Question

A patient needs to be given exactly 500 mL of a 5.0% (w/v) intravenous glucose solution. The stock solution is 65% (w/v). How many milliliters of the stock solution are needed to prepare the fluid for the IV bag?

Which equation will determine how much water is needed to prepare the 5.0% (w/v) glucose solution?

a.) Volume of stock solution needed Volume given to patient (500 mL)

b.) Volume given to patient (500 mL) / Volume of stock solution needed

c.) Volume of stock solution needed / Volume given to patient (500 mL)

d.) Volume given to patient (500 mL) – Volume of stock solution needed

Answer 1

According to law of dilution   MV = M'V'

Where M = concentration of stock = 65%(w/v)

V = Volume of the stock = ?

M' = concentration of dilute solution = 5.0%(w/v)

V' = Volume of the dilute solution = 500 mL

Plug the values we get V = (M'V')/M

                                     = ( 5.0*500)/65

                                     = 38.5 mL

So volume of the stock needed is 38.5 mL

Volume of water added = final volume - volume of stock solution

                                 = 500 mL - 38.5 mL = 461.5 mL

a.) Volume of stock solution needed Volume given to patient (500 mL) is 38.5 mL

b.) Volume given to patient (500 mL) / Volume of stock solution needed = 500mL/38.5 mL = 13.0

c.) Volume of stock solution needed / Volume given to patient (500 mL) = 38.5 mL / 500 mL = 0.077

d.) Volume given to patient (500 mL) – Volume of stock solution needed = 500 mL - 38.5 mL = 461.5 mL