculated concentration too high
(C) Systematic error — calculated concentration too low
(D) No significant error
Answer
(C) — Overshooting endpoint means using too much titrant, so the acid concentration appears lower than actual.
29. Which separation technique would best isolate a dissolved solid from a liquid when the solid is heat-sensitive?
(A) Evaporation to dryness
(B) Filtration
(C) Crystallization at low temperature
(D) Distillation
Answer
(C) — Cold crystallization avoids decomposing heat-sensitive solids.
30. What does it indicate if a solution turns from orange to green when dichromate(VI) is added during a reaction?
(A) Precipitation occurred
(B) An acid–base reaction
(C) A reduction reaction
(D) The temperature increased
Answer
(C) — Orange dichromate(VI) is reduced to green chromium(III) during redox.
31. In an experiment, why should distilled water be used to prepare solutions rather than tap water?
(A) Tap water is too expensive
(B) Distilled water improves taste
(C) Tap water may contain ions that interfere with results
(D) Distilled water reacts with glass
Answer
(C) — Tap water contains ions and impurities that can alter chemical reactions and measurements.
32. Which apparatus should be used to deliver exactly 20.0 mL of solution with the least error?
(A) Beaker
(B) Measuring cylinder
(C) 20 mL pipette
(D) Buret
Answer
(C) — A pipette is designed for precise delivery of fixed volumes.
33. During gravimetric analysis, why is it important to dry a precipitate thoroughly before weighing?
(A) To increase mass
(B) To remove water, ensuring accurate measurement of only solid
(C) To reduce error from temperature fluctuations
(D) To neutralize acids
Answer
(B) — Residual water would increase the measured mass and introduce error.
34. A student observes effervescence when magnesium is added to dilute hydrochloric acid. What is the identity of the gas formed?
(A) Oxygen
(B) Carbon dioxide
(C) Hydrogen
(D) Nitrogen
Answer
(C) — Magnesium reacts with HCl to produce hydrogen gas.
35. In a flame test, a brick-red color is observed. Which ion is responsible?
(A) Calcium
(B) Barium
(C) Sodium
(D) Potassium
Answer
(A) — Calcium ions produce a brick-red flame.
36. State one observation when iron(III) chloride solution is added to sodium hydroxide solution.
Answer
A reddish-brown precipitate forms.
37. Describe how to test for the presence of chloride ions in solution.
Answer
Add silver nitrate; a white precipitate of silver chloride indicates chloride ions.
38. Why should a volumetric flask be filled to the calibration mark at eye level?
Answer
To avoid parallax error and ensure accurate volume measurement.
39. What is the purpose of using a boiling chip (anti-bumping granule) during heating?
Answer
To ensure smooth boiling and prevent sudden, violent boiling (bumping).
40. Give one reason why the burette must be rinsed with the titrant before use in titration.
Answer
To prevent dilution of the titrant by water or previous solutions, ensuring accurate concentration.
41. How do you test for ammonia gas released during an experiment?
Answer
Hold damp red litmus paper in the gas; it will turn blue if ammonia is present.
42. Explain the advantage of crystallization over evaporation for purifying a solid.
Answer
Crystallization gives purer crystals, as impurities remain in the solution, unlike evaporation where impurities may remain with the solid.
43. What is meant by the term “meniscus” in laboratory measurements?
Answer
The curved upper surface of a liquid in a tube; readings are taken from the bottom of the meniscus.
44. State one precaution when filtering a hot solution.
Answer
Use preheated glassware and filter paper to avoid crystallization during filtration.
45. How can the presence of water in a sample be confirmed using cobalt(II) chloride paper?
Answer
The paper turns from blue to pink in the presence of water.
46. Suggest a reason why repeated titrations are carried out in experiments.
Answer
To obtain concordant (consistent) results and improve accuracy.
47. Describe how to safely dilute concentrated hydrochloric acid.
Answer
Always add acid slowly to water with stirring, never the reverse.
48. Why should a crucible be allowed to cool in a desiccator before weighing?
Answer
To prevent absorption of moisture and avoid inaccurate mass measurements.
49. What is the purpose of using a fume hood when handling volatile chemicals?
Answer
To safely ventilate harmful vapors and protect users from inhaling toxic substances.
50. Name the process used to separate a mixture of ethanol and water and explain why it works.
Answer
Fractional distillation; it works because ethanol and water have different boiling points.