Question

10.   How is H (plate height) affected by a very high linear flow velocity?

A.   Increased              B. Decreased              C. Unchanged

11.   How is H (plate height) affected by increasing the column length?

A.   Increased              B. Decreased              C. Unchanged

12.   How is k’ (capacity factor) affected by increasing the column length?

A.   Increased              B. Decrease                C. Unchanged

Answer 1

10) The Van Deemter equation is given as

H = A + B/u + C*u

where H = height equivalent to theoretical plates; A = eddy diffusion constant; B = longitudinal diffusion constant; C = resistance to mass transfer and u = linear flow velocity.

Under normal conditions, the B term doesn’t contribute much and the A and C terms are significant. C increases linearly with the mobile phase velocity, i.e, u; hence H is increased with a very high linear flow velocity (ans).

11) An alternative definition of H is in terms of L, the length of the column as

H = L/N where N = number of theoretical plates.

Assuming N is constant, when L is increases, H will increases proportionately (ans).