Concentration of solutions

CONCENTRATION OF SOLUTIONSDay 4

CONCENTRATION A measurement of the amount of

solute in a given amount of solvent or solution (unit of measurement = molarity)

Kind of like the “strength” of the solution

MOLARITYMolarity (M)=

mol solute

L solution

MOLARITYExample #1: If we put 0.500 mol of sodium hydroxide into 1.00 L of solution, what is the molarity of the solution?

Molarity= mol solute/L sol’n

M= 1.00 L

0.500 mol NaOH

=0.500 M NaOH

Example #2: What is the molarity if we have 80.0 g NaOH in 1.00 L of solution?

Molarity= mol solute/L sol’n

M=

1.00 L

2.00 mol NaOH=2.00 M NaOH

80.0 g NaOH

40.0 g NaOH

1 mol NaOH =2.00 mol

MOLARITY

Example #3: How many moles of KOH are in 0.500 L of 0.100 M KOH?

Molarity= mol solute cross multiply! 1 L sol’n

mol KOH=

(0.500 L)(0.100 M KOH)

=0.0500 mol KOH

MOLARITY

Ex 4: How many grams of KOH are in 2.75 L of 0.25 M KOH?

MOLARITY - DILUTIONSome chemicals are sold as pre-prepared concentrated solutions (stock solutions).

To be used, stock solutions usually must be diluted.

ALWAYS ADD ACID

2.) MOLARITY - DILUTION

MSVS = MDVD

• MS – Molarity of stock solution

• VS – Volume of stock solution (L or mL)

• MD – Molarity of dilute solution

• VD – Volume of dilute solution (L or mL)

*In dilution calculations, the units for volume must be the same.

2.) MOLARITY - DILUTION

Example #1: How much 12.0 M HCl is required to make 2.50 L

of a 0.500 M solution? Ms * Vs = MD * VD

MS VS = MD VD OR M1 V1 = M2 V2MS = 12.0 M HCl MD = 0.500 M HCl

VS = ?? VD = 2.50 L

VS =(0.500 M HCl)(0.500 M HCl)(2.50 L)(2.50 L)

(12.0 M HCl)(12.0 M HCl)

= 0.104 L HCl0.104 L HCl

2.) MOLARITY - DILUTION

Example #2: What volume of a 1.50 M solution can be made using 0.0250 L of 18.0 M H2SO4

? MS VS = MD VD

MS VS = MD VD

MS = 18.0 M H2SO4 MD = 1.50 M H2SO4

VS = .0250 L VD = ????

VD =(18.0 M (18.0 M H2SO4))(.0250 L)(.0250 L)

(1.50 M (1.50 M H2SO4))= 0.300 L 0.300 L H2SO4