Rucete ✏ AP Chemistry In a Nutshell
14. Experimental Chemistry — Practice Questions 3
This chapter covers experimental planning, apparatus selection, observation skills, advanced separation techniques, and data reliability in the chemistry laboratory.
(Multiple Choice — Click to Reveal Answer)
1. Which apparatus is most suitable for accurate transfer of a fixed volume of solution?
(A) Measuring cylinder
(B) Conical flask
(C) Volumetric pipette
(D) Beaker
Answer
(C) — A volumetric pipette is designed for accurate fixed-volume transfer.
2. What is the safest method to detect the odor of a chemical in the lab?
(A) Inhale deeply above the bottle
(B) Waft the vapor gently toward your nose
(C) Ask a friend to smell it
(D) Remove the lid and sniff directly
Answer
(B) — Wafting prevents direct inhalation of possibly harmful vapors.
3. What is the primary function of a wash bottle containing distilled water during experiments?
(A) To rinse glassware and transfer solutions
(B) To provide water for drinking
(C) To extinguish flames
(D) To clean benches
Answer
(A) — Distilled water is used for rinsing and transferring solutions.
4. A student observes a solution change from blue to colorless when zinc powder is added. What is the most likely explanation?
(A) Formation of a precipitate
(B) Reduction of Cu²⁺ ions to copper metal
(C) Oxidation of water
(D) Production of ammonia gas
Answer
(B) — Zinc reduces blue Cu²⁺ ions to colorless copper metal (or to a colorless ion, depending on context).
5. Which test would confirm the presence of nitrate ions in solution?
(A) Add barium chloride; white precipitate forms
(B) Add sodium hydroxide and heat; pungent gas forms
(C) Add iron(II) sulfate and concentrated sulfuric acid; brown ring forms
(D) Add silver nitrate; yellow precipitate forms
Answer
(C) — The brown ring test confirms nitrates.
6. Why is it important to label all reagents and solutions in an experiment?
(A) To avoid confusion and prevent mistakes
(B) To improve color changes
(C) To increase reaction speed
(D) To reduce evaporation
Answer
(A) — Proper labeling prevents mix-ups and enhances lab safety and accuracy.
7. Which method best separates dissolved colored pigments in a plant extract?
(A) Filtration
(B) Simple distillation
(C) Paper chromatography
(D) Crystallization
Answer
(C) — Paper chromatography separates colored compounds based on solubility.
8. Which observation indicates that a gas is being evolved in a reaction?
(A) Color change
(B) Temperature decrease
(C) Formation of bubbles or effervescence
(D) Precipitate formation
Answer
(C) — Bubbles or effervescence show gas evolution.
9. When preparing a standard solution, why must the solute be fully dissolved before making up to the mark?
(A) To avoid cloudiness
(B) For safety reasons
(C) To ensure the solution is of accurate concentration
(D) To make filtration easier
Answer
(C) — Undissolved solute would cause inaccurate solution concentration.
10. What color is observed when potassium manganate(VII) acts as an oxidizing agent in acidic solution and is reduced?
(A) Stays purple
(B) Colorless
(C) Green
(D) Orange
Answer
(B) — The deep purple color disappears; the reduced Mn²⁺ is nearly colorless in dilute solution.
11. Which item is used to dry an organic liquid by removing traces of water?
(A) Filter funnel
(B) Anhydrous calcium chloride
(C) Glass rod
(D) Bunsen burner
Answer
(B) — Anhydrous CaCl₂ absorbs water from organic liquids.
12. What is the first step if a chemical is accidentally splashed in your eye?
(A) Rub the eye
(B) Blink several times
(C) Wash immediately with plenty of water
(D) Close eye tightly and call teacher
Answer
(C) — Immediate rinsing with water is the correct first response.
13. Which process is used to obtain pure crystals of a solute from its aqueous solution?
(A) Filtration
(B) Fractional distillation
(C) Crystallization
(D) Sublimation
Answer
(C) — Crystallization yields pure crystals from a solution.
14. When using a burette, what should be done before titration begins?
(A) Fill with water
(B) Rinse with the solution to be used
(C) Shake vigorously
(D) Heat with a Bunsen burner
Answer
(B) — Rinsing with the solution prevents dilution by water.
15. What is the main reason for swirling the conical flask during titration?
(A) Prevent glass breakage
(B) Mix reactants evenly
(C) Lower the endpoint
(D) Create bubbles
Answer
(B) — Swirling ensures the acid and base mix fully for an accurate endpoint.
16. Which statement describes a benefit of using a digital pH meter over universal indicator paper?
(A) Cheaper cost
(B) Faster color change
(C) More precise and quantitative readings
(D) Larger sample needed
Answer
(C) — Digital pH meters provide accurate and precise measurements.
17. Which observation suggests a chemical, not a physical, change during an experiment?
(A) Boiling
(B) Evaporation
(C) Formation of a gas with temperature change
(D) Melting
Answer
(C) — Gas evolution with temperature change often indicates a chemical reaction.
18. What is the safest action if you spill a flammable solvent on your clothing in the lab?
(A) Stand near a flame to dry quickly
(B) Leave the lab and wash immediately
(C) Wait for it to evaporate
(D) Cover with a lab coat
Answer
(B) — Remove contaminated clothing and wash skin thoroughly, away from ignition sources.
19. Which apparatus is best for measuring the melting point of a solid sample?
(A) Thermometer and oil bath
(B) Beaker and tripod
(C) Measuring cylinder
(D) Filter funnel
Answer
(A) — A thermometer and oil bath are used for accurate melting point determination.
20. Which solution would show a deep blue color with aqueous ammonia?
(A) Fe²⁺ solution
(B) Cu²⁺ solution
(C) Zn²⁺ solution
(D) Al³⁺ solution
Answer
(B) — Cu²⁺ ions form a deep blue complex with aqueous ammonia.
21. What is the best way to detect the presence of hydrogen sulfide (H₂S) in a sample?
(A) Observe blue litmus paper
(B) Use filter paper soaked in lead(II) acetate
(C) Shine UV light
(D) Test with phenolphthalein
Answer
(B) — H₂S turns lead(II) acetate paper black due to formation of lead sulfide.
22. If a liquid boils sharply with bumping during heating, what is most likely missing?
(A) Thermometer
(B) Boiling chips
(C) Distilled water
(D) Cooling tube
Answer
(B) — Boiling chips provide nucleation sites for smooth boiling.
23. Which of the following is most important for reliability when comparing two sets of experimental data?
(A) Using the same apparatus
(B) Calculating the mean
(C) Conducting repeats and averaging results
(D) Using colored indicators
Answer
(C) — Repeats and averaging increase data reliability.
24. What is a precaution to avoid contamination when using a dropping pipette for reagents?
(A) Rinse it in tap water
(B) Use the same pipette for all reagents
(C) Never return unused reagent to original bottle
(D) Heat before use
Answer
(C) — Never return excess reagent to avoid contaminating the stock bottle.
25. Which method is used to remove water of crystallization from a hydrated salt?
(A) Gentle heating
(B) Shaking
(C) Adding acid
(D) Passing electricity through solution
Answer
(A) — Gentle heating removes water from hydrated salts.
26. Which error would most likely cause all titration results to be lower than the true value for the analyte’s concentration?
(A) Overshooting the endpoint
(B) Air bubble in burette tip
(C) Not rinsing pipette with the solution
(D) Reading burette from below eye level
Answer
(C) — If the pipette is not rinsed, the delivered volume is diluted, making the analyte appear less concentrated.
27. What is the best method to obtain a pure sample of sodium chloride from a mixture of sand and salt?
(A) Filtration, then evaporation
(B) Chromatography
(C) Sublimation
(D) Distillation
Answer
(A) — Sand is filtered out, and salt is recovered by evaporating the filtrate.
28. Which observation indicates that a reducing agent is present in a reaction with acidified potassium dichromate(VI)?
(A) Solution turns green from orange
(B) White precipitate forms
(C) Gas with choking smell evolved
(D) Blue color appears
Answer
(A) — Orange dichromate(VI) is reduced to green Cr³⁺ by a reducing agent.
29. Which change in apparatus would most improve accuracy in measuring the volume of an irregular solid?
(A) Use a ruler
(B) Use a beaker
(C) Use a measuring cylinder and water displacement
(D) Use filter paper
Answer
(C) — Water displacement in a measuring cylinder is accurate for irregular volumes.
30. A student uses a dirty burette with a drop of water remaining inside before filling with titrant. What is the most likely effect on results?
(A) Endpoint will occur sooner
(B) No effect at all
(C) Calculated concentration of analyte will be too low
(D) Titrant will be more concentrated
Answer
(C) — Residual water dilutes the titrant, so more is needed for the endpoint, making analyte seem less concentrated.
31. In a flame test, which error would give a false positive for sodium?
(A) Using platinum wire
(B) Not cleaning the wire properly
(C) Using too much sample
(D) Not heating long enough
Answer
(B) — Sodium contamination from previous samples gives persistent yellow color.
32. Which sequence best describes the steps for preparing a dry sample of copper(II) sulfate crystals from solution?
(A) Filtration → Dry between filter papers
(B) Evaporate to dryness
(C) Heat to crystallization → Filter → Dry
(D) Distillation → Sublimation
Answer
(C) — Heat to crystallization, filter out crystals, and dry them.
33. What is the most suitable way to collect and measure a gas that is soluble in water?
(A) Downward delivery
(B) Over water
(C) Upward delivery into a dry test tube
(D) Collect in a balloon
Answer
(C) — Gases soluble in water should not be collected over water; upward delivery into a dry tube works for gases lighter than air.
34. What is the advantage of using an analytical balance over a top-loading balance for mass measurement?
(A) Lower cost
(B) More portable
(C) Higher accuracy and precision
(D) Larger capacity
Answer
(C) — Analytical balances are designed for extremely precise measurements.
35. Which procedural change would best reduce random error in a colorimetric experiment?
(A) Use freshly prepared solutions
(B) Take multiple absorbance readings and average them
(C) Use a wider cuvette
(D) Use a higher temperature
Answer
(B) — Averaging repeated measurements reduces the impact of random error.
36. Describe a safe method to test for hydrogen gas produced during a reaction.
Answer
Bring a lit splint near the mouth of the test tube; hydrogen produces a 'pop' sound.
37. Why is it important to repeat measurements and calculate the average in experiments?
Answer
To improve reliability and reduce the impact of random errors.
38. State one observation that would indicate a precipitate has formed in a reaction mixture.
Answer
The solution becomes cloudy or a solid settles out.
39. What is the correct way to read the volume in a burette?
Answer
At eye level, from the bottom of the meniscus.
40. How can you test for the presence of water using anhydrous copper(II) sulfate?
Answer
Anhydrous copper(II) sulfate turns from white to blue in the presence of water.
41. Why is it recommended to cool a solution before filtering to obtain maximum crystals?
Answer
Solubility decreases as temperature drops, allowing more crystals to form.
42. Explain why concentrated sulfuric acid should always be added to water, not water to acid.
Answer
Adding acid to water dissipates heat safely and prevents violent splattering.
43. State one reason why glassware should be cleaned and rinsed with distilled water before use.
Answer
To remove impurities or residues that could affect the results.
44. How do you confirm the presence of carbon dioxide gas in an experiment?
Answer
Bubbling the gas through limewater turns it milky due to CaCO₃ formation.
45. What is the purpose of using filter paper in gravity filtration?
Answer
To separate solids from liquids by allowing only the liquid to pass through.
46. Describe a precaution to avoid parallax error when measuring volumes.
Answer
Ensure your eye is level with the meniscus when reading measurements.
47. Why should solutions be swirled continuously during a titration?
Answer
To mix the reactants thoroughly and ensure a uniform reaction.
48. Give one advantage of using fractional distillation over simple distillation.
Answer
It allows the separation of mixtures with closer boiling points.
49. Explain why direct heating of volatile organic solvents is dangerous.
Answer
They can easily catch fire and cause explosions when exposed to open flames.
50. Suggest a method for confirming the identity of a metal cation in solution using precipitation reactions.
Answer
Add specific reagents that form characteristic colored precipitates with certain metal ions.