Question

You wish to prepare 100 mL of 0.750 M HCl from concentrated HCl (11.65 M). You are provided with a 100 mL volumetric flask and a 10 mL graduated pipet with 0.00 line at the top and calibration lines each 0.1 mL. When filled to the 0.00 mL line this pipet would dispense 10.00 mL of solution when drained leaving only the final inside drop. At what volume reading on the pipet should you start dispensing the 11.65 M HCl to have the correct number of moles to give the 0.750 M solution when dispensed into the volumetric flask?

Answer 1

0.75 M HCl, means in 1L solution, 0.75 moles of HCl

so in 100 mL, moles of HCl will be 0.075 moles

applying the simple formulae of M1V1 = M2V2

0.75 X 100 = 11.65 X V2

therefore V2 = (0.75 X 100) /11.65  = 6.44 mL = inbetween 6.4 mL and 6.5 mL approximately.

we need add 6.66 mL of HCl of the concentration 11.65M in the 100 mL volumetric flask and then add water to make it upto 100 mL.

when the volume filled in pippett in 10 mL it shows the value 0.00 mL on pipette

therefore 6.5 mL will show the value 10.0 - 6.5 = 3.5 mL on pippette

and 6.4 mL will show value 10.0 - 6.4 = 3.6 mL

so fill the pipette in between 3.5 and 3.6 mL shown in pipette and drain it into volumetric flask