1.Molecules can diffuse across living cells in very small fractions of a seond.

Question

1.Molecules can diffuse across living cells in very small fractions of a seond. the width of cells is increased by a factor of 10, then by what factor would the average time required for molecules to diffuse across them increase? (Answer: 100)

2.If the diffusion coefficient of CO-hemoglobin in water at 20 degrees celsius is 6.2x10^-11 m^2/s and for CO-hemoglobin in an unkown liquid is 15.5x10^-11 m2/s what is the viscocity of unkown liquid? (Aswer: 4.0x10^-4)

3. a certain kind of spherical molecule is observed to diffuse through water so that one-third of the molecules cover at least o.5cm in a time of 10h at 20c. compute the radius of the molecule. (answer: 1.9x10-9m)

Explanation / Answer

Q1.

using Einstein's approximation equation, the diffusion time is directly proportional to square of diffusion length.

so as length increases by 10 times, the time will increase by 10^2=100 times

Q2.

viscocity of water at 20 degree celcius=0.001002 kg/(m.s)

using Einstein-stokes relationship,

diffusion coefficient*viscosity is constant

hence 6.2*10^(-11)*0.001002=15.5*10^(-11)*viscosity of unknown liquid

==>viscosity of unknown liquid=4.008*10^(-4)

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