Question

imagine that you have been assigned five substances for which you will observe the rate of diffusion. the only information that you have about your materials is the molecular weight of each substance, listed below: substance #1: 212 g/mol substance #2: 1918 g/mol substance #3: 50 g/mol substance #4: 4 g/mol substance #5: 700 g/mol if the substances are allowed to diffuse for one hour, what can you predict about the rate of diffusion? multiple choice substance #2 will diffuse fastest at first, but the other materials will catch up within the hour. substance #4 will diffuse fastest at first, but the other materials will catch up within the hour. the rate of diffusion for the five substances will be equal. substance #2 will diffuse farthest because the molecular weight is greatest. substance #4 will diffuse farthest because the molecular weight is least.

Explanation:

Step1: Recall diffusion - molecular weight relation

The rate of diffusion is inversely proportional to the square - root of the molecular weight of a substance. Lighter substances diffuse faster.

Step2: Compare molecular weights

Substance #1: 212 g/mol, Substance #2: 1918 g/mol, Substance #3: 50 g/mol, Substance #4: 4 g/mol, Substance #5: 700 g/mol. Substance #4 has the lowest molecular weight.

Step3: Predict diffusion rate

Since Substance #4 has the lowest molecular weight, it will diffuse the fastest and farthest in the given one - hour time period.

Answer:

Substance #4 will diffuse farthest because the molecular weight is least.