Describe how you would prepare 10 mL each of 2 M, 1.5 M, and 1 M NaCl solutions from a 2 M stock

Question

NaCl solution. Describe your actions–exactly what you would do –step-by-step–when preparing this
solution. Also show all calculations. Be sure all amounts include units of measurement.

Answer 1

the idea is to take out the exact volume from the stock solution and dilute it with water to make up 10mL total volume giving the concentration needed.

before commencing, ensure that you transfer sufficient volume of the stock solution into a 100mL beaker to use.

Method 1: If you happen to have no 10mL volumetric flask;
for the 2M solution, just pipette 10mL from the beaker into another empty, dry and clean 100mL beaker. No dilution required.

for the 1M solution, a dilution is needed: pipette out 5ml of the stock solution (using a 5mL pipette for accuracy) into a beaker (say 100mL beaker) and add 5mL water using another 5mL pipette.

for the 1.5M solution, pipette 7.5mL of the stock solution and dilute it with 2.5mL water using a 5mL pipette.

The calculation:
use the dilution formula M1V1=M2V2 where M1 is the concentration of the stock, V1 is the volume you need to extract (need to be calculated), M2 is the concentration of the solution to prepare and V2 is 10mL. Just rearrange the formula to solve for V1 (do not bother for mL conversion to liters; don't matter as long as you use consistent units).

A more accurate method:
if you have a 10mL volumetric flask, then just pipette out the volume you calculated (V1) into the flask, and top up the solution to the mark with water using a wash bottle. this is only for the 1.5M and 1M solutions as they require dilution. Close the lid and invert the flask with one hand with a thumb holding the lid.

Minimize contamination: each preparation must be done with separate/clean pipette with clean and dry containers.