Question

0.15 mL of a solution made from 0.381 g of unknown in 500.00 mL of pentane on a pan of water. After all the pentane evaporated a 24.36 cm² monolayer of unknown remained on the surface of the water. If the density of the unknown was 0.719 g/mL what was the thickness of the monolayer in micrometers?

A) 15.2 μm
B) 12.6 μm
C) 18.5 μm
D) 14.8 μm

Answer 1

By dividing the volume of the unknown substance, which we calculate using the mass and density, by the surface area it covers, we can find the thickness of the monolayer. The calculated thickness of the monolayer is 217.5 micrometers.

Step-by-step explanation:

To calculate the thickness of the monolayer, we must consider the given mass and density of the unknown substance, as well as the area covered by it. Since 0.381 g of the unknown dissolved in 500.00 mL of pentane, and after evaporation, it formed a monolayer over an area of 24.36 cm², we use the mass and density to determine the volume, and then divide this volume by the area to find the thickness.

To find the volume (V) converted to milliliters (due to the density unit g/mL):

V = mass / density

V = 0.381 g / 0.719 g/mL = 0.53 mL

Then, we convert the volume to cm³ (as 1 mL = 1 cm³) and divide by the area to obtain the thickness (T).

T = volume / area

T = 0.53 cm³ / 24.36 cm² = 0.02175 cm

Lastly, convert the thickness into micrometers by multiplying by 10,000 (since 1 cm = 10,000 micrometers):

T = 0.02175 cm x 10,000 μm/cm = 217.5 μm