Question

Custom made primers are shipped as DNA powders. A student received a tube containing 19.5 nmoles of primer. To make 75 µM primer solution, she needs to add ___ µl water to the tube.

Answer 1

Ans. Given-

            Moles of DNA = 19.5 mmol = 1.95 x 10^-8 mol

            [Primer] = 75 uM = 7.5 x 10^-5 M

Now,

            Required volume = Moles / Molarity

                                                = (1.95 x 10^-8 mol) / (7.5 x 10^-5 M)             ; [1 M = 1 mol/L]

                                                = (1.95 x 10^-8 mol) / (7.5 x 10^-5 mol / L)

                                                = 2.600 x 10^-4 L                                             ; [1 L = 10³ mL]

                                                = 2.600 x 10^-1 mL                                         ; [1 mL = 10³ uL]

                                                = 260.0 uL

Therefore,

To make 75 uM primer solution, she need to add 260.0 uL water to the tube.