Qualitative Analysis of Ions - Higher Difficulty Problems
Q. In a qualitative analysis using paper chromatography, which factor primarily affects the Rf value of a substance?
A.Solvent polarity
B.Temperature
C.pH of the solution
D.Molecular weight
Solution
The Rf value is primarily affected by the polarity of the solvent used in paper chromatography, as it influences the interaction between the stationary phase and the analyte.
Correct Answer: A — Solvent polarity
Q. In a titration to determine the presence of acetic acid, which indicator would be most appropriate?
A.Phenolphthalein
B.Methyl orange
C.Bromothymol blue
D.Litmus
Solution
Phenolphthalein is the most appropriate indicator for titrating weak acids like acetic acid against strong bases, as it changes color at the relevant pH range.
Correct Answer: A — Phenolphthalein
Q. In qualitative analysis, what does a positive test for the presence of sulfate ions typically involve?
A.Formation of a white precipitate
B.Formation of a colored solution
C.Gas evolution
D.No visible change
Solution
A positive test for sulfate ions typically involves the formation of a white precipitate of barium sulfate when barium chloride is added.
Correct Answer: A — Formation of a white precipitate
Q. What is the main advantage of using mass spectrometry in qualitative analysis?
A.High sensitivity
B.Low cost
C.Simplicity of operation
D.Speed of analysis
Solution
Mass spectrometry offers high sensitivity, allowing for the detection of trace amounts of substances in qualitative analysis.
Correct Answer: A — High sensitivity
Q. What is the primary purpose of using a buffer solution in electrophoresis?
A.To increase the voltage
B.To maintain pH stability
C.To enhance sample concentration
D.To reduce sample size
Solution
Buffer solutions are used in electrophoresis to maintain a stable pH, which is crucial for the proper migration of charged species.
Correct Answer: B — To maintain pH stability
Q. What is the role of a chelating agent in qualitative analysis?
A.To increase solubility
B.To stabilize metal ions
C.To enhance color change
D.To precipitate ions
Solution
Chelating agents stabilize metal ions in solution, which can help in the identification and quantification of metal ions during qualitative analysis.
Correct Answer: B — To stabilize metal ions
Q. Which of the following ions can be detected using a flame test that produces a green flame?
A.Sodium
B.Barium
C.Potassium
D.Calcium
Solution
Barium ions produce a green flame during a flame test, while sodium produces a yellow flame, potassium a lilac flame, and calcium an orange-red flame.
Correct Answer: B — Barium
Q. Which of the following ions would produce a characteristic yellow precipitate when treated with lead(II) nitrate?
A.Chloride
B.Bromide
C.Iodide
D.Sulfate
Solution
Iodide ions produce a characteristic yellow precipitate of lead(II) iodide when treated with lead(II) nitrate.
Correct Answer: C — Iodide
Q. Which reagent is commonly used in the qualitative analysis of halides to form a precipitate?
A.Barium chloride
B.Silver nitrate
C.Lead(II) nitrate
D.Calcium sulfate
Solution
Silver nitrate is used to test for halides, forming a precipitate of silver halide when halide ions are present.
Correct Answer: B — Silver nitrate
Q. Which technique is best suited for separating and identifying amino acids in a mixture?
A.Gas chromatography
B.High-performance liquid chromatography
C.Thin-layer chromatography
D.Capillary electrophoresis
Solution
Capillary electrophoresis is particularly effective for separating and identifying amino acids due to their charge and size differences.
