Rucete ✏ AP Chemistry In a Nutshell
14. Experimental Chemistry — Practice Questions
This chapter introduces essential laboratory techniques, safety protocols, equipment usage, error analysis, and chemical identification methods through qualitative and quantitative approaches.
(Multiple Choice — Click to Reveal Answer)
1. Which piece of glassware is best for measuring exactly 25.00 mL of liquid?
(A) Graduated cylinder
(B) Buret
(C) Beaker
(D) Volumetric pipet
Answer
(D) — A volumetric pipet is designed to deliver a very precise fixed volume.
2. A student smells a strong rotten egg odor during a lab. Which gas was likely produced?
(A) CO2
(B) O2
(C) NH3
(D) H2S
Answer
(D) — H2S has a characteristic rotten egg smell.
3. Which ion gives a crimson-red flame in a flame test?
(A) Na+
(B) Li+
(C) K+
(D) Ca2+
Answer
(B) — Lithium gives a crimson-red flame color.
4. What is the best method to isolate a fine precipitate?
(A) Distillation
(B) Filtration
(C) Vacuum filtration
(D) Centrifugation
Answer
(D) — Centrifugation is effective for isolating fine precipitates that pass through filters.
5. What is the purpose of rinsing a buret with the solution it will contain before titration?
(A) To clean it
(B) To prevent dilution errors
(C) To dry it
(D) To measure pH
Answer
(B) — Rinsing ensures no dilution of the solution by residual water.
6. Which color indicates the presence of Cu2+ ions in solution?
(A) Green
(B) Blue
(C) Red
(D) Yellow
Answer
(B) — Copper(II) ions typically form a blue-colored solution.
7. When heating a test tube, what direction should the mouth of the test tube face?
(A) Toward your face
(B) Toward a lab partner
(C) Away from everyone
(D) Directly upward
Answer
(C) — Always point the open end of a test tube away from yourself and others when heating.
8. What is the first step if acid is spilled on your skin?
(A) Wipe it off
(B) Apply a base
(C) Rinse with plenty of water
(D) Go to the hospital immediately
Answer
(C) — Immediate rinsing with large amounts of water is the correct first aid procedure.
9. Which material is best used to dry a wet solid product in the lab?
(A) Fume hood
(B) Desiccator
(C) Hot plate
(D) Bunsen burner
Answer
(B) — A desiccator is used to remove moisture from solids without applying heat.
10. What does the presence of a white precipitate when adding silver nitrate suggest?
(A) Sulfate ions
(B) Chloride ions
(C) Carbonate ions
(D) Nitrate ions
Answer
(B) — Silver nitrate reacts with chloride ions to form a white precipitate of AgCl.
11. Why is it important to use a lid on a crucible during heating?
(A) To keep the crucible cold
(B) To prevent splashing
(C) To reduce heat loss and prevent contamination
(D) To increase reaction rate
Answer
(C) — The lid helps contain contents and maintain temperature consistency.
12. What is a test for the presence of carbon dioxide gas?
(A) Pops with a flame
(B) Turns limewater milky
(C) Burns with a blue flame
(D) Turns red litmus blue
Answer
(B) — Carbon dioxide turns limewater cloudy due to formation of calcium carbonate.
13. What color is phenolphthalein in a basic solution?
(A) Colorless
(B) Blue
(C) Pink
(D) Red
Answer
(C) — Phenolphthalein turns pink in basic conditions (pH > 8.2).
14. Which technique is best for separating a mixture of two soluble liquids with different boiling points?
(A) Filtration
(B) Chromatography
(C) Distillation
(D) Crystallization
Answer
(C) — Distillation separates liquids based on differences in boiling point.
15. What piece of equipment is used to deliver a precise volume of liquid in titration?
(A) Beaker
(B) Buret
(C) Flask
(D) Pipette bulb
Answer
(B) — A buret is designed for accurate delivery of varying volumes during titration.
16. What is the role of an anti-bumping granule in boiling liquids?
(A) Increase temperature
(B) Prevent superheating
(C) Increase pressure
(D) Remove impurities
Answer
(B) — Anti-bumping granules ensure smooth boiling by preventing superheating and sudden boiling.
17. Which of the following is not a safety rule in the chemistry lab?
(A) Wear goggles
(B) Smell chemicals directly
(C) Tie back long hair
(D) Never taste chemicals
Answer
(B) — Chemicals should never be smelled directly; wafting is the correct technique.
18. What is the function of a fume hood?
(A) Protect from UV light
(B) Contain chemical spills
(C) Remove toxic gases
(D) Heat chemicals safely
Answer
(C) — Fume hoods ventilate harmful or volatile vapors during chemical experiments.
19. Which metal ion gives a green flame color in a flame test?
(A) Copper
(B) Sodium
(C) Barium
(D) Iron
Answer
(A) — Copper (especially as CuCl2) gives a green flame color.
20. What happens when hydrogen gas is tested with a lit splint?
(A) Pops
(B) Burns silently
(C) Changes color
(D) Explodes violently
Answer
(A) — Hydrogen gas burns with a characteristic 'pop' sound.
21. What is the function of litmus paper in a lab experiment?
(A) Identify reducing agents
(B) Determine acidity or alkalinity
(C) Measure temperature
(D) Absorb moisture
Answer
(B) — Litmus paper indicates whether a solution is acidic or basic.
22. When excess gas is released in a reaction, which apparatus should be used to safely contain and measure it?
(A) Beaker
(B) Gas syringe
(C) Conical flask
(D) Pipette
Answer
(B) — A gas syringe accurately collects and measures gas volume.
23. Which technique is best for purifying a solid substance?
(A) Filtration
(B) Crystallization
(C) Decantation
(D) Boiling
Answer
(B) — Crystallization is used to purify solids from solutions.
24. What should be done before lighting a Bunsen burner?
(A) Close the air hole
(B) Open the gas tap fully
(C) Point it toward yourself
(D) Light it with a match over the barrel
Answer
(A) — Closing the air hole produces a safety flame that is easier and safer to light.
25. What should be used to measure 7.35 mL of a liquid most accurately?
(A) Beaker
(B) 10 mL graduated pipette
(C) 100 mL measuring cylinder
(D) Watch glass
Answer
(B) — A 10 mL pipette provides high accuracy for small liquid volumes.
26. A student adds excess sodium carbonate to dilute hydrochloric acid and collects the gas. What confirms that CO2 is the gas evolved?
(A) It extinguishes a glowing splint
(B) It turns limewater milky
(C) It produces a pop with a flame
(D) It changes cobalt chloride paper color
Answer
(B) — CO2 turns limewater cloudy due to formation of CaCO3.
27. Which method would best separate sand and salt after mixing them with water?
(A) Distillation
(B) Chromatography
(C) Filtration followed by evaporation
(D) Centrifugation
Answer
(C) — Filtration removes sand, and evaporation recovers salt from solution.
28. Which of the following is most important when choosing an appropriate indicator for a titration?
(A) Indicator color
(B) Volume of titrant
(C) Equivalence point pH
(D) Type of acid used
Answer
(C) — The indicator must change color near the equivalence point of the titration.
29. A student spills a few drops of concentrated sulfuric acid on the bench. What is the proper first response?
(A) Wipe it with a paper towel
(B) Pour water over it
(C) Neutralize with sodium carbonate
(D) Ignore it and continue
Answer
(C) — Neutralizing the acid with a base like sodium carbonate is the safest method.
30. In a redox reaction experiment, what would be observed when acidified potassium manganate(VII) is added to a reducing agent?
(A) The purple color fades
(B) A white precipitate forms
(C) Gas is released
(D) Solution turns blue
Answer
(A) — Potassium manganate(VII) is reduced and loses its purple color.
31. During an experiment, a student uses an impure sample of solid to prepare a solution. Which of the following is a likely consequence?
(A) Higher temperature
(B) Incorrect molarity
(C) Lower vapor pressure
(D) Delayed reaction time
Answer
(B) — Impurities affect the calculated mass and lead to inaccurate concentration (molarity).
32. Which of the following experimental setups best allows for collection of gas over water?
(A) Closed conical flask with a balloon
(B) Delivery tube into an inverted measuring cylinder
(C) Funnel over a Bunsen flame
(D) Open beaker in fume hood
Answer
(B) — Gas collected over water should be directed into an inverted container submerged in water.
33. A student records a titration volume of 24.80 mL from a buret. What is the uncertainty of this measurement if the buret reads to ±0.05 mL?
(A) ±0.05 mL
(B) ±0.10 mL
(C) ±0.01 mL
(D) ±0.50 mL
Answer
(B) — Titration involves two readings (initial and final), each with ±0.05 mL → total uncertainty = ±0.10 mL.
34. When testing for the presence of sulfate ions using barium chloride, what is the expected result?
(A) Effervescence
(B) White precipitate
(C) Blue solution
(D) No visible change
Answer
(B) — Barium sulfate forms a white precipitate, confirming sulfate ions.
35. Which error will most significantly affect a calculated molarity if a volumetric flask is not filled to the calibration line?
(A) Systematic error — concentration too high
(B) Random error — color inconsistency
(C) Systematic error — concentration too low
(D) No significant error occurs
Answer
(A) — If solution volume is lower than intended, the calculated molarity will be artificially higher.
36. Describe how to test for the presence of ammonia gas in the laboratory.
Answer
Hold damp red litmus paper near the gas; it will turn blue in the presence of ammonia.
37. Why is it important to swirl the flask continuously during a titration?
Answer
To ensure that the acid and base mix completely and the reaction occurs uniformly.
38. State a safety precaution when heating a substance in a test tube.
Answer
Always point the mouth of the test tube away from yourself and others.
39. How can the presence of carbon dioxide gas be confirmed?
Answer
Bubbling the gas through limewater; it turns milky if CO₂ is present.
40. Why is it necessary to cool a crucible before weighing it?
Answer
Hot crucibles cause air currents and may damage the balance, leading to inaccurate readings.
41. State the use of a desiccator in experimental chemistry.
Answer
To dry substances by keeping them in a moisture-free environment.
42. What is the function of filter paper in filtration?
Answer
It separates solid particles from a liquid by allowing only the liquid to pass through.
43. Why is it better to use a volumetric pipette instead of a beaker to measure 25.0 mL of liquid?
Answer
Because the pipette gives a much more accurate and precise measurement than a beaker.
44. State one observable change when copper(II) carbonate is heated.
Answer
Green solid turns black and a gas is released (carbon dioxide).
45. How do you safely dilute concentrated sulfuric acid?
Answer
Add acid slowly into water with constant stirring (never the reverse).
46. What is the advantage of using a digital balance instead of a triple beam balance?
Answer
It provides quicker, easier, and more precise mass measurements.
47. State one reason why repeating an experiment is useful.
Answer
To improve reliability and ensure consistent results.
48. What does the presence of effervescence indicate in a reaction with an acid?
Answer
A gas is being produced, commonly CO₂ if carbonate is involved.
49. Why should you never stopper a flask during a gas-evolving reaction?
Answer
Pressure from the gas buildup can cause the flask to explode.
50. How can you test for the presence of water using cobalt chloride paper?
Answer
Blue cobalt chloride paper turns pink in the presence of water.