1. Suppose you prepared a sodium hydroxide solution in the lab using exactly 45.

Question

1.       Suppose you prepared a sodium hydroxide solution in the lab using exactly 45.1323g sodium hydroxide pellets.  And, the volume of the solution was measured accurately using a 500.00 mL volumetric flask.

a)      What is the expected concentration of the sodium hydroxide solution as prepared?

b)      Why does this solution need to be standardized?

c)       Would you expect the standardized concentration to be higher or lower than the calculated concentration, WHY?

Suppose you prepared a sodium hydroxide solution in the lab using exactly 45.1323g sodium hydroxide pellets. And, the volume of the solution was measured accurately using a 500.00 mL volumetric flask. What is the expected concentration of the sodium hydroxide solution as prepared? Why does this solution need to be standardized? Would you expect the standardized concentration to be higher or lower than the calculated concentration, WHY?

Explanation / Answer

(a) Moles of NaOH = mass/molar mass of NaOH

= 45.1323/39.99715 = 1.128388 mol


Concentration = moles/volume of NaOH

= 1.128388/0.50000

= 2.2568 M


(b) Solution needs to be standardized as NaOH is hygroscopic and absorbs moisture from the atmosphere

=> actual mass of NaOH is less than weighed mass


(c) Since actual mass of NaOH is less than weighed mass

=> actual moles of NaOH is less than calculated moles

=> standardized concentration is lower than calculated concentration

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