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Oil Film Method: Estimating Molecular Size Quiz

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What is the basic principle behind measuring molecular diameter using the oil film method?

Oil Film Method: Estimating Molecular Size Quiz - Quiz Questions

Test your understanding of the oil film method for estimating molecular size, including experimental principles, formula calculations, error analysis, and experimental design.

1. What is the basic principle behind measuring molecular diameter using the oil film method?

A. Oleic acid forms a monolayer on the water surface, and the film thickness equals the molecular diameter
B. Oleic acid dissolves completely in water, and the molecular size is calculated from the solution concentration
C. An optical microscope is used to directly observe oleic acid molecules
D. The molecular size is deduced from the evaporation rate of oleic acid

2. What is the purpose of sprinkling talcum powder on the water surface in this experiment?

A. To make the oil film boundary clearly visible so its outline can be traced
B. To accelerate the spreading of oleic acid on the water surface
C. To prevent evaporation of the water
D. To increase the area of the oil film

3. In one trial, the oleic acid–alcohol solution concentration is $1:10000$, the drop volume is $0.05\ \text{mL}$, and the oil film area is $80\ \text{cm}^2$. What is the approximate molecular diameter of oleic acid?

A. $6.25 \times 10^{-10}\ \text{m}$
B. $6.25 \times 10^{-8}\ \text{m}$
C. $6.25 \times 10^{-12}\ \text{m}$
D. $5.0 \times 10^{-6}\ \text{m}$

4. Why is oleic acid diluted with alcohol in this experiment?

A. So that each drop of solution contains only a tiny amount of pure oleic acid, enabling a sufficiently thin monolayer to form on the water surface
B. Alcohol increases the diameter of oleic acid molecules
C. Alcohol makes the oleic acid sink to the bottom of the water more easily
D. Alcohol increases the surface tension of the water

5. If too much oleic acid is used and the oil film overflows the boundary of the shallow tray, what effect does this have on the experiment?

A. The true oil film area cannot be measured, and the calculated molecular diameter is too large
B. The measurement result is unaffected
C. The calculated molecular diameter is too small
D. The oil film changes from a monolayer to a bilayer

6. In this experiment, the grid counting method stipulates that "partial squares count as half squares." What is the physical basis for this rule?

A. Statistical averaging: among a large number of partial squares, roughly equal numbers are more than half covered and less than half covered
B. Every partial square is covered by exactly half its area
C. To make the calculated result larger
D. It is merely a convention with no physical basis

7. If the solution concentration ($1:10000$) is kept constant and the drop volume is increased from $0.05\ \text{mL}$ to $0.10\ \text{mL}$, how will the oil film area change?

A. The area approximately doubles
B. The area approximately quadruples
C. The area remains unchanged
D. The area increases by a factor of approximately $\sqrt{2}$

8. Which of the following actions would cause the measured molecular diameter to be too small?

A. Tracing the oil film outline larger than its actual size
B. Sprinkling the talcum powder too thickly, hindering the film from spreading
C. Using an overestimated concentration when calculating the pure oleic acid volume
D. Using an expired, degraded oleic acid–alcohol solution

9. This experiment yields an oleic acid molecular diameter of approximately $10^{-10}\ \text{m}$. Which of the following comparisons best helps convey this scale?

A. About one ten-billionth of the diameter of a ping-pong ball
B. About one-tenth of the diameter of a human hair
C. About the same size as a bacterium
D. About the same as the wavelength of visible light

10. In this simulation, what is the correct experimental method for investigating how concentration affects the oil film area?

A. Keep the drop volume constant, vary the concentration, and compare the oil film areas at different concentrations
B. Change both the concentration and the drop volume at the same time
C. Keep the concentration constant and change the drop volume
D. Draw a conclusion from a single trial