Question

How would you prepare 250.mL of a .200M solution of HCI from a 5.00M HCI solution. Describe how it's done.

Answer 1

DILUTION
Molarity= moles of solute/ volume of solution (L)
Moles of solute= molarity* volume (L)
Now, the no. of moles doesn't change during dilution because we add water (or solvent) to the
already existing solution to make it as the required concentration.
Therefore, no. of moles, n= constant
n=M*V = constant
M1V1 = M2V2

Now,

M1= 5 M

M2=0.2 M

V2= 250mL= 0.25 L

M1V1 = M2V2

5*V1 = 0.2*0.25

V1= 0.01 L = 10 mL

To prepare this diluted acid solution in lab take a flask and since we've to prepare a solution of 250 mL. Fill about 240 mL with water and then slowly add 10 mL of the 5M acid to make a solution of 250 mL of 0.2M diluted acid and if possible stir the solution while adding acid.

Do not add water to acid as mixing of acid and water is a highly exothermic reaction and water acts as a heat sink. Instead add acid slowly into water.