20 mL of NaOH solution was added to the conical flask. Indicator was added & titrated with 0.1 M HCl solution. The HCl used in the titration was read as 18.3 mL. What is the molar concentration of NaOH?

[NaOH] = 0.1 Molar ... Note => the brackets around formula;i.e., "[ ]" is generally accepted in the chemistry community as concentration in Molar terms.

Explanation:

The metathesis rxn, or double replacement rxn, equation is:

(Molarity x Volume) of acid = (Molarity x Volume) of base, or

(M·V)acid = (M·V)base => M(base) = M·V(acid)/V(base)

= 0.1M × 18.3ml / 20ml = 0.0915M(base) = 0.1M (1 sig-fig) = [NaOH]