Answer :
The concentration of the original NaOH solution is approximately 0.387M.
To determine the concentration of the original NaOH solution, we can use the concept of stoichiometry and the volume and concentration information of the acid used for neutralization.
The balanced chemical equation for the reaction between NaOH and HBr is:
NaOH(aq) + HBr(aq) → NaBr(aq) + H₂O(l)
From the equation, we can see that the mole ratio between NaOH and HBr is 1:1. Therefore, the moles of NaOH used can be calculated as follows:
Moles of NaOH = Volume of NaOH solution (in L) × Concentration of HBr (in M)
= 20.0 ml × (38.8 ml / 1000 ml) × (0.200 M)
= 0.1552 moles
Since the moles of NaOH and HBr are equal, the moles of NaOH in the original solution are also 0.1552 moles. To find the concentration of the original NaOH solution, we divide the moles by the volume in liters:
Concentration of NaOH = Moles of NaOH / Volume of NaOH solution (in L)
= 0.1552 moles / 0.020 L
= 0.387M
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