Pure substances, mixtures and chromatography
8th grade (Year 9 in England) · 16 questions · Common Core: NGSS.MS-PS1-2 · England: KS3 Chemistry: Pure and impure substances, KS4 Combined Science: Chemical analysis
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Date
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Question 1
Why is the start line on chromatography paper drawn in pencil, not pen?
- A. Pencil makes the dyes move faster
- B. Pencil is easier to see
- C. Pen is too expensive
- D. Pencil (graphite) does not dissolve in the solvent
Question 2
In a chromatogram the solvent moved 12 cm and a dye spot moved 9 cm from the start line. What is the Rf value of the dye? (Give 2 decimal places.)
Answer
Question 3
Purity and chromatography: which statement is NOT true?
- A. In chromatography, a more soluble dye usually travels further.
- B. Impurities have no effect on melting point.
- C. Air is a mixture of gases.
- D. A pure substance has a fixed melting point.
Question 4
Why is the start line on chromatography paper drawn in pencil, not pen?
- A. Pencil is easier to see
- B. Pencil (graphite) does not dissolve in the solvent
- C. Pencil makes the dyes move faster
- D. Pen is too expensive
Question 5
In a chromatogram the solvent moved 5 cm and a dye spot moved 1.3 cm from the start line. What is the Rf value of the dye? (Give 2 decimal places.)
Answer
Question 6
Purity and chromatography: which statement is NOT true?
- A. Mixtures can be separated by physical methods.
- B. Impurities have no effect on melting point.
- C. Air is a mixture of gases.
- D. A pure substance has a fixed melting point.
Question 7
In chemistry, what does "pure" mean?
- A. made of only one substance
- B. very expensive
- C. natural, with nothing added by people
- D. clean and safe to drink
Question 8
In a chromatogram the solvent moved 8 cm and a dye spot moved 4.8 cm from the start line. What is the Rf value of the dye? (Give 2 decimal places.)
Answer
Question 9
Purity and chromatography: which statement is NOT true?
- A. In chromatography, a more soluble dye usually travels further.
- B. Impurities have no effect on melting point.
- C. Air is a mixture of gases.
- D. A pure substance has a fixed melting point.
Question 10
Why is the start line on chromatography paper drawn in pencil, not pen?
- A. Pencil is easier to see
- B. Pen is too expensive
- C. Pencil (graphite) does not dissolve in the solvent
- D. Pencil makes the dyes move faster
Question 11
In a chromatogram the solvent moved 6 cm and a dye spot moved 1.5 cm from the start line. What is the Rf value of the dye? (Give 2 decimal places.)
Answer
Question 12
Purity and chromatography: which statement is NOT true?
- A. Mixtures can be separated by physical methods.
- B. A pure substance has a fixed melting point.
- C. Impurities have no effect on melting point.
- D. Air is a mixture of gases.
Question 13
An ink gives three separate spots on a chromatogram. What does this show?
- A. The ink is a pure substance
- B. The ink is insoluble
- C. The ink is a mixture of at least three dyes
- D. The paper was dirty
Question 14
In a chromatogram the solvent moved 10 cm and a dye spot moved 7.5 cm from the start line. What is the Rf value of the dye? (Give 2 decimal places.)
Answer
Question 15
Purity and chromatography: which statement is NOT true?
- A. Air is a mixture of gases.
- B. A pure substance has a fixed melting point.
- C. Orange juice is a pure substance.
- D. Mixtures can be separated by physical methods.
Question 16
An ink gives three separate spots on a chromatogram. What does this show?
- A. The ink is insoluble
- B. The ink is a pure substance
- C. The paper was dirty
- D. The ink is a mixture of at least three dyes
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